PetroleumGeologyof South

Australia

PetroleumGeologyof South

Australia

Volume 3:Volume 3:

Officer BasinOfficer Basin

edited by:J.G.G. Morton and J.F. Drexel

MINES and ENERGY

RESOURCESSOUTH

AUSTRALIA

The Petroleum Geology ofSouth Australia

Volume 3: Officer Basin

Edited byJ.G.G. Morton and J.F. Drexel

1st EditionApril 1997

SA Department of Mines and Energy Resources191 Greenhill RoadPO Box 151EASTWOOD SA 5063

Telephone: National (08) 8274 7680

International +61 8 8274 7680

Facsimile National (08) 8373 3269

International +61 8 8373 3269

Web Page http://www.mines.sa.gov.au/petrol/index.html

Report Book 97/19

Front cover: Observatory Hill 1 being drilled in theOfficer Basin in 1985. (Photo 35507)

Prepared for publication by:Publication Section

Mines and Energy Resources South Australia

Printed by Rainbow Colour Copy CentreApril 1997

i

Bibliographic reference:Entire volume:

Morton, J.G.G. and Drexel, J.F., 1997. The petroleum geology of South Australia. Vol 3: Officer Basin. South Australia.Department of Mines and Energy Resources. Report Book, 97/19.

Individual chapter:

O’Neil, B.J., 1997. History of petroleum exploration. In: Morton, J.G.G. and Drexel, J.F. (Eds), The petroleum geology ofSouth Australia. Vol 3: Officer Basin. South Australia. Department of Mines and Energy Resources. Report Book,97/19:7-22.

Petroleum Geology of South Australia

1st ed.Includes bibliographical referencesISBN 0 7308 0644 8 (set).ISBN 07308 0643 X (v.1).ISBN 07308 0762 2 (v.2).ISBN 07308 0164 0 (v.3: prepublication).

1. Petroleum — Geology — South Australia. 2. Petroleum — Geology — Otway Basin (Vic. and S. Aust). 3. Petroleum —Geology — Officer Basin (S. Aust and W.A.). 4. Petroleum — Geology — Eromanga Basin. 5. Petroleum reserves —South Australia. 6. Petroleum reserves — Otway Basin (Vic. and S. Aust). 7. Petroleum reserves — Officer Basin (S. Aust.and W.A.). 8. Petroleum reserves — Eromanga Basin. I. Morton, John George Godfrey. II. Drexel, J.F. (John F.), 1952-.III. Alexander, Elinor M. IV. Hibburt, J. V. South Australia. Dept. of Mines and Energy. Petroleum Division. (Series:Report book (South Australia. Dept. of Mines and Energy); 95/12.

553.28099423

Keywords: Petroleum geology / South Australia / Stratigraphy / Structural geology / Tectonics / Petroleum reservoircharacterisation / Source rock studies / Officer Basin / Palaeozoic.

ii

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

Chapter 1: Introduction and summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Chapter 2: History of petroleum exploration

Discovery of the ‘Officer Basin’ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Early European exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Weapons testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Post-World War II geological exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Aboriginal land rights and exploration access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Petroleum industry exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

OEL 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16OEL 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16OEL 19 and 28 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16OEL 33 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Downturn to discovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19PEL 10, 11 and 12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20PEL 13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20PEL 23 and 30 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20PEL 24 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21PEL 29 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21PEL 33 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Revitalisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21PEL 61 and 63 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Chapter 3: Natural and cultural environment

Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Landforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Western sandplains region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Central tablelands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Nullarbor Plain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Native vegetation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Environmental considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

National parks and reserves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Summary of environmental regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Cultural heritage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24European heritage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24Aboriginal heritage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Aboriginal lands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Access to Aboriginal lands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

AP Lands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26MT Lands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Access for seismic surveys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Other land issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Commonwealth land . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Maralinga and Emu nuclear weapon test sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

iii

Woomera Prohibited Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Mintabie Precious Stones Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Chapter 4: Infrastructure and groundwater

Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Transport links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Pipelines and production facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Access to potential markets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Industries in the region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Crude oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Surface water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Aquifers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Recharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Local recharge potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33Potentiometric surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Water quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Chapter 5: Geological setting and structural history

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35Plate tectonic setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36Basement structural elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Eastern margin ---- Gawler Craton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Tallaringa Trough and Nawa Ridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Northern margin ---- Musgrave Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Middle Bore Ridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Mafic dykes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Coompana Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Structures beneath the basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Basin architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Munyarai Trough . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Birksgate Sub-basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Marla Overthrust Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Ammaroodinna Ridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43Manya Trough . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43Murnaroo Platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43Nullarbor Platform . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Structural history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Stage 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Stage 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Stage 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Stage 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Chapter 6: Lithostratigraphy and environments of deposition

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Officer Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Undrilled sequence below the Callanna Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Callanna Group equivalents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Pindyin Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Alinya Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51Coominaree Dolomite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Cadlareena Volcanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Umberatana Group equivalents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54Chambers Bluff Tillite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54Wantapella Volcanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Lake Maurice Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Tarlina Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Meramangye Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

iv

Murnaroo Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58Ungoolya Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Dey Dey Mudstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59Karlaya Limestone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60Tanana Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Wilari Dolomite Member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Munyarai Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Narana Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Munta Limestone Member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66Mena Mudstone Member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Punkerri Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67Marla Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

Relief Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68Ouldburra Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70Observatory Hill Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72

Cadney Park Member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73Wallatinna Member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74Parakeelya Alkali Member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75Moyles Chert Marker Bed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75Oolarinna Member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

Arcoeillinna Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76Apamurra Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Mount Johns Conglomerate Member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78Trainor Hill Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Late Cambrian Volcanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79Kulyong Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Munda Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80Mount Chandler Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

Byilkaoora Member . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81Indulkana Shale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82Blue Hills Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Devonian Sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83Mimili Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Arckaringa Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84Eromanga Basin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86Tertiary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Chapter 7: Biostratigraphy and correlation

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87Neoproterozoic stratigraphy and age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Stromatolites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87Early Neoproterozoic acritarchs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88Late Neoproterozoic acritarchs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88Late Neoproterozoic invertebrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89Geochronology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89Chemo- and magnetostratigraphy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89Lithology and event stratigraphy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

Cambrian stratigraphy and age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94Invertebrate fossils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94Acritarchs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95Geochronology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95Lithology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

Ordovician stratigraphy and age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95Ichnology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95Geochronology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96Lithology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Devonian stratigraphy and age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96Vertebrate fossils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

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Palynomorphs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97Geochronology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

Chapter 8: Source rock distribution and quality

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99Formation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

Alinya Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99Coominaree Dolomite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101Meramangye Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101Dey Dey Mudstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102Karlaya Limestone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102Tanana Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103Munyarai Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103Narana Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103Ouldburra Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104Observatory Hill Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106Apamurra Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108Indulkana Shale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

Chapter 9: Petroleum maturation and migration

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109Oil-source correlation and maturity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

Trainor Hill Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109Observatory Hill Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109Ouldburra Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112Relief Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112Cambrian maturity mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112Tanana Formation, Karlaya Limestone and Dey Dey Mudstone . . . . . . . . . . . . . . . . . . . 113Murnaroo Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114Alinya Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114Proterozoic maturity mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

Thermal maturity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114Permian vitrinite reflectance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114Fluid inclusion microthermometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116Apatite fission track analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

Geohistory modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117Manya Trough . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118Ammaroodinna Ridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119Marla Overthrust Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

Chapter 10: Reservoirs and seals

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121Formation description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

Pindyin Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121Tarlina Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121Murnaroo Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122Relief Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123Ouldburra Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125Arcoeillinna Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125Trainor Hill Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126Mount Chandler Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

Chapter 11: Potential traps and prospects

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129Previous unsuccessful tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

Arcoeillinna Sandstone in Munyarai 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130Arcoeillinna Sandstone in Ungoolya 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130Arcoeillinna Sandstone in Karlaya 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130Arcoeillinna Sandstone in Lairu 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130Murnaroo Sandstone in Munta 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

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Potential trap types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131Potential trap volumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

Prospect A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131Prospect B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131Prospect C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131Prospect D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

Chapter 12: Exploration and production economics

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141Exploration success ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141Exploration and development scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

Case 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142Case 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142Royalty and licence fees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14320 mmbbl OOIP case study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144Minimum economic field size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145Upside potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

Chapter 13: Undiscovered resources

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147Discussion of parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148Potential plays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150

Pindyin Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150Tarlina Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150Murnaroo Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150Relief Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150Ouldburra Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151Arcoeillinna Sandstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

Appendices

1.1 Abbreviations used throughout the text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1533.1 Sections of the Pitjantjatjara Land Rights Act 1981

relevant to petroleum exploration in the Officer Basin . . . . . . . . . . . . . . . . . . . . . . . . 1543.2 Sections of the Maralinga Tjarutja Land Rights Act 1984

relevant to petroleum exploration in the Officer Basin . . . . . . . . . . . . . . . . . . . . . . . . 15912.1 Economic model data and assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168

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This summary of the of the petroleum geology of theSouth Australian portion of the Officer Basin forms the thirdvolume of the Petroleum geology of South Australia series.It follows on from Volume 1: Otway Basin published in 1995and Volume 2: Eromanga Basin published in 1996. Theremaining volumes will be published on the followingschedule:

1998 Volume 4: Cooper Basin

1999 Volume 5: Stansbury, Arrowie andWarburton Basins

2000 Volume 6: Duntroon and Bight Basins

It is intended that the volumes be ‘fit for purpose’ and,consequently, this has resulted in some compromise on printquality and cost. To avoid delays in publication, the volumesare not being indexed. However, this approach enables eachvolume to be updated and republished quickly as significantnew data come to hand. Seismic contour maps andimage-processed data which include the latest open fileinterpretations are continuously available on request fromMESA’s seismic interpretation digital database.

Any and all comments or criticisms on this volume on theOfficer Basin are welcome and will assist us in improvingfuture publications. Please address correspondence to theDirector, Petroleum Division, MESA, PO Box 151,Eastwood, SA 5063. Email: rlaws@msgate.mesa.sa.gov.au.

Further information is available through our World WideWeb site: http://www.mines.sa.gov.au/petrol/index.html

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The idea for a series of publications on the petroleumbasins of South Australia was originally conceived by BobLaws, Director, Petroleum Division, MESA, who hasenthusiastically supported the project.

Thanks are due to Greg Borchers (AP Legal Service) andAndrew Collett (MT Legal Service) for their comments ontext relating to Aboriginal issues. Drs John Lindsay andJames Leven (AGSO) kindly provided a pre-print of theirpaper on the tectonic evolution of the Officer Basin. JohnNaylor (Hemley Exploration Pty Ltd) generously furnishedinformation for use in the economic model. Information onroad construction costs and airports was provided by officersof the South Australian Department of Road Transport.

In addition to the authors, Colin Gatehouse, Paul Rogers,Reza Moussavi-Harami and Wenlong Zang read earlyversions of the text and made valuable comments. DavidGravestock and Wenlong Zang compiled the lithology logsfor the reference sections and provided photographs andassistance through many discussions on the stratigraphy ofthe Officer Basin (Ch. 6). John Iredale, Don Vinall and PeterHough assisted in compiling the seismic section figures forChapter 11.

Editing was by John Morton and John Drexel, withassistance by David Gravestock. Word processing was byJeanette Bell and Melanie Lenuzzi. The references werecompiled and checked by John Drexel from the authors’contributions.

The figures were drafted by Elaine Appelbee, GayleBruggemann, Adrian Francis, Tricia Fraser, Todd McKenzie,Michael Ross, Jeff Weber and Jamie Williams under thesupervision of Barry Frost. Spatial data were provided byNeil Sandercock. The publication was designed and desktoppublished by Rachel Froud.

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The Officer Basin covers an area of >300 000 km2 inSouth Australia and Western Australia; this publicationsummarises the petroleum potential of the 100 000 km2 inSouth Australia (Fig. 1.1).

An industry survey conducted by Morton (1996a)indicated that the petroleum industry in general was unableto make a judgement on the prospectivity of the Officer Basin(as well as the other Cambrian Basins in South Australia).Those representatives that could comment were generallynegative in their views, quoting unfavourable economics,lack of geological knowledge, difficulties with land accessand poor source quality as the main deterrents to exploration.These views are not shared by all industry members however,and exploration activity in the area is at an all time high, withtwo licences granted and a third under application (Fig. 1.2).This publication is written specifically for a petroleumindustry audience, and aims to dispel some of the mythssurrounding the Officer Basin’s petroleum potential.

The Officer Basin has close geological affinities with theproductive Amadeus Basin in the Northern Territory, andwith basins in the former USSR and Oman, both of whichhost giant oil and gas fields and have proven oil reserves inthe order of billions of barrels. Numerous oil shows areknown in the Officer Basin from mineral and stratigraphicdrillholes, although there has been little on-structure drillingfor petroleum targets. Excellent reservoir quality and sourceare proven. Exploration economics are favourable, even atrelatively low oil prices (US$18/bbl), and the area is onewhere Native Title considerations are not a major issue. TheOfficer Basin represents one of the last remaining onshorefrontier exploration areas where large petroleum discoveriesmay still be made.

Previous exploration in the Officer Basin has been limitedto a few shallow wells (mostly off-structure and drilled formineral or stratigraphic purposes), a few regional seismiclines, and aeromagnetic and surface mapping by theGovernment . Petroleum l icences have been issuedsporadically in the area since 1954, but little modernpetroleum exploration has taken place. The reasons for thishave been the area’s remoteness, previous access restrictions(atomic bomb testing and weapons testing), and perceptionthat little oil will be found in Proterozoic and early Palaeozoicrocks in Australia. The State and Federal Governments havelong been involved in geological investigations in the area,and have carried out most of the petroleum orientatedexplorat ion, including source rock studies , seismicacquisition, reservoir core analysis, surface mapping,aeromagnetic surveys, and stratigraphic drilling. Less than

7200 km of seismic data have been recorded and only 30drillholes deeper than 500 m have been drilled; of these onlyseven had petroleum targets, and only one has subsequentlybeen shown to have been a valid structural test. Explorationcommitments for the current licences total $22 million overthe next five years, and this effort should begin to validly testthe potential of the area.

The natural environment in the Officer Basin is regardedas harsh desert, with low and irregular rainfall, and extremelyhot conditions in the summer months. Landforms compriseundulating plains and extensive dunefields (Great VictoriaDesert) with vegetation of low open woodlands, deceptivelylush in spite of the harsh desert climate, low tablelands withundulating plains covered in rubble, and in the south theNullarbor Plain, a flat featureless limestone plain. Nativevegetation in these latter areas is very sparse and comprisessaltbush and grasses only.

There are six parks and reserves in the region, all of whicha l low exp lora t ion access excep t fo r the UnnamedConservation Park on the western State border, and theNullarbor National Park on the southern coastal region. Mostof the area is held as Aboriginal land (as a freehold title by abody corporate), the Anangu Pitjantjatjara (AP) in the northand the Maralinga Tjarutja (MT) in the south. In both of theseareas, the Aboriginal people have the right to control entry totheir lands and seek compensation for disturbance to theirways of life. Industry have successfully negotiated access tothese lands for exploration and production. In the case of MTLands, compensation at the exploration stage is limited to thatwhich would apply to any other landowner in the State, asprovided under the Petroleum Act. Some land accessrestrictions also apply to small areas around the atomic bombtest sites and in the Woomera Prohibited Area (access may begranted by the Department of Defence).

Infrastructure in the region is relatively limited, with thefully sealed Stuart Highway the main road link to Adelaideand Darwin. The Central Australia Railway links toAdelaide, and airstrips suitable for small aircraft are availableat several locations. No pipelines cross the Officer Basin,although the Alice Springs--Darwin gas pipeline is 550 km tothe north, and the Moomba--Port Bonython liquids pipeline~600 km to the east. It is likely that a transcontinentalpipeline will be built in the next 10--20 years to link the NorthWest Shelf and Timor Sea gas fields with markets in thepopulated southeastern parts of Australia; this pipeline wouldmost likely cross part of the Officer Basin. Surface watersupplies in the area are virtually non-existent and rely ongroundwater which is mostly highly saline.

1

2

Fig. 1.1

The basin in South Australia is bounded to the north bythe Musgrave Block, to the southwest and southeast by theCoompana Block and Gawler Craton respectively, but ispoorly defined to the northeast where it merges with theWarburton and Amadeus Basins and is covered byArckaringa and Eromanga Basin sediments. Sediments arethickest in the Munyarai Trough, and are abruptly truncatedby thrust faults against the southern margin of the MusgraveBlock. Thrusting is most clearly seen in the Marla OverthrustZone. Other significant depocentres are the TallaringaTrough, Birksgate Sub-basin and Manya Trough. Thesouthern part of the basin, designated the Nullarbor Platform,is poorly known due to Tertiary cover of the Eucla Basin, butis most likely to be Neoproterozoic sediments only.

The structural history of the Officer Basin, frommid-Neoproterozoic to Late Devonian (~820–360 Ma),comprises four stages. Stage 1 (~780–760 Ma) was thedevelopment of a Centralian Superbasin which linked theOfficer Basin with the other main central AustralianProterozoic to early Palaeozoic basins, and which were also

in close proximity to basins with similar geology in NorthAmerica, Siberia and the Persian Gulf prior to the breakup ofthe Rodinian Supercontinent. Evaporitic units began tomove soon after deposition and were responsible for some ofthe present structural architecture of the basin. At the end ofthis stage, ~100–500 m of erosion may have occurred due toglaciogenic processes associated with deposition of theoverlying Sturtian tillite. Stage 2 (~560–550 Ma) marked theonset of compressional basin development, deposition offurther Neoproterozoic sediments, and culminated in thePetermann Ranges Orogeny with extensive thrust faultingand up to 3000 m of erosion. Stage 3 (~536–507 Ma)comprised Cambrian deposition in elongate troughs(possibly mildly extensional) halted by up to 2000 m of upliftassociated with the Delamerian Orogeny. Some reactivationof earlier thrust faulting also occurred at this time. Stage 4(~500–360 Ma) comprised Ordovician to Devoniandeposition as a thick wedge, thickening to the north againstthe Musgrave Block, and terminated by the Alice SpringsOrogeny.

Fig. 1.2 Well locations and seismic coverage, Officer Basin.

3

The lithostratigraphy of the basin is still relatively poorlyknown, due mainly to poor stratigraphic control and amultitude of sedimentary units with similar environments ofdeposition but of differing ages. The stratigraphy is complex,with at least 26 mappable formations and many members.The formations have been grouped to reflect the structuralstages described above. The Callanna Group sedimentscomprise fluvial and aeolian sandstone (Pindyin Sandstone),and marginal marine evaporitic units (Alinya Formation andCoominaree Dolomite). The intervening Sturtian glacialsequence (Chambers Bluff Tillite) is found only in thenorthern margin of the basin. Both this and the CallannaGroup sequences are terminated by volcanics, also knownonly from the northern margin of the basin. The overlyingLake Maurice Group comprises fluvio-deltaic to aeoliansediments (Tarlina Sandstone, Meramangye Formation andMurnaroo Formation), which is overlain by the lowerUngoolya Group of more marine origin (Dey Dey Mudstone,Karlaya Limestone, Tanana Formation and MunyaraiFormation). The Narana Formation (upper Ungoolya Group)is interpreted to have been deposited as a submarine canyonfill. The basal Cambrian Marla Group comprises the aeolianto marine Relief Sandstone intercalated with the marineOuldburra Formation. The overlying Observatory HillFormation has been well studied and records a variety ofpalaeoenvironments from fluvial to alkaline playa lake. Theupper Marla Group comprises shallow marine to fluvialsandstones (Arcoeillinna and Trainor Hill Sandstones)separated by the shallow marine Apamurra Formation. Theshallowest sediments of the Officer Basin, separated from theMarla Group by the poorly known Kulyong Formation(volcanics and sands), are the marginal marine MountChandler Sandstone, Indulkana Shale and Blue HillsSandstone of the Munda Group. The youngest unit in thebasin is the Devonian non-marine Mimili Formation,restricted to the central Munyarai Trough.

Previous ly there have been s igni f icant problemsassociated with a lack of biostratigraphic correlation tools forthe largely non-marine and Precambrian succession in theOfficer Basin. This has recently been dramatically altered bythe demonstration of abundant acritarchs in the more marineparts of the sequence and establishment of five preliminaryacritarch assemblages that can be used for Proterozoic wellto well correlations. Other biostratigraphic tools that havebeen or may be used in the basin are stromatolites, marineinvertebrates and trace fossils. Other techniques, such asgeochronology, magneto- and chemostratigraphy, and event-and lithostratigraphy, have also proven useful for regionalcorrelation.

The Officer Basin has undoubtedly sourced oil asevidenced from the oil shows recorded, some of which havebeen proven f rom biomarkers to have der ived f romNeoproterozoic sources. Potential source rocks appear to bequite organically lean on average, but this is largely due toconventional sampling techniques not being suitable for thecyanobacterial mat source prevalent in the Officer Basin,where the source lithologies occur as thin laminae in a leanmatrix. In the Siberian Platform, the source for the prolificoil and gas fields is believed to average only 0.3% TotalOrganic Carbon (TOC) and is of similar cyanobacterialorigin. The main source rock formations in the Officer Basin

(Alinya Formation, Dey Dey Mudstone, Karlaya Limestone,Ouldburra Formation and Observatory Hill Formation) haveaverage TOC between 0.2 and 0.42%, but locally may rangeup to 4.6%. Kerogen type is generally oil prone Type I to III,and maximum genetic potentials range from 0.91 to 7.34 kghydrocarbon per tonne of source rock.

Maturity of the Officer Basin sediments cannot be derivedusing conventional vitrinite reflectance measurements due tolack of land plant material in pre-Devonian rocks. Instead,t h e d i s t r i b u t i o n o f t r i a r o m a t i c h y d r o c a r b o n s(methylphenanthrene index ---- MPI) extracted from sourcerocks and oil shows can be used and calculated as anequivalent vitrinite reflectance (VRcalc). The source rocks inthe Officer Basin are thermally mature, with large areas ofboth the Proterozoic and Cambrian source formations beingwithin the present-day oil window (VRcalc = 0.65--1.0),although some areas of the Munyarai Trough, MarlaOverthrust Zone and Manya Trough appear to be overmature. There are difficulties in modelling maturity for theOfficer Basin wells due to inadequate temperature, maturityand kinetic data. The Ouldburra Formation in the ManyaTrough is calculated to have entered the oil window between510 and 370 Ma, and entered the dry gas window at 315 Ma,where it remains at present. On the Ammaroodinna Ridge,the Precambrian succession entered the oil window at570 Ma (and is still within it), and the Dey Dey Mudstoneand Karlaya Limestone are presently just within it. In theMarla Overthrust Zone, the Dey Dey Mudstone and KarlayaLimestone entered the oil window at ~570 Ma and the wetgas window at 550 Ma. In contrast, the Observatory HillFormation entered the oil window at 450 Ma, where itremains.

At least eight reservoir horizons have been identified inthe Officer Basin, nearly all of which are fluvial or aeolianarkosic sandstones with secondary porosity. Reservoirthicknesses are generally in the range 100--400 m, with theexception of multiple sandstone reservoirs in the OuldburraFormation which average 4 m, but cumulatively may reach100 m in individual wells. Carbonate reservoirs with vuggyporosity are also known from the Ouldburra. Core analysisof the sandstone reservoirs indicate excellent characteristics,w i t h a v e r a g e p o r o s i t i e s i n t h e r a n g e 1 0 --2 5 % a n dpermeabilities up to 8000 md. The sands are generally cleanwith low clay content. It is considered that there is low riskassociated with reservoirs or seals in the Officer Basin.

There have been few valid tests of the variety ofcompressional structural traps that have been identified in theOfficer Basin. Trap types consist of foreland and detachedthrusts (including trapdoor structures), tilted fault blocks(associated with salt withdrawal) and salt walls, domes, etc.Potential also exists for subcrop unconformity traps,s t ra t igraphic t raps and palaeo-rel ief associated withsubmarine canyon cutting. Potential volumes of typical trapsare very large, up to billions of barrels, and the smallest areof the order of several hundred million barrels (unrisked oilin place).

Explorat ion and production economics have beenmodelled to quantify the minimum prospect size that couldbe targeted by potential explorers. This model accounted forboth exploration expenditure prior to discovery (dry holes,

4

exploration seismic, etc.) and development capital andoperating expenditures; a 12.5% real discount rate was used.At an oil price of ~US$25/bbl, a 5 million barrel (800 000kL) oil in place field would be economic to produce andexplore for, provided that the field was discovered within theinitial five-year term of a PEL. If the oil price wereUS$18/bbl, the minimum economic field size would be10 million barrels (1.59 million kilolitres) oil in place. Inboth these scenarios, oil would be trucked to market. If alarger field was discovered (50 million barrels (7.9 millionkilolitres)), then construction of a pipeline to Port Bonythonwould be economic.

The undiscovered resource potential of the basin has beenassessed using Monte Carlo techniques, with a 50%probability of exceeding 500 million kilolitres (3 billionbarrels) of recoverable oil. The range of estimates was a 90%probability of exceeding 260 million kilolitres (1.6 billionbarrels) to a 10% chance of exceeding 744 million kilolitres(4.7 billion barrels). While this assessment may appear to beunrealistically large, other Precambrian and Cambrianpetroleum basins (with which the Officer Basin hassignificant geological similarities) in the USSR (MoscowBasin and Lena-Tunguska Province), China and Oman havepotential oil reserves up to 16 billion barrels. Six mainreservoir plays (Pindyin Sandstone, Tarlina Sandstone,Murnaroo Formation, Relief Sandstone, sands of theOuldburra Formation and the Arcoeillinna Sandstone) wereassessed using relatively conservative input parameters, suchas a wildcat success rate of 1 in 10 wells, gross reservoirthickness of 16 to 100 m, net to gross ratios of 35--87%, andreservoir porosities of 12--18%. The potentially productivearea for each play is mapped using all available data on sourcerock distribution, maturity, reservoir distribution andprobable depths to targets.

Abbreviations used in this text are summarised inAppendix 1.1.

5

6

DISCOVERY OF THE ‘OFFICER BASIN’

Petroleum exploration in the South Australian sector ofthe Officer Basin from 1954 in essence has comprised basicsurface mapping, exploratory and stratigraphic drilling, a fewlimited gravity and magnetic surveys, and cursory seismictraverses. The sedimentary basin underlies the Great VictoriaDesert. The remoteness and desolation of the inhospitable,almost inaccessible and largely uninhabitable regionhindered exploration and limited interest in its hydrocarbonprospectivity. But these were factors which led to a large partof the area being proclaimed as the North-West AboriginalReserve in 1921 and being used for the United Kingdom--Australia missile testing program from 1946 to 1980 and forthe British nuclear tests from 1952 to 1963.

One aspect of the preparation for the testing of long-rangemissiles and atomic weapons was the commencement ofmodern geological work in the region. Hydrological surveysby the then Mines Department assisted in establishing sitesfor these programs. As a consequence of this, and a growinginterest in South Australia’s petroleum prospectivity, the firstindications of the basin came through a Bureau of MineralResources (BMR) small-scale reconnaissance aeromagneticsurvey in 1954, which indicated some thick sedimentarysequences (Quilty and Goodeve, 1958).

Earlier announcements about the petroleum prospectivityof the far west and northwest of South Australia had not beenvery encouraging. For example, although there had not beenany drilling for oil in the far west, in 1944 the GovernmentGeologist, Dr Keith Ward, discounted the Precambrian rocksof the northwest because there were then no producingoilfields of Precambrian age in the world (Ward, 1944).

The introduction of specialists and advisers with expertisein new exploration techniques, such as improved drillingstandards and equipment (rotary and percussion drillingreplacing cable tool drilling), geophysics (seismic, gravityand aeromagnetic surveys) and theoretical constructs forinvestigating buried structures rather than deposits (as the oilsearch demanded), was critical to the search after World WarII (O’Neil, 1982, 1995). Evidence of the new approach wasseen in the efforts of the Frome-Broken Hill Co. Pty Ltd, inconjunct ion with the BMR, in the east of the Stateimmediately after the war (O’Neil, 1996a).

Until the mid-1950s, the whole of the far west and muchof the northwest was still known geologically as the EuclaBasin. This comprised an area of ~388 500 km2 in westernSouth Austral ia and southeastern Western Austral ia ,

including 178 700 km2 of the Nullarbor Plain. The MinesDepartment commenced a geological survey, for minerals, inthe northwest in 1953 under geologist Reg Sprigg, who laterclaimed to have referred informally to the area as the OfficerBasin and that it was formally named in 1954 by F.H. Quiltyand P.E. Goodeve (Sprigg, 1983). Although Quilty andGoodeve did report indications of a basin from the results oftheir survey across the area to as far east as Oodnadatta inMay 1954, they did not refer to it as the Officer Basin. Theseparation of the basin into the Eucla and Officer Basins was,however, recorded in the 1959--60 Annual Report of theMines Department. It can be assumed that the name of thebasin is related to Mount Officer and Officer Creek, whichextends from the Musgrave Ranges via Fregon west ofEverard Ranges and into the northern part of the basin.

EARLY EUROPEAN EXPLORATION

In September 1873 during his second trip into the SouthAustralian interior, Ernest Giles and another party member,William Tietkens, had an ‘encounter’ with an estimated 200male Aborigines. Shots were fired by the Europeans inretaliation for the spears thrown. The Europeans escapedunharmed; Giles did not record if there were any blackcasualties. However, he acknowledged that the usual causeof Aboriginal aggression throughout the history of landexploration by Europeans in Australia was white trespass onblack land (Giles, 1889). He named the river at the scene ofthis confrontation ‘The Officer’; it was renamed OfficerCreek six decades later. A hill to the northeast of the creekand west of Mount James-Winter was named Mount Officer---- C.M. Officer was a contributor to the fund raised by BaronFerdinand von Mueller in Melbourne for this expedition(Manning, 1990).

Several exploration parties visited the far west andnorthwest of South Australia in the quest for water supplies,overland stock routes or pastoral land, and to establish linesof transport or communication. Some of these explorationswere also made with an interest in the geology or mineralogyof the land. Edward John Eyre’s overland journey during1840--41 to central and Western Australia attempted to linkSouth Australia with its colonial neighbour. On the way, Eyrepassed through the southern margin of the basin. In 1870,John Forrest, travelling Eyre’s route in reverse, was the firstperson to cross from west to east.

Ernest Giles made five trips to the interior of Australiabetween 1872 and 1876, the first two (1872 and 1873--74)using horses and the next three camels. The ‘ships of thedesert’ were the preferred means of transport for most of the

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explorations in the outlying regions. Giles was accompaniedby Tietkens on the second to fourth trips: Tietkens himselfcontinued exploring and later led the Central AustralianExploring Expedition in 1889 (Tietkens, 1890). It was inSeptember 1873 during his second trip that Giles namedOfficer Creek.

At that time an expedition by William Gosse was tryingto find a route from the Overland Telegraph line (completedin 1872) to the west coast (Gosse, 1874). Gosse and his partyreached Mount Davies in the Tomkinson Ranges in thatAugust, followed a month later by Giles. In 1874, JohnForrest travelled from the west to the Overland Telegraph lineto the south of Oodnadatta across the area of the MusgraveBlock. In the same year, J. Ross examined the area for freshwater supplies and explored for pastoral land west of LakePhillipson (Ross, 1875; Jack, 1931).

During Giles’ fourth expedition, which went fromBeltana to Port Augusta to Perth during May to July 1875, hedespatched Tietkens and Jess Young to examine the area northof Ooldabinna. Giles spelt this as ‘Yooldil-beena’, meaning‘swamp where I stood to pour out water’. It was a native wellnorthwest of Tietkens Wells, which was 70 km north ofOoldea. They went slightly north of latitude 28°, between130° and 132° longitude, to a point which was approximatelythe boundary of the Musgrave Block and the Officer Basin.Giles had hoped that they would find sufficient water suppliesto establish a route from Fowlers Bay to the MusgraveRanges, but this was not to be. Even Tietkens’ Wells, sunkin 1875, were abandoned as one was dry at 18 m and the otherwas very saline at 37 m. Tietkens returned to the vicinity tosupervise further water drilling operations in 1879 (Gara,1994).

Ernest Giles’ fifth expedition, between November 1875and April 1876, was from Geraldton in Western Australia,across the Gibson Desert to the Overland Telegraph line, andto Blinman in South Australia in an easterly traverse throughthe far northeastern reaches of the Officer Basin (includingthe Musgrave Ranges, Mount Officer, The Officer, EverardRanges and Alberga River).

Between 1883 and 1892, the South Australian LandsDepartment undertook triangulation surveys of the area andthe colonial borders (Carruthers, 1892). Carruthers Depotwas named after Jonathon Carruthers, the Department’ssurveyor. During 1891--92, the Elder Scientific ExploringExpedition under the sponsorship of Sir Thomas Elder andcommand of David Lindsay, and including geologist VictorStreich, crossed part of the area while travelling fromWarrina, a railway siding on the Marree--Alice Springsrailway line to Coolgardie, during an investigation intocentral and Western Australia (Lindsay, 1891; Streich, 1892).

There were repeated requests from members of the publicand through debates in Parliament for the northwest regionin the vicinity of the Musgrave Ranges to be examined. Thisinterest focused on the likely mineral (especially gold)potential of the area, the possible expansion of the railwaynetwork to the ranges and the expectation of unlocking moreland for pastoralists and agriculturalists, in particular to helprelieve the unemployment being endured in the 1890sdepression (O’Neil, 1982). Thus, Government GeologistH.Y.L. Brown was sent to Western Australia to examine the

Coolgardie region, which he visited between October andDecember 1895. He reported that the country north of theNullarbor Plain adjacent to the Western Australian border wasa continuation of the geological formation in WesternAustralia and so it could be gold prospective. But theprospecting to then had been cursory and the vast area to theMusgrave Ranges required a more thorough examination(Brown, 1896). Brown himself was an inveterate explorerand between April and June 1896 he explored the westernpart of South Australia from Ooldea north for ~160 km,returned to Ooldea and then went to Mount Eba and Marree(Brown, 1898--99).

Other explorers or prospectors identified with the areainclude J. Lamb (1894), A.H. Warman (~1900) and W.J.Cockrum (~1900). The 1896--97 South Australian StockRoute Expedition, under Captain S.G. Hübbe with WilliamMurray in the party, took nine months to travel fromOodnadatta to Kalgoorlie (Hübbe, 1897). Murray thenrecorded the position of The Officer more precisely (Hübbe,1897). In 1900, a party from the North-Western ProspectingSyndicate of Western Australia reached Oodnadatta aftersuffering various hardships, including encountering strongresistance from Aborigines in South Australia’s northwest(Advertiser, 11.4.1901).

Between 1897 and 1903, Richard Maurice undertook atleast eight expeditions relating to the Great Victoria Desertwhile living for most of this period at Pidinga, 128 kmnorthwest of Fowlers Bay. He recorded data on the plants,animals and landscape as well as collecting mineralogical,biological and ethnographical specimens. During 1898--99he travelled north from Fowlers Bay across the desert,through the Everard Ranges to Stuart (later Alice Springs),and west to Hermannsburg Mission Station in the NorthernTerritory. His 1901 expedition was accompanied by WilliamMurray. This search for water and pastoral land includedsome mineral examination, and attempted to fill in the gapsbetween the expeditions of Giles and Lindsay. They crossedsouthwest to northeast from Ooldea to Tallaringa Well (anAboriginal soak), Oolarinna Spring and the Everard Ranges,and back to Ooldea by a westerly route. Then the party wentfrom Ooldea to Punthanna Native Well and west-northwestpast Pat Auld’s Vat to the western border (Jack, 1931).During this exploration they saw evidence of the visits by theWestern Australian prospectors, Warman, Cockrum, and theLindsay and Hübbe expeditions. The party camped on TheOfficer while travelling to Oolarinna and Ooldea; and againwhen they went to the Northern Territory in 1902 (George,1904; Advertiser, 11.4.1901). In 1902, Maurice and Murraywent north from Fowlers Bay to the Kimberley district inWestern Australia. The mineral specimens they collectedwere given to the Mines Department for analysis.

The South Australian House of Assembly passed a motionin December 1901 that the Government undertake amineralogical examination of the country between Tarcoola,the Musgrave Ranges and the northwest of the State. In thef o l l o w i n g D e c e m b e r , t h e G o v e r n m e n t N o r t h - W e s tProspecting Expedition, including Lawrence Wells, HerbertBasedow and Frank George set forth (Wells and George,1904; Basedow, 1905, 1914). Between April and September1903 the party journeyed northwest from Oodnadatta to‘Todmorden’, Alberga River, Mount Mystery, Krupps Hill

8

and Indulkana (the far northeastern extent of the basin), andreturned. The expedition helped to fill in gaps of the Elderand Horn expeditions; the Horn Scientific Expedition hadgone to cent ra l Aust ra l ia f rom Oodnadat ta in 1894(Winnecke, 1896). The North-West Expedition found littleconclusive evidence of valuable minerals but H.Y.L. Browndoubted its results because of the short time available toprospect properly. Instead he relied on his own impressionsof the region and of geology in suggesting that gold and othermineral discoveries would be made there.

In April 1904, Brown again left Adelaide and visited theregion from Lake Phillipson to the Wildingi granite (Brown,1905; Jack, 1931). His route took him slightly west of MountByilkaoora and north to the Northern Territory border, StuartRange area, ‘Todmorden’, Indulkana, Alberga and BitcheraCreek.

Using Maurice’s camels and equipment, Frank George(then a Mines Department surveyor) led a prospectingexpedition in 1904 from Fowlers Bay to northwest of LakeDey Dey and across the State border to the Boundary Damsalt lakes in Western Australia. He named Lake Maurice,which had been discovered but not named by Ernest Giles in1875, and reported that gold and other metallic mineraldiscoveries were unlikely in the region (George, 1905).Another of his Government prospecting expeditions, during1905--06, went to the southwest of the Northern Territory;upon George’s dea th , Murray ( then wi th the MinesDepartment) took charge and the party went to the Buxtonand Davenport Ranges from Oodnadatta via ‘Todmorden’and Indulkana (George, 1907).

Between 1912 and 1917, the east--west Trans AustralianRailway across the Nullarbor Plain was constructed by theCommonwealth Government in the southern part of thebasin. The geological and surveying work for this projectwas naturally directed towards ensuring the best possibleroute for the line.

The year 1914 was one of severe drought in the State butit was at the end of this year that the Assistant GovernmentGeologist, R. Lockhart Jack, made the hazardous trek to theMusgrave Ranges. The expedition was a geological surveyand an examination for water supplies, minerals and possiblepastoral land south of the ranges. The noted ornithologist,Captain Samuel White, accompanied Jack to ‘Todmorden’,

96 km northwest of Oodnadatta where the GovernmentAstronomer, George Dodwell, joined the group (AR*, 1914;Jack, 1915). Jack was unimpressed with the mineralpossibilities there.

Also during that year a petroleum specialist, Arthur Wade,was appointed by the State Government, at the request ofseveral parties interested in discovering petroleum, toinvestigate several supposed oil-bearing areas in the State(Wade, 1915). Wade’s brief examination of lower EyrePeninsula, essentially the coastal region, extended west toStreaky Bay. He reported in passing that gas in connectionwith mound springs, petroleum-like streaks on Streaky Bayand a ‘bitumen’ discovery at one locality were not evidenceof oil or gas seeping to the surface. His expectations of theState’s petroleum potential were not encouraging and hedismissed the possibility of petroleum supplies being foundin this region in particular.

For the next 40 years there was little activity or eveninterest in the mineral or petroleum prospects of the basin. In1917, Talbot and Clarke from the Western AustralianGeological Survey travelled east as far as Mount Gosse andthe western Musgrave Block. In 1925, Ward and Jack visitedan area lying beyond the occupied pastoral holdings in thenorthwest and reported on prospecting for water there, and twoyears later they inspected areas of the far west where watersupplies might be located (AR, 1925, 1927). Prior to leavingthe Department in 1931, Jack investigated the geology northand nor thwes t o f Ta rcoo la and wen t to ‘Wi lgena’ ,‘Commonwealth Hill’, Coober Pedy, Tallaringa Well amongstother sites on the periphery of the basin (Jack, 1931).

Several of these explorers are renowned for the heroic andepic nature of their journeys. Nevertheless, their endeavoursrarely met their expectations: the land was not conducive tosupporting large populations, it was not good enough forpastoral and agricultural pursuits, nor did it providesubstantial water supplies. Just as these desired outcomeswere not achieved, the mineral and petroleum potentialremained to be tested more thoroughly. From the mid-1950s,however, geological, geophysical and drilling explorationwere to generate limited information from sparse programs.

WEAPONS TESTINGAs part of a fledgling effort to bring South Australia into

the atomic age, such was the interest being generated by theState’s uranium supplies at Mount Painter and Radium Hillfrom the mid-1940s, the desert then seemed an apt site fortests on long-range weapons and atomic bombs (Morton,1989; O’Neil, 1996b). Although they originated as discreteprojects, the tests overlapped in the initial period after theatomic tests were moved to the Australian mainland in 1953.In the context of limited resources, the harsh environment andthe same British, Australian and South Australian politicalmasters, it made practical sense to share equipment, facilities,communications, transport and working time (Morton,1989). For example, the Native Patrol Officers scoured thedesert in respect of both projects as did Len Beadell inestablishing sites and routes, planes from the Maralinga

Lockhart Jack’s party leaving for the Musgrave Ranges from Wan-tapella Well on ‘Indulkana’ in 1914. The Government Astronomer,George Dodwell, is in the lead with his dog, Speck, not far behind.(Photo N679)

*Annual Report , under varying ti t les, issued by the Mines De-partment.

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atomic tests were decontaminated at the long-range weaponsbase at Woomera (named after a non-local Aboriginal spearthrowing and carrying implement) and the Mines Departmentconducted groundwater investigations and drilling for bothprojects.

A major missile testing range operated in South Australiafrom 1946 to 1980 under joint United Kingdom andAustralian control. The general firing direction was fromWoomera over the South Australian desert towards thenorthwest of the continent. Thus, part of the Officer Basinfell within the Woomera Prohibited Zone, an area under thecontrol of the Australian Government, to which access wasrestricted. All people were required to be issued with a permitfrom the authorities at Woomera before entering this area andmovement within the area was often under scrutiny, at leastin theory if not in practice. In 1954, for example, when theAustralian Mining and Smelting Co. was considering a workprogram as part of its licence commitments, Premier TomPlayford wrote to Prime Minister Robert Menzies on behalfof the company to secure access to the zone.

On the mainland, two atomic bombs were exploded in1953 at Emu Field, ~500 km west of Woomera and 250 kmwest of Coober Pedy, in the prohibited zone and in the firingline of the rocket range (Symonds, 1985). The first (Totem 1)was exploded at Emu on 15 October 1953. Some Aborigineshave attributed a ‘black mist’ passing over ‘Wallatinna’ and‘Welbourn Hill’ from this test as a cause of their ill health(Lester, 1993).

Emu, a remote claypan, was difficult to access and thelogistics of the exercise meant that after a second test there,the atomic program was moved to a site 80 km north ofWatson on the Trans Australian Railway. The new site,Maralinga (an Aboriginal word meaning ‘thunder’), is177 km south-southwest of Emu. Seven bombs were testedthere between September 1956 and October 1957. ‘Minortrials’ of small nuclear weapons, which dispersed plutonium,continued at Maralinga until 1963 and the site was abandonedin 1966. Clean-up exercises in 1964 and 1967 were found bythe Australian Royal Commission into British Nuclear Testsin Australia (1984--85) to have not only been ineffectual butalso made the site more dangerous. As a result of this mostrecent inquiry, MESA has been associated with preparationsfor the current clean-up operation.

The Mines Department undertook geological and drillingwork for both atomic testing projects. This began in 1947when Assistant Government Geologist Tom Barnes prepareda hydrological survey with some geological work in thenorthwest for the Long-Range Weapons Project (AR, 1947).A preliminary data search by the Department for the area ofthe atomic tests included checking the region west of thenorth-south railway line to the Western Australian border, andnorth from the Trans Australian Railway to the NorthernTerritory border (O’Neil, 1995). Over the years (and evenafter he became the Director of Mines in 1956), Barnescontinued his special hydrological investigations. Throughthe 1950s, percussion-drilled deep and shallow bores weresunk at Maralinga for underground water and for specialpurpose bores. The water work continued into the 1960s.

The Federal Government’s Petroleum Search SubsidyScheme from 1957 subsidised stratigraphic drilling butrequired the results of work programs to be published or elsethe funding was likely to be refused (Passmore, 1994). Asexploration in the Officer Basin required clearances from theauthorities in charge of both Woomera and Maralinga,security concerns meant that permission was also necessarybefore results could be published.

POST-WORLD WAR II GEOLOGICALEXPLORATION

In 1953, a Departmental party led by Reg Sprigg andi n c l u d i n g R o n C o a t s w e n t t o M o u n t D a v i e s o n amineralogical expedition essentially to investigate uraniumdeposits, but some of the samples collected showed traces ofnickel. (A gold lease had been pegged in the area by theprospector Cockrum in 1900.) In 1954, Special MiningLease 20 was pegged by Gold and Mineral Exploration NLin the Mount Davies area of the Musgrave Block adjoiningthe Officer Basin. The lease was taken over by SouthwesternMining Ltd in 1955. In this period, the Department sankeight bores for private hirers in the vicinity, of which threewere productive (AR, 1955). Nickel mineralisation in thenorthwest province continued to attract attention into the nextdecade. In November 1965, a low-level survey of parts ofthe MANN and WOODROFFE 4-mile sheet areas was flownby the Department as part of an investigation into basic andultrabasic rocks in the area, which was the prime focus of theregional mapping and nickel investigations.

R e g i o n a l g e o p h y s i c a l s u r v e y s w e r e c o n d u c t e dspasmodically in the Officer Basin after the first aerial surveyin 1954. Aeromagnetic surveys over the far northwest,including the Tomkinson, Mann and Birksgate Ranges, wereflown by BMR in June 1960. The Mines Department wasmapping in the field: this focus was essentially mineralogical,with nickel in the Tomkinson Ranges being the target.Nevertheless, in 1960, the first field work on petroleum in thebasin commenced. On behalf of Exoil, the Department’sGeophysics Section ran a single ground traverse of gravityand magnetic observations from Ooldea north along the 131°line of longitude across the Officer Basin using a helicopterto transport the equipment. The survey, which gave furtherevidence of a basin, was conducted along the easternperimeter of Maralinga because permission was refused toenter the area (Mumme, 1961).

Petroleum industry exploration is reviewed in a sectionbelow. The following refers to some of the State Governmentw o r k . D u r i n g 1 9 6 1 --62 , a Depar tmen ta l geo log i s taccompanied a brief aerial reconnaissance of the southernOfficer Basin and part of the Eucla Basin with Exoilrepresentatives. A Departmental seismic crew was operatingwest of Emu Field: international seismic crews were alsointroduced to the basin under contract for reflection andr e f r a c t i o n s e i s m i c s u r v e y s . D u r i n g 1 9 6 4 --6 5 , t h eDepartment’s Seismic Geophysics Section spent 31⁄2 monthsin the South Austra l ian par t of the Eucla Basin onreconnaissance work and detected a sedimentary trough at am u c h g r e a t e r d e p t h t h a n a n t i c i p a t e d . A s e i s m i creconnaissance was made from Maralinga to north of Emuand then from Emu to Mabel Creek (AR, 1965--66).

10

Although the Department was then scaling down itslarge-scale seismic operations, it ran a seismic survey in theeastern Officer Basin in July 1966. The combined seismicreflection, seismic refraction and gravity survey was run as asingle traverse across a marked aeromagnetic low beginningat Emu 1 and extending 122 km north to the lower reaches ofthe Officer Creek. This was considered as ‘probably the mostdi f f icul t se ismic t raverse’ the Depar tment had everundertaken as the dune-covered terrain comprised east--westtrending, scrub-covered sand ridges which made accessdifficult even with the use of a bulldozer. The mobile campwas serviced with fresh water from either Maralinga or‘Everard Park’, making for long hauls. The water for drillingwas saline, and was obtained from shallow bores near EmuField and bulldozed soaks 80 km north of Emu. Thereflection shooting indicated a probable thick sedimentarysection in the north of the basin (AR, 1966--67; Wopfner,1969, 1970).

During the 1960s, the Department was concerned toincrease the quantity and quality of exploration in the basinand to expand the evolving knowledge of the basin’s geology.The first significant geological traverse of the Tallaringa Wellarea was made in 1966 by Departmental geologists BruceWebb and Bryan Forbes, although Brown and Jack had madethe first geological investigations there decades before(Benbow, 1993). In the mid-1960s, the Departmentre-examined all of the rock samples from the basin and usedthe services of Amdel for petrographic testing of newsamples. Departmental petroleum and regional mappinggeologists visited the basin to investigate sedimentary rock

outcrops. Reconnaissance work, including two regionalhelicopter surveys of the Officer and Eucla Basins during1968--69, helped to define targets and further delineated themargins of the basins.

From the early 1970s, the Department also undertookstratigraphic dril l ing, including Mount Willoughby 1(November 1970), Wallira West 1 (Arckaringa Basin, March1971), Marla 1 and Manya 1 (September 1974), andMurnaroo 1 (November 1976). Marla 1 and Manya 1 wereon the far eastern perimeter of the Officer Basin. Also drilledwere Marla 1A and 1B; drilling problems caused Marla 1B,~20 m from Marla 1A, to be abandoned at 379 m (Pitt et al.,1980).

However, the Department’s basic exploration work thenwas often curtailed because of funding constraints. Thecessation of field work in the basin came at a critical time;the similarity between the sequences in the basin and thoseat Palm Valley and Mereenie in the Northern Territoryrequired further assessment. During 1971--72, the drilling ofa major well on the southern shelf of the Munyarai Troughwas not carried out due to lack of funds, but a ground traversewas conducted between Everard and Watson, and someexperimental seismic work was recorded from WallatinnaWaterhole into the Munyarai Trough. During 1972--73,seismic profiling produced poor results in a narrow extensionof the basin in the east; on the northern margin, south of theEverard Ranges, gravity, magnetic and seismic data wererecorded. In 1974, the Department continued its seismicoperations in the eastern Officer Basin and recorded 140 km.

Mapping and drilling in the Musgrave, Everard andTomkinson Ranges in the northwest (particularly at MountDavies for nickel) continued during the 1960s and into the1970s. But, by the mid-1970s, access to the area for theDepartment and mining and petroleum companies hadbecome increasingly more restricted. Despite the promisingindications of potential mineral wealth in the area and thevastly underexplored petroleum potential, Departmental andcompany work programs ground to a halt there (O’Neil,1995).

ABORIGINAL LAND RIGHTS ANDEXPLORATION ACCESS

The Aboriginal occupants of the area had several differentclan backgrounds but they are now labelled broadly asPitjantjatjara and Maralinga people, though within thesegroups there are strong tribal and regional differences: forexample, ‘According to missionary Violet Turner, OoldeaSoak ... was visited for ceremonial purposes by ‘‘Kukatasfrom Tarcoola, the Minnings from Eucla, the Aluridjas fromthe Musgraves, the Wongapitchers from the Mann Ranges’’.’(Mattingley and Hampton, 1988, p.235). However, for muchof the period, the Aborigines were treated as a monoculturalrace and this is evident in the promotion of reserves for theirprotection and improvement or, in some cases, to ease theirpresumed passing. Daisy Bates, at Ooldea from 1918 to1934, was one who attempted to retain the Aboriginalpeople’s independence.

The Officer Basin seismic survey, looking south along the surveyline from shot point EO 155, in 1966. (Photo N16912)

Refuelling the helicopter during the Officer Basin gravity survey inMay 1962. (Photo T3372)

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For its part, the Mines Department had elsewhereconfronted the question of Aborigines, their relationship tothe land and mining by Europeans. In 1905, the Departmentreserved land near Parachilna for Aborigines to use in theirtraditional way. Another instance occurred after Jack’s tripin 1914 to the Musgrave Ranges; in 1919 he reported on thedesirability of establishing a reserve for Aborigines in thenorthwest (Jack, 1919). An important development followedwhen in 1921 the State Government gazetted more than56 700 km2 of the land as the North-West Aboriginal Reserveto safeguard the Aborigines against encroachment by whitepeople, be they settlers or transient interest groups such asminers and prospectors. Additions were made to the reservein 1938, 1949 and 1974; by 1949, the area proclaimed inSouth Australia was 71 500 km2, which with additional areasin Western Australia and Northern Territory formed theCentral Aboriginal Reserve.

Establishing reserves for Aborigines began soon afterSouth Australia was colonised, but those reserves werei n t e n d e d t o b e p l a c e s w h e r e A b o r i g i n e s w o u l d b e‘Christianised and civilised’. The North-West AboriginalReserve, however, was in part more of a case of ‘out of sight,out of mind’, as was the nearby Ernabella Mission (run bythe Presbyterian Board of Missions) which combined thereligious theme with an encouragement of Aboriginal cultureafter it was established in 1937 in the Musgrave Ranges(O’Neil, 1995). The United Aborigines Mission, founded atOoldea in 1933, closed in 1952 and the people were movedto Yalata Aboriginal Reserve, ostensibly because of theimpending long-range weapons and atomic tests. Amata(then ‘Musgrave Park’, 130 km west of Ernabella) wasfounded in 1961; later reserves were established at Fregonand Indulkana, the latter in 1968 from a small section of theGranite Downs pastoral lease.

The reserves were not inviolate for all time and they weresubject to European intrusion for defence, mineral andpetroleum exploration, and geological mapping. However,companies wishing to work in the North-West AboriginalReserve had to observe rather strict guidelines in theirrelations with the local Aborigines. In 1954, when theAustralian Mining and Smelting Co. was proposing itslicence commitments, the Director of Mines wrote to theAborigines Protection Board to request information onaccess conditions. The company subsequently advised himthat it did not intend to enter any areas covered by theAboriginal reserves although it did not have a map showingthese (MESA file 2658/1953).

The South Australian Government’s Aboriginal LandsTrust Act 1966, prepared by Don Dunstan when he wasAttorney-General and Minister of Aboriginal Affairs from1965 to 1967, set the pace for the nation on legislation andpolicies on Aboriginal affairs. A Government proposal toprovide compensation to the Aboriginal people to ensure tothem control of mineral rights in any lands held as Aboriginallands was defeated in the Legislative Council . TheGovernment instead signed an Indenture with the AboriginalLands Trust to the effect that all royalties for any mining onAboriginal Lands Trust land would be paid to the AboriginalLands Trust.

Under the Act, the Aboriginal Lands Trust was authorisedto hold land titles in trust on behalf of Aborigines in SouthAustralia. The Act did not permit Aboriginal land owners tonegotiate mining agreements; the M ining and Petroleum Actsapplied to Trust land but could be subject to additionalconditions. The Act was amended in 1973 to permitAboriginal communities to control mining and explorationon Trust land, which was then exempted from the M ining andPetroleum Acts; exploration and mining activities could notbe prohibited, but the Trust and an individual communitycould stipulate conditions of access and operation, and theGovernor could proclaim these special conditions. TheGovernment could grant money to the Trust from explorationlease payments or mining royalties obtained through activityon Trust land. However, the Trust preferred to seek moretitles to land rather than engage in managing the titlesacquired, an activity which, in its view, was the responsibilityof the Aboriginal communities concerned. Up to 30 June1984, the Trust held 485 585 ha of land; as there had been nomining on this land, no mining royalties had been paid(Mattingley and Hampton, 1988).

The North-West Aboriginal Reserve included part of theOfficer Basin which, in contrast to Jack’s earlier views, wasnow considered to have mineral and petroleum prospectivity.Since World War II, the Department had sought to promoteexploration opportunities in the area by mapping and drilling,especially in the 1960s, and companies such as SouthwesternMining, Exoil and Conoco had explored in the area too. In1972, the Governor of South Australia, Sir Mark Oliphant,

1. Each member of any party entering the reserve to supplytwo personal references of character from reputablepersons preferably Justices of the Peace, GovernmentOfficials, Ministers of Religion, the Director of Mines[or the company’s Managing Director].

2. Each member to supply a medical certificate to theeffect that the person is in good general health and isnot suffering from any contagious disease.

3. That the leader of any party give an assurance that hewill do all in his power to prevent any members of theparty from clashing with the aborigines, will notencourage or permit the aborigines to congregate neara n y c a m p a n d t h a t t h e l e a d e r w i l l a c c e p t t h eresponsibility of seeing that none of the party areintimate with female aborigines.

4. That no member of the party shall remove from ther e s e r v e n o r t r a d e w i t h t h e a b o r i g i n e s f o r a n yethnological specimens and shall not distribute to thenatives any goods or chattels by way of barter orexchange.

5. That the leader of the party shall supply the AboriginesProtection Board with regular reports covering thenumbers and conditions of any aborigines encounteredand places where they met, any incidents whichoccurred between the party and the aboriginals, andanything of general interest to this Department.

On 1 April 1954, the Secretary of the Aborigines Protection Boardwrote to the Director of Mines (MESA file 2658/1953) stipulatingthe guidelines for persons wishing to enter an Aboriginal reserveon behalf of the Australian Mining & Smelting Co. Ltd.

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included the Musgrave Ranges, Ernabella and Everard Parkin a tour that he made to inspect the Aboriginal situation inthe State.

An Australia-wide campaign for Aboriginal land rightshad been stimulated and intensified by the Aboriginal tent‘embassy’ on the lawns of Parliament House in Canberrabetween January and July 1972. Almost immediately uponthe e lect ion of the Whit lam Federal Government inDecember 1972, A.E. Woodward QC was commissioned toinquire into Aboriginal land rights in Federal territories. InMay 1974, the Woodward Commission recommended thatAborigines should receive title where traditional landownership in Aboriginal reserves and other unalienatedCrown lands could be shown, and in alienated land wheretraditional land ownership could be demonstrated or if titlewas socially and economically desirable. The Commissionconsidered that mining on reserves should be allowed butonly with Aboriginal consent, except where mining was inthe national interest. Aboriginal claims to mineral rightswere rejected.

Fo l lowing the S ta t e ’ s p ionee r ing l eg i s l a t ion onAboriginal land and in accordance with the WoodwardCommission’s recommendation, in May 1974 the DunstanGovernment announced an important initiative. In respect tomineral exploration and mining, Aborigines living in the areaconcerned were to be consulted so that they would fullyunderstand the proposed work and, upon consenting to it,could participate in the venture to the fullest extent that theywere able. Only in matters of State or national importancewould Cabinet consider over-riding this (AR, 1973--74).

Government officials met with the Aboriginal people atYalata early in July 1974 to discuss implementation of theGovernment’s rules. Meanwhile, active exploration was heldover in 1974 and 1975 when the Pitjantjatjara people and theDepartments of Mines and Community Welfare undertook toidentify and locate Aboriginal sacred sites in the reserve. Ina sense this continued the concern for the local Aboriginesthat had led to the Reserve’s creation. For example, seismiclines were to be positioned so that sites of significance wouldbe avoided, training and employment were offered to someAboriginal people to work with the exploration parties, and

the land would be open under protection so that theDepartment and companies could go there amicably byagreement. An industry and Departmental preference forcompletely unrestricted access was not likely.

The crews would occasionally help Aboriginal groupsduring Departmental field trips to the Musgrave Ranges areaof the reserve. In September 1976, Departmental geologistColin Gatehouse and other Government officials consultedwith the Aboriginal people, and at Coffin Hill (on the northernperimeter of the Officer Basin) Gatehouse completed somejobs for the Aborigines. During the course of theirdiscussions with him concerning exploration and mining inthat area, the tribal elders made known their wish for the landto be transferred to them.

There was increasing public interest in handing back landto the Aboriginal people (Toyne and Vachon, 1984). Basedon experiences of Aboriginal communities in the NorthernTerri tory, part icularly through the impact of miningcompanies and their activit ies, the Pit jantjatjara andYankunytjatjara communities in the northwest of the Stateformed the Pitjantjatjara Council in 1976. The Departmenthad already experienced some difficulty in getting itsscientific parties into Pitjantjatjara country, and this was awarning of tougher times to come. The council pursued itsclaim to land title without reference to the Aboriginal LandTrust, arguing that, because the Pitjantjatjara’s link with theland and their lifestyle had been maintained, then their landshould not be subject to other Aboriginal people who had losttheir traditional ways. Premier Dunstan’s election policy in1977 committed the Government to implementing land rightsfor the Pitjantjatjara people and, in November 1978,Parliament considered the Pitjantjatjara Land Rights Bill. Itspassage was delayed by the Premier’s resignation because ofill-health and the subsequent electoral defeat of his successorin September 1979. A modified version of the Bill was finallypassed by the Tonkin Government on 4 March 1981, thoughit was not proclaimed until October of that year.

The Mines Department drilled for water in and around the North-West Aboriginal Reserve in 1970 and 1971 on behalf of the Depart-ment of Aboriginal Affairs. Four engine-driven and sevenhand-operated pumps, four windmills and storage tanks were in-stalled to provide water supplies for the Pitjantjatjara people.Being erected by the Department at Indulkana in 1971 were this5000 gallon tank on a 30-foot stand and 48-foot windmill. (Photo

T21773)

A Mayhew drilling plant at site 4 on the Indulkana AboriginalReserve, July 1970. Ordovician sandstone of the Indulkana Rangeis in the background to the north. (Photo T12568)

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The Ministers of Mines and Energy wanted to ensure thatthe Bill would not totally block that land off for any futureexploration and development; a lengthy process of protest,extensive negotiation and consultation about the legislationwith the Aboriginal people ensued. Although successiveGovernments supported the concept of land rights, theyopposed sterilising huge tracts of land from any activity at allfor all time. The Department’s previous investigations in thePitjantjatjara Lands, in particular into the potential forpetroleum, had aroused interest from companies and, with theland rights issue apparently resolved, access to the OfficerBasin was encouraged by the Department, especially becauseof traces of oil bleeding from Byilkaoora 1, a stratigraphicwell drilled in May 1979 at Mount Byilkaoora in thenortheastern reaches of the Officer Basin. Although theMinister had previously called for expressions of interest inthe area from companies, it was still too early to becomeexcited about oil because the Pitjantjatjara were concernedwith winning their battle for land rights, and a proposedexploration program was continually deferred.

T h e o r i g i n a l Pit jant jat jara Land Rights Bi l l h a destablished Anangu Pitjantjatjara (Pitjantjatjara people ofcentral Australia) as a legal entity with title to ‘nucleus’ lands,that is the North-West Aboriginal Reserve and any pastoralleases in the region held by Aborigines. It also proposed aright to claim ‘non-nucleus’ land, such as nearby pastoralleases held by non-Aboriginal people, and a right to banexplora t ion and mining on the i r land. The TonkinGovernment objected particularly to these latter proposalsand, in February 1980, Premier David Tonkin announced thatmineral exploration would be allowed on non-nucleus lands.In addition, the Government announced there would be aworking party to register sacred sites on Pitjantjatjara landbut this idea was unacceptable to the Pitjantjatjara Counciland the sacred sites working party proposal lapsed withoutthe party holding a meeting.

Fur the r nego t i a t ions r e so lved the c l a ims to thenon-nucleus lands, the controls over exploration and mining,the rights of opal miners at Mintabie, and the Granite Downslease. The Government incorporated significant concessionsto the mineral ownership, royalty and disturbance provisionsof the Bill. The inalienable freehold title to 102 630 km2 ofarid Reserve land and vacant Crown land was vested inAnangu Pitjantjatjara. Some non-nucleus land at GraniteDowns was to be included in the deal, from 2008 when theleases expired, but no further claims were to be allowed there,nor could other vacant Crown land on pastoral leases outsidethe Reserve be claimed. Exploration and mining were notbanned, but the Pi t jant jat jara people could st ipulateconditions of access and operations and were entitled tocompensatory payments for disturbance to their land, peopleand way of life. The Minister of Mines and Energy retainedthe right to appoint an independent arbitrator if explorationor mining was vetoed or allowed but subjected to conditionsto which the mining company objected. The economicsignificance of a mining project to either the State or Australiawould be a pr ime considera t ion for over- r id ing thePitjantjatjara’s interests. The opal miners were granted a21-year lease for the township of Mintabie.

The transfer of the land title to Anangu Pitjantjatjara wasmade at a ceremonial occasion presided over by PremierTonkin on 4 November 1981 near Ernabella. Yami Lester(1993, pp.148-149) recalled the occasion:

I’ll always remember the premier’s speech that day. Hesaid: ‘All the world and the people of South Australia arewatching you and what you’re going to do with this land’.So I often remind Anangu about that: ‘They’re watchingyou’. If we don’t do the right thing on this land, theGovernment is always watching to take it away. And that’sthe thing I can’t understand. It’s hard! We know this hasalways been our land. We got the stories, we got the culture;we got the language; we got the Law -- our own Law. Sowhy is the white man saying we’re watching you, watchingwhat you’re going to do? The land was ours all the time.OK, we didn’t have a piece of paper, but it was still ours.

While the Act recognised Aboriginal interests, thesubsequent closure of the land to exploration, and often toentry, indicated that in practice the mining and petroleumindustries were discouraged.

Monster of Community Welfare

Dear Sir

We want this areas. So we can try to get this land for us.So we have meeting at Coffin Hill all old people want thisLand this is what they want. 39 Gilpi wati have been thismeeting and we been writed the Line on the map showingor country Some Old Gilpi write name on map to show theytrue country and after this meeting we want Mr Busbridgeand Mr Nicholas to come to Indulkana for meeting so wecan have meeting in Dec the 6 and we want this country fora l l the people wi th name underneath Manage I l turCommunity.

Punch Thompson TaylorWindlass Jim PingeyJimmy Stewart WillyMike Willy MurrayPunch DanJack Cox MurrayJack Windlass Harry WilandRay Ayaiya Charlie TunkinPaddy Wilbur BrooksCharlie Tambo Mark AndersonTommy Tommy QueamaMicky Norman

King Everard Bob JonesJimmy David Jack BakerTaylor HarryCon Joe WindlassLarry Jimmy N.Old Everard Killy B.Mike

Transcript of a letter written to the Minister of Community Welfare,Ron Payne, by a group of Pitjantjatjara males (Gilpi -- tjilpi -- anold man or elder of the group; wati -- a man) at Coffin Hill in theNorth-West Aboriginal Reserve on 27 September 1976. Not allsignatures could be transcribed accurately and the second listprovides additional names of some of those who signed the map ofthe North-West Aboriginal Reserve.

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During the process of proclaiming the Pitjantjatjara LandRights Act, the Department had eight applications involving16 companies under consideration for exploration in the area.However, after so long in the balance, the Government’simmediate moves to encourage exploration on Pitjantjatjaraland did not give the Pitjantjatjara time to adapt to the newregime. In 1980, a consortium led by Haematite PetroleumPty Ltd (the precursor of BHP Petroleum) had already appliedfor a Petroleum Exploration Licence (PEL) in the OfficerBasin in Pitjantjatjara land.

After about a year of negotiating the process broke downwhen discussing the question of up-front payment ofcompensation for exploration work (the seismic lines, roads,airstrips, etc.) for disturbing the homelands out fromIndulkana, Mimili and Fregon. The Bannon Government,elected in November 1982, maintained support for land rightsbut downplayed the significance of the mining sector and soindicated to companies to give the Pitjantjatjara time to thinkthrough and discuss the issues. The Act was now beinginterpreted in a way which had not been intended so thatexploration could be frustrated or denied. But the outcomewas one which really pleased neither the Government nor theDepartment. Another decade was to pass before real progresswas made to resolve land access issues.

While the Act specified compensation for disturbance,Haemat i te refused to budge on the i ssue of payingcompensation up-front for disturbance to the land during theinitial exploration. Claiming that arbitration would involveexpensive legal fees, Haematite also did not want to establisha precedent for the mining or petroleum industries by payingcompensation (McRae et al., 1991; Advertiser, 11.7.1984;MESA confidential file SR 27/2/43). The Government’sunderstanding was that there would be no up-front paymentsfor exploration; compensation clauses would apply if aresource was found. In July 1984, the Haematite consortiumwithdrew its licence application.

The Maralinga Tjarutja Land Rights Act 1984, althoughsimilar in many respects to the Pitjantjatjara Land Rights Act1981, modified the conditions for mining on Aboriginal land;‘exploration’ was defined more clearly than under the Miningand Petroleum Acts, sacred sites were excluded from initial

tenements, the Minister of Aboriginal Affairs was to beinvolved in decision making, and compensation for work ordisturbances in the exploration phase was limited to thatallowed in the Mining and Petroleum Acts (McRae et al.,1991). The new Act generally limited the Yalata (southernPitjantjatjara) Aborigines’ influence over mining on theirland. A resort to arbitration was retained at the productionstage but the requirement for the Yalata Aborigines’ consentfor access to their land was lessened. Compensatorypayments to the Yalata Aborigines were maintained forexploitation agreements. The freehold title to the 76 420 km2

of Maralinga Tjarutja land was granted on 6 December 1984;the land grant document was presented ceremoniously on 18December 1984 near Maralinga.

While it was fine in theory that companies and Aboriginesmight negotiate successfully, there was a substantial degreeof difficulty in reaching agreement, especially as the view ofthe industry at that time was that petroleum and mineralpotential was not high. Although relations between thePitjantjatjara people and the Department could also becometense on occasions, the Department became more attuned tonegotiat ing and assist ing Aboriginal groups, and themid-1980s saw remote Aboriginal communities providedwith better electricity supplies and water wells being drilledby the Department on Aboriginal land. By then the higherworld oil prices of the early 1980s had again spurredpetroleum exploration in the Officer Basin.

Premier Tonkin symbolically proclaiming the Pitjantjatjara LandRights Act at Ernabella on 4 November 1981. (Photo T23104)

South Australian Premier David Tonkin and Pantju Thompson on2 October 1980 signing an agreement enabling the PitjantjatjaraLand Rights Bill to proceed. (Photo 32375)

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The first PEL granted within Pitjantjatjara lands wasissued in November 1985 to Amoco Australia Petroleum Co.(50%; the operator), AP Oil Pty Ltd (20%), CrusaderResources NL (15%) and Quadrant Energy Development Ltd(15%). PEL 29 covered 20 749 km2 of the Officer Basin inthe southeast of the Pitjantjatjara Lands. The Amoco groupreached an agreement with a company owned by thetraditional owners to become involved in a joint PEL. Afterthe Haematite episode, the Pitjantjatjara Council had appliedfor a PEL in October 1984. The Department advised theMinister to refuse the request because the application failedto demonstrate that the Council had the financial resourcesand technical expertise to fulfil the licence conditions. TheCouncil acted on suggestions from the Department’s Oil, Gasand Coal Division and pursued expressions of interest fromrecognised petroleum companies. The Pitjantjatjara Councilformed AP Oil Pty Ltd and then negotiated to share in alicence with the Amoco consortium and an amendedapplication was resubmitted.

The agreement with the Amoco consortium involved thegroup funding the Council’s ‘administration expenses’ andincluded the novel provision for AP Oil to hold a 10% votein the management of the operation. In return, the Councilexercised its statutory right not to claim compensation fordisturbances to the local community during exploration andproduction. The agreement also provided that AP Oil wouldhold a 20% carried interest share in the licence during theexploration phase. This did not include any contribution toexploration costs. On the discovery of an economicpetroleum deposit, AP Oil had the right to convert this carriedinterest to a 20% working interest on the payment of 40% ofthe cost to date. Alternatively, they could choose to retain a10% net profit interest in the discoveries.

This agreement was an interesting development inAustralian petroleum exploration as it predicted a wayforward for mining and exploration on Aboriginal land.However, the project stalled in October 1987 when thelicence was cancelled due to the effects of the oil crash; oneof the joint venturers collapsed following the fall in world oilprices in 1986. Anangu Pitjantjatjara remained prepared toenter joint ventures with companies which combinedtechnical expertise with a respect for the Pitjantjatjarainterests and concerns.

The Department continued to signal its desire to haveAboriginal land opened up for mineral searches. Forexample, in 1989 it re-assessed the mineral potential of theMaralinga lands (Flint et al., 1989) and late in 1991 a datapackage t i t led Geology and minera l po ten t ia l o f thePitjantjatjara lands was released. These areas were the leastexamined mineral frontiers in the State. Departmentalofficers had continued talking with Anangu Pitjantjatjara,who seemed to favour o i l explora t ion over minera lexploration, since petroleum companies were considered tohave substantial financial resources. Furthermore, the focusfor the proposed petroleum searches is well away from thearea of rock outcrops in the Musgrave Ranges whereAboriginal communities and sites of significance areconcentrated. More recent exploration initiatives involvingPitjantjatjara land are described below under ‘Revitalisation’.

PETROLEUM INDUSTRY EXPLORATION

OEL 8

The first Oil Exploration Licence (OEL) for the OfficerBasin was granted to the Australian Mining and Smelting Co.Ltd (operating through Frome--Broken Hill with fundingfrom Consolidated Zinc Corporation Pty Ltd) for two yearsfrom January 1954. This followed the discovery of oilelsewhere in Australia, notably at Rough Range in WesternAustralia in 1953 which stimulated exploration in SouthAustralia (including the formation of Santos and Geosurveysin March 1954) and brought a revised approach to explorationthinking. OEL 8 covered 125 486 km2 of the southwesterncorner of the State (Fig. 2.1). The company’s work wasconfined to the southern portion of the licence and extendedinto Western Australia. In December 1953, Frome-BrokenHill requested BMR to survey part of the area, and Quilty andGoodeve (1958) first reported on the basin after BMR hadflown six flights in May 1954, including from Oodnadatta toCeduna, Kalgoorlie to Oodnadatta, and Forrest to MountHarriet, Cook and Ceduna. In March 1955, the companyproposed sending a field party to study rocky outcrops southof the Musgrave Ranges but the company’s director, MaurieMawby, held little hope for the area. He wrote to the Directorof Mines prior to surrendering the licence in May 1955 that:‘It would ... appear that the only area of thick sedimentarysection in the Eucla Basin lies immediately south of theWarburton--Musgrave Ranges and there the sediments holdlittle prospect of oil generation’ (MESA file 354/1955).

OEL 12

After the withdrawal of Australian Mining and Smelting,Clarence River Basin Oil Exploration Co. NL lodged twoapplications for OEL in February 1956. The first was grantedin May 1956 as OEL 12 over an area between Coober Pedyand Pimba. The second application over an area of the EuclaBasin lapsed because the company was unable to completethe geological studies necessary to formulate a properapplication for the area (MESA file 244/1956). At this time,the Department suggested to the Minister of Mines that afurther investigation with air and ground field work of theNullarbor Plain over about six months was warranted todetermine if test drilling was necessary. Tom Barnes wrotein March 1956 (MESA file 244/1956):

It is my personal belief that the Nullarbor Plain is anarea where the Government might well undertake acomprehensive geological survey on its own accord ---- thearea is very poorly understood geologically, and hasconsiderable hydrological interest, both for W.R.E. inrelation to Maralinga, and also the few landowners; inaddition to the unknown oil prospects.

In such an isolated area it would be impossible toexercise effective control over an exploratory company, anda l icence should only be granted to a company ofunquestioned integrity.

OEL 19 and 28

OEL 19 was granted over 222 160 km2 in the Officer andEucla Basins to Oil Drilling and Exploration Pty Ltd inOctober 1958. The company drilled Eyre 1 and Gambanga 1in the Eucla--Madura portion of the Eucla Basin. OEL 19 was

16

transferred to its subsidiary Exoil Pty Ltd in July 1959 andwas surrendered in September 1962, but a consortium led byExoil (Oilmin NL from July 1973) held it until 1976; by thenthe area had been reduced progressively to 24 605 km2

through subsequent renewals (being reissued as OEL 28 inOctober 1962 over 160 000 km2 and as PEL 10, 11 and 12).

The exploration boom that permeated the Australianmining scene from the mid-1960s introduced several newplayers to the northwest oil and gas search. Transoil Pty Ltd,

Continental Oil Co. of Australia Ltd (Conoco) and AustralianSun Oil Co. Ltd were farm-in companies to Exoil’s licencebetween December 1964 and September 1969. The methodof a licensee ‘farming-out’ areas to others prepared to‘farm-in’ to a joint arrangement was legislated for by the StateGovernment’s amendment to the M ining (Petroleum) Act1940 in 1958, which also allowed a company to chequerboardits permit area and work the new blocks over five years insteadof one. The introduction of these companies, particularly Conoco,strengthened exploration prospects in the area.

Fig. 2.1 History of Officer Basin petroleum tenements, 1954--97.

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Exoil’s Mabel Creek seismic survey from April to August1962 did not provide good quality data but it did reveal thefirst definite proof of a thick, subhorizontally beddedsedimentary sequence (MESA confidential file SR 11/5/29).The Namco traverse of 470 km went west across the basinalong ‘Giles Road’ north of Lake Dey Dey to Serpentine Lakeson the border and into Western Australia. Exoil’s initialseismic and gravity surveys were followed up by the drillingof Emu 1, the first petroleum wildcat well in the basin, whichthe Department drilled as a shallow stratigraphic test well nearthe Emu Field for Exoil. It was spudded in August 1963 andabandoned two months later at 417 m after reachingunmetamorphosed shale and sandstone (Grasso, 1963).

Conoco participated in an aeromagnetic survey over theeastern Officer Basin after farming into the area. The survey,which covered ~155 400 km2 between latitudes 27° and 30°S,and longitudes 129° to 134°E, was conducted from October1964 to April 1965 except for three weeks when theMaralinga aerodrome was closed. The aircrew was based atMaralinga, Forrest and Oodnadatta. The survey identifiedthe western half of the permit as having more petroleumpotential because of the average thicker sections (~ 2440 m)on the southwest shelf and trough with ‘more foothills typeof structures’ developed within it (Steenland, 1965).

In 1965--66, Seismograph Services Ltd carried out aVibroseis reflection survey for Conoco near Serpentine Lakesin the northwest of OEL 28. This was followed by ahelicopter-supported stratigraphic survey beginning inMarch 1966 over outcrops to the north of the licence and onits margins. The Munyarai structure was discovered by theDepartment’s 1966 seismic line (the EO line). Conocosubsequently detailed the structure by an additional seismicgrid and drilled stratigraphic well Officer 1 (TD 183 m;Krieg, 1967) in November 1966 at the northern end of the EOline.

Two deep wildcat wells, Birksgate 1 and Munyarai 1,were then drilled. Birksgate 1, spudded in January 1967, waspositioned on a minor anticline as defined from the seismicwork and reached 1878 m (Henderson and Tauer, 1967). Thedrilling required access clearance from CommonwealthDepartment of Supply and the South Australian Departmentof Aboriginal Affairs. Constructing a road to the site wasexpensive and so heavy loads were carried by large trucksfitted with desert tyres; earth moving equipment was used andan airstrip was laid down at the drill site. Access was difficultbecause of the high sand dunes and there was a lack of water.A stratigraphic well also at Birksgate, spudded in November1966, was drilled to 644 m, plugged back to 392 m andcompleted as a standby water well. Birksgate 1 passedthrough probable Precambrian sediments to its total depth.In February 1967, Conoco proposed leaving this and anotherwater well at Birksgate to the Mines and/or Aboriginal AffairsDepartments because the effort to find potable water wasexpensive and it would have been a waste not to retain them.Aboriginal Affairs was very interested and arranged with theMines Department for one well to be capped and the other tobe fitted with a windmill and tank.

In the following year Namco, on behalf of Conoco,followed up the structural lead with more detailed seismicwork using the ‘thumper’ method. As a result, a largeanticlinal structure was delineated and a site for Conoco todrill Munyarai 1 was chosen. But heavy rain prevented thewell from being spudded until July 1968. Munyarai 1terminated at 2899 m without hydrocarbon shows beingrecorded (Conoco, 1969).

Looking south past the leading vibrator truck along a longitudinalline east of Serpentine Lakes in the Officer Basin on 1 March 1966.(Courtesy H. Wopfner; Photo 44362)

Personnel and no. 2 core at Continental’s bore in the Officer Basin,December 1966. (Photo T7157)

Using a Mayhew to drill a shothole with compressed air at GilesJunction, west of Emu, for Namco International Geophysics Ltd in1962. (Photo T6491)

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OEL 33

In 1964, licensee Al Jergins (Outback Oil Co. NL) andDepartmental officials made a two-day aerial reconnaissanceof the Eucla Basin from Ceduna to Forrest (WesternAustralia) and back to Ceduna via the coastline. Some ‘geo-morphological’ anomalies and joint or fault controls werenoted. The company had taken up OEL 33 (126 910 km2 ofthe Eucla Basin and offshore) in January 1964. The focuswas still the Eucla Basin to the south, where in November1964 Outback Oil drilled Cook 1C (A and B were unsatis-factory sites but the third attempt became Cook 1) near Cookin the northern Eucla Basin. It was abandoned as a dry wellafter bottoming in probable Neoproterozoic sediments at279 m.

Outback Oil undertook a helicopter gravity survey overmuch of its licence area west of 130°45’E followed by anaeromagnetic survey of its offshore area. Between Februaryand May 1966, four shallow wells (Hughes 1, 2, 3 andDenman 1) were drilled near Hughes on the Trans AustralianRailway; Tertiary and Cretaceous sediments were noted to adepth of ~229 m, and possible early Palaeozoic sedimentswere noted below that unconformity but no significanthydrocarbon shows were reported (AR, 1965--66). Thissection is now considered to be Neoproterozoic (Ch. 5).

In the South Australia portion of the Eucla Basin thecompany undertook several photogeological studies whichrevealed some ‘geomorphological anomalies’. These wereinspected by a ground survey team. Farminees to the licencebetween June 1966 and June 1968 included Union Texas(Aust.) Co., Rock Island Oil and Refining Co. Inc., TennecoAustralia Inc. and Coastal Petroleum NL. The licenceexpired in January 1969 and the onshore area was then issuedto Outback Oil as PEL 4. From June 1969, Outback Oildrilled Mallabie 1, which proved a thicker sedimentarysect ion than previously thought , thus improving theexploration potential though the dry well was plugged andabandoned (TD 1672 m). PEL 4 expired in January 1974.

DOWNTURN TO DISCOVERY

Oil and gas discoveries elsewhere in Australia had sustainedhopes for the Officer Basin search (O’Neil, 1995, 1996a;Wilkinson, 1988). For example, in the Cooper Basin,Innamincka 1 in 1959 revealed a Permian basin below the GreatArtesian Basin and hydrocarbon shows in the Permiansediments suggested its oil prospectivity. The Gidgealpa--Merrimelia Trend was first identified on seismic lines shot bythe Mines Department in August 1962 and Gidgealpa 2 wasdrilled on this structure; the well produced gas and condensate.This testing of commercial quantities of gas from the Permianwas the first petroleum discovery in the Cooper Basin and setSouth Australia’s petroleum industry on the way. The discoveryof gas at Gidgealpa on 31 December 1963 and Moomba inMarch 1965, and oil at Tirrawarra in 1970, in the Cooper Basinindicated that the local efforts were not in vain. Gas productionfrom Permian Cooper Basin reservoirs in the Gidgealpa andMoomba fields to Adelaide commenced in 1969. Follow-updrilling in 1970 and 1971 through farmout arrangements withseveral new companies resulted in significant Cooper Basin oiland gas discoveries.

As petroleum developments in the Cooper Basin beganto unfold under their own momentum, the Department beganto concentrate on collecting basic data in the areas of low ormarginal prospectivity to encourage companies to exploreareas such as the Arckaringa and Officer Basins. By the late1960s, the Permian sequences east of the Officer Basin wereconsidered as possible petroleum sources and some attentionwas given to them. When no hydrocarbon discoveries weremade, the exploration focus shifted to the central and westernArckaringa Basin--eastern Officer Basin area where ap r e - P e r m i a n c a r b o n a t e --r e d b e d e v a p o r i t e s e q u e n c e(Observatory Hill Formation) was considered to haveeconomic hydrocarbon potential (Hibburt, 1984). Theevaporites in Cootanoorina 1 in the Boorthanna Trough of theArckaringa Basin and in the area to the southwest wereidentified as being of Devonian age. The evaporite bedsbelow the Permian north of Coober Pedy were equivalent tothe Observatory Hill Formation. Observatory Hill nearMaralinga was named by Len Beadell in 1955 as the hill wassimilar in shape to an astronomical dome. The ArckaringaBasin was another little-known basin in a high explorationrisk category but information from the west and northwest ofthat basin was ‘of direct importance to the understanding ofthe Officer Basin ... which contains at least 16 000 feet ofPalaeozoic sediment-fill [and] is one of the real challengesand its investigation is a natural follow-on from the workcarried out in the Arckaringa Basin’ (AR, 1970--71, p.8).

A downturn in the petroleum industry occurred from 1973under the imposts of a Federal Government which terminatedthe Petroleum Search Subsidy Scheme, abolished taxconcessions, banned the export of LPG and moved againstthe involvement of foreign companies such as Aquitaine andDelhi. It also moved to create a Petroleum and MineralsAuthority. In South Australia, the inability to secure apetrochemical plant despite strenuous efforts throughout the1970s was also a disincentive to explorers discoveringliquids-rich gas. Exploration and development drilling wasall but abandoned; only one well was drilled in 1973, andnone in 1974 and 1975. Few seismic surveys wereconducted. Although there was little exploration by eithercompanies or the Department in the Officer Basin from 1969to 1974, thereafter the Department drilled seven wells to 1979to establish how widely spread the pre-Permian sequencewas. Of these wells, Byilkaoora 1 and Wilkinson 1 inter-sected oil-mature Cambrian source rocks (Hibburt, 1984).

Between July and December 1976, the Departmentdrilled four shallow stratigraphic wells in the southernOfficer Basin ---- Murnaroo 1 (7 km south of ObservatoryHill; TD 628 m), Ooldea 1 and Reid 1 and 1A ---- which wereall dry and abandoned though Murnaroo 1 revealed apotential reservoir sandstone. Then Wilkinson 1 wasspudded in June 1978 and completed as a dry and abandonedwell in August 1978 (TD 710 m). This hole, with its excellentoil-source potential, encouraged more exploration and led theDepartment to form an Officer Basin Study Group (therebeing an Eromanga Basin Group also), which began to drawtogether previous work on the basin and to reassess itspetroleum potential.

As a result, Byilkaoora 1 was drilled on the northeasternmargin of the basin in the Mount Johns Range. This well,~300 km north-northeast of Wilkinson 1, was spudded in

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May 1979 and completed in July 1979 to 497 m. Oil-sourcerock correlations in Byilkaoora 1 indicated an alkaline playa--lacustrine origin for the immature crude (McKirdy andKantsler, 1980). Carbonates equivalent to the hydrocarbonshows found in Byilkaoora 1 were detected in Marla 1A and1B.

This drilling suggested that the Cambrian carbonatesequences in the basin correlated to the Observatory HillFormation, which by 1980 was ‘considered to be the majorpotential source of petroleum in the eastern Officer Basin’(Pitt et al., 1980, p.209). Although the signs at Wilkinson 1gave a good reason for companies to want to resumeexploration in the basin, it was the oil bleeding fromByilkaoora 1 cores which provided the first really significantoil shows, confirmed the prospects revealed by Wilkinson 1,and raised expectations even higher.

Complementing the work in the northeastern OfficerBasin, in 1979--80 the Department undertook a helicopter-based geological survey over 48 000 km2 of South Australia’swestern portion of the basin in order to better understand thislittle studied region. The exercise had three main objectives:‘ to delineate further the rock units (part icularly theObservatory Hill Formation) mapped or intersected indrillholes to the east; to recognise Officer Basin rock unitsmapped in eastern Western Australia; and to assess the degreeof deformation in the area with a view to identifying structuralleads for petroleum exploration’ (Pitt et al., 1980, p.215).

PEL 10, 11 and 12

There was little company exploration in the basin foralmost 15 years after OEL 28 became PEL 10 and 11 inAugust 1969. PEL 10 was held by Exoil over 24 864 km2

and PEL 11 was held by Conoco, Transoil NL and AustralianSun Oil Co. Ltd over 24 346 km2. When PEL 10 and 11 wererelinquished in January 1971, PEL 12 was granted to Exoiland Transoil over a portion (24 605 km2) of the old areas. Thearea bordered the Everard Ranges and included the southernreaches of Officer Creek. No active work followed in theshort term and efforts to farm out were unsuccessful untilJune 1974 when Shell Development (Aust.) Pty Ltd joinedfor nine months. Shell recommenced the exploration phaseand ran 154 line km of seismic (the Everard seismic survey)in October and November 1974. The results of this were latershown not to be as expected. PEL 12 was surrendered in June1976.

PEL 13

PEL 13 was issued in September 1972 to PlanetExploration Co. Pty Ltd over 24 518 km2 in the ArckaringaBasin, the far west of the Great Artesian Basin. The northernperimeter of the licence, which extended west of Coober Pedyand north of Lake Phillipson, was on the northeastern marginof the Officer Basin but PEL 13 was surrendered in December1973 without being explored.

PEL 23 and 30

Active company petroleum exploration returned to theOfficer Basin with Comalco Aluminium Ltd holding PEL 23and 30 from January 1983 and February 1985, respectively,until early 1989. Comalco became interested in thepe t ro leum prospec t s o f the Of f ice r Bas in a f t e r theByilkaoora 1 discovery; its mineral exploration in the periodfrom 1979 included 20 fully cored drillholes in its mineraltenements in the region. Comalco’s search was essentiallyfor evaporite minerals, base metals and coal. Although itsex tens ive explora t ion program fa i led to f ind a lka l ievaporites, indications of enhanced prospectivity for thebasin were noticed; oil bleeds were detected whereverComalco drilled the Observatory Hill Formation and theunderlying Rodda beds.

Commencing in March 1984 with a 1200 line kilometreseismic survey, Comalco’s petroleum exploration included2613 km of reconnaissance and semi-detailed seismic, and thedrilling of five cored wells (at an average depth of 2000 m).This work improved the understanding of the geology andpetroleum prospectivity of the eastern Officer Basin. Thecompany partially completed its own review of the basinstratigraphy prior to drilling the first exploration well (Giles 1)during September--October 1985 (TD 1327 m; Stainton et al.,1988). Of Comalco’s plugged and abandoned dry wells,Ungoolya 1 (November 1985) revealed encouraging oil showsover several hundred metres in low porosity, early Palaeozoicand Neoproterozoic clastics; Karlaya 1 (April 1987), Lairu 1(July 1987) and Munta 1 (September 1987) also showed tracesof oil in these sediments.

PEL 23 had been applied for in 1980 but a delay ingranting was caused through stalled negotiations with

Drilling Byilkaoora 1 in 1979. (Photo T14751)

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another company for adjoining acreage. PEL 23, from Emuto the Marla area, was renewed for five years in January 1988and the area reduced from 23 222 km2 to 15 505 km2 byrelinquishing in the southeast and north of the licence. PEL 30was granted over 434 km2 adjoining the northwestern perimeterof PEL 23. Both PEL were surrendered early in 1989.

PEL 24

In November 1983, CRA Exploration Pty Ltd was grantedPEL 24 over 21 778 km2 on the southern margins of theOfficer and Arckaringa Basins. A $6.4 million explorationprogram was proposed, including the drilling of at least fourwells over the five-year licence term. However, only 435 linekilometres of seismic were recorded in 1985 and 1986, andArkeeta 1, the only well, was drilled in December 1986. InJuly 1987, Pacific Oil and Gas Pty Ltd became the operatorbut the licence was surrendered four months later.

PEL 29

Exploration by Amoco, the operator, recorded 235 km ofseismic including a section between Ungoolya 1 andMunyarai 1, but no wells were drilled. This, and the work byComalco, delineated a number of large structures capable oftrapping hydrocarbons. Amoco obtained good qualityseismic data in the Munyarai Trough in 1987.

PEL 33

PEL 33 was issued to a consortium of small companies---- Median Oil NL (operator), Geometals Oil ExplorationLtd, Heron Petroleum Pty Ltd, Malita Exploration Pty Ltd,Gulf Resources NL, Southern Cross Exploration NL, ForsythOil and Gas NL, Antarctic Petroleum Pty Ltd, Spectrum GoldNL ---- in June 1985 over 23 793 km2 in the Eucla Basin wherean experimental seismic survey of 40 km was recorded beforethe licence was cancelled in April 1989.

REVITALISATION

The Department continued its regional geological studiesand assisted Comalco in refining the stratigraphy of theOfficer Basin (Brewer et al., 1987). From the mid-1980s, thehydrocarbon potential of the basin was promoted by theDepartment in data packages prepared with seismic, drilling,mapping and reports. Companies were encouraged to take

up new permits in the Pitjantjatjara and Maralinga lands ofthe Officer Basin. Petroleum exploration was plannedonshore in the Officer Basin in 1990 and discussions wereheld with the Pitjantjatjara Council about access for proposedlicence holders. Three potential reservoirs ---- MurnarooForma t ion , Re l i e f Sands tone and Obse rva to ry Hi l lFormation ---- had been determined by the time a data packagewas released on 44 300 km2 in and adjoining Aboriginal landin four areas of the basin in late 1990. Although there hadnot yet been any commercial hydrocarbon discoveries, thebasin’s potential reservoirs were then estimated to containmore than 523 bcf of sales gas or more than 451 mmbl ofrecoverable oil (Morton, 1992).

An Officer Basin team of professional and technical staffwas formed within the Department in August 1992 to liaisewith the Pitjantjatjara and Maralinga people, to carry outwater well drilling and to survey for a seismic transect. Thissurvey had been proposed in 1989 by the Department for theAust ra l ian Geologica l Survey Organisa t ion (AGSO,formerly the BMR) to undertake. AGSO was to interpretexisting geological and geophysical data, and to acquire newseismic, source rock, stratigraphic and petrophysicalinformation. This was intended to form part of a major studyby the Department on the structure, stratigraphy, petroleumsource and reservoir potential of the Officer Basin in SouthAustralia. The important potential of the basin would thusbe highlighted. In the new regime applying to exploration,an th ropo log i ca l work and work co r r i do r c l ea r ancedemonstrated the modern approach to Aboriginal liaison ande n v i r o n m e n t a l m a n a g e m e n t . T h e r e s u l t s i n c l u d e destablishing a better correlation with the Amadeus Basin inthe Northern Territory where oil and gas was already beingproduced at the Palm Valley and Mereenie fields, ani m p r o v e d k n o w l e d g e o f t h e s a n d s t o n e r e s e r v o i r s ,hydrogeological and structural features of the basin, andbetter seismic interpretation from the reprocessing of existingdata. Aerial surveys were f lown by AGSO and theDepartment as part of its South Australian ExplorationInitiative (SAEI).

Under the Nat ional Geosc ience Mapping Accord(NGMA) and the SAEI, the Department funded petroleumexploration to acquire seismic data in areas that had beenignored by the private sector but where the Department

Company oil exploration in the Officer Basin in 1987. (Photo 36174)

Anthropologist Scott Cane, at right, with southern Pitjantjatjaratribal elders during line scouting for the seismic survey on Mara-linga Lands in November 1993. (Courtesy S. Cane)

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considered there was petroleum potential. A frontiergeological province such as the Officer Basin required earlierinformation to be revised. This work was now subject toagreements with the Aboriginal landholders for access forwater well drilling, seismic line surveying and seismicsurveys. The planned NGMA transect of 600 km from theMusgrave Block in the north to the Nullarbor Plain wasmodified when access to the unnamed conservation park wasdenied, and seismic test work on the Nullarbor Plain couldnot penetrate the surficial cavernous limestone (Gravestockand Lindsay, 1994). Reflecting the modern regime, theAGSO--MESA transect in 1993 included environmentalaudits of seismic practices.

In conjunction with AGSO, the Department conductedseismic surveys in unexplored Pitjantjatjara and MaralingaLands in the eastern Officer Basin late in 1993 (Gravestockand Lindsay, 1994). AGSO undertook a 550 km regionaltransect to tie a northern line, including reprocessed 1966seismic data, to a series of lines in the south. This formedpart of the NGMA with Federal Government funds and SouthAustralian logistical support on Aboriginal liaison, linesurveying and water wells. (See Ch. 3 for more detail on theland access arrangements.)

As well as investigations to establish water supplies formineral and petroleum companies during 1993, especially inthe desert areas outside the Great Artesian Basin, theDepartment examined water supply options in the OfficerBasin and at Oak Valley where the Maralinga people hadformed an outstation since 1984. An earlier camp had beenat Dey Dey. These projects identified water of stock qualityin the eastern Eucla Basin through to potable supplies in theMusgrave Ranges.

The Department reviewed seismic data for the Marla areaand contracted 378 km of seismic survey work along nineregional lines west of Marla. The NGMA transect was thefirst in the barely explored central and southern Officer Basin,while the SAEI grid linked seismic acquired in the mid-1980sby Comalco and Amoco in the eastern Officer Basin. Some140 km of Comalco seismic data were reprocessed to thesame standard. The new seismic acquired in the basinfollowed a reinterpretation of Comalco’s 1983--85 data(Mackie and Gravestock, 1993).

The $5 million of surveys and associated geologicals t u d i e s i n d i c a t e d t h a t c o n s i d e r a b l e u n d i s c o v e r e dhydrocarbon potential exists in the Officer Basin but thatfurther studies would be needed to assess its potential. Theinvestigation confirmed ‘thrust faulting (Alice SpringsOrogeny) along the structural northern basin margin, thethrusts propagating south within as well as beneath thes e d i m e n t a r y c o v e r ’ i n d i c a t e d ‘ 6 k m o r m o r e o fNeoproterozoic sediment in the Birksgate sub-basin [butthat] the southern Murnaroo Platform is unlikely to containlarge structures’, strengthened ‘biostratigraphic correlationwith the Amadeus Basin and confirm[ed] the utility ofacritarchs for Neoproterozoic zonation’ and indicated ‘apotential sabkha-associated source rock near the base of thesuccession’ (Gravestock and Lindsay, 1994, p.65). Theprospects for major investigations were enhanced by thediscovery of sufficient ground water in the south-centralOfficer Basin to support shothole drilling.

The new seismic investigated the southwestern extensionof the Manya Trough and Marla Overthrust Zone, which haverevealed most of the oil shows. As well, biostratigraphic andpetrophysical studies of wells throughout the basin correlatedthe Neoproterozoic more effectively and improved theknown reservoir characterisation. New structural dataadjacent to known oil-bearing rocks in the Marla OverthrustZone were obtained in the adjacent troughs and ridges butthey are poorly delineated by seismic and are relativelyundrilled. Furthermore, the Mesoproterozoic Amma-roodinna Inlier poses questions as to its origin and structuralposition southwest of the Marla Overthrust Zone. Thecorrelation between strata in the Munyarai and ManyaTroughs, both potentially oil-generating kitchens, requiresfurther invest igat ion to reveal their s ignif icance forpetroleum exploration (Gravestock and Lindsay, 1994).

PEL 61 and 63

In May 1996, PEL 61 and 63 were granted over 6258 and19 930 km2, respectively, in the Marla area of the OfficerBasin, after Hemley Exploration Pty Ltd successfullyconc luded access nego t i a t ions wi th the Abor ig ina llandowners. Drilling is scheduled to commence in 1997.

CONCLUSION

The search to date of the Officer Basin has been sparseand <7200 km of seismic data have been recorded and only30 wells deeper than 500 m drilled. Only 12 of the ~70drillholes are petroleum exploration wells of sufficient depthto enable the stratigraphy to be pieced together. Core andwireline logs from mineral, groundwater and stratigraphicdrillholes, especially in the eastern part of the basin, provideuseful data. There has been limited wildcat exploration butthe promising potential of the region is such that it deservesmore attention, especially given that the logistical problemsand land access issues can be overcome. The current interestdemonstrates that the Officer Basin is now regarded, at leastby some parts of the industry, as having significant petroleumpotential.

Geosystems Pty Ltd Vibroseis trucks operating on the Officer Basinseismic survey in August 1993. (Photo 41474)

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CLIMATE

Whilst extending south to the coast in the vicinity ofNullarbor National Park, the Officer Basin for the greater partlies inland and is comprised of relatively level terrain withfew hills or mountains. As a result there is little variation inthe climate throughout the region.

The average annual rainfall is low and variable, rangingfrom ~250 mm/year in the north (Fig. 3.1) to 300 mm/yeartowards the southern coastal region. Rainfall events showonly a weak seasonal pattern, with the southern marginsreceiving more winter rainfall whilst the northern areas mayexperience summer rainfall.

Long sustained periods of rain are rare although large fallscan occur over short periods. In the northern areas, heavyrainfall can occur during any month of the year although it isnot uncommon to experience 2–3 very dry months.Prolonged droughts are frequent throughout the area andevaporation rates are very high, often exceeding3800 mm/year.

The summer months from December through to Februarytend to be the hottest time of the year. Mean maximum dailytemperatures usually exceed 32°C and are often over 37°C,with the temperature dropping 10–20°C at night. During thewinter months it can be mild to warm with a mean maximumtemperature of 17°C and a mean minimum of ~5°C.

LANDFORMS

The Officer Basin underlies a vast area of land totallingover 375 000 km2, and covers a wide range of landforms.

These landforms can be grouped into three majorenvironmental regions; the western sandplains, the centraltablelands and the Nullarbor Plain. Each region consists ofa number of major landforms, including dunefields,undulating plains, sandplains, tablelands, clay pans and saltlakes. A number of minor landform patterns orenvironmental units occur within each of these majorlandforms. The occurrence of minor landforms can vary,depending upon the detailed morphological characteristics ofa major landform based upon the local geology, soil type,topography, drainage patterns and biota.

Western sandplains region

The western sandplains region is characterised byundulating plains and extensive dunefields. Throughout thedunefields there are occasional silcrete rises, salinedepressions and low gibber-covered rises with occasionallow hills and ridges. This region includes the Great VictoriaDesert which is a transitional zone between the northernmargin of the Nullarbor Plain region and the westernsandplains region. The Great Victoria Desert is characterisedby longitudinal sand ridges up to 20 m high and 100 km long.The desert is so named because of the lack of modern surfacedrainage.

Central tablelands

The central tablelands consist of undulating plainscovered with silcrete pebbles and rubble. The plains are cutby several large seasonal creek beds and associatedfloodplains, along with scattered groups of dissectedtablelands, mesas, clay pans and salt pans.

Fig. 3.1 Average monthly rainfall and average maximum dailytemperature for Marla.

Spinifex and mallee vegetation, western sandplains, Officer Basin.(Photo 43105)

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Nullarbor Plain

The Nullarbor Plain is characteristically an undulating,featureless limestone plain with occasional sinkholes andcaves, and traces of surface drainage in the form of elongatedchains of dry lakes.

NATIVE VEGETATION

The natural vegetation associations throughout theOfficer Basin vary considerably, ranging from woodlandsand tall shrublands, to hummock grasslands, chenopodshrublands, grasses, ephemeral forbs and occasionallysamphire associations.

Many regions within the basin area, whilst classified asdesert, appear very unlike the traditional concept of what adesert should look like. For example, low open woodlands,which generally occur on dunefields, can be foundthroughout the basin in a variety of topographic situations.Often these woodlands are comprised of one or a number ofdifferent species such as myall, black oak, northern cypresspine or mallee.

The understorey of woodlands on the dunes typicallyconsists of tussock grasses, spinifex or sclerophyll shrubs,whereas the understorey on interdunal lows generallyconsists of various species of saltbush and bluebush.Throughout the plains, the woodlands often give way tomixed chenopod shrubland comprised of species such assaltbush or bluebush with a hummock or tussock grassunderstorey, or tall shrubland comprised of species such ascassia or mulga with a grass or chenopod understorey.

Vegetation throughout the Officer Basin can vary fromvery dense to sparse. Generally each plant communityoccupies a particular habitat, with the distribution ofvegetation often reflecting the landform and soil types.

Although there are often large areas with only onevegetation association, many instances occur where there arecomplexes of two or more different vegetation associations,each occupying a specific niche in the environment.

Small differences in habitat such as depressions or drainagelines may produce slightly more growth and a greater varietyof species. Perennial plants throughout the region haveadapted to endure long dry spells and extreme temperatures,whilst the appearance of herbaceous plants can be episodicand infrequent depending upon suitable climatic conditions.

ENVIRONMENTAL CONSIDERATIONS

National parks and reserves

Six parks and reserves are fully or partly located withinthe boundaries of the Officer Basin (Fig. 3.2). These werecreated to preserve the best examples of vegetation andlandforms within the region. Access for exploration andmining is allowed in all parks except the UnnamedConservation Park and Nullarbor National Park. Theconditions for access vary from park to park, based on thetype of reserve classification (Conservation Park, NationalPark or Regional Reserve), the activity proposed and theimpact it is likely to have on the environment.

Summary of environmental regulation

A number of environmental issues are pertinent topetroleum exploration in the Officer Basin, all of which canbe resolved by proper operational planning in the initialstages. In order to ensure that activities are undertaken in amanner which minimises environmental impacts, a numberof documents are required before approval to commenceoperations is given.

A Declaration of Environmental Factors (DEF) isrequired from the licensee. This is the licensee’s assessmentof the environmental impact of an activity.

A Code of Environmental Practice (CEP) is also requiredby regulation. The code describes the procedures that theproponent will adopt during the planning, assessment, fieldmanagement auditing and monitoring phases of theoperation. A CEP for seismic operations within the OfficerBasin has been developed by MESA and is available tolicensees. This provides advice on environmental issues thatneed to be taken into consideration in planning a project. Acompany may either adopt this code or use its own CEPsubject to approval by MESA.

Although a number of documents are required, theapproval process is not onerous. MESA is able to assistlicensees by providing examples of the documentation andadvising on their scope.

CULTURAL HERITAGE

European heritage

Sites of European heritage significance such as historicbuildings, graves and geological monuments may be foundin the Officer Basin. These are indicated on environmentalsensitivity maps which can be purchased from MESA. Themajority of sites are small and easily avoided by explorationand production activities.

Aboriginal heritage

In South Australia it is an offence to disturb or destroyAboriginal sites, objects or remains. Standard procedures fordetermining the presence of Aboriginal heritage prior tocommencement of activities have been determined. Theseinvolve consulting with the relevant Aboriginal organisationand maintaining a watch for sites, objects or remains duringexploration. These sites are generally no larger than a fewhundred square metres and are easily avoided. Since theMeramangye Lake, Officer Basin. (Photo 43070)

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inception of the Aboriginal Heritage Act 1988, there havebeen no conflicts between Aboriginal heritage sites andexploration or production activities. MESA can provideadvice to companies on Aboriginal heritage.

The Aboriginal Heritage Act also applies to Aboriginallands held in freehold, including the Anangu Pitjantjatjaraand Maralinga Tjarutja Lands. Access to Aboriginal land forsite clearance must be negotiated with the traditional owners(see ‘Aboriginal lands’).

ABORIGINAL LANDS

History

Following the arrival of Europeans in the 1920s to thedesert regions of northwestern South Australia, many of theAboriginal people who lived in those regions moved in threemain directions — to Areyonga in the Northern Territory,Ernabella Mission just south of the Northern Territory border,and south to Ooldea Mission on the Trans Australian Railway.

Fig. 3.2 Parks and reserves, Aboriginal lands, and defence areas covering the Officer Basin area.

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Ooldea Mission closed in 1952 and the people weretransferred to a new mission at Yalata. In 1953, the BritishGovernment established a base 35 km north of the old OoldeaMission on what is now known as Maralinga Lands. Thepurpose of the base was for nuclear weapons testing. Evenif Ooldea Mission hadn’t closed prior to arrival of the British,it would have had to close due to the proximity of the nucleartesting.

In 1981, the Pitjantjatjara Land Rights Act was passedunder which a body corporate — the Anangu Pitjantjatjara(AP) — holds the land under inalienable freehold title. TheAct also gives to AP control of entry to the lands and a shareof the production of petroleum royalties earned from the land.

The Aboriginal people south of the AP Lands soughtsimilar legislation and, in 1984, the Government recognisedtheir claim and passed the Maralinga Tjarutja Land RightsAct. Under this Act, a corporate body called the MaralingaTjarutja (MT) was established to receive freehold title to theland.

The AP Lands abut the northern border of the MT Landsand extend as far north as the Northern Territory, covering anarea of ~103 000 km2. The MT Lands extend south to theTrans Australian Railway, covering ~80 764 km2. Whilst theOfficer Basin incorporates all of the MT Lands, only thesouthern portion of the AP Lands falls within its boundaries.

Traditional owners believe that their role with respect to‘land rights’ is to fulfil their responsibilities to that land.They are under social and cultural direction to ensure that theland is protected and that sites of significance are avoided.To enable them to discharge that responsibility, traditionalowners have to be fully informed of any activities proposedwithin the lands and the impacts of those activities on thelands. To ensure that all of the people with responsibilitiesfor the land under consideration have been consulted, it isnecessary for exploration companies to submit an applicationwith the traditional owners at the earliest possible stage of anexploration program.

Maralinga Tjarutja work closely with the PitjantjatjaraCouncil in relation to areas of common interest such aspetroleum exploration. It is important that potentialexplorers are prepared to work with the traditional owners toensure that a reasonable balance is struck.

Access to Aboriginal lands

Exploration activities have been successfully undertakenin both MT and AP Lands, and the traditional owners are wellacquainted with the transient land use of exploration. Boththe MT and AP are proud of the work they have done withpetroleum companies and have indicated a wish to continueto work towards balancing their own sense of responsibilitytowards the land and the interests of those who seek toexplore and produce from it. In the access agreementnegotiated for PEL 61 in AP Lands, provision was made forcompensation for exploration activity (expected to be~$20 000/year) for a joint-venture partenership option for theAboriginal owners of the land, and payment of productionroyalties of 1–3% based on a sliding scale linked to thequantity of oil or gas produced (in the event of a commercialdiscovery). This royalty to AP is in addition to the 10% State

royalty, which is shared 1⁄3 to AP, 1⁄3 for all Aboriginal peoplein South Australia, and 1⁄3 to South Australian generalrevenue.

AP Lands

Except for a limited number of instances as set out in thePitjantjatjara Land Rights Act, all non-Pitjantjatjara peopleare required to apply for permission to enter AP Lands.Exploration companies must first obtain the approval of theMinister administering the Mining and Petroleum Acts toapply to AP for permission to enter those lands. Oncepermission is obtained, a company may submit an applicationto the Executive Board of Anangu Pitjantjatjara which thenhas 120 days from the date of application to grantunconditional permission, permission subject to conditionsor to refuse the application.

If the AP refuses permission or imposes conditionsunacceptable to the applicant, or the applicant has notreceived a notice of a decision by AP within 120 days fromthe date of application, the applicant may request the Ministerfor Mines to refer the matter to an arbitrator. A determinationunder this section is binding upon the AP, the applicant andthe Crown. There are special provisions in Sections 20 to 24of the Act in relation to applicants for petroleum explorationand mineral licences (Appendix 3.1).

MT Lands

Whilst provisions in the Maralinga Tjarutja Land RightsAct relating to access for exploration companies are similarto those for AP Lands, there are two main differences — theMaralinga Tjarutja Land Rights Act limits the amount ofcompensation provided at the exploration stage to no greaterthan the amount of compensation provided for under theMining and Petroleum Acts, and there is a slightly differentprocedure for appeals.

Where the MT refuses permission or imposes conditionsunacceptable to the applicant, or the applicant has notreceived a notice of a decision by MT within 120 days fromthe date of application, the applicant may request the Ministerfor Mines to attempt to resolve the matter by arbitration withthe assistance of the Minister for State Aboriginal Affairs.These conditions are set out in detail in Sections 21 to 26 ofthe Maralinga Tjarutja Land Rights Act 1984 (Appendix 3.2).

Signing the access agreement for the Maralinga Seismic Survey,1992. (Photo 40420)

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Access for seismic surveys

No petroleum exploration was carried out between 1988and 1992 following withdrawal of Comalco and Amoco fromthe Aboriginal lands, but two seismic surveys have beencarried out since 1992. The first, of 550 km, was recorded aspart of the National Geoscience Mapping Accord (NGMA)by the Australian Geological Survey Organisation (AGSO),partly in AP Lands but mainly in MT Lands. The secondsurvey, of 379 km, was recorded by MESA as part of theSouth Australian Exploration Initiative (SAEI) in eastern APLands. Land access was summarised by Gravestock andLindsay (1994) as follows.

Discussions with AP and MT outlining plans for theNGMA transect commenced in 1990. These involvedseveral visits to Aboriginal communities by AGSO andMESA personnel, and the wide distribution of a leafletillustrating seismic recording techniques and their effect onthe land. In 1992, discussion was formalised and embodiedin two agreements signed separately by AP, MT and the SouthAustralian Minister for Mines and Energy. A third agreementbetween AP and the Minister, modelled on its predecessors,was signed in 1993 to enable the SAEI seismic program tocommence.

In essence, each agreement sets out the access conditionsfor a line scouting stage followed by the line clearing andrecording stage. All personnel involved in the scoutingteams, both Aboriginal and non-Aboriginal, were fullybriefed as to the nature and type of work to be undertaken.In the scouting stage, groups of four men and four womenresponsible for safeguarding sites of significance wereaccompanied by anthropologists and MESA officers to markthe route of seismic lines (using GPS) and to clear a workarea 200 m either side of the proposed line with due regardto cultural significance. Where necessary, seismic lines weremoved or bent to avoid sites of significance withoutcompromising the objectives of the survey. The cleared workcorridors were agreed to in writing by AP, MT and MESA.All visitors to the Aboriginal lands were issued with permitsstipulating the conditions of entry.

Seismic line preparation followed the marked route aheadof the recording crews, at which time one or more seniorAboriginal men were employed by the AP and MT Councilsto act as liaison officers. Liaison officers were chosen to actas representatives for each Council to ensure that the dailymanagement of the seismic program proceeded in accordancewith the access agreements. The men had several importantduties to perform:

• they were responsible for the pre-work culturalbriefing in the field for the seismic crews and othercontractors

• they ensured that permit entry conditions werehonoured

• crews were kept within the agreed work corridors,except for surveyors and water drillers who wereaccompanied to trig points and drillsites

• they were responsible for providing an account of theimpacts of the seismic lines to their respectiveAboriginal communities.

Advice from the liaison officers was passed to the crewchief or the Minister’s representative. In addition, these men(and sometimes their families) took off-duty crew memberson ‘bush tucker trips’. Immediately before crew departure,the liaison officers accompanied AGSO, MESA andcontracted personnel on a line inspection to ensure that allrubbish was removed or buried and, where required, seismiclines were rendered impassable to future visitors. As a resultof requests, some lines were left open for 4WD vehicles.

The practice of carrying out a scouting stage followed bya monitoring stage for petroleum exploration is likely tobecome standard practice for licence holders. The cost of thisexercise for the seismic surveys varied between $100 and$150 per kilometre recorded.

OTHER LAND ISSUES

Commonwealth land

Commonwealth land includes defence facilities, variousrailway easements, post offices, aerodromes, lighthouses,telecommunication facilities and prohibited areas such as theMaralinga test site known as ‘Section 400’. Access toCommonwealth land may be granted, subject topredetermined conditions, by the relevant Commonwealthdepartment with the exception of sensitive defence areas.

Maralinga and Emu nuclear weapon test sites

Between 1953 and 1963, the British Governmentconducted a program of nuclear weapons development trialsat the Maralinga and Emu sites in South Australia. Duringthat period nine atomic bombs were detonated and 700 minortrials were undertaken. The Maralinga site covers~3000 km2. The Emu test site, 200 km north of Maralinga,covers ~500 km2. The Maralinga site is owned by theCommonwealth whilst the Emu site is owned by the Crown.

Areas within both test sites are contaminated byradioactive wastes, the principal contaminant beingplutonium used during the minor trials. In 1985, theAustralian Government established a Royal Commissioninto British nuclear tests in Australia which proposed that theMT Lands be cleaned up and decontaminated, and that thetraditional Maralinga owners be compensated. TheAustralian Government recently initiated decontamination ofthe site, with the British Government agreeing to contributeto the cost. It is expected that the clean-up will be completedby the end of 1998, after which the land will be returned tothe traditional owners. Public access to the Maralinga andEmu test sites is generally prohibited.

Woomera Prohibited Area

This area, covering 133 300 km2 (13.5% of SA), wasestablished under the Defence (Special Undertakings) Act1952. Public access is restricted to Woomera township,Stuart Highway and the Coober Pedy–William Creek road.Access elsewhere in this area is by permit, which can beobtained from the Area Administrator at the Defence SupportCentre in Woomera. There is no formal avenue for appeal ifthe Area Administrator refuses to issue a permit to enter.

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Operators within the prohibited area are required to carry$7 million public liability insurance.

Mintabie Precious Stones Field

Opal was first discovered at Mintabie in the 1920salthough it was not until 1976 that heavy earth movingmachinery moved in, after which several large finds weremade. In 1988, Mintabie produced an estimated $39 milliondollars worth of opal, making it the largest producer ofprecious opal in the world at that time.

Mintabie is referred to as a ‘precious stones field’ and, forthose wishing to prospect or mine for opal, a Precious StonesProspecting Permit is required. Many hundreds of opalworkings occur throughout the field and consist primarily oflarge areas ripped by bulldozers to remove the overburdenand expose the shallow opal seams.

The Mining Act 1971 provides for stratified titles(section 63(a)), which are proclaimed by the Governor underSection 8(1)(ba). This enables a petroleum explorationlicence or production licence to be acquired over a subsurfacestratum where the surface is being mined for opal. However,the nature of opal mining in the Mintabie Precious StonesField could make access for petroleum exploration hazardousdue to the number of open cuts.

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INFRASTRUCTURE

Transport links

The main road in the region is the sealed Stuart Highwaywhich links Adelaide and Darwin (Fig. 4.1). Adelaide(population ~1 million) is 1000 km southeast of the Marlaregion by road. Alice Springs (population 27 500) is 550 kmto the north by road. Port Bonython (740 km), and Thevenardnear Ceduna (525 km), are the nearest State commercial deepsea ports; Whyalla (740 km) is the nearest privately operateddeep sea port. Important towns in the region include Marla(population 243) and Coober Pedy (the main regionaladministrative centre, population ~4000).

The Central Australia Railway links Adelaide to AliceSprings (Fig. 4.1). The railway may eventually be extendedto Darwin, where modern port facilities provide a link tosoutheast Asia. The nearest airport is Coober Pedy (sealedand gravel runways); a number of settlements and towns haveairstrips, including Fregon (sand silt), Indulkana (silt clay),Marla (gravel), Granite Downs (silt clay) and Oodnadatta(Fig. 4.1).

Pipelines and production facilities

The Moomba Plant, operated by Santos Ltd ~660 km eastof Marla (Fig. 4.2), produces sales gas for Adelaide andSydney, and processes 25.4 million m3 (902 mmcf) of rawgas and 6 600 kL (42 000 bbl) of condensate and crude oilper day. Condensate, LPG, crude and some ethane aretransported as a ‘cocktail’ via pipeline to Port Bonythonwhere they are separated and marketed within Australia andoverseas. The Port Bonython liquids plant, also operated bySantos, produces crude, naphtha, butane and propane.

A mini-refinery adjacent to the Port Bonython plantproduces 95 kL/day (600 bbl/day) of gasoline by refining

naphtha feedstock from the liquids plant. The mini-refinerysupplies the northern Spencer Gulf region.

The nearest pipelines in South Australia to Marla are the659 km Moomba–Port Bonython Liquids Line and the781 km Moomba–Adelaide Pipeline, operated by EPICEnergy (Fig. 4.2).

In the Northern Territory, ~550 km north of Marla, is the1500 km Amadeus Basin–Darwin gas pipeline, completed in1986 and operated by NT Gas Pty Ltd. This has a maximumdaily capacity of 2.5 million m3 (87 mmcf), and en routesupplies Northern Territory towns as well as several goldmines and a major lead–zinc mine at McArthur River. Thecapacity of the McArthur spur is 0.45 million m3/day(16 mmcf/day). The current Northern Territory market forgas is 15 PJ/year; a major potential market is the aluminarefinery at Gove which would consume 20–25 PJ/year ifconverted from diesel.

The 270 km Mereenie–Alice Springs oil pipeline in theNorthern Territory was constructed in 1985. It is operated bySantos Ltd and has a capacity of 1490 kL/day (9400 bbl/day);current throughput is 480 kL/day (3000 bbl/day). Oil istransported to a tankfarm and railhead at Brewer Estate,20 km south of Alice Springs, where it is loaded into tankrailcars on a spur line of the Central Australia Railway andtransported 1500 km by rail to Port Adelaide. From here itis trucked to Port Stanvac refinery, 10 km south of Adelaide.

Airstrip in the Officer Basin. (Photo 40271) Aerial view of Port Bonython tanker loading facilities. (Photo 40416)

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A transcontinental gas pipeline, linking gas reserves in theNorthwest Shelf and Timor Sea to markets in southeasternAustralia, is likely to be constructed in the next 10–20 years(Australian Gas Association, 1988). It is possible that sucha pipeline would be routed through the Amadeus Basin toMoomba where it would link with the existing Moomba–Sydney gas pipeline. The economics of Officer Basin gascould be significantly improved if sufficient reserves werediscovered prior to construction, and the pipeline routed viathe basin.

Port Stanvac refines petroleum products mainly for theSouth Australian market. The refinery commencedoperations in 1963 and the adjacent lubricating oil refinerycame on stream in 1976. The main products are LPG,solvents, motor gasoline, jet fuel, kerosene, diesel (bothautomotive and industrial), lube oil basestocks for Australianand overseas markets, fuel oil and bitumen.Fig. 4.1 Officer Basin infrastructure.

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ACCESS TO POTENTIAL MARKETS

Industries in the region

The northern part of South Australia is sparsely populatedand relatively undeveloped due to its remoteness and harshclimate. The main primary industry in the Officer Basinregion is cattle, which are run on large pastoral leases.Tourism (including an eco-tourism venture by AnanguPitjantjatjara) is a growing industry in the region. A largeproportion of the world’s opal is mined at Coober Pedy andMintabie.

The Olympic Dam Mine, 480 km southeast of Marla, isthe world’s largest copper–uranium deposit. Western MiningCorporation is planning to more than double copperproduction from the current level of 85 000 t/year to~200 000 t/year, together with associated uranium, gold andsilver. The township of Roxby Downs supports the mine, andhas a population of 2700 which will grow as the expansion

commences. Current energy usage is 30–40 MW/day(~1.5 PJ/year).

Extensive mineral exploration is currently underway onthe Gawler Craton, south of the Officer Basin. High-gradegold intersections have been made at Challenger prospect andsignificant gold mineralisation has been discovered at otherprospects (Campfire Bore and Golf Bore). The prospects forcommercial gold developments in the region are rated veryhighly by the mineral exploration industry.

Extensive subeconomic Early Permian coal deposits(~15 billion tonnes) occur in the Arckaringa Basin, in theCoober Pedy region. The South Australian Steel and Energy(SASE) Project is investigating development of iron ore andcoal resources south of Coober Pedy. The project plans toapply Ausmelt technology to produce pig iron. A pilot plantis being built at Whyalla.

Some of these projects may be potential users of naturalgas.

Fig. 4.2 Australian gas and liquids pipelines, treatment plants and refineries.

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Gas

Ex-field natural gas prices in South Australia are freelynegotiated between buyer and seller, and the Commonwealth,States and Territories have agreed to remove impediments toacross State borders trade in gas from July 1996. The rightsof access to gas transmission and reticulation pipelines willbe provided, and direct negotiations between consumers andproducers facilitated.

Crude oil

A free market was introduced in 1988 for all oil andcondensate produced in Australia. There is no restriction onimports or exports of crude oil or refined petroleum products.A similar regime has applied since 1991 for LPG. Marketsfor crude oil and condensate exist in South Australia andAustralia, and low sulphur light crude oils find a readydomestic and overseas market.

GROUNDWATER

The Officer Basin occurs in an area of low rainfall andhigh evaporation. Surface water (ephemeral and permanent)is virtually non-existent, and groundwater, where present, isusually highly saline. Although data on groundwater are verysparse, it is unlikely that more extensive searching in thisenvironment will yield any major resources of low salinitygroundwater.

Surface water

There is little evidence of surface water in the OfficerBasin region. The ephemeral streams of the Musgrave Blockto the north and Eromanga Basin to the east vanish abruptlyin the environment of higher permeability and porosity of thePalaeozoic sandstones in the Officer Basin, which result infaster penetration of water into the subsurface and a lowerwatertable. The ephemeral Officer Creek, which flows intothe area from the north, extends into the basin ~50 km beforebeing absorbed, but is by far the most persistent of suchfeatures. Other indications of the gathering of surface watersfor recharge are very few and uncertain.

The only other evidence of surface water of any kindcomprises the salt lakes around the southern edge of the basinoutcrop at Serpentine Lakes, at Lakes Dey Dey and Maurice,at Wyola and Wilkinson Lakes, and north of Emu Junction.These highly saline environments, which occur along thesouthern boundary of the north-dipping Palaeozoicsediments of the basin, are interpreted as discharge zones(Fig. 4.3; Lau et al., 1995a,b).

Aquifers

On the basis of the very sparse information that exists,Lau et al. (1995a,b) referred to all known groundwater asbeing interlinked in one unconfined system, with thePrecambrian surface regarded as hydrogeological basement.While this may be a simplification, there is insufficientevidence to justify subdivision.

The system extends from surface in the discharge zonessouth of the basin to considerable depth in Birksgate 1, and

spans a host time range from Tertiary palaeochannelsediments to Cambrian Observatory Hill Formation. Thesesediments are highly variable in composition and areimpossible to divide into aquifers and aquitards on theavailable information. Shale of the Observatory HillFormation contains sand sequences, while the Trainor HillSandstone may be impermeable in parts. A major increase inthe density of geological information is needed before thereis any hope of mapping individual aquifers, if such exist.

Lau et al. also noted that there may well be perchedaquifers in the palaeodrainage channels, hosted by TertiaryHampton Sandstone or Pidinga Formation.

A confined or semi-confined aquifer may be present inthe Murnaroo Formation, which is intersected in severalholes in the southeastern part of the basin. This aquiferyielded saline water in the Tallaringa Trough and nearMaralinga, and is probably recharged in the area of the NawaRidge where the formation is closest to surface and subcropsunder Tertiary sediments.

Recharge

Subsurface water flow may occur through the Tertiarypalaeochannels which extend southwards from the MusgraveBlock over the full surface extent of the Officer Basin. Whilethere is no firm evidence of such water movement, it must beexpected on the basis of the proven water content in thesefeatures to the north, the permeability of the sediments, andthe potentiometric gradient. Such waters would be expectedto be saline.

Below the base of the Tertiary sediments, any southwardflow of groundwater into the basin is expected to be blockedby the steep, fault-controlled northern edge of the basin andthe steeply dipping Adelaidean sediments.

Movement of water from Western Australia eastwardsinto the South Australian portion of the Officer Basin ispossible, but the potentiometric surface indicates that themajor flow direction is to the south.

Thus, apart from surface flow, most recharge into thegroundwater system of the Officer Basin is expected to comefrom local recharge.

Marla township showing groundwater recharge swamps, railwayline and airstrip. (Photo T22004)

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Local recharge potential

While there are no statistics from the area of outcroppingOfficer Basin sediment, rainfall in the basin is expected torange from 150 mm in the south to no more than 250 mm inthe ranges along the northern margin. This precipitation levelis low by any standards and, when combined with highdaytime temperatures and consequent high evapotranspir-ation rates, does not auger well for recharge.

According to Jacobson et al. (1994), the monthly rainfallin the arid zone must exceed 130 mm before there is anycontribution to recharge. However, using the approxima-tions implicit in Thornthwaite’s equation (Thornthwaite andMather, 1957), monthly rainfall and temperature figures forErnabella which, while not in the Officer Basin is nearenough to assist in such estimates, yield rather moreoptimistic figures, as shown on Figure 4.4. Combining thetwo estimates, and bearing in mind that the figures forpotential recharge on Figure 4.4 usually require that therecharge occurs over one, or at most two months, it wouldappear that for this location significant recharge can beexpected in at least 12 years of the 45 for which data areavailable, or one year in four on average. This is much betterthan the one year in 15–20 suggested by Jacobson et al., but

their figure may well be more applicable for the Officer Basinitself, which has significantly lower rainfall than Ernabellain the Musgrave Ranges. The increased elevation and greaterlikelihood of monsoonal rains from the north increase theprecipitation at Ernabella compared to that for the OfficerBasin.

Whichever scenario is taken, it is clear that local rechargeis a rare event in the Officer Basin and its surrounds,occurring on average every four to 15 years.

Discharge

The only evidence of surface discharge from OfficerBasin aquifers is the salt lakes along the southern margin.

Subsurface discharge may occur into the overlying EuclaBasin to the south of the Ooldea Range, but this isspeculative. Since the Officer Basin sediments dip gentlynorthwards, and the base of the Cambrian is not deep belowthe Ooldea Range, the presence of impermeable ‘Wirrildarbeds’ in seismic shotholes in this area may be a barrier tosouthward groundwater movement and may be partlyresponsible for the surface discharge in this area. Thus, there

Fig. 4.3 Groundwater potentiometric surface and salinity (after Lau et al., 1995a,b).

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may be little or no movement of water between the Officerand Eucla Basins.

It is presently thought that virtually all discharge from theOfficer Basin sediments is through the salt lakes near theOoldea Range.

Potentiometric surface

The potentiometric surface reflects the smoothedtopographic surface, and confirms the general southwardgradient (Fig. 4.3).

Water quality

Salinity contours indicate that groundwater is usuallysaline to very saline (Fig. 4.3). These contours give a generalidea of what can be expected, but are much biased by a fewsamples, such as Birksgate 1 which is the only sample overa large area and could well be a more local anomaly tappinga small area of local recharge.

In the Musgrave Block to the north of the Officer Basin,it is common for groundwater to have nitrate and chlorinelevels in excess of WHO approved limits. This could alsoapply to groundwater in the Officer Basin.

In the Maralinga area, groundwater in the Tertiarypalaeochannels and possibly in the underlying Officer Basinsediments tends to be very acidic (pH ~4) and have a veryhigh iron content (>200 mg/L). Similar impurities are foundin palaeochannels in the Lake Maurice area. Such problemwaters tend to be associated with water that has resided for along time in the Tertiary Pidinga Formation sediments, whichoften contain pyrite and lignite. An undesirably high contentof radioactive minerals is also common. Impurities such asthese are not anticipated in the northern part of the OfficerBasin, but are expected to become more prevalent to thesouth, parallelling the higher salinity.

The drilling of water wells in the western portion,particularly on NOORINNA and WELLS map areas, havegenerally been successful within 100 m of surface, withyields of 2–3 L/s being common. The salinity is reasonablyhigh, ~10 000 mg/L, and becomes more saline to the south.It seems most likely that the unconfined aquifer is reasonably

continuous over this area but with little local recharge, so thatthere is little likelihood of lower salinity water other than veryrestricted, fragile supplies.

It is probable that the low salinity (<1 500 mg/L) suppliesencountered at Birksgate 1 and near Coffin Hill in theBIRKSGATE map area are the result of local recharge. Assuch, they could be fragile and of limited extent. The lowrecharge potential of the area precludes large supplies ofpotable water.

Fig. 4.4 Annual potential groundwater recharge at Ernabella. Themonthly potential recharge (precipitation less potentialevapotranspiration) is calculated from precipitation andtemperature data. The annual potential recharge is the sum ofpositive monthly potential recharge figures.

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INTRODUCTION

The Officer Basin of southern Australia occupies an areaof ~375 000 km2, with its present-day margins bounded bythe Yilgarn Craton to the west, Musgrave Block to the northand Gawler Craton to the southeast. The northeastern extentof the basin is poorly known, but its strata are presumed tocontinue beneath Mesozoic and Permo-Carboniferous rocksinto the Amadeus and Warburton Basins. The relationship ofthe Officer Basin to surrounding regions is illustrated on

Figure 5.1, which also shows the approximate positions ofthe East Antarctic and Laurentia continental blocks inNeoproterozoic time. The Tasman Line marks theapproximate margin of the Australian continental plate afterthe separation of Laurentia and before the accretion ofmicrocontinents in Palaeozoic time.

The mid-Neoproterozoic to Late Devonian (~820–360 Ma) geological evolution of the Officer Basin can mostsimply be described in four stages, each terminated by an

Fig. 5.1 Outline of the Officer Basin and adjacent regions of continental Australia. The cross-section is shown on Figure 5.3.

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orogenic episode or a major unconformity. Adopting theterminology of Hoskins and Lemon (1995), these are:

• Stage 1 — sag development of the ~2 x 106 km2

Centralian Superbasin, culminating in uplift anderosion (~780–760 Ma).

• Stage 2 — onset of compressional basin developmentculminating in the Petermann Ranges Orogeny(~560–550 Ma).

• Stage 3 — Cambrian deposition halted by upliftassociated with the Delamerian Orogeny (~507 Ma).

• Stage 4 — Ordovician to Devonian depositionterminated by the Alice Springs Orogeny (~360 Ma).

PLATE TECTONIC SETTING

The position of Australia relative to other continentalblocks in Neoproterozoic time is shown on Figure 5.2. TheSWEAT (Southwest US–East Antarctic) hypothesis

(Moores, 1991; Hoffman, 1991) places Laurentia oppositeEast Antarctica and Australia prior to opening of thePalaeopacific Ocean in Early Cambrian time. As Figure 5.1shows, the North American Cordillera (Laurentia) ispresumed to have faced south-central Australia across theTasman Line. The similarities of the Neoproterozoic glacialand interglacial successions of the Adelaide Fold Belt and theNorth American Cordillera were emphasised by Young(1992).

Using Hoffman’s (1991) reconstruction (Fig. 5.2), thereis a pronounced alignment of the major Neoproterozoic andCambrian salt deposits although, by the end of the EarlyCambrian, palaeomagnetic data show that Australia,Laurentia and Siberia would have been separated by thePalaeopacific Ocean. Most of these salt deposits areassociated with petroleum source rocks (see Ch. 8).

The Hormuz Series and Punjab Saline Series of theIran–Pakistan salt basin are Neoproterozoic, as is the Alinya

Fig. 5.2 Neoproterozoic continental reconstruction (after Hoffman, 1991), showing Neoproterozoic and Cambrian saline basins: 1. Iran–Pakistan basin (Neoproterozoic); 2. Centralian Superbasin (Neoproterozoic) and component Officer Basin (Neoproterozoic plus Cambrian);3. North Canada basins (McKenzie, Colville, Big Bear; Cambrian); 4. Siberian Platform (Cambrian). Arrows crossing the CentralianSuperbasin indicate direction of compression.

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Formation of the eastern Officer Basin and equivalentselsewhere in the Centralian Superbasin. OuldburraFormation salt in the Officer Basin and the Saline RiverFormation of the McKenzie, Colville and Big Bear Basins inCanada (Morrell, 1995) are Early Cambrian in age. Spanningboth the latest Proterozoic and Early Cambrian are the halite–anhydrite–dolomite complexes of the Danilov and UsolFormations of the Siberian Platform (Kuznetsov et al., 1992).

Officer Basin evolution in the era between the depositionof Neoproterozoic salt and Early Cambrian salt (~800–535 Ma) is punctuated by compressional tectonic activitywhich caused the Centralian Superbasin to be foreshortenedin a north–south direction and thus form into separatecomponent basins, of which the Officer is the most southerly(Walter and Gorter, 1994). A cross-section through thesebasins, and a scale comparison with the Persian Gulf andSiberian regions, is shown on Figure 5.3. Lindsay and Leven(1996) regarded the polyphase evolution of the Officer Basinto have been governed by forces acting at continental platescale. Shaw (1991) came to the same conclusion for theAmadeus Basin.

Li et al. (1996) suggested that after ~800 Ma, the historyof the Rodinia supercontinent was largely extensional asdifferent crustal blocks separated episodically during theNeoproterozoic and Palaeozoic. Whilst this may have beenthe case for blocks on the Tasman Line margin of thesupercontinent, compression was clearly the major forceoperating on the interior basins. Contrary to Li et al. (1996),it is also contended here that Laurentia andAustralia–Antarctica did not separate until Early Cambriantime (as evidenced by the great volumes of within-plate basaltin the Early Cambrian of southern Australia). The separationof Siberia and Laurentia is also constrained to the EarlyCambrian (Pelechaty, 1996). The direction of compressionalstress, which terminated stages 2 to 4 tectonism in the OfficerBasin, is illustrated by opposing arrows on Figure 5.2. Thesedeformations are interpreted here as responses to differentialrotation between the China continental blocks to the northand the Australia–Antarctic block to the south.

BASEMENT STRUCTURAL ELEMENTS

Basement beneath the Officer Basin cannot bedetermined directly except at rare outcrops and in a fewdrillholes. However, by basinward extrapolation of thesurrounding basement block characteristics usingaeromagnetic and deep seismic data, something can belearned of what lies beneath the basin floor. Interpretationsof aeromagnetic and/or gravity data in specific areas havebeen made by Finlayson (1979), Ashley (1984), Womer et al.(1987) and Benbow (1993), and reviewed at basin scale byLeven and Lindsay (1992). A map of total magnetic intensityillustrates some of the features of the basin’s deep structureand provides a basis for delineating its major structuralelements (Fig. 5.4). Further details of the eastern reaches ofthe basin, where structural complexity is greatest, are shownon Figure 5.5.

Eastern margin � Gawler Craton

The Archaean to Palaeoproterozoic Gawler Craton hasbeen studied in detail because of its mineral potential. It is

separated from the Officer Basin by the Karari Fault whichexhibits dip-slip displacement greater than 1000 m, and hasan aeromagnetic signature which can be traced for more than300 km. Limb’s (1980) suggestion that major faulting mayhave produced less dense material at depth suggests that theKarari Fault is overthrust to the northwest. The magneticanomaly associated with the Karari Fault dips 60º towards135º (Benbow, 1993), adding further evidence for thrustfaulting.

A southwest–northeast curvilinear belt of magneticanomalies on the Gawler Craton and subparallel to the KarariFault Zone has been interpreted by Daly (1996) as aPalaeoproterozoic collision zone between the Gawler Cratonand the Yilgarn Craton the west. If so, the Karari Fault Zoneand adjacent Tallaringa Trough overlie a mobile belt ofconsiderable antiquity.

Tallaringa Trough and Nawa Ridge

The Tallaringa Trough (Fig. 5.4) is almost 200 km long,40 km wide, and contains the richest oil-prone source rocksin the Officer Basin (see Chs 8 and 9). It was initiallyrecognised from aeromagnetic data as a syncline, barelydelineated by single east–west flight lines (Steenland, 1965).Subsequent seismic and gravity surveys have detailed smallportions of the Tallaringa Trough (Townsend, 1976; Milton,1974, 1975; Benbow, 1993) and revealed it to be structurallycomplex. Near its centre, the trough contains up to 600 m ofCambrian strata and possibly 1600 m of underlyingNeoproterozoic sedimentary rocks above magneticbasement.

The Tallaringa Trough is bounded to the northwest by theNawa Ridge, a positive structure composed of Gawler Cratoncrystalline rocks covered by a thin veneer of NeoproterozoicOfficer Basin strata. Basement rocks are mainly gneiss andbanded iron formation (BIF) which forms linear to complex,high-amplitude magnetic anomalies. This region of shallowbasement is known as the Nawa Subdomain, and itsnorthwestern margin (shown by dots on Fig. 5.4) is regardedas the subsurface margin of the Gawler Craton (Parker andDaly, 1993).

Northern margin � Musgrave Block

A major contribution by Steenland (1965, p.12) was hisrecognition based on regional aeromagnetic data that ‘theforedeep or trough [Munyarai Trough] just south of the front[S. margin of Musgrave Block]...is broken with many localstructures...which are steep, probably thrust faulted on theirsouthern flanks’. It has taken a number of years, using acombination of magnetic, gravity and seismic data, toconfirm that thrust faults do indeed truncate the northernmargin of the Officer Basin (Milton and Parker, 1973;Lindsay, 1995; Lindsay and Leven, 1996).

Outcropping crystalline rocks of the Musgrave Blockhave a complex aeromagnetic signature and consist ofamphibolite–granulite facies acid metamorphic rocks(mainly gneiss) intruded by felsic plutons, and basic andultrabasic rocks. The rocks may be up to 1600 million yearsold, but a major thermal event (Musgravian Orogeny) wasrecorded at ~1200 Ma (Major and Conor, 1993). Faults in

37

Fig. 5.3 Cross-section through dismembered components of the Centralian Superbasin. The Persian Gulf Basin and Siberian Platform arecompared at the same scale.

38

the Musgrave Block were reactivated during the PetermannRanges and Alice Springs Orogenies.

Middle Bore Ridge

The Middle Bore Ridge lies south of the Manya Troughand is parallel to the Ammaroodinna Ridge (Figs 5.4, 5.5).Comalco Middle Bore 1, drilled in 1985, intersectedcrystalline basement beneath the Early Cambrian OuldburraFormation. Basement is composed of undifferentiatedpyroxene granulite in fault contact with the Cambrian coverrocks. The pyroxene granulite is part of the Nawa Sub-domain, thus the Middle Bore Ridge is on the northwesternsubcropping margin of the Gawler Craton. Aeromagneticdata confirm this interpretation (Hamer, 1994).

Mafic dykes

Aeromagnetic surveys have revealed a system ofnorthwest-trending parallel mafic dykes (Fig. 5.5) which passnorthwestwards from the Gawler Craton, through the NawaSubdomain including the Middle Bore Ridge, across the floorof the Munyarai Trough and into the Musgrave Block. Theseare part of the Gairdner Dyke Swarm which either slightlypre-dates or is the same age as the oldest Officer Basin strata.Orientation of the dyke swarm implies northeast–southwestextension (Ashley, 1984; Cowley and Flint, 1993). Animportant characteristic of the aeromagnetic image is thatthere is little or no lateral offset of the dykes, thus strike-slipfaulting has been very minor and the Ammaroodinna andMiddle Bore Ridges are major dip-slip thrust features.

Fig. 5.4 Aeromagnetic map of Total Magnetic Intensity showing principal structural elements of the eastern Officer Basin.

39

Coompana Block

The Coompana Block, situated west of the Gawler Craton(Fig. 5.1), is composed of Archaean to Mesoproterozoicgneiss and granite intruded by northwest-trending maficdykes (?equivalent to the Gairdner Dyke Swarm), andoverlain by Nullarbor Platform cover. K–Ar geochronologyindicates that the gneiss was deformed between ~1180 and1160 Ma, indicating a Musgravian Orogeny overprint (Flintand Daly, 1993).

Structures beneath the basin

The northward thickening Birksgate Sub-basin andMunyarai Trough are overthrust by the Musgrave Block andramp gently up-dip onto the broad Murnaroo Platform. Deepseismic data show basement beneath these regions to bepervaded by a complex of north-dipping reflectors whichLindsay and Leven (1996) interpreted as faults. Thesereflectors appear to commence near the base of the crust(depth ~42 km) and are terminated by the unconformity at

Fig. 5.5 Aeromagnetic map of Total Magnetic Intensity of the northeastern Officer Basin showing selected mafic dykes, locations of twoseismic lines (see Fig. 5.6), and time structure contours of base of Cambrian (after Womer et al., 1987; Mackie, 1994; Lindsay, 1995).

40

the base of the Officer Basin. Lindsay and Leven (1996, p.6)also pointed out that several of these faults have beenreactivated ‘by later compressional events to form majorthrust complexes’.

A gravity and coincident magnetic anomaly known as theNurrai Ridge strikes north–south beneath the easternBirksgate Sub-basin (Fig. 5.4). The ridge has been suggestedto be responsible for facies differences between the easternand central regions of the Officer Basin (Stainton et al., 1988;Zang, 1995a). The southern part of the anomaly wasinvestigated by seismic which revealed no structuraldislocation across it (Lindsay, 1995; Lindsay and Leven,1996; Gravestock and Lindsay, 1994). Further south, thereare other anomalies similar to the Nurrai Ridge (Leven andLindsay, 1992), and a major magnetic feature runsnortheasterly beneath the Murnaroo Platform (betweenarrows on Fig. 5.4). These are interpreted as very old features(Ashley, 1984) which have no discernible structuralexpression within the basin itself. However, somesuperimposed magnetic features may be thrusts.

A ‘channel’ or ‘graben’, presumably striking east–west,is visible on seismic beneath the Officer Basin (Fig. 5.6a).This graben, ~7 km wide and a short distance north ofUngoolya 1, underlies the Pindyin Sandstone and AlinyaFormation as illustrated by Hoskins and Lemon (1995), andZang (1995a). The graben is considered by Zang (1995a,Zang and Preiss, in prep.) to contain strata of Willouran age,based on his assumption that the basal succession in Manya5 is also within a similar graben, or represents graben fill. Analternative seismic interpretation shown on Figure 5.6bsuggests that the basal section drilled in Manya 5 representsa sediment wedge that onlaps a basement outlier of theAmmaroodinna Ridge in a northwesterly direction (Mackieand Gravestock, 1993). The succession was not restricted tograbens but was widespread prior to erosion, as evidenced byoutcrops of a succession similar in all respects to that coredin Manya 5, but 200 km distant in the Peake and DenisonRanges (Ambrose et al., 1981; see Ch. 6).

A graben or channel clearly exists but has not yet beendrilled. An analogous succession beneath the AmadeusBasin was thought to represent an early rift sequence(Lindsay and Korsch, 1991). This sequence of fluvialclastics and volcanics is now thought to pre-date the initialdevelopment of the Amadeus Basin (Korsch et al., 1993).

The existence of these ‘grabens’ may be of considerablesignificance for petroleum exploration. A grid of very large(hundreds of kilometres long by tens of kilometres wide)‘rifts’ or ‘transverse aulacogens’ underlies the SiberianPlatform and contains organic matter of Early Riphean age(~1000–800 Ma). Average organic matter content of the riftfill is only 0.3% (Surkov et al., 1991), but these Ripheanrocks are the source of most of the oil found in the Vendianand Cambrian of the Siberian Platform (A.Yu. Rozanov,Palaeontological Institute, Russian Academy of Sciences,pers. comm., 1995). It is unlikely that the sub-Officer Basinstructures reached similar dimensions, but they should not beignored as possible hydrocarbon source areas.

BASIN ARCHITECTURE

The thickest Officer Basin strata are contained in anarcuate string of asymmetric sub-basins or troughs whichdeepen towards the overthrust southern margin of theMusgrave Block. They are the Yowalga, Lennis and WaigenSub-basins in Western Australia, and the Birksgate Sub-basinand Munyarai Trough in South Australia. The BirksgateSub-basin and Munyarai Trough abut the almost flat-lyingMurnaroo Platform to the south and are interpreted to beunderlain by Mesoproterozoic crystalline basement (Lindsayand Leven, 1996). In the more structurally complex easternreaches of the basin, basement is in fault contact with rocksas young as Cambrian. The chief elements of basinarchitecture are described below.

Munyarai Trough

The Munyarai Trough (the ‘foredeep’ of Steenland, 1965)is an elongate southwest–northeast orientated forelandtrough which deepens asymmetrically towards the MusgraveBlock (Figs 5.4, 5.5). The trough contains up to 10 km of fillbased on geophysical data (Womer et al., 1987) and is~7500 km2 in area. The youngest rocks are of Late Devonianage and are lacustrine. In contrast to the Amadeus Basin,syn-orogenic Devonian conglomerates have not beenrecognised. The conglomerate drilled in Officer 1 (TD183 m) is thought to be Permian glacial outwash. Thedeepest well in the trough is Munyarai 1 (TD 2899 m) drilledon a large anticline.

Birksgate Sub-basin

The Birksgate Sub-basin is adjacent to the MunyaraiTrough and is separated from it by a broad structural archwhich does not correspond to the Nurrai Ridge but lies eastof it (Fig. 5.4). As far as can be determined from limitedseismic data, the arch is 50–100 km wide. The Nurrai Ridgeis beneath the Birksgate Sub-basin (Lindsay, 1995; Fig. 5.4).A sediment thickness of 5 km is interpreted from seismic(Lindsay, 1995). The oldest (Willouran) strata form largeelongate ridges and anticlinal outcrops near the northernthrust margin, and the youngest (Ordovician) are distributedas flat-lying outcrops further south (Krieg in Lindsay, 1995;Major, 1973b). The only well in the Birksgate Sub-basin isBirksgate 1 (TD 1878 m).

Marla Overthrust Zone

The most significant oil shows in the Officer Basin arefrom nine mineral and stratigraphic wells drilled in the MarlaOverthrust Zone, as reviewed by Hibburt et al. (1995). TheMarla Overthrust Zone lies at the eastern end of the MunyaraiTrough (Fig. 5.5) and is a complex series of anastomosingthrust ramp and duplex structures which affect rocks as youngas Ordovician (Mackie, 1994; Gravestock and Lindsay, 1994;Lindsay, 1995; Hoskins and Lemon, 1995). This zone marksthe point of closest convergence of the Musgrave Block andGawler Craton, and the propagation of thrust faults into theCambrian cover may result from lack of a décollementsurface at the basin floor (J.F. Lindsay, AGSO, pers. comm.,1995). This could be due to lack of evaporites in the Alinya

41

Fig. 5.6 Seismic sections: (a) part of Amoco Line IP-2A (vibroseis) showing graben; (b) part of Comalco lines 83-600 and 84-620 (thumper),showing onlap of the lowest strata onto crystalline basement (after Mackie, 1994).

42

97-0235 MESA

0

KILOMETRES

5

KILOMETRES

0 5

CrystallineBasement

CrystallineBasement

‘Graben’

Alinya Formation

Formation in this part of the basin. Ordovician rocks arepreserved at the surface and the oldest unit drilled to date isthe Meramangye Formation in Marla 9. The basin fill has notbeen fully drilled in the Marla Overthrust Zone, most wellshaving reached total depth in the Cambrian Observatory HillFormation.

Ammaroodinna Ridge

A small outcrop of basement rocks named theAmmaroodinna Inlier occurs immediately southwest of theMarla Overthrust Zone and ~80 km south of the MusgraveBlock (Krieg, 1972, 1993). It is composed of schist, gneissand granitoid rocks and, like the Musgrave Block, was alsoaffected by the ~1200 Ma Musgravian Orogeny. However,this sliver of basement has been emplaced tectonically. Krieg(1972) noted that faults bounding the inlier also displaced theCambrian Observatory Hill Formation and thus wererelatively young. Seismic records show that the inlier islocated on a major southwest-trending thrust fault complex— the Ammaroodinna Ridge — that separates the Munyaraiand Manya Troughs (Stainton et al., 1988; Thomas, 1990;Mackie, 1994).

The Ammaroodinna Ridge is at least 140 km long (Figs5.4, 5.5) and, though unnamed, was first recognised onaeromagnetic data by Steenland (1965). The ridge has beenvariously named ‘Ammaroodinna High’ by Stainton et al.(1988), ‘Ammaroodinna High Platform’ by Thomas (1990)and ‘Ungoolya Hinge’ by Zang (1995b). All of theseinvestigators recognised that the ridge or hinge controlledsedimentation, facies changes and structural style within thebasin.

Manya Trough

The Manya Trough lies between the AmmaroodinnaRidge and Middle Bore Ridge. Like the adjacent WintinnaTrough (Fig. 5.5), the Manya Trough is characterised bycoincident positive gravity and negative aeromagneticanomalies. The high gravity value results from carbonates ofthe Ouldburra Formation which are almost 1000 m thick.Manya Trough strata have not been fully penetrated, thedeepest well being Manya 6 which reached TD 1765 m in theRelief Sandstone. It is worth noting that the numerous halitebeds at the Ouldburra–Relief transition have not beentectonically disturbed in this well, despite its proximity to theMarla Overthrust Zone.

Prior to recognition of the Middle Bore Ridge, the Manyaand Wintinna Troughs were not differentiated. Here, theWintinna Trough is considered as a structural element of theArckaringa Basin because it contains at least 800 m ofPermian strata (cf. 324 m in Manya 6).

Murnaroo Platform

The Murnaroo Platform extends south of the BirksgateSub-basin and Munyarai Trough. It is a poorly definedregion crossed diagonally by the Ammaroodinna Ridgewhich divides the platform into eastern and western portions(Fig. 5.4). Regional seismic data in the western portionindicate a very gentle (0.3º) ramp from the Birksgate

Sub-basin onto the Murnaroo Platform (Lindsay, 1995;Lindsay and Leven, 1996), whereas in the eastern portion thetransition from the Munyarai Trough to Murnaroo Platformis more abrupt, via the Ammaroodinna Ridge (Stainton et al.,1988; Thomas, 1990).

Four key wells — Murnaroo 1, Observatory Hill 1, LakeMaurice West 1 and Lake Maurice East 1 — have been drilledon the Murnaroo Platform, but only the last listed haspenetrated to crystalline basement. In Lake Maurice East 1,high-grade gneiss of the Palaeoproterozoic Nawa Subdomainis overlain unconformably at 691 m by the Marinoan TarlinaSandstone. The Cambrian Arcoeillinna Sandstone andObservatory Hill Formation comprise the youngestoutcropping strata.

Nullarbor Platform

The Nullarbor Platform is a stable region of relatively thin(~2 km) sedimentary cover which overlies the CoompanaBlock. In ascending stratigraphic order, the platformcomprises Neoproterozoic–Cambrian Officer Basin,Permo-Carboniferous Denman Basin, Jurassic–CretaceousBight Basin, and Tertiary Eucla Basin. The modern surfaceof the platform is the Nullarbor Plain. The Nullarbor andMurnaroo Platforms are contiguous but are almost separatedlocally by shallow crystalline basement as drilled in Ooldea 1(Fig. 5.7). This basement rise, named the Watson High(Rankin in Parker, 1993, fig. 2.4), also forms the southernmargin of the Tallaringa Trough. The deepest well on theNullarbor Platform is Mallabie 1 which drilled 905 m ofsandstone, arkose and basic volcanics before intersecting theCoompana Block. The age of the volcanics is unknown, butthey post-date the ~1200 Ma Musgravian Orogeny and areundeformed. The Cadlareena Volcanics of the Peak andDenison Inliers (Ambrose et al., 1981) and the volcanicsintersected in Manya 5 may be correlatives.

Fig. 5.7 Cross-section through the Nullarbor Platform, the mostsoutherly structural element of the Officer Basin.

43

Drillholes Hughes 1, 2 and 3, located ~120 km northwestof Mallabie 1, intersected clastics and carbonates assumed byGravestock and Hibburt (1991) to be Cambrian in age.However, seismic recorded in 1993 indicates that theCambrian has been eroded (Lindsay, 1995; Lindsay andLeven, 1996), thus the Hughes wells are now considered tohave intersected Neoproterozoic strata; lithologies arereminiscent of the Alinya Formation.

STRUCTURAL HISTORY

Stage 1

Originally the Officer Basin was a component of the 2 x106 km2 Centralian Superbasin, a giant sag basin initiated bycrustal extension as evidenced by the Gairdner Dyke Swarm(Ashley, 1984). However, as Lindsay and Leven (1996, p.18)pointed out, the thick crust and north-dipping deep crustalreflectors suggest ‘large-scale subcrustal processes’ ratherthan mechanical extension. Similarly, the sub-basin‘channel’ or ‘graben’ near Ungoolya 1 implies that the OfficerBasin’s prehistory is more complex than previouslyenvisaged.

Seismic stacking patterns and the even spacing of basaland top reflectors indicate that Stage 1 sediments represent‘the infilling of a broad, shallow, intra-cratonic sag basin’(Hoskins and Lemon, 1995, p.398). Thomas (1990)envisaged an initial ‘platform stage’ followed by creation ofa topographic gradient as salt migrated within the AlinyaFormation. According to Lindsay and Leven (1996),evaporitic units within the Alinya Formation began to flowsoon after deposition and continued sporadically until theDevonian Alice Springs Orogeny. Stage 1 is illustrated onFigure 5.8a.

There is a major hiatus between the Alinya Formation andoverlying late Neoproterozoic in much of the eastern OfficerBasin. An intervening Sturtian tillite is known only from thenortheastern reaches of the basin, suggesting a lacuna of atleast 20 million years. However, as the Alinya Formation andoverlying units are structurally concordant, there is noevidence of a Stage 1 terminal orogeny. Moussavi-Haramiand Gravestock (1995) have estimated uplift and erosion of100–500 m of strata from above the Alinya Formation due toglaciogenic processes, but a reason for the termination ofStage 1 remains essentially unknown.

Stage 2

Stage 2 spans late Neoproterozoic deposition, terminatingin the Petermann Ranges Orogeny. This stage may bedivided into upper and lower successions by a localisedthough prominent canyon incision surface which initiated onthe Ammaroodinna Ridge and extended northwestwards intothe Munyarai Trough, with canyons up to 700 m deep(Thomas, 1990; Sukanta et al., 1991; Lindsay and Leven,1996). Hoskins and Lemon (1995) noted that north–southcompression was responsible for differentiation of the basininto the Munyarai Trough and Murnaroo Platform, separatedby the Ammaroodinna Ridge (cf. extensional model ofGravestock and Sansome, 1994). However, Badley (1988)was the first to recognise that the seismic reflection patternis explicable by a model involving up-slope propagation of

faults, the gravity driven collapse of ‘half-graben’ fill anddetachment on salt beds in the Alinya Formation. Badley alsonoted that at least two compressions and one major uplift hadaffected the basin since salt withdrawal in the AlinyaFormation. According to Hoskins and Lemon (1995),compression was also responsible for:

• uplift of the Musgrave Block, culminating in thePetermann Ranges Orogeny

• northward tilt of the basin floor, sediment loading andsalt movement

• submarine canyon erosion.

The Petermann Ranges Orogeny (~560–550 Ma) severedconnection with the Centralian Superbasin by way of theMusgrave Block. Earlier workers (e.g. Gravestock andSansome, 1994) ascribed the main phase of thrust-relateddeformation to the Late Devonian Alice Springs Orogeny, butHoskins and Lemon are emphatic, and Lindsay and Leven(1996) concur, that the Petermann Ranges Orogeny wasresponsible for an earlier phase of thrusting. Up to 3000 mof strata are estimated to have been eroded during thisorogeny (Moussavi-Harami and Gravestock, 1995). Stage 2of Officer Basin development is shown schematically onFigure 5.8b.

Stage 3

During Stage 3, the thickest Cambrian sediments, chieflycarbonates, were deposited in elongate troughs between theKarari Fault Zone and Ammaroodinna Ridge. Thinnersediment packages extended into the Munyarai Trough to thenorthwest and onlapped the Murnaroo Platform and probablyalso the Gawler Craton to the southeast. Lindsay and Leven(1996) suggested that regional subsidence in a mildlyextensional regime characterises the Cambrian; alluvial fanconglomerates (e.g. Wallatinna Member of the ObservatoryHill Formation) attest to contemporaneous localised uplifts.Hoskins and Lemon (1995) illustrated a diapiric piercementstage (Fig. 5.8c) which Thomas (1990) suggested may haveoccurred somewhat earlier during the Neoproterozoic.

Cambrian deposition in the Adelaide Fold Belt was haltedby the Delamerian Orogeny which commenced at ~507 Ma.In the Officer Basin, the Delamerian Orogeny caused upliftand erosion, estimated to have exceeded 2000 m in the farnortheast of the basin (Moussavi-Harami and Gravestock,1995). Stage 2 thrust faults were also reactivated (Badley,1988; Hoskins and Lemon, 1995).

Stage 4

Relatively little is known of Stage 4 which commencedwith deposition of a thick wedge of Ordovician (?andSilurian) siliciclastic sediments and culminated in the LateDevonian–Early Carboniferous Alice Springs Orogeny.About one-quarter of the sediment fill in the northernMunyarai Trough is Devonian on seismic evidence but, as thesection is undrilled, the presence of a syn-orogenic molassesuch as the Brewer Conglomerate of the Amadeus Basinremains speculative (Fig. 5.8d). Lindsay and Leven’s (1996)estimate of Devonian in the trough (‘almost half’) appearstoo high. Part of this section may alternatively be

44

Ordovician–Silurian (Gravestock and Sansome, 1994;Hoskins and Lemon, 1995), but this is also untested.

Heat flow associated with the Alice Springs Orogeny wassurprisingly widespread as evidenced by fission trackannealing in apatites from pre-Devonian strata (see Ch. 9).Thrust faults were reactivated and others may have beeninitiated; locally they propagated as ramps and duplexstructures in the Marla Overthrust Zone (Mackie and

Gravestock, 1993) and Ammaroodinna Ridge (Hoskins andLemon, 1995).

Elevation of basement blocks in central Australia (e.g.Musgrave Block, Arunta Block) has been suggested as amajor trigger for Carboniferous glaciation (Veevers andPowell, 1989), which initiated the Gondwanan depositionalphase over the eroded remnants of the CentralianSuperbasin.

Fig. 5.8 Schematic section from the Murnaroo Platform to Musgrave Block, showing four stages of Officer Basin evolution (after Thomas,1990; Hoskins and Lemon, 1995).

45

46

INTRODUCTION

The Officer Basin spans 350 000 km2 of central Australia,from the Yilgarn block in Western Australia to the GawlerCraton in South Australia. It is an arcuate depression~500 km long with six main depocentres containing up to10 000 m (Womer et al., 1987) of gently foldedNeoproterozoic and Palaeozoic sediments.

In spite of its large areal extent, the stratigraphy of thebasin is relatively poorly known compared to other SouthAustralian basins, possibly due to:

• Wells with stratigraphic information are often shallow,and are widely spaced.

• Outcrops are poor and of limited stratigraphic intervalbecause of low dips and subdued topography; this hasled to many, possibly synonymous, names beingintroduced.

• The stratigraphy is complex, with at least 33 mappablestratigraphic units identified.

Biostratigraphic control is poor. The early Palaeozoicsediments are largely non-marine and lithologically similarto Neoproterozoic sediments. Biozonation of theNeoproterozoic based on acritarchs has recently beenachieved (Zang, 1994, 1995a,b), which has significantlyimproved correlation.

Previous nomenclatures are summarised on Figure 6.1,and that recommended for use in the future on Figure 6.2.This chapter has been compiled using the published data andinterpretations of Major and Teluk (1967), Major (1973a,b,c,1974), Benbow (1982), Gatehouse et al. (1986), Brewer etal. (1987), Gaughan and Warren (1990), Gravestock andHibburt (1991), Preiss (1993), Gravestock and Sansome(1994), Zang (1994, 1995a,b), Gravestock et al. (1995) andMoussavi-Harami and Gravestock (1995). Radiometric agesof the Palaeozoic section are based on those in Tucker andMcKerrow (1995).

Because of the poor biostratigraphic control, sequencestratigraphy has been used as an aid to correlation (Thomas,1990; Gravestock and Hibburt, 1991; Sukanta, 1993;Gravestock and Sansome, 1994; Zang, 1995a,b; Moussavi-Harami and Gravestock, 1995). Depositional sequences inopen marine and deep sea environments are demonstrated tobe controlled by eustatic sea-level change. However, theintracratonic Officer Basin was strongly influenced bytectonism which generated accommodation space. Themajor sequence boundaries in the eastern Officer Basin arecorrelated with tectonically generated unconformities

(Moussavi-Harami and Gravestock, 1995; Zang, 1995b).Twelve sequence sets were recognised by Preiss (1993) in theNeoproterozoic in the Adelaide Fold Belt (AdelaideGeosyncline), but in the eastern Officer Basin they areincomplete. Ten sequence sets (super-sequences) from theNeoproterozoic to the Devonian can be recognised, somesequence boundaries can be observed in core and in the field,but most are interpreted from seismic data. Some have beendivided into smaller (third order) sequences. Systems tracts(Moussavi-Harami and Gravestock, 1995) have also beenassigned for each sequence (Fig. 6.2). These includelowstand systems tract (LST), transgressive systems tract(TST), highstand systems tract (HST), maximum marineflooding surface (MFS) and incised valley fill (IVF).

The subcrop geology of the Officer Basin is shown onFigure 6.3.

OFFICER BASIN

UNDRILLED SEQUENCE BELOW THE

CALLANNA GROUP

On some seismic lines (e.g. IP1-2A, Fig. 5.6), a sequenceof sediments is present in valley fill or narrow grabens~10 km wide and up to 1300 m thick. This sequence has notbeen drilled, but is older than the Callanna Group equivalents.Zang (1995a) suggested that the Pindyin Sandstone andAlinya Formation are younger than the Callanna Group(equivalent to the Burra Group), and that the undrilledsequence is the Younghusband Conglomerate andCoominaree Dolomite of the Peake and Denison Inliers,which are considered to be Callanna Group equivalents. Thesediments may be an equivalent of the Pandurra Formation(fluvial sandstone) on the Gawler Craton and Stuart Shelf,which is of late Mesoproterozoic age (Mason et al., 1978;Preiss, 1987). The Moorilyanna Formation (Wilson, 1952;Coats, 1963; Gravestock et al., 1995) and the LevengerFormation (Major, 1973d), both of which occur in isolatedgrabens in the Musgrave Block, may be equivalents. In theAmadeus Basin, the Mount Harris Basalt, and the fluvialBloods Range and Dixon Range beds, interpreted to be anearly rift sequence (Lindsay and Korsch, 1991), may also beequivalents. The nature of these sediments will remainspeculative until they are drilled.

CALLANNA GROUP EQUIVALENTS

The Pindyin Sandstone, Alinya Formation, CoominareeDolomite and Cadlareena Volcanics were probably depositedin response to the initial Neoproterozoic sag during the

47

Willouran, and have been designated Sequence W. TheCoominaree Dolomite, Cadlareena Volcanics and an earlierPindyin Sandstone equivalent (YounghusbandConglomerate) in the Peake and Denison Inliers have beencorrelated with the Arkaroola Subgroup of the CallannaGroup in the Adelaide Fold Belt (Preiss, 1987; Rogers andFreeman, 1996).

Seismic evidence indicates that the Callanna Group iswidespread subsurface in the Officer Basin. It forms themajor detachment for propagation of thrust faults and is the

source of salt in halokinetic structures (Gravestock andSansome, 1994). To the east of the Marla Overthrust Zone,the facies change from clastic to carbonates and volcanics(Coominaree Dolomite and Cadlareena Volcanics), althoughZang (1995a) considered these to be older than the PindyinSandstone–Alinya Formation succession.

The lowest siltstone of the Alinya Formation wasprobably deposited in a TST, with seismic interpretationsuggesting the possible onlap from northwest to southeast(Zang and McKirdy, 1993; Zang, 1995a). The Pindyin

Fig. 6.1 Summary of previous stratigraphic nomenclature.

48

Fig. 6.2 Summary of current stratigraphic nomenclature (Palaeozoic dates after Tucker and McKerrow, 1995).

49

Sandstone is inferred to be a LST to TST. The upper part ofthe Alinya Formation and Coominaree Dolomite represent aHST in a sabkha to marine palaeoenvironment; the top wasextensively eroded during glaciogenic uplift in the Sturtian.The Alinya Formation is overlain by the CadlareenaVolcanics east of the Marla Overthrust Zone (Moussavi-Harami and Gravestock, 1995).

Pindyin Sandstone

Definition and nomenclature

Thomson (1969) first used the term Pindyin Sandstone,which was later defined as Pindyin Beds by Major (1973b),and renamed Pindyin Sandstone by Zang (1995b). TheTownsend Quartzite (Townson, 1985) of the western OfficerBasin may be a synonym.

Type section

North Pindyin Hills (outcrop), as defined by Major(1973b). A subsurface reference section is defined as1289–1326.8 m in Giles 1 (Fig. 6.4; TD was in PindyinSandstone).

Lithology and distribution

The formation is generally composed of fine tocoarse-grained quartzose sandstone. In places, the sandstoneis feldspathic and contains rare quartz pebbles and clay galls.

Fig. 6.3 Subcrop geology map (pre-Tertiary) of the Officer Basin.

Outcrop of Pindyin Sandstone, Belundinna Hill. (Photo 44370)

50

28°

97-0070 MESA

29°

132° 134°130°

MUSGRAVE BLOCK

ARCKARINGABASIN

EROMANGA BASIN

OFFICER BASIN

GAWLER CRATON

123

Chambers BluffMt Johns RangeIndulkana Range

KILOMETRES

0 50

Purndu HillsPindyin Hills

Punkerri Hills

MESOZOIC

PALAEOZOIC

NEOPROTEROZOIC

MESOPROTEROZOIC

CRETACEOUS–JURASSICBulldog Shale, Cadna-owie Formation,Algebuckina Sandstone

PERMIANMount Toondinna Formation,Stuart Range Formation, Boorthanna Formation

DEVONIANMimili Formation

ORDOVICIAN–SILURIANMunda Group

CAMBRIANKulyong Formation, Marla Group

MARINOANUngoolya Group, Lake Maurice Group

STURTIANWantapella Volcanics, Chambers Bluff Tillite

TORRENSIAN–WILLOURANCallanna Group

Basement

Stratigraphic well

Dry exploration well

Well with oil show

A basal pebble conglomerate occurs at the type section. Theupper part of the unit comprises pink quartzose sandstone,and minor shale interbeds. The unit is presumed to bewidespread in the deeper parts of the basin based on seismicdata, and may occur on the Nullarbor Platform.

Relationships and boundary criteriaThe Pindyin unconformably overlies crystalline

basement or the older undrilled sequence, and is conformablyoverlain by the Alinya Formation. It may be equivalent tothe basal part of the Younghusband Conglomerate of thePeake and Denison Inliers (although Zang (1995b) disputedthis and considers the Younghusband Conglomerate to beolder), the Heavitree Quartzite in the Amadeus Basin, and theArkaroola Subgroup in the Adelaide Fold Belt.

ThicknessIn outcrop the sandstone is ~200 m thick; in Giles 1 only

the top 39 m were penetrated, but seismic data suggest thethickness ranges from 100 to 200 m.

AgePrecambrian, Neoproterozoic, Willouran to Torrensian

Epochs. Zang (1995b) considered the unit to be Torrensianbecause of its wide distribution based on seismic evidence.

Sedimentology and palaeoenvironmentIn the lower part of the type section, the presence of

conglomerate along with sedimentary structures such astrough cross-bedding and some large-scale, low-anglecross-bedding suggest a fluvial palaeoenvironment.Palaeocurrent interpretation of cross-beds, the southwardthinning of the conglomerate and the orientation of ripplemarks imply a northern provenance. The overlyingsandstone is characterised by herring bone cross-bedding,asymmetrical ripple marks and mudcracks, probablyindicating a tidal or peritidal depositional setting, with finergrained transgressive shallow marine sandstone higher in thesection. The Pindyin Sandstone on the Murnaroo Platformis interpreted to have a different depositional setting, possiblyaeolian, due to the presence of minor anhydrite, halite, andwell-rounded haematite-rimmed quartz grains.

Alinya Formation

Definition and nomenclature

The formation was included in the Pindyin Beds by Major(1973b). It was originally named the Alinya beds by Staintonet al. (1988), and renamed Alinya Formation by Zang(1995b).

Type section

Not originally defined, but here proposed as 1233–1289 m in Giles 1 (Fig. 6.4).

Fig. 6.4 Giles 1 — type section for Alinya Formation, and referencesection for Pindyin Sandstone.

Tidal-influenced ripple marks in the upper part of the PindyinSandstone, North Pindyin Hills. (Photo 44372)

Herringbone cross-bedding in the Pindyin Sandstone, BelundinnaHill. (Photo 44371)

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Lithology and distribution

Zang (1995b) divided the Alinya Formation into upperand lower units. The lower unit consists of red-brownsiliciclastics (siltstone and sandstone) and evaporite(anhydrite). The upper unit comprises stacked cycles of greysiltstone, black shale, grey-green silty shale, anhydrite andred-brown siltstone and dolomite beds rich in microbialmatter (cyanobacterial mats), with sand capping the cycles.The Alinya is widespread, and may occur on the NullarborPlatform, but is interpreted to change facies in the east intothe Coominaree Dolomite.

Relationships and boundary criteria

The formation conformably overlies the PindyinSandstone, and is unconformably overlain by the TarlinaSandstone or conformably overlain by the CadlareenaVolcanics. In the Peake and Denison Inliers, the equivalentis the upper part of the Younghusband Conglomerate(Ambrose et al., 1981; cf. Zang, 1995b), and in the AmadeusBasin the equivalent is the Bitter Springs Formation (GillenMember). The Browne and Lefroy beds (Townson, 1985) ofthe western Officer Basin, and the lower part of the WrightHill beds (Major, 1973c), may be equivalents.

Thickness

The thickness is 56 m in Giles 1 but may reach 500 m,derived from seismic data.

Age

Precambrian, Neoproterozoic, Willouran to TorrensianEpochs, acritarch assemblage AAW 1a (Giles 1) and AAW 1b(Manya 5). Zang (1995b) considered the unit to beTorrensian.

Sedimentology and palaeoenvironment

The lower siltstone and sandstone units were depositedon a tidal flat. The upper cyclic unit was deposited in acoastal sabkha setting. The sandstone at the top of each cycleis of aeolian origin.

Coominaree Dolomite

Definition and nomenclature

The unit was defined in the Peake and Denison Inliers byAmbrose et al. (1981).

Type section

Outcrop in the Peake and Denison Inliers, latitude28°26’35”S, longitude 135°59’11”E. A subsurface reference

Alinya Formation (lower part) at 1272 m in Giles 1, showingred-brown sandstone and grey-green siltstone interbeds. Scale baris 10 mm for each black and white grid. (Photo 44373)

Pindyin Sandstone at 1324.5–1327 m in Giles 1; the sandstone isof probable aeolian to fluvial origin. Scale bar is 10 mm for eachblack and white grid. (Photo 42401a)

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section for the Officer Basin is here defined as 1155–1265 min Manya 5 (Fig. 6.5).

Lithology and distribution

The formation has been subdivided into two units inoutcrop. The lower is interbedded dolomite with minorsandstone and conglomerate. The upper unit consists ofdolomite, which is oolitic at the base and stromatolitic at thetop. The Coominaree is restricted to the eastern part of thebasin, in the Manya Trough area.

Relationships and boundary criteria

The unit is probably a lateral facies equivalent of theupper Alinya Formation, although this is disputed by Zang(1995b), and may correlate with the Skates Hill Formation(of the western Officer Basin, Savory Sub-basin). It isconformably overlain by the Cadlareena Volcanics.

Thickness

Up to 77 m in outcrop, but 110 m thick in Manya 5.

Age

Precambrian, Neoproterozoic, Willouran to TorrensianEpochs. Zang (1995b) considered the unit to be Willouran.The stromatolites have been identified as Acaciella sp.(possibly A. australica), which is apparently restricted to theCallanna Group (Grey, 1995).

Sedimentology and palaeoenvironment

The Coominaree Dolomite was probably originallycalcareous or aragonitic. The presence of stromatolites

indicates a shallow marine palaeoenvironment (Ambrose etal., 1981).

Cadlareena Volcanics

Definition and nomenclature

The formation was defined in the Peake and DenisonInliers by Ambrose et al. (1981).

Type section

Outcrop in the Peake and Denison Inliers: basal part —latitude 28°6’21”S, longitude 135°53’29”E; upper part —latitude 28°42’45”S, longitude 135°15’9”E. A subsurface

Fig. 6.5 Manya 5 — reference section for Coominaree Dolomiteand Cadlareena Volcanics.

Alinya Formation (upper part) at 1242–1245 m in Giles 1, showinggrey-green shale and red-brown siltstone; anhydrite is common(Zang, 1995b). Scale bar is 10 mm for each black and white grid.(Photo 44374)

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reference section for the Officer Basin is here defined as1076–1155 m in Manya 5 (Fig. 6.5).

Lithology and distribution

The unit has been intersected only in Manya 5 in thenortheastern Officer Basin, where it consists of basalts,redbeds and pyroclastics. The amygdaloidal basalt andredbeds in Mallabie 1 in the far south of the basin may alsobe attributable to this formation. In outcrop, the formationcomprises altered vesicular basalt and dolerite, with minorandesite, dacite, rhyolite, and lapilli tuff beds. Lenticular redshale and quartzose sandstone may also be present. Theformation is not observed in Giles 1, the only other well topenetrate the Alinya Formation, and distribution may bepatchy due to erosion.

Relationships and boundary criteria

The lower boundary is probably conformable on theCoominaree Dolomite or Alinya Formation. In the type area(Peake and Denison Inliers), the unit either unconformablyoverlies crystalline basement or conformably overliesYounghusband Conglomerate. The upper boundary isunconformable, and overlain by the considerably youngerTarlina Sandstone. The Cadlareena Volcanics may beequivalent to the Wooltana and Boucaut Volcanics, whichcovered an area of ~210 000 km2 in the Adelaide Fold Belt,and the Kilroo Formation in the Polda Basin (Flint et al., 1988).

Thickness

The thickness is 79 m in Manya 5, and may be up to 730 min outcrop in the Peake and Denison Inliers.

Age

Precambrian, Neoproterozoic, Willouran to TorrensianEpochs (780–760 Ma). Zang (1995b) considered the unit tobe Willouran. Radiometric dating of possible correlatives inthe Adelaide Fold Belt (Boucaut Volcanics; Fanning, 1989)gave an average U–Pb age of 783±42 Ma, and in the PoldaBasin (Kilroo Formation; Flint et al., 1988) gave K–Ar ageson plagioclase of 768±9 and 764±42 Ma.

Sedimentology and palaeoenvironment

The volcanics are subaerial lava flows, with individualflows 20–30 m thick. Reworking of the volcanics intoshallow water (?lacustrine) environments is evident inoutcrop.

UMBERATANA GROUP EQUIVALENTS

Neoproterozoic glaciogenic successions in the AdelaideFold Belt (Umberatana Group) include lower Sturtian tillites,upper Marinoan tillites and thick (up to 4000 m) interbeddedsiliciclastics and carbonate sediments. Equivalent units inthe Officer Basin region are informally assigned Sequence Sand crop out northwest of the Marla region, but have not beenintersected in the Munyarai Trough or on the MurnarooPlatform. The Chambers Bluff Tillite and WantapellaVolcanics are exposed in fault-bounded outcrops along thenorthern overthrust margin of the basin. The relationship ofthese units to the underlying Callanna Group and overlyingLake Maurice Group sequences is poorly known due to thelack of subsurface intersections, but they occur inNicholson 2 below the Tarlina Sandstone and are presumedto occur in the deeper parts of the Manya Trough (Fig. 6.6).

Chambers Bluff Tillite

Definition and nomenclature

The unit was defined by Wilson (1952). Townson (1985)defined the Lupton and Turkey Hill beds in the westernOfficer Basin, which are considered synonymous.

Type section

Outcrop 9.6 km north-northwest of Chambers Bluff onthe northern overthrust margin of the basin. A subsurfacereference section is defined as 384–816.3 m in Nicholson 2.

Lithology and distribution

The tillite comprises yellow to pale green, pebbly, siltydiamictite in the lower part with beds of sandstone becomingmore common westwards. A 1.2 m thick bed of partly sandy,partly stromatolitic, flaggy pink-buff dolomite is presenttowards the top of the formation. The unit is poorly knownin the subsurface, but is present east of the Manya Trough,and may be more widespread.

Cadlareena Volcanics at 1118.5–1119.65 m in Manya 5; the arrowindicates a contact between the underlying mafic volcanics and aninterbedded red sandstone. Scale bar is 10 mm for each black andwhite grid. (Photo 42400c)

Coominaree Dolomite at 1160.1–1160.3 m in Manya 5; note thestromatolites (Acaciella sp.). (Photo 42400b)

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Relationships and boundary criteria

The formation is unconformably(?) overlain by theWantapella Volcanics (Krieg, 1973) or the Lake MauriceGroup, and in the Peake and Denison Inliers unconformablyoverlies the Callanna Group. It is equivalent to a range ofglacigene formations of the Adelaide Fold Belt (Preiss,1987), the Calthorinna Tillite in the Peake and DenisonInliers (Ambrose et al., 1981) and the Areyonga Formationin the Amadeus Basin.

Thickness

The thickness is over 432 m in Nicholson 2.

Age

Precambrian, Neoproterozoic, Sturtian Epoch.

Fig. 6.6 Chambers Bluff Tillite and Wantapella Volcanics cross-section (Chambers Bluff, Wantapella Anticline, Nicholson 2). Nicholson 2lithology by W. Zang.

Glaciogenic diamictite of the Chambers Bluff Tillite at 678.0–678.15 m in Nicholson 2. Scale bar is 10 mm for each black andwhite grid. (Photo 42403a)

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Sedimentology and palaeoenvironment

Palaeoenvironments range from fluvioglacial, glacio-lacustrine to supraglacial. Erratics of fresh basalt in thefluvioglacial deposits and the diamictite may be from erodedCadlareena Volcanics, and black chert pebbles probably camefrom eroded remnants of Torrensian rocks which are severalkilometres thick in the Peake and Denison Inliers 480 km tothe southeast (Gravestock and Sansome, 1994).

Wantapella Volcanics

Definition and nomenclature

The name was used by Krieg (1973) and later by Preiss(1993) without formal definition.

Type section

Here designated as the Chambers Bluff section of Preiss(1993).

Lithology and distribution

The volcanics consist of altered grey-green amygdaloidaltholeiitic basalt. A few gritty sandstone interbeds are present.The formation has not been intersected in the subsurface, butmay be present in the Marla Overthrust Zone.

Relationships and boundary criteria

The lower boundary with the Chambers Bluff Tillite isinferred to be disconformable, but has not been observed inoutcrop (Preiss, 1993). The overlying unit contains aconglomerate that is entirely of volcanic derivation, andPreiss (1993) suggested that the time break may not havebeen very long.

Thickness

The thickness in outcrop appears to be ~190 m, andprobably increases to the northeast.

Age

Precambrian, Neoproterozoic, either late Sturtian or earlyMarinoan Epochs.

Sedimentology and palaeoenvironment

The volcanics were probably extruded subaerially asmultiple flows.

LAKE MAURICE GROUP

Zang (1995a) introduced the name Maurice Group for thetransgressive–regressive cycle designated Sequence M byMoussavi-Harami and Gravestock (1995). Due to priorusage of the name elsewhere, it is here modified to LakeMaurice Group.

The Lake Maurice Group consists of the TarlinaSandstone, Meramangye Formation and MurnarooFormation, forming a complete transgressive–regressivecycle. The basal Tarlina Sandstone contains a bed of lowstandfluvial conglomerate and grades upwards into transgressive tohighstand siltstone and silty mudstone of the MeramangyeFormation. A regression is indicated by continuouslyshallowing-upwards into shoreface and estuarine–fluvialsediments of the Murnaroo Formation. The Officer Basin wassubject to relatively rapid subsidence during deposition of theLake Maurice Group; this is particularly evident on theMurnaroo Platform. In Giles 1, the Lake Maurice Group(Sequence M) contains 585 m of sediment, while Sequence Wand the Ungoolya Group are only 270 and 63 m thick,respectively. Rapid subsidence might also have resulted inmore siliciclastics being transported into the basin.

Tarlina Sandstone

Definition and nomenclature

Originally introduced as Tarlina beds by Stainton et al.(1988), and changed informally to Tarlina Sandstone bySukanta (1993), the unit was formally defined by Zang(1995a).

Type section

The type section is here redefined from Zang (1995a) to1064–1233 m in Giles 1 (Fig. 6.7). A reference section wasdefined by Zang (1995b) as 532–691.3 m in Lake MauriceEast 1 (TD was in Tarlina Sandstone).

Lithology and distribution

The lithology consists predominantly of sandstone withminor thin silty mudstone interbeds. The sandstone is brownto light brown, fine to coarse-grained, quartzose tofeldspathic. The base is conglomeratic and the amount ofmudstone increases up-section. The unit occurs on theMurnaroo Platform and is interpreted seismically in the

Coarse alluvial sandstone of the Tarlina Sandstone at 1227.4–1227.6 m in Giles 1. Scale bar is 10 mm for each black and whitegrid. (Photo 42404b)

Outcrop of Chambers Bluff Tillite and Wantapella Volcanics uncon-formably overlain by lower Lake Maurice Group at Chambers Bluff.(Photo T5965)

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Munyarai Trough. Tarlina Sandstone was intersected on theNawa Ridge (Sukanta, 1993) and may occur in the TallaringaTrough and on the Nullarbor Platform. It is probablylithologically transitional upwards and laterally with theMeramangye Formation.

Relationships and boundary criteria

The Tarlina Sandstone unconformably overlies the AlinyaFormation, Wantapella Volcanics, Chambers Bluff Tillite ormetamorphic basement, and is conformably overlain by the

Meramangye Formation or Murnaroo Formation. TheMeramangye Formation may be a lateral equivalent in theChambers Bluff and Wantapella Anticline area.

Thickness

The formation is 169 m thick in Giles 1, but is up to 373 mthick in Manya 5.

Age

Precambrian, Neoproterozoic, early Marinoan Epoch,acritarch assemblage AAM 1.

Sedimentology and palaeoenvironment

The sandstone at the type section is poorly sorted,commonly massive and lacks bedding features. Gradedbedding is often present when sandstone is associated withthin silty mudstone. Angular breccia or pebble beds arepresent in the lower part. The sandstone was probablydeposited in a fluvial–lacustrine environment and maypossibly be deltaic in the upper part. The basal conglomerateis probably fluvial.

Meramangye Formation

Definition and nomenclature

Originally introduced as Meramangye beds (Stainton etal., 1988) and Giles Mudstone (Sukanta, 1993), the unit wasdefined as Meramangye Formation by Zang (1995a).

Type section

The type section was defined by Zang (1995a) and ismodified here to 869–1064 m in Giles 1 (Fig. 6.7). Referencesections were also defined by Zang (1995b), and forMeramangye 1 is here modified to 451–690 m. The sectionin Lake Maurice East 1, assigned to the MeramangyeFormation by Zang (1995b), is now considered more likelyto be Tarlina Sandstone.

Lithology and distribution

The lithology consists of red-brown and minorgreen-grey silty mudstone interbedded with thin siltstone orfine-grained sandstone, with minor silty limestone. Theformation is present on the Murnaroo Platform and isinterpreted seismically in the Ungoolya Hinge Zone andMunyarai Trough. A lateral equivalent of this unit may bepresent in the Birksgate sub-basin.

Fig. 6.7 Giles 1 — type sections for Tarlina Sandstone andMeramangye Formation, and reference section for MurnarooFormation.

Prodelta silty mudstone and siltstone of the Meramangye Formationat 979.2–983.15 m in Giles 1. Scale bar is 10 mm for each blackand white grid. (Photo 42405a)

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Relationships and boundary criteria

Contacts with the underlying Tarlina Sandstone andoverlying Murnaroo Formation are conformable at the typesection. The Meramangye Formation unconformablyoverlies Wantapella Volcanics in the northern outcrop areas.It is equivalent to part of the Wright Hill beds of Major(1973b).

Thickness

The formation is 195 m thick in Giles 1 but is over 239 mthick in the Munyarai Trough (Meramangye 1).

Age

Precambrian, Neoproterozoic, early Marinoan Epoch,acritarch assemblage AAM 1.

Sedimentology and palaeoenvironment

Sedimentary structures include thin-bedded to laminatedmudstone, siltstone with planar cross-beds, ripplecross-lamination and graded beds. Slump structures arecommon. Upward-shallowing parasequences from siltymudstone to siltstone indicate a passage from prodelta todelta front settings.

Murnaroo Formation

Definition and nomenclature

The Murnaroo Formation was defined by Gatehouse etal. (1986).

Type section

The type section is 316.8–627.5 m in Murnaroo 1 (sectionnot fully penetrated). A reference section was defined asLake Maurice East 1, here modified to 117.3–508.3 m, whichis a complete section. However, the Murnaroo in this welloverlies Tarlina Sandstone, and thus the lower boundarycannot be definitively identified. For this reason, a newreference section is here defined as 583–869 m in Giles 1(Fig. 6.7).

Lithology and distribution

The lithology consists predominantly of sandstone, palegrey-green to pale green when fresh, altered to dark brown

and dark red-brown by iron oxide in groundwater. Thesandstone is generally poorly sorted with occasional verywell rounded, in part bimodal, fine to coarse-grained andminor granule quartz sand with rare conglomerate; lithicgrains and clay clasts are variably rare to common. Feldsparand heavy minerals are present, the latter often asconcentrations on bedding planes; biotite and muscovite aresimilarly concentrated. Shale interbeds are more commonnear the top but are scattered randomly throughout thesection. Cement most commonly is silica, with carbonate toa lesser extent. Accessory minerals include feldspar, raregypsum, and possibly glauconite.

Relationships and boundary criteria

The Murnaroo Formation conformably to unconformablyoverlies Meramangye Formation, Tarlina Sandstone orAlinya Formation. The upper boundary is conformablyoverlain by the Dey Dey Mudstone or unconformably by theRelief Sandstone (Manya 5). The unit is equivalent to partof the Wright Hill beds of Major (1973b).

Thickness

Variable, from 4 m in Marla 9 to 391 m in Lake MauriceEast 1.

Estuarine fluvial shoreface sandstone of the Murnaroo Formation(lower part) at 736.3–736.45 m in Giles 1. Scale bar is 10 mm foreach black and white grid. (Photo 42406a)

Slumped prodelta siltstone of the Meramangye Formation at873.65–873.8 m in Giles 1. Scale bar is 10 mm for each black andwhite grid. (Photo 42405b)

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Age

Precambrian, Neoproterozoic, early Marinoan Epoch.

Sedimentology and palaeoenvironment

Sukanta (1993) recognised local aeolian palaeoenviron-ments in the hinterland to the southwest, with distal fan, sheetoutwash, channelised fluvial and tidal deposits progressingnorthwards.

UNGOOLYA GROUP

The name Ungoolya Group was introduced as ‘UngoolyaFormation’ by Dunster (1987a), and changed informally toUngoolya Group by Sukanta (1993) before being formallydefined by Zang (1995b). The group has also previouslybeen termed Rodda beds (Brewer et al., 1987) and in part theWright Hill beds of Major (1973b). Sequence E ofMoussavi-Harami and Gravestock (1995) is an informalequivalent.

Ungoolya Group has been intersected in 10 wells acrossthe Murnaroo Platform (Fig. 6.8), Ungoolya Hinge andMunyarai Trough, and four higher order sequences can berecognised. The lower two (Dey Dey Mudstone and TananaFormation) were deposited in deep to shallow marineenvironments during TST and HST (Moussavi-Harami andGravestock, 1995). These two sequences were cut by a

submarine canyon (IVF), which probably represents initialmovement of the Petermann Ranges Orogeny (~575 Ma).The upper part of the Ungoolya Group (Narana Formationand equivalents) was deposited in very shallow marine toshoreline environments, TST to HST. Moussavi-Harami andGravestock (1995) estimated that >4000 m of UngoolyaGroup sediments were originally deposited in the MunyaraiTrough area prior to the Petermann Ranges Orogeny, butwere folded at ~560 Ma and more than 2000 m eroded.

Dey Dey Mudstone

Definition and nomenclature

The formation was informally introduced as Dey DeyMudstone by Sukanta (1993) and formally defined by Zang(1995b), who subdivided it into upper and lower units. TheDey Dey has previously been termed lower ‘UngoolyaFormation’ (cf. Dunster, 1987a), and lower Rodda beds (cf.Brewer et al., 1987; Thomas, 1990).

Type section

The type section of Zang (1995b) in Lake Maurice West 1is here modified to 316.3–479.7 m. The reference section forMunta 1 is also modified to 1675–1973 m (Fig. 6.9), andMurnaroo 1 is unchanged at 208.9–316.8 m.

Lithology and distribution

Two units are recognised, separated by a bed of dolomiticintraclasts which may be correlated seismically with a bed oflimestone in the Munyarai Trough. The lower unit containsmainly red-brown with some green-grey silty mudstone; theupper unit comprises dolomitic or calcareous siltstone andmudstone. The basal Dey Dey Mudstone is locallyconglomeratic. The formation is widely distributed over theMurnaroo Platform and in the Munyarai Trough, andprobably occurs in the Birksgate Sub-basin.

Relationships and boundary criteria

The Dey Dey Mudstone conformably or unconformablyoverlies sandstone of the Murnaroo Formation and is overlaintransitionally by the Karlaya Limestone. The boundarybetween the lower and upper units is marked by a bed ofdolomitic ribbon intraclasts on the Murnaroo Platform.

The Dey Dey is correlated with unit 4 of the Wright Hillbeds in the central Officer Basin, Bunyeroo Formation in theAdelaide Fold Belt, and Yarloo Shale on the Stuart Shelf. Theupper unit correlates with unit 5 of the Wright Hill beds andlower part of the Wonoka Formation in the Adelaide FoldBelt. The Dey Dey Mudstone is considered to correlate withthe Pertatataka Formation in the Amadeus Basin.

Thickness

From 86 m in Giles 1 to 298 m in Munta 1. Generally theDey Dey Mudstone thickens towards the Munyarai Troughwhere it may be up to 900 m thick.

Age

Precambrian, Neoproterozoic, mid-Marinoan Epoch,acritarch assemblage AAM 2 to 3.

Ripple cross-bedded sandstone with mudstone rip up clasts of theMurnaroo Formation (upper part) at 615.7–615.8 m in Giles 1.Scale bar is 10 mm for each black and white grid. (Photo 42406c)

Fluvial cross-bedded sandstone of the Murnaroo Formation (upperpart) at 615.8–615.9 m in Giles 1. (Photo 42406b)

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Observatory Hill 1 (355.0 m) and Lake Maurice West 1(440.78 m) contain a debris layer correlated with the Acramanmeteorite impact ejecta, which also occurs in the AdelaideFold Belt and Stuart Shelf.

Sedimentology and palaeoenvironment

The basal conglomerate was probably deposited in afluvial environment. The red-brown silty mudstone in thelower unit is massive to laminated and occasionallycross-bedded, grading up to rhythmite or tempestite, whichis considered to have been deposited in delta front to prodeltaenvironments. The upper unit contains massive to laminateddolomitic siltstone and mudstone with intraclasts, exhibitingmarine influence, and was probably deposited in prodelta toshelf settings with reducing sediment supply (Zang, 1995b).

Karlaya Limestone

Definition and nomenclature

The unit was informally introduced as Karlaya Limestoneby Sukanta (1993) and formally defined as a member of theTanana Formation by Zang (1995b). As the unit iswidespread and mappable seismically, it is here raised toformation status.

Type section

The Karlaya 1 type section is here modified to 2024–2090 m (Fig. 6.10). The reference section in Lake MauriceWest 1 is here modified to 237.6–316.3 m. The referencesection in Munta 1 is now considered to be Tanana Formation.

Lithology and distribution

The Karlaya Limestone is predominantly micriticlimestone with thin silty mudstone interbeds. It is distributedover the Murnaroo Platform and Munyarai Trough, and is adistinct seismic marker in the Officer Basin. The formationhas been recognised in Birksgate 1.

Dey Dey Mudstone at 505.9–506 m in Giles 1; note dolomiteintraclasts. Scale bar is 10 mm for each black and white grid. (Photo42407b)

Dey Dey Mudstone (lower part) at 527.7–527.8 m in Giles 1. Scalebar is 10 mm for each black and white grid. (Photo 42407a)

Acraman impact debris in the Dey Dey Mudstone at 440.73–440.78 m in Lake Maurice West 1. (Photo 42408a)

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Relationships and boundary criteria

The Karlaya Limestone conformably overlies thedolomitic and calcareous Dey Dey Mudstone, and isconformably overlain by the Tanana Formation. Itunconformably overlies the Wilari Dolomite on theMurnaroo Platform.

Thickness

From 13 m in Giles 1 to 64 m in Munyarai 1.

Age

Precambrian, Neoproterozoic, mid-Marinoan Epoch,acritarch assemblage AAM 2 to 3.

Sedimentology and palaeoenvironment

Mainly horizontal thin-bedded micritic limestone, withdark grey mudstone layers; some limestone intraclasts areoccasionally present, indicating a subtidal shelf environment,probably below fair weather wave base (Zang, 1995b).

Fig. 6.8 Neoproterozoic cross-section: Lake Maurice West 1, Murnaroo 1, Giles 1, Munta 1, Munyarai 1, Marla 9.

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Tanana Formation

Definition and nomenclature

The unit was formally defined by Zang (1995b), but waspreviously termed Upper ‘Ungoolya Formation’ (cf. Dunster,1987a), and upper Rodda beds (cf. Brewer et al., 1987;Stainton et al., 1988).

Type section

The type section in Munta 1 is here modified to 1152–1675 m (Fig. 6.11). Reference sections are also modified to1695–2024 m in Karlaya 1, 2155–2581 m in Munyarai 1, and421–484 m in Giles 1. The reference section in Lake MauriceWest 1 is now considered to be Karlaya Limestone.

Lithology and distribution

The lithology consists of limestone, calcareous siltstoneand minor sandstone. The formation is distributed over theMurnaroo Platform and Munyarai Trough, and may occur inthe Birksgate Sub-basin.

Relationships and boundary criteria

The basal contact is conformable. Where the upperboundary is eroded by canyon deposits of the NaranaFormation, the boundary is unconformable, but the overlying

Fig. 6.9 Munta 1 — Dey Dey Mudstone reference section.

Dey Dey Mudstone (lower part) at 323.5–323.6 m in Lake MauriceWest 1; note graded beds (probable slope deposits). (Photo 42408b)

Dey Dey Mudstone (upper part) at 319.9–320 m in Lake MauriceWest 1; note dolomitic breccia. Scale bar is 10 mm for each blackand white grid. (Photo 42408c)

Karlaya Limestone at 1662.1–1662.3 and 1651–1651.15 m inMunta 1. Scale bar is 10 mm for each black and white grid. (Photo42411b)

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Munyarai Formation is conformable. The formation iscorrelated with unit 6 of the Wright Hill beds in the westernOfficer Basin, and middle and upper members of the WonokaFormation in the Adelaide Fold Belt. The shale unit in themiddle part of the formation was informally named LeemurraMudstone by Sukanta (1993), but is not recognisedregionally.

Thickness

From 118 m in Marla 9 to 665 m in Ungoolya 1.

Age

Precambrian, Neoproterozoic, mid-Marinoan Epoch,acritarch assemblage AAM 3.

Sedimentology and palaeoenvironment

The formation contains a limestone unit at the top whichis fractured and contains intraclasts, and may have been

Fig. 6.10 Karlaya 1 — Karlaya Limestone type section.

Fig. 6.11 Munta 1 — Tanana Formation type section.

Tanana Formation at 1196.8–1196.95 and 1233.05–1233.20 m inMunta 1; note graded bedding and erosional structure (probableslope deposits). Scale bar is 10 mm for each black and white grid.(Photo 42411c)

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formed in intertidal to upper subtidal shelf settings. Thesiltstone or silty mudstone is massive to laminated,occasionally cross-bedded or slump cross-bedded, and wasprobably deposited in prodelta, distal delta front to shelfsettings. The upper part of the formation (= channel units,cf. Sukanta, 1993) contains red-brown to green-grey siltstoneinterbedded with thin sandstone; cross-bedding and erosionalsurfaces are common. The formation was probablydeposited in subtidal, intertidal shelf, shoreface to fluvialsettings. Sequentially the sedimentary features in the TananaFormation indicate a shallowing-upward depositionalenvironment (Zang, 1995b). Zang interpreted the section inUngoolya 1 as a succession of mainly siliciclastics with sloperibbon limestone, conglomerate and turbidites, indicating asubmarine fan deposit.

Wilari Dolomite Member

Definition and nomenclature

The unit was informally introduced as Wilari Dolomiteby Sukanta (1993) and formally defined as a member of theTanana Formation by Zang (1995b).

Type section

The type section was defined by Zang (1995b) as266.3–289.3 m in Lake Maurice West 1. This section is nowconsidered to be a reference section for the KarlayaLimestone, and the 166.6–182 m reference section inMurnaroo 1 is here defined as a new type section. A referencesection is defined as 178.26–239.7 m in Observatory Hill 1(Fig. 6.12).

Lithology and distribution

The dolomite is vuggy and weathered, massive tooccasionally thin bedded, with thin siltstone layers. Thedolomite is probably secondary. The member is intersectedon the southeastern Murnaroo Platform but is unknownelsewhere in the basin.

Relationships and boundary criteria

Both the upper and lower boundaries are erosional. Themember unconformably overlies the Karlaya Limestone andis unconformably overlain by the Early Cambrian ReliefSandstone or Cadney Park Formation.

Thickness

Thickness ranges from 14.3 m in Murnaroo 1 to 61.6 min Observatory Hill 1.

Age

Precambrian, Neoproterozoic, mid-Marinoan.

Sedimentology and palaeoenvironment

The Wilari Dolomite Member was probably deposited onan intertidal to subtidal shelf (Zang, 1995b).

Munyarai Formation

Definition and nomenclature

The unit was defined by Zang (1995b).

Type section

The type section is 1707–2155 m Munyarai 1 (Fig. 6.13).The reference section defined in Karlaya 1 is now consideredto be Narana Formation.

Lithology and distribution

The lithology consists of grey to dark grey calcareoussiltstone with thin limestone interbeds in the lower part. Theformation is distributed over the Munyarai Trough.

Relationships and boundary criteria

The Munyarai Formation conformably overlies theTanana Formation and is unconformably overlain by canyondeposits of the Narana Formation. The formation is

Fig. 6.12 Observatory Hill 1 — Wilari Dolomite Member (TananaFormation) reference section.

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correlated with unit 7 of the Wright Hill beds in the westernOfficer Basin, and Bonney Sandstone in the Adelaide FoldBelt.

Thickness

The thickness is 448.1 m in Munyarai 1.

Age

Precambrian, Neoproterozoic, mid- to late MarinoanEpoch, acritarch assemblage AAM 4.

Sedimentology and palaeoenvironment

The formation is massive to laminated with gradedbedding, and is considered to have been deposited in prodeltato shelf environments (Zang, 1995b).

Narana Formation

Definition and nomenclature

The unit was defined by Zang (1995b).

Type section

The type section in Munyarai 1 is here modified to 1699–1707 m (Fig. 6.13). Reference sections are also modified to1281.7–1526 m in Ungoolya 1, 1367–1695 m in Karlaya 1,and 900–1152 m in Munta 1.

Lithology and distribution

The Narana comprises conglomerate (clasts of chaotic toimbricated mudstone, sandstone, and micritic and ooliticlimestone), sandstone, dark grey silty mudstone and siltylimestone in varying proportions in different areas. Theformation is distributed over the Munyarai Trough and inchannels incised into the Murnaroo Platform.

Relationships and boundary criteria

The Narana Formation unconformably overlies theMunyarai Formation or Tanana Formation with an erosiveboundary. It is unconformably overlain by Marla Groupsediments. The Narana may correlate with the PoundSubgroup in the Adelaide Fold Belt. The equivalent unit inthe Amadeus Basin is the lower Arumbera Sandstone.

Fig. 6.13 Munyarai 1 — Munyarai Formation and NaranaFormation type sections.

Breccia and sandstone (submarine fan deposits) of the NaranaFormation at 1297.4–1299.5 m in Ungoolya 1. Scale bar is 10 mmfor each black and white grid. (Photo 42409b)

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Thickness

From 8 m in Munyarai 1 to 328 m in Karlaya 1. Seismicdata indicate thicknesses of up to 1500 m in the northeasternMunyarai Trough (seismic line IP1-8).

Age

Precambrian, Neoproterozoic, late Marinoan Epoch,acritarch assemblage AAM 4.

Sedimentology and palaeoenvironment

The formation contains two canyon-fill sequences. Thelower consists of debris flow deposits grading to tidal flatdeposits at the top. The upper turbidite sequence wasdeposited on a transgressive to highstand deeper watersubmarine fan, shallowing to marine shelf limestone andmudstone, which become dominant towards the top (Zang,1995b).

Munta Limestone Member

Definition and nomenclature

The unit was defined informally as Munta Limestone bySukanta (1993); it is here defined as a member of the NaranaFormation.

Type section

Here defined as 1420–1447 m in Karlaya 1 (Fig. 6.14).Reference sections are defined as 1650–1670 m in Lairu 1,and 1495–1526 m in Ungoolya 1.

Lithology and distribution

The member consists of grey to greenish grey, massiveand laminated micritic limestone and marl. Limestone andmarl units are rhythmically interbedded, with sharp, lowerboundaries to the limestone, grading upwards into marl(Sukanta, 1993). The member is present in the MunyaraiTrough.

Relationships and boundary criteria

The Munta Limestone Member is conformably underlainby the canyon fill sequences, and overlain either conformablyby the Mena Mudstone Member, or unconformably by MarlaGroup sediments.

Thickness

The thickness varies from 20 m in Lairu 1 to 45 m inMunta 1.

Unconformable contact between Tanana and Narana Formationsat 1152.5 m in Munta 1. (Photo 42412b) Narana Formation calcareous siltstone with slump structures at

987.35–989.6 m in Munta 1. Scale bar is 10 mm for each black andwhite grid. (Photo 42412d)

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Age

Precambrian, Neoproterozoic, late Marinoan Epoch.

Sedimentology and palaeoenvironment

Sukanta (1993) reviewed the possible palaeoenviron-ments represented by the Munta Limestone Member.Generally, low energy subtidal marine shelf environments arerepresented, but deeper environments, perhaps upper slope,may be represented in the Lairu and Ungoolya area.

Mena Mudstone Member

Definition and nomenclature

The unit was defined informally as Mena Mudstone bySukanta (1993); it is here defined as a member of the NaranaFormation.

Type section

Here defined as 1367–1420 m in Karlaya 1 (Fig. 6.14).Reference sections are defined as 1409–1650 m in Lairu 1,and 1282–1495 m in Ungoolya 1.

Lithology and distribution

The member consists of grey-green mudstone with thinparallel laminae and contains interbeds of grey-greenmedium to coarse-grained sandstone. It is similarlithologically to parts of the Cambrian Ouldburra Formation,but the latter may contain burrows (Sukanta, 1993). Themember occurs in the Munyarai Trough.

Relationships and boundary criteria

The Mena Mudstone Member conformably overlies theMunta Limestone Member and is unconformably overlain byMarla Group sediments. The uppermost part of the membermay pass laterally westwards into the Punkerri Sandstone.

Thickness

The thickness varies from 53 m in Karlaya 1 to 241 m inLairu 1.

Age

Precambrian, Neoproterozoic, late Marinoan Epoch.

Sedimentology and palaeoenvironment

The mudstone is finely laminated, but the sandstoneinterbeds are poorly sorted with sharp erosive bases and maydisplay graded bedding, ripple and rare trough cross-bedding.Rare mudclasts are present at the erosive base of thesandstones. The mudstone is presumed to have formed in alow energy subtidal shelf environment. Poorly sorted andcoarse-grained sandstone is better developed up section, andindicates shallowing (eustatic sea-level regression) and,finally at the level of the unconformity with the overlyingMarla Group, the red oxidised mudstone may indicatesubaerial exposure and erosion (Sukanta, 1993).

Punkerri Sandstone

Definition and nomenclature

The unit, first mentioned as Punkerri Sandstone byThomson (1969), was defined as Punkerri Beds by Major(1974), and is here redefined as Punkerri Sandstone.

Type section

The type section (Fig. 6.15) was defined by Major (1974)in outcrop, and is located across the southern flank of thePunkerri Hills at 27°40’ latitude and 130°25’ longitude.

Lithology and distribution

The formation was informally subdivided into two unitsby Major (1974). The lower is generally a purple orred-brown, medium-grained flaggy quartzose sandstone withsome feldspar and biotite. The upper unit consists of red andwhite, medium-grained feldspathic sandstone and somequartzose sandstone with interbedded red sandstone andsiltstone (Major, 1974). Outcrops of the Punkerri arerestricted to the Birksgate Sub-basin, but it is presumed tooccur at depth in the western part of the Officer Basin.

Fig. 6.14 Karlaya 1 — Munta Limestone Member and MenaMudstone Member (Narana Formation) type sections.

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Relationships and boundary criteria

The upper and lower boundaries are not seen in outcrop,but both the base and top are presumed to be unconformable.The formation is equivalent to the Pound Subgroup in theAdelaide Fold Belt (Preiss, 1993).

Thickness

The formation is over 1200 m thick in the type section.

Age

Precambrian, Neoproterozoic, latest Marinoan Epoch.

An Ediacara type fauna, with at least five genera, isknown from loose rocks in the northern Punkerri Hills, which

are presumed to have come from the upper PunkerriSandstone.

Sedimentology and palaeoenvironment

Sedimentary structures in the lower Punkerri Sandstoneinclude scour casts, ripple marks, pellets and flakes ofsiltstone. The upper unit shows some cross-bedding, andclasts of siltstone and quartz pebbles. The environment ofdeposition is tidally influenced shallow marine, similar to thePound Subgroup of the Adelaide Fold Belt (Preiss, 1987).

MARLA GROUP

The term ‘Marla Sequence’ was introduced by Krieg(1973) and defined as Marla Group by Benbow (1982). Thelower part of the group, comprising aeolian and fluvial ReliefSandstone and evaporitic Ouldburra Formation, containsthree third order sequences (Gravestock and Hibburt, 1991;Moussavi-Harami and Gravestock, 1995). Major regressiontook place at the end of Relief–Ouldburra time, and thesucceeding units (Wallatinna and Cadney Park Members ofthe Observatory Hill Formation) were formed in an alluvialfan to alluvial plain environment. The remainder of theObservatory Hill Formation was also a non-marinehinterland tract in playa lakes. The fluvial to shorelineArcoeillinna Sandstone followed, then a major transgressionbegan in the east and deposited the shallow marine ApamurraFormation. The Trainor Hill Sandstone was deposited in afluvial environment in the north and sandy tidal flats in thesouth. Total thickness of the Marla Group was probablyoriginally >2600 m in the Manya Trough, but only 1000 mon the Murnaroo Platform, indicating a depocentre to thenortheast and major erosion (1–2 km) in the central part ofthe basin as a result of the Petermann Ranges Orogeny(Fig. 6.16).

The Moorilyanna Formation (Coats, 1963; Gravestock etal., 1995) and Levenger Formation (Major, 1973d), both ofwhich occur in isolated grabens in the Musgrave Block, maycorrelate with either the upper or lower Marla Group,although there is a possibility that they may be older proximalequivalents to the Pindyin Sandstone, or the earlier undrilledgraben-fill sequence which may be equivalent to the PandurraFormation of the Gawler Craton and Stuart Shelf.

Relief Sandstone

Definition and nomenclature

The formation was defined by Brewer et al. (1987).

Type section

The type section in Meramangye 1 is here redefined as359–451 m (Fig. 6.17). Reference sections are 304–421 min Giles 1, and 155.2–178.3 m in Observatory Hill 1.

Lithology and distribution

Gaughan and Warren (1990) subdivided the formationinto nine stratigraphic units based on lithology andinterpreted palaeoenvironment (Fig. 6.18). In general, theformation is characterised by well sorted, fine tomedium-grained or poorly sorted fine to coarse-grained

Fig. 6.15 Punkerri Sandstone section (after Major, 1974).

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slightly feldspathic sandstone with clay coated grains (illite,variably corroded). Quartz overgrowths and carbonatecement are found mainly in the Marla area.

Relationships and boundary criteria

The formation disconformably overlies either UngoolyaGroup formations or earlier Murnaroo or MeramangyeFormations. The unit is synchronous and intercalates withthe more marine Ouldburra Formation, and is conformablyor disconformably overlain by the Observatory HillFormation. In Manya 5, the top of the unit is eroded and isunconformably overlain by Mount Chandler Sandstone.There may be an equivalent to the Relief Sandstone belowthe Cootanoorina Formation (Townsend and Ludbrook,1975) in the Boorthanna Trough (Weedina 1).

Thickness

Thickness varies from 23.1 m in Observatory Hill 1 topossibly 168 m in Manya 5.

Age

Early Cambrian, 540–524 Ma, based on stratigraphicposition and synchroneity with the Ouldburra Formation.The unit is unfossiliferous.

Sedimentology and palaeoenvironment

Gravestock and Sansome (1994) suggested that much ofthe Relief Sandstone could be recycled Punkerri Sandstone.

Fig. 6.16 Marla Group cross-section, through Wilkinson 1, Murnaroo 1, Giles 1, Munta 1, Munyarai 1 and Marla 3.

Relief Sandstone at 1671.2 m in Manya 6; core diameter is 38 mm.(Photo 44375)

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Gaughan and Warren (1990) determined the palaeoenviron-ments to range from aeolian and fluvial to tidal, which arerelated to marine lowstand–highstand cycles, and probablysynchronous with sequences in the adjacent marineOuldburra Formation (Gravestock and Hibburt, 1991).Aeolian lithofacies are characterised by fine to medium-grained, well to very well sorted, subangular to subrounded,low to high angle cross-bedded, pale brown to red sandstone.Fluvial lithofacies are characterised by poorer sorting, locallycoarser grain size, shale intraclasts, and planar and troughcross-bedding. Tidal lithofacies are laminated with thin, fineto coarse interbeds, ripple cross-lamination, and mud drapes.

Ouldburra Formation

Definition and nomenclature

The formation was defined by Brewer et al. (1987).

Fig. 6.17 Meramangye 1 — Relief Sandstone type section.

Fig. 6.18 Relief Sandstone palaeoenvironments in Giles 1 (afterGaughan, 1989; Gaughan and Warren, 1990).

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Type section

The type section was originally defined as 571.4–1685.4 m in Manya 6. It is here redefined in Manya 6 as571–1558 m, as the section below 1558 m is predominantlysandstone and is thus more correctly attributed to the ReliefSandstone (Fig. 6.19). Reference sections are 493–607 m inMarla 3, and 199 m (top eroded) to 685.5 m in Wilkinson 1.

Lithology and distribution

The formation comprises mainly interbedded muddylimestone, dolostone, sandstone and evaporites. In the typesection, the basal part is typified by halite and minorsandstone grading up to stacked sand–silt–mudstone setswhich become increasingly calcareous. These are overlainby a thick sequence of calcareous and dolomitic carbonateswith sporadic clastics and gypsum–anhydrite interbeds. Thecarbonate lithofacies are dominated by laminated and siltycarbonate mudstone. The top of the formation is typically anintercalation of laminated carbonate mudstone and redbedsiltstone with abundant nodular sulphate evaporite andbedded ‘chicken wire’ anhydrite. The unit is present in theManya and Tallaringa Troughs.

Relationships and boundary criteria

The formation disconformably overlies Ungoolya Groupformations or earlier Murnaroo or Meramangye Formations.It overlies and is intercalated with the non-marine ReliefSandstone, and is conformably overlain by the ObservatoryHill Formation or Wallatinna Formation in Byilkaoora 1. TheOuldburra may be equivalent to part of the CootanoorinaFormation (Townsend and Ludbrook, 1975) in theBoorthanna Trough.

Thickness

The thickness ranges from 114 m in Marla 3 to 987 m inManya 6 (the type section), but could be up to 1100 m wherenot eroded (Gravestock and Sansome, 1994).

Age

Early Cambrian, 536–524 Ma, acritarch assemblageAAC 1.

Fig. 6.19 Manya 6 — Ouldburra Formation type section.

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The middle part of the formation in the type sectioncontains an undescribed species of trilobite (Abadiella sp.),suggesting an Atdabanian age (Jago et al., 1994), butarchaeocyaths suggest a Botomian age (Gravestock andSansome, 1994). Acritarch assemblage AAC 1 is present.

Sedimentology and palaeoenvironment

The lower part of the Ouldburra Formation is a cyclicsuite deposited in isolated salinas on a shallow marine tosubaerially exposed sandy mudflat which extendedsouthwestwards into the Tallaringa Trough (Dunster, 1987a).The main part of the formation is more marine, and records‘sawtooth’ epeiric sea transgressive–regressive sequences.Trilobites and archaeocyaths are found in this part of theformation. The upper part of the formation was deposited ina regressive redbed and carbonate sabkha.

Observatory Hill Formation

Definition and nomenclature

The name was introduced by Wopfner (1969) as‘Observatory Hill Beds’, and designated a formation byBrewer et al. (1987).

Type section

Outcrop at latitude 28°58.2’S, longitude 131°57.7’E, andthe subsurface section at 0–155.2 m in Observatory Hill 1.This well was spudded just above the base of Wopfner’soutcrop type section. Reference sections are defined at30.5–335 m in Emu 1, and 8–304 m in Giles 1 (Fig. 6.20).

Lithology and distribution

The main part of the formation consists of multicolouredmicaceous siltstone and claystone, calcareous and dolomiticin part, with minor light yellow-brown, very fine-grainedsandstone and light grey to dark grey limestone and dolomite.The siltstone and claystone are dominantly red-brown tobrown but range through purple and greenish grey to darkgrey, especially where they are interbedded with thecarbonates. The formation was deposited over a wide areaof the eastern Officer Basin.

Relationships and boundary criteria

The formation was deposited conformably above theOuldburra Formation or Relief Sandstone, anddisconformably above the Ungoolya Group in the Manya andMunyarai Troughs. The upper contact with the ArcoeillinnaSandstone is conformable. The formation may be correlatedwith part of the ‘Wirrildar beds’ of the central Officer Basin(Major, 1973a), and is equivalent to the Billy CreekFormation in the Arrowie Basin.

Thickness

The thickness varies from 155.2 m in Observatory Hill 1to 466 m in Marla 3.

Ouldburra Formation feldspathic sandstone with dolomitic intra-clasts at 664.1 m in Marla 6. The vuggy porosity is due to thesolution of dolomite. (Photo 44377)

Evaporitic salina; interbedded halite and dolomitic siltstone of theOuldburra Formation at 657.7 m in Wilkinson 1. (Photo 44376)

Cherty dolomite of the Observatory Hill Formation; upper typesection. (Photo 43061)

Observatory Hill Formation type section. (Photo 43062)

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Age

Early Cambrian, 524–520 Ma, based on stratigraphicposition.

Sedimentology and palaeoenvironment

The Observatory Hill Formation has been the subject ofdetailed studies and is generally non-marine, withpalaeoenvironments ranging from distal alluvial fan, fluvial,and ephemeral lake, to alkaline playa lake. At least threelacustrine complexes are recorded (White and Youngs, 1980;Southgate and Henry, 1984; Southgate et al., 1989; Breweret al., 1987; Gravestock et al., 1995).

Cadney Park Member

Definition and nomenclature

The unit has been in informal use for many years as the‘Cadney Park’ Formation, and is defined as a member of theObservatory Hill Formation herein.

Type section

The type section is here defined as 116–493 m in Marla 3.Reference sections are defined as 236–304 m in Giles 1(Fig. 6.20), and 254–359 m in Meramangye 1.

Lithology and distribution

The member comprises red, sandy to calcareous siltstonewith occasional conglomerate. It is widespread, and isgenerally found in most wells which fully penetrate theObservatory Hill Formation. In Manya 2, the Cadney ParkMember overlies the Wallatinna Member, and is not easilydistinguished from it.

Relationships and boundary criteria

The member was deposited conformably above theOuldburra Formation or Relief Sandstone, anddisconformably above the Ungoolya Group in the Manya andMunyarai Troughs. It is conformable with the main part ofthe Observatory Hill Formation.

Thickness

The thickness varies from 54 m in Lairu 1 to 377 m inMarla 3. The base is seismically mappable (Stainton et al.,1988).

Age

Early Cambrian, 524–522 Ma, based on stratigraphicposition.

Sedimentology and palaeoenvironment

The member was deposited in a distal alluvial fan toephemeral lake environment (Gravestock and Sansome,1994).

Fig. 6.20 Giles 1 — Observatory Hill Formation and Cadney ParkMember reference sections.

Contact of Observatory Hill Formation and overlying ArcoeillinnaSandstone, Mount Johns Range. (Photo 30890)

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Wallatinna Member

Definition and nomenclature

The unit was defined by Benbow (1982) as the WallatinnaFormation. As it is restricted in distribution, and is not easilydistinguished from conglomeratic facies of the Cadney ParkMember, it is here redefined as a member of the ObservatoryHill Formation.

Type section

The type section is defined from outcrop on the northernmargin of the Mount Johns Range. A subsurface referencesection is defined as 378–486 m in Byilkaoora 1 (Fig. 6.21).

Lithology and distribution

The unit comprises flat-bedded, coarse-grained to granulearkose with interbedded conglomerate and siltstone. Thearkose is moderately to well sorted, with angular tosub-rounded grains of quartz, feldspar and minor biotite.Calcite cement is locally abundant. The conglomerate maycontain well rounded clasts up to 0.3 m diameter of whitegranitoid and more rarely black chert and grey limestone.The unit is restricted to the northeastern part of the basin inthe vicinity of the Mount Johns Range.

Relationships and boundary criteria

The basal contact is apparently conformable, but outcropevidence suggests that it may be unconformable (Benbow,

Fig. 6.21 Byilkaoora 1 — reference sections for WallatinnaMember, Parakeelya Alkali Member, Moyles Chert Marker Bed andOolarinna Member (Observatory Hill Formation).

Alluvial fan conglomerate of the Observatory Hill Formation (Wal-latinna Member) in Byilkaoora 1. (Photo 44378)

Observatory Hill Formation (Wallatinna Member), northwesternside of the Mount Johns Range. (Photo 30887)

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1982). The upper contact is conformable and is generallyoverlain by the Oolarinna Member.

Thickness

The thickness ranges from 50 m in Byilkaoora 2 to 260 min outcrop, and 298 m in Byilkaoora 3.

Age

Early Cambrian, 524–522 Ma, based on stratigraphicposition.

Sedimentology and palaeoenvironment

The unit was deposited in a proximal alluvial fanpalaeoenvironment (Gravestock and Sansome, 1994;Benbow, 1982).

Parakeelya Alkali Member

Definition and nomenclature

The unit was defined as a member of the Observatory HillFormation by Brewer et al. (1987).

Type section

The type section is 240–334.5 m in Byilkaoora 1(Fig. 6.21).

Lithology and distribution

The unit comprises a sequence of laminated to thinlybedded, dominantly light brownish grey and greenish grey todark grey limestone, dolomite, siltstone and claystone.Unique characteristics include the presence of abundantdesiccation features, chert lenses, nodules and fragments, andcalcite and dolomite crusts and pseudomorphs afterevaporitic minerals (trona). The member is widelydistributed in the Manya and Munyarai Troughs, and on theMurnaroo Platform.

Relationships and boundary criteria

The upper and lower boundaries are conformable withinthe Observatory Hill Formation.

Thickness

The thickness ranges from 62 m in Observatory Hill 1 to138 m in Byilkaoora 1.

Age

Early Cambrian, 522–521 Ma, based on stratigraphicposition.

Sedimentology and palaeoenvironment

The member was deposited in an alkaline playa lakeenvironment. Detailed studies of the palaeoenvironmentsrepresented by this unit were published by Stainton et al.(1988), and Southgate et al. (1989).

Moyles Chert Marker Bed

Definition and nomenclature

The member was defined by Brewer et al. (1987) as theMoyles Chert Marker Bed.

Type section

The reference section of Brewer et al. (1987) is hereassumed to be the type section (200–213.1 m in Byilkaoora 1;Fig. 6.21).

Lithology and distribution

The member consists of greenish grey to dark greylimestone, dolomite and siltstone containing abundant chertnodules and lenses. The Moyles Chert Marker Bed is adistinctive seismic reflector and is widespread over much ofthe eastern part of the basin.

Relationships and boundary criteria

The upper and lower boundaries are conformable withinthe Observatory Hill Formation.

Thickness

The thickness is 13 m in Byilkaoora 1, but ranges up to36 m in Byilkaoora 2.

Laminated chert and carbonate of the Observatory Hill Formation(Parakeelya Alkali Member) in Byilkaoora 1; salina and mudflatfacies. (Photo 44379)

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Age

Early Cambrian, 521 Ma, based on stratigraphic position.

Sedimentology and palaeoenvironment

The marker bed was deposited in an alkaline playa lakeenvironment.

Oolarinna Member

Definition and nomenclature

The unit was defined as a member of the Observatory HillFormation by Benbow (1982).

Type section

The type section is defined as outcrop on the northernmargin of the Mount Johns Range. A subsurface referencesection is defined as 156–200 m in Byilkaoora 1 (Fig. 6.21).

Lithology and distribution

The unit consists of red-brown, thinly bedded micaceoussiltstone and claystone, with interbedded pebble conglom-erate and sandstone. The unit is presumed to be present overmost of the basin, except where removed by erosion.

Relationships and boundary criteria

The lower boundary is conformable within theObservatory Hill Formation; the upper boundary with theArcoeillinna Sandstone may be partly unconformable to thenorth but is also conformable to the south.

Thickness

The thickness ranges up to 44 m in Byilkaoora 1.

Age

Early Cambrian, 521–520 Ma, based on stratigraphicposition.

Sedimentology and palaeoenvironment

The Oolarinna Member indicates more oxidisingconditions relative to the Parakeelya Alkali Member, and wasprobably deposited in a fluvial environment.

Arcoeillinna Sandstone

Definition and nomenclature

The sandstone was defined by Benbow (1982).

Type section

The type section is defined in outcrop on the eastern flankof the Mount Johns Range. Subsurface reference sections aredefined as 1037–1191 m in Karlaya 1 (Fig. 6.22), and98.5–156 m in Byilkaoora 1.

Lithology and distribution

The lithology is predominantly red-brown, very fine tomedium-grained feldspathic sandstone. Minor interbedsconsist of claystone and siltstone similar to the OolarinnaMember of the Observatory Hill Formation. Some pebblyhorizons occur, composed of rounded, elongate green,red-brown and white claystone (Benbow, 1982). Theformation is widely distributed in the Officer Basin.

Relationships and boundary criteria

The Arcoeillinna conformably overlies the ObservatoryHill Formation (usually the Oolarinna Member), and isconformably overlain by Apamurra Formation orunconformably overlain by Mount Johns Conglomerate. Itmay be equivalent to part of the ‘Wirrildar beds’ in the centralOfficer Basin (Major, 1973a). The interpreted equivalentunit in the Arrowie Basin is the upper part of the Billy CreekFormation (Gravestock and Hibburt, 1991).

Thickness

The thickness ranges from 46 m in Byilkaoora 2 to 172 min Munta 1.

Age

Early Cambrian, 520–518 Ma, based on stratigraphicposition.

Calcite pseudomorphs after trona in the Observatory Hill Forma-tion (Parakeelya Alkali Member) at 320 m in Byilkaoora 1. (Photo42435)

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Sedimentology and palaeoenvironment

Many of the grains have a thin film of red iron oxidewhich was present before compaction of the sediment, andsedimentary structures include abundant cross-bedding.Soft-sediment slump features and scour and fill structures arepresent in the coarser sediments. Benbow (1982) interpreteda fluvial-lacustrine palaeoenvironment, with an aeolianinfluence. Current directions and increasing thicknesssuggest a west or southwest provenance.

Apamurra Formation

Definition and nomenclature

The unit was originally defined as the Apamurra Memberof the Mount Johns Conglomerate by Benbow (1982). It is

here raised to formation status (and the Mount JohnsConglomerate reduced to member status) to moreappropriately reflect the more widespread and finer grainedfacies.

Type section

The type section was defined from outcrop on thesouthwestern margin of the Mount Johns Range (Benbow,1982). Subsurface reference sections are defined as959–1037 m in Karlaya 1 (Fig. 6.22), and 49.6–98.5 m inByilkaoora 1.

Fig. 6.22 Karlaya 1 — upper Marla Group reference section(Arcoeillinna Sandstone, Apamurra Formation and Trainor HillSandstone).

Arcoeillinna Sandstone at 137.7 m in Byilkaoora 1. (Photo 44380)

Cross-bedding in Arcoeillinna Sandstone, Mount Johns Range.(Photo 30891)

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Lithology and distribution

The formation consists of two units, a basal conglomerateand sandstone (the Mount Johns Conglomerate Member),and a generally thicker upper unit consisting of calcareousand dolomitic, red-brown, fine to very fine-grained sandstoneand siltstone. The finer sediments are bimodal, with fine tocoarse-grained angular and subangular sand grains scatteredthroughout. Minor lithologies include thin, light greenlimestone, and light green siltstone and sandstone (Benbow,1982). The unit is widespread over the Officer Basin and isseismically mappable (Stainton et al., 1988).

Relationships and boundary criteria

The upper and lower contacts are conformable, althoughthe base of the Mount Johns Conglomerate Member isprobably at least locally disconformable. The unit may beequivalent to part of the ‘Wirrildar beds’ (Major, 1973a) inthe central Officer Basin. Interpreted equivalent units in theArrowie Basin are the Aroona Creek and WirrealpaLimestones (Gravestock and Hibburt, 1991).

Thickness

The thickness ranges from 27 m in Munyarai 1 to 78 min Karlaya 1.

Age

Early Cambrian, 518–516 Ma, based on stratigraphicposition.

Sedimentology and palaeoenvironment

The silt matrix is heavily stained with iron oxide, butminor tangential and herringbone cross-bedding is present incoarser, well-sorted sandy interbeds (Benbow, 1982). Tracefossils (Rusophycus) which are generally attributed totrilobites are common. These indicate a shallow marine totidal flat palaeoenvironment for the finer grained unit. Thelower conglomeratic unit is interpreted to have beendeposited in a proximal alluvial fan environment, with fluvialand floodplain environments also possibly being represented(Benbow, 1982).

Mount Johns Conglomerate Member

Definition and nomenclature

The unit was introduced by Krieg (1973) and defined witha type area by Benbow (1982). It is here redefined as amember of the Apamurra Formation.

Type section

The type section is outcrop on the northern margin of theMount Johns Range. A subsurface reference section is heredefined as 504–505.6 m in Byilkaoora 2.

Lithology and distribution

The member is characterised by poorly sorted, red-brownconglomerate and red-brown sandstone. The conglomeratecontains well-rounded clasts up to 0.2 m in size, comprisingdiverse lithologies including arkose, quartzite, pegmatite,

siltstone and vein quartz. The sandstone is only slightlyfeldspathic, and individual grains may be coated with ironoxide or clay. The unit is restricted to the northern part of thebasin, and is absent to the south.

Relationships and boundary criteria

The lower boundary with the Arcoeillinna Sandstone maybe locally disconformable (Benbow, 1982), but the upper

Southerly view of the east side of the Mount Johns Range. Thelow-lying area to the left is Observatory Hill Formation with a lowridge of Arcoeillinna Sandstone; the area immediately flanking therange is Apamurra Formation (Mount Johns Member) and theprominent ridge is Trainor Hill Sandstone. (Photo 30894)

Apamurra Formation (Mount Johns Conglomerate Member) at97.8 m in Byilkaoora 1; the black mineral in the vugs is probablyhaematite. (Photo 44381)

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contact with the finer grained facies of the ApamurraFormation is gradational and conformable. Gravestock et al.(1995) suggested that the Moorilyanna Formation (Coats,1963) and Levenger Formation (Major, 1973d), which occurin isolated grabens in the Musgrave Block, may becorrelatives of the Mount Johns Conglomerate. However, asnoted earlier in this chapter, these graben filling units may beas old as Mesoproterozoic.

Thickness

The thickness ranges from 1.6 m in Byilkaoora 2 to 78 min outcrop.

Age

Early Cambrian, 518–516 Ma, based on stratigraphicposition.

Sedimentology and palaeoenvironment

Sedimentary structures in the sandstone include tabularcross-bedding which suggests a northwesterly provenance.Rapid thickening of the member to the north also suggests anorthern provenance. A proximal alluvial fan palaeoenviron-ment (with fluvial and floodplain environments also probablyrepresented) was interpreted by Benbow (1982).

Trainor Hill Sandstone

Definition and nomenclature

The unit was introduced by Krieg (1973), with the baseimmediately above the Observatory Hill Formation and thetop within the Mount Chandler Sandstone. The formationwas defined by Benbow (1982).

Type section

The type section was defined from outcrop on thesouthwestern margin of the Mount Johns Range. Subsurfacereference sections are defined as 512–959 m in Karlaya 1(Fig. 6.22), and 245–460 m in Byilkaoora 2.

Lithology and distribution

The lithology consists of a well-sorted, medium tofine-grained, white to light grey, kaolinitic and feldspathicsandstone, with minor interbeds of red-brown micaceoussiltstone and claystone, and pebbly horizons. The sandstonebecomes light red-brown, feldspathic, calcareous anddolomitic towards the top (Benbow, 1982). The unit iswidely distributed in the Officer Basin.

Relationships and boundary criteria

The base of the Formation is sharp but there is littleevidence for an unconformity. The upper boundary iserosional and unconformable, with up to 500–600 m oferosion (Gravestock and Sansome, 1994). The unit may beequivalent to part of the ‘Wirrildar beds’ (Major, 1973a) inthe Birksgate Sub-basin. The interpreted equivalent in theArrowie Basin is the Moodlatana Formation.

Thickness

The thickness ranges from 87 m in Munyarai 1 to 420 min outcrop, and 520 m in Lairu 1. As the top is eroded, it mayhave originally been up to 1000 m thick in the Mount Johnsarea (Gravestock and Sansome, 1994).

Age

Middle Cambrian, 516–510 Ma, based on stratigraphicposition.

Sedimentology and palaeoenvironment

Cross-bedding is common throughout the unit , and istrough-like near the base, but steeply tangential to tabularhigher in the section. Some cross-beds have been overturned.The finer grained units display herringbone cross-beds andripple marks. Trace fossils (Skolithos ichnofacies), clay gallsand desiccation cracks are also present. Facies in the TrainorHill Sandstone have been interpreted to include tidal channelsand flats, upper shoreface (beach and bar) sands, and deltaicsands, which were deposited in a transgressive barrier barsystem (Rudd, 1995). Current directions generally indicatea southwesterly source, but a northwesterly source isindicated in the north where facies are more typical of fluvialpalaeoenvironments (Benbow, 1982).

LATE CAMBRIAN VOLCANICS

Kulyong Formation

Definition and nomenclature

The unit was defined by Major and Teluk (1967) as theKulyong Volcanics. Jackson and van de Graaff (1981)suggested that the Kulyong Volcanics and Table Hill

Trainor Hill Sandstone at 114.7 m in Marla 10; note the blackcryptomelane (KMn8O16) staining. (Photo 44382)

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Volcanics (Compston, 1974) comprise a single tholeiiticbasalt suite and the latter is therefore a synonym. The unit isherein changed to ‘Kulyong Formation’ to include the relatedunderlying sedimentary units.

Type section

Outcrop at latitude 27°36’20”S, longitude 129°26’E(Fig. 6.23). No subsurface reference section is designated asthe unit has not been encountered in any well, but it isexpected to occur at depth in the central and western OfficerBasin.

Lithology and distribution

The lower 2 m of the volcanic unit is soft, grey andvesicular whereas the upper 1 m is hard, red-brown, fine-grained rock with no recognisable layering. Petrographicallyit is a sub-ophitic mesh of plagioclase and augite, the browncolour being due to films of haematite. The rock is of basicigneous composition and is classified as a tholeiite. In placesthere occurs crystalline quartz, agate, pyrolusite and minoramounts of a dark green mineral, probably chlorophaeite,which resembles chrysocolla in hand specimen (Major andTeluk, 1967).

The underlying sedimentary units comprise thinlybedded, silicified ferruginous sandstone, silicifiedgreywacke (possibly tuffaceous) and fine-grained micaceoussandstone with a thin (50 mm) limestone interbed.

The unit occurs in outcrop and at depth over >20 000 km2

in the western Officer Basin (Townson, 1985).

Relationships and boundary criteria

The unit in outcrop has no top, but from the relative heightdifference to the nearest outcrop of Mount ChandlerSandstone, and assuming a regional dip of 0.5°, it is probablethat the Mount Chandler Sandstone conformably overlies the

Kulyong Formation. The formation unconformably overliesthe gently folded Trainor Hill Sandstone or earlier units.

Thickness

The volcanics are up to 3 m thick in outcrop, and theunderlying sedimentary units are up to 8 m thick. Themaximum drilled thickness of Table Hill Volcanics in thewestern Officer Basin is 118 m (Townson, 1985).

Age

Middle-Late Cambrian, 507–505 Ma.

K–Ar geochronology suggests an Early Ordovicianminimum age of 485±20 to 475±20 Ma for the KulyongVolcanics (Major and Teluk, 1967), and a poorly constrainedRb–Sr age of ~570 Ma for the Table Hill Volcanics(Compston, 1974; Jackson and van de Graaff, 1981). Bothof these determinations are questionable, and an age of nogreater than late Middle Cambrian age is more likely basedon stratigraphic position and the relative lack of foldingcompared to the underlying Trainor Hill Sandstone(Gravestock et al., 1995).

Sedimentology and palaeoenvironment

The vesicular nature of the volcanic unit suggests asubaerial flow, but no upper contact is seen. Possible flutecasts are present in the ferruginised sandstone underlying thebasalt. The thickness of the sandstone varies from 0.15 to0.6 m. The greywacke is only weakly stratified but the basalsandstone is thin bedded. The limestone interbed has minorcross-bedding. The presumed palaeoenvironment isnon-marine, to shallow marine at the base.

MUNDA GROUP

The ‘Munda Sequence’ was defined by Krieg (1973) forthe predominantly Ordovician sequence of formations, andis redefined here as the Munda Group. The group is boundedby two unconformities formed during the DelamerianOrogeny and Rodingan Event. The sequence of formationsgenerally records a major transgression, from LST in theMount Chandler Sandstone, to TST in the Indulkana Shale,which was formed during maximum transgression. Theuppermost unit, the Blue Hills Sandstone, was formed in aHST. The maximum thickness of the Munda Group wasprobably more than 3000 m in the Marla area, increasingtowards the Amadeus Basin (Moussavi-Harami andGravestock, 1995). This would indicate that 1500–2000 mof erosion may have occurred.

Mount Chandler Sandstone

Definition and nomenclature

The name ‘Mount Chandler Sandstone’ was introducedby Coats (1963). The formation was redefined by Benbow(1982) who separated the Byilkaoora Formation, which ishere redefined as a basal member of the Mount ChandlerSandstone. This sandstone should not be confused with theChandler Formation of the Amadeus Basin, which is acarbonate–evaporite unit.

Fig. 6.23 Kulyong Formation section (after Major and Teluk,1967).

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Type section

The type section has not been defined previously, and ishere defined as 40–512 m in Karlaya 1. Reference sectionsare defined as 33–245 m in Byilkaoora 2, and 1189–1355 min Munyarai 1 (Fig. 6.24).

Lithology and distribution

The lower part of the formation comprises quartzosesandstone to friable, well-sorted, well-rounded, fine-grainedwhite sandstone. In the upper part, the sandstone is slightlyfeldspathic, and is orange-brown to slightly reddish. Minorlayers of rounded to subangular polished white quartzpebbles occur. The unit is widely distributed over the OfficerBasin.

Relationships and boundary criteria

The basal contact is unconformable, and the upper iseither conformable with the Indulkana Shale orunconformable with Permian sediments of the ArckaringaBasin in the Manya Trough. The unit is probably equivalentto the Pacoota Sandstone of the Amadeus Basin.

Thickness

The thickness varies from 160 m in Manya 5 to 472 m inKarlaya 1, but may be up to 609 m in outcrop in the CartuHill area (Benbow, 1982).

Age

Late Ordovician, 457–450 Ma, based on stratigraphicposition.

Sedimentology and palaeoenvironment

Thick-bedded tabular cross-bedding is commonthroughout the unit, and a tide-dominated fluvial deltaicpalaeoenvironment is interpreted for the formation. Tracefossils are present in the unit and include Diplocraterion andSkolithos. These are characteristic of the Skolithosichnofacies (Seilacher, 1967) which generally indicates asandy, high-energy shore environment.

Byilkaoora Member

Definition and nomenclature

Originally the basal part of the Mount ChandlerSandstone, the unit was defined as the Byilkaoora Formationby Benbow (1982). The unit is here redefined as a memberof the Mount Chandler Sandstone as it is too thin to recognisein the subsurface.

Type section

The type section is defined as outcrop north of MountJohns, and an outcrop reference section is defined on theeastern margin of Mount Byilkaoora. No subsurface sectionscan be defined, although it is likely to occur in Byilkaoora 2and 3, which are near the type area.

Fig. 6.24 Munyarai 1 — Munda Group reference section (MountChandler Sandstone, Indulkana Shale and Blue Hills Sandstone).

Skolithos, top of the Mount Chandler Sandstone, northwesternMount Johns Range. (Photo 30902)

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Lithology and distribution

The unit is characterised in the type section byconglomerate with well-rounded clasts of grey feldspathicsandstone (?Trainor Hill Sandstone), with light blue,fine-grained quartzose sandstone, quartz, veined quartzite,and shale. A sandy facies is also present, comprising whitekaolinitic, very fine-grained sandstone with minor siltstoneand claystone.

Relationships and boundary criteria

The basal contact is sharp and unconformable; the upperis gradational and difficult to clearly identify.

Thickness

The unit is 15–20 m thick in outcrop in the type area.

Age

Late Ordovician, 457–455 Ma, based on stratigraphicposition.

Sedimentology and palaeoenvironment

Tangential cross-bedding is present in the sandstoneinterbeds. A predominantly fluvial palaeoenvironment wasinterpreted by Benbow (1982). The conglomerate interbedsthin to the south, suggesting a north to northwesterlyprovenance.

Indulkana Shale

Definition and nomenclature

The name was introduced informally by Packham andWebby (1969), and used by Krieg (1973).

Type section

The type locality was nominated as outcrop on thenorthern side of the Indulkana Range. Subsurface referencesections are defined as 282–293 m in Lairu 1 and 1180–1189 m in Munyarai 1 (Fig. 6.24), although the lattercorrelation is not certain (Womer et al., 1987).

Lithology and distribution

The lithology consists of maroon and green shale withthin, flaggy sandstone beds bearing clay pellets near the baseand top. Limestone lenses and micaceous silty sandstoneoccur locally. The formation is generally irregularlydistributed over the basin due to removal by erosion, but ispresent in the Munyarai Trough.

Relationships and boundary criteria

Both the upper and lower contacts are conformable. Theunit is probably equivalent to the Horn Valley Siltstone of theAmadeus Basin.

Thickness

The thickness varies from 9 m in Munyarai 1 to 11 m inLairu 1, but may be up to 60 m in outcrop in the IndulkanaRange (Krieg, 1973).

Age

Late Ordovician, 450–445 Ma, based on stratigraphicposition and radiometric data.

Rb–Sr whole-rock ages of 460±15 Ma (Webb, 1978) and438±10 Ma (Womer et al., 1987) suggest a minimum Middleto Late Ordovician age.

Indulkana Shale, Blue Hills. (Photo T11207)Mount Chandler Sandstone east of Mount Byilkaoora. (Photo 30900)

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Sedimentology and palaeoenvironment

Sedimentary structures recorded by Packham and Webby(1969) in the sandstone facies include ripple marks anddesiccation cracks. Trace fossils in the sandstone includeDiplocraterion and Skolithos. A very shallow marine,probably tidal bay to shoreface palaeoenvironment isindicated.

Blue Hills Sandstone

Definition and nomenclature

The unit was introduced informally by Packham andWebby (1969) as ‘Policeman Well Sandstone’, and the nameBlue Hills Sandstone was introduced by Krieg (1973). Theoverlying ‘Cartu beds’ and ‘Mintabie beds’ (Packham andWebby, 1969; Krieg, 1973; Townsend, 1990) are here takenas synonyms.

Type section

The type locality was nominated in outcrop as southwestof Mount Johns, near Policeman Well. Subsurface referencesections are defined as 95–282 m in Lairu 1 and 1018–1180 m in Munyarai 1 (Fig. 6.24).

Lithology and distribution

The lower parts of the formation most likely to beencountered in Officer Basin wells consists of fine tomedium-grained quartzose sandstone, with some thinconglomerate beds. Overlying this are soft, kaoliniticsandstone and well-sorted porous sandstone. In the Mintabiearea, and possibly higher in the section, the sandstone isfeldspathic and micaceous. The formation is very irregularlydistributed in the Officer Basin, being present in theMunyarai Trough where not removed by later erosion, but ismore likely to be present to the northeast.

Relationships and boundary criteria

The lower contact with the Indulkana Shale isconformable, and the upper contact is unconformable withthe overlying Mimili Formation. The equivalent unit in theAmadeus Basin is the Stairway Sandstone, but the upper partsof the unit may be equivalent to the Stokes Formation andCarmichael Sandstone.

Thickness

The thickness varies from 162 m in Munyarai 1 to 187 min Lairu 1, but may be over 1900 m in outcrop to the east(Krieg, 1973).

Age

Late Ordovician to Early Silurian, 445–435 Ma, based onstratigraphic position.

Sedimentology and palaeoenvironment

Sedimentary structures are dominated by thick sets ofcross-bedding, but other features include Skolithos andprobable Cruziana trace fossils, desiccation cracks, andripples which indicate tidal to fluvial-deltaic palaeo-environments.

DEVONIAN SEQUENCE

Mimili Formation

Derivation of name

The formation is named after the Mimili Aboriginalsettlement.

Definition and nomenclature

This name is introduced here for the youngest sandstoneunit in the Officer Basin.

Type section

Surface to 1018 m in Munyarai 1 (Fig. 6.25).

Lithology and distribution

Tucker (1994) recognised three units in the type section.The lowermost consists of fine to medium-grainedmicaceous and occasionally calcareous clean arkosicsandstone. The middle unit is fossil-bearing and composedof interbedded greenish grey micaceous, calcareousmudstone with minor siltstone and fine to medium-grainedsandstone. The uppermost unit is generally ferruginised,muddy brown arkosic sandstone. Seismic data suggest thatthe Mimili Formation is restricted to the Munyarai Trougharea (Figs 6.26, 6.27).

Relationships and boundary criteria

The upper contact is not known, but is presumed to beunconformably overlain by Permian, Cretaceous or youngersediments. The basal contact with the Blue Hills Sandstoneis disconformable, but has not been cored. The formationmay correlate with the Pertnjara Group and possibly theMereenie Sandstone of the Amadeus Basin.

Thickness

The Mimili Formation is over 1018 m thick inMunyarai 1, with the top eroded; from seismic data it may beup to 2000 m thick.

Age

Late Devonian, Frasnian (375–360 Ma). A vertebrate fishfauna indicates an Early to Middle Devonian (Eifelian) age,and palynology indicates a Late Devonian (Frasnian) age —

Mount Chandler Sandstone (foreground), Indulkana Shale and BlueHills Sandstone, northwestern margin of the Mount Johns Range.(Photo 30904)

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the latter is considered more reliable. The upper and lowerparts of the sequence are barren, and thus the age spanned bythe Mimili Formation is wider than indicated by fossils.

Sedimentology and palaeoenvironment

Planar and ripple laminations are present in the basal partof the sequence, but the vertebrate faunas are found elsewhere

in Australia in both marine and freshwater palaeoenviron-ments (Long et al., 1988). From a regional perspective, anon-marine palaeoenvironment is favoured (Tucker, 1994).

ARCKARINGA BASIN

Permo-Carboniferous Arckaringa Basin sediments arefound overlying the eastern Officer Basin, and comprise theBoorthanna, Stuart Range, and Mount Toondina Formations.The geology of the Arckaringa Basin was summarised byAlexander and Sansome (1996). The ‘Waitoona beds’(Krieg, 1973) in Officer 1 were previously thought to beDevonian in age. However, based on the common presenceof organic-walled worm tubes, they are now known to beequivalent to or younger than the Stuart Range Formation,and are considered synonymous with the Arckaringa Basinsuccession.

Shearer (1994) recently mapped the Permian sedimentsfrom seismic uphole and stratigraphic drillhole data.Townsend (1976) and Moussavi-Harami (1994) providedlithofacies details.

The total Permian thickness is generally 100–400 m, andis greater in the troughs than over ridges. The Permian is verythin to absent in the Marla Overthrust Zone. Palaeoenviron-

Fig. 6.25 Munyarai 1 — Mimili Formation type section.

Mimili Formation at 923.5 m in Munyarai 1. (Photo 44383)

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Fig. 6.26 Seismic line IP1-2, through Munyarai 1 (see Fig. 6.27 for location).

Fig. 6.27 Mimili Formation subcrop map.

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ments range from fluvioglacial outwash in the lower parts ofthe succession to shallow marine in the upper parts.

EROMANGA BASIN

A thin veneer of Eromanga Basin sediments also occursover the eastern Officer Basin, and the units found are theAlgebuckina Sandstone, Cadna-owie Formation and BulldogShale. These are described in more detail by Alexander andSansome (1996).

TERTIARY

The Officer Basin region is crossed by southerly directedpalaeochannels which drained into the Tertiary Eucla Basin.Visible on NOAA-AVHRR imagery, the channels haveincised locally to depths exceeding 100 m and are filled withEocene to early Pliocene sediments (Benbow, 1995; Benbowet al., 1995; Statham-Lee, 1995).

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INTRODUCTION

In a basin with an area of 100 000 km2 and a stratigraphicsuccession up to 6 km thick, the problem of having too littlebiostratigraphic data means that there will inevitably be arange of plausible depositional models. With hindsight,some of these prove to be widely off target, as was the casein the eastern Officer Basin when Munyarai 1 was drilled byContinental Oil Company of Australia (Conoco, 1969). Priorto the drilling of Ungoolya 1 in 1986, and despite radiometricage evidence to the contrary (see below), the MunyaraiTrough was thought to contain Devonian strata to at least2399 m, the total depth of Munyarai 1. However, thisinterpretation did not sit comfortably with outcrops on theeastern and southern margins of the Munyarai Trough whichwere interpreted to be mainly Neoproterozoic to Ordovician(Krieg, 1973; Krieg et al., 1976). In fact, certain isolatedoutcrops mapped as Mintabie beds were thought to beDevonian because of the evidence from Munyarai 1 (Krieg,1969, 1973).

A seismic tie from Ungoolya 1 to Munyarai 1 finallysettled the order of succession in the Munyarai Trough —Devonian on Cambro-Ordovician on Neoproterozoic — eventhough conflicting interpretations were still emerging fromcareful palynological processing of core samples (Womer etal., 1987).

Since 1980, there have been several macrofossildiscoveries in the Palaeozoic and major advances in acritarchbiostratigraphy in the Neoproterozoic, leading to a moredetailed understanding of the Officer Basin’s depositionalsequences. This chapter is concerned chiefly with thebiostratigraphic scheme as currently understood, but alsoreviews radiometric, lithologic and other data that assistcorrelation in the eastern Officer Basin.

NEOPROTEROZOIC STRATIGRAPHYAND AGE

The Neoproterozoic has been defined globally asbeginning at 1000 Ma. In the sense used here, earlyNeoproterozoic refers to the first three stages of the localAdelaidean succession, namely the Willouran, Torrensianand Sturtian stages. The age of the base of the Willouranstage is ~850 Ma, which corresponds to the late Riphean inRussian terminology.

Lack of macrofossils has caused emphasis to be placedon lithostratigraphic comparisons with better known regionssuch as the Adelaide Fold Belt (Krieg, 1973; Preiss, 1993),the Officer Basin in Western Australia (Townson, 1985) and

the Amadeus Basin (Stainton et al., 1988). Now, however,biostratigraphic correlation is possible using acritarchs.

Recently, Zang and Walter (1992) demonstrated theutility of acritarch studies in parts of the Neoproterozoic andCambrian of the Amadeus Basin. The biostratigraphy ofacritarch assemblages, though still at a preliminary stage, hasalso greatly improved correlation within the Officer Basin.The preservation of microflora in deeply weatheredexposures of the Adelaide Fold Belt is too poor to permitinterpretation but samples from cored drillholes on the StuartShelf have been tied to a biostratigraphic scheme proposedby Zang (1994).

Recent work by Zang (much of it unpublished), based on207 samples from Officer Basin wells, has added greatly tounderstanding the composition of acritarch assemblages inthe eastern Officer Basin. In his scheme, Zang (1994; Zangand Preiss, in prep.) distinguished eight informalNeoproterozoic acritarch assemblages based on the firstappearance of key species. The number has now beenreduced to six, as listed in Table 7.1 which also allows for apossible new assemblage (AAC 1) from Cambrian strata.Two Ordovician assemblages (AAO 1, AAO 2) known in theWarburton Basin (Zang, 1994) have been added, based on thelikelihood that acritarchs will be recovered from rocks of thisage in the Officer Basin.

Key elements of the Neoproterozoic microfloralassemblages can also be recognised on the Stuart Shelf.From there, lithostratigraphic correlation provides the onlytie to the Neoproterozoic of the Adelaide Fold Belt. TheOfficer Basin correlations reviewed below are based on avariety of attributes. These include acritarchs andstromatolites in the Neoproterozoic, Cambrian invertebrates,Devonian vertebrates and palynomorphs, and magneto-,chemo- and event stratigraphy, all of which have been appliedby different workers to obtain a clearer history of the OfficerBasin.

Stromatolites

Stromatolites occur in the Coominaree Dolomite of thePeake and Denison Ranges, and two species — Acaciella cf.australica and Gymnosolen cf. ramsayi — were described byPreiss (1973); these were later amended to Acaciella f. indetand Gymnosolen f. indet (Preiss, 1987). Acaciella alsooccurs in the Coominaree Dolomite in Manya 5 (Preiss,1993). This form is very similar to A. australica whichoccurs in the Skates Hill Formation of the Savory Basin(=Savory Sub-basin of the WA Officer Basin (Perincek,1996)), and in the Bitter Springs Formation of the Amadeus

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Basin. A. australica appears to be restricted to the CallannaGroup at the base of the Adelaidean succession, although itsfull stratigraphic range is not known (Grey, 1995).

Early Neoproterozoic acritarchs

Acritarchs from the Alinya Formation in Giles 1 areinterpreted by Zang (1995a; Zang and Preiss, in prep.) to beTorrensian in age. His species (Zang, 1995a, fig. 22)correlate with those from the Bitter Springs Formation (Zangand Walter, 1992), thus Zang places both units and theircorrelatives in the Torrensian. Zang (1995a; Zang and Preiss,in prep.) reserved a Willouran age for the CadlareenaVolcanics–Coominaree Dolomite– YounghusbandConglomerate suite, and has extracted acritarchs fromManya 5 core which he interpreted to be YounghusbandConglomerate. Zang considered this suite to berepresentative of a graben system beneath the widespreadAlinya Formation–Pindyin Sandstone stratal package. TheCadlareena–Younghusband suite crops out in the Peake andDenison Ranges and was fully cored in Manya 5. Thesestrata were not deposited in a graben, and they are consideredmore or less coeval with the Alinya–Pindyin suite (Fig. 5.6),though they may be slightly older (Arkaroola Subgroupversus Curdimurka Subgroup).

This work follows the more widely held view that theAlinya–Pindyin of the eastern Officer Basin, the Browne–Lefroy–Townsend [≡Skates hill–Munjdajini– Spearhole] ofthe Savory Basin and western Officer Basin, and the BitterSprings–Heavitree of the Amadeus Basin, are all Willouranin age. The Manya 5 acritarch assemblage is designatedAAW 1b in Table 7.1. It may be older than, or the same ageas, the Giles 1 acritarch assemblage, designated AAW 1a inTable 7.1. The two assemblages contain a number of speciesin common, but six species occur only in Manya 5 (Zang andPreiss, in prep.). Zang’s (1995a) correlation raises thequestion as to what does constitute the fill of the channel or‘graben’-like features evident on seismic beneath theAlinya–Pindyin stratal package. As discussed in Chapter 5,this underlying sedimentary pile is thought to be older thanthe Adelaidean.

In the eastern Officer Basin there is a major hiatusbetween the Alinya Formation and the late Neoproterozoic(Marinoan) Tarlina Sandstone. A Sturtian tillite doesintervene but this is restricted to the northeast near ChambersBluff and to Nicholson 2. There remains uncertainty as tothe existence of a disconformity in the Chambers BluffTillite, with upper beds being possibly Marinoan in age(Preiss, 1993). No diagnostic acritarchs have been recoveredfrom this part of the succession, although Zang (1994)reported Favosphaeridium and Comaspheridium in aninter-tillitic shale. However, both genera are long ranging,which emphasises the need to identify assemblages to specieslevel for more reliable correlation.

Late Neoproterozoic acritarchs

Arcritarchs from late Neoproterozoic strata were firstdocumented in Munyarai 1 (Narana–Dey Dey) by van Neil(1984). He recognised a large (~350 µm) form possiblyreferable to Micrhystridium, but this genus ranges throughthe Neoproterozoic and Phanerozoic and is of no value forcorrelation. Van Neil also recognised algal filaments andsphaeromorphs in the Tanana Formation and Dey DeyMudstone in Murnaroo 1; again, these are long-rangingforms.

Possible Trachysphaeridium laufeldi was noted by Eames(in Womer et al., 1987) from 1251.3 m in Birksgate 1,suggesting a likeness to forms known to be of Neoproterozoicage. With regard to Munyarai 1 however, Womer (in Womeret al., 1987) stated ‘The persistent reports of MiddleDevonian Ancryospora below 1550 metres tends to supportthe interpretation that this interval is an Indulkana Shaleequivalent, although...this conclusion is very tenuous’.

It was not until 1992 that Jenkins et al. (1992) and Zang(unpublished report to Comalco) began to carefully extractand systematically document the fragile late Neoproterozoicacritarchs from Officer Basin wells. Jenkins et al. recoveredtwo acritarch assemblages, an older assemblage mainly fromthe lower Karlaya Limestone in Murnaroo 1 (AAM 3, Table7.1), and a younger one from the Narana Formation inUngoolya 1 (AAM 4, Table 7.1). Seismic data (e.g. Sukanta

Table 7.1 Officer Basin acritarch assemblages (after Zang, 1994, 1995a,b).

Zang (1994, 1995a,b assemblages) ‘Giles’ ‘Manya’ 1,2,3 4 5 6

New assemblage names AAW1a AAW1b AAM1 AAM2 AAM3 AAM4 AAC1 AAC2 AAO1 AAO2

Genus/species

Amadeusphaeridium cyathospora kAmbiguaspora parvula kComasphaeridium magnum kComaspaeridium strigosum kCymatiosphaeridium kullingii kGoniosphaeridium cebrum kUnispinosphaeridium n.sp. kHocosphaeridium scaberfacium kLeiofusa squama kPetaloferidium sp. kSkiagia spp. kTongzia meitana kTrachystrictosphaera aimika kTrachystrictosphaera vidalii kUnispinosphaeridium willouranum gen et sp nov. k

k=Key first appearance species

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et al., 1991) indicate that the beds yielding these assemblagesare separated by a canyon-cutting unconformity. Jenkins etal. (1992) noted that the older assemblage consisted ofdiverse spinose acritarchs and few filamentous forms. Theyounger assemblage was dominated by filamentous typeswith 8–10 species of very large, unsculptured spheroidalforms. Jenkins et al. (1992, p.405) noted that the differencesbetween the two microfloral assemblages ‘may be due tochronological or biofacies differences, or both’.

Zang (1994, p.204) noted that both abundance anddiversity of species increased during marine transgressionswhich he interpreted as ‘a transfer of phytoplankton fromrelatively calm offshore environments to turbulent shelfenvironments with rising sea level’ necessitating adaptation.The schematic curve on Figure 7.1 (right hand column)illustrates the change in species diversity which reached amaximum of more than 80 species in the upper Dey DeyMudstone, representing the Hocosphaeridium scaberfacium–Goniosphaeridium crebrum Assemblage (Zang 1994).Many of the species in this assemblage (AAM 3, Table 7.1)had not previously been found in strata older than Palaeozoicalthough several, including the nominate species, have beenrecorded from the Pertatataka Formation in the AmadeusBasin by Zang and Walter (1992). Another significantdiscovery by Zang (1994) is the oldest occurrence of thetrilete spore Ambiguaspora parvula in chert from thePunkerri Sandstone in the Birksgate Sub-basin (AAM 4,Table 7.1), the first record of a higher plant anywhere in theworld.

Late Neoproterozoic invertebrates

Specimens of the soft-bodied Ediacara fauna have beenrecorded from loose blocks in the Punkerri Sandstone. Daily(in Major, 1974) recorded Charnia, ?Charniodiscus,Tribrachidium, Rangea and a ‘double spiral’, presumably a

trace fossil. The fauna permits correlation from the EdiacaraMember of the Adelaide Fold Belt to at least part of thePunkerri Sandstone. Impressions resembling the attachmentstalk of Charniodiscus have been found near Albany morethan 1500 km distant (Cruse et al., 1993), attesting to the widedistribution of this fauna. Jenkins (1992) suggested thatacritarchs may have constituted the food supply for some ofthe Ediacara metazoans, and Zang (1993) regarded the oldest‘semi-aquatic’ plant (parent of the trilete spores in thePunkerri Sandstone) as another food source.

Geochronology

As mentioned above, Compston (in Conoco, 1969)obtained an isochron of 650 Ma from the MunyaraiFormation in Munyarai 1. However, Webb (in Preiss, 1993)calculated a considerably younger Rb–Sr age of 588±35 Mafrom the Yarloo Shale of the Stuart Shelf which correlateswith the Dey Dey Mudstone. Since the Dey Dey underliesthe Munyarai Formation, an age discrepancy of at least 70million years is evident. Greater Rb–Sr ages have beenobtained: 731±54 Ma from the Rodda beds east of ChambersBluff and 715±210 Ma for the Dey Dey Mudstone inMurnaroo 1 (Webb in Womer et al., 1987), demonstratingthat geochronology has not assisted Neoproterozoiccorrelation in the Officer Basin. Nevertheless, the agedifference between the Devonian Mimili Formation andNeoproterozoic Munyarai Formation, shown on Figure 7.2,should have been evident shortly after Munyarai 1 wasdrilled.

Chemo- and magnetostratigraphy

Patterns of secular change in isotopes of carbon, sulphurand strontium can indicate rates of burial of organic carbonas well as biological events such as major extinctions, anderosional cycles. It may be possible to track parallel

Fig. 7.1 Eastern Officer Basin Neoproterozoic lithostratigraphy and acritarch assemblages. The curved line in the right-hand columnrepresents relative acritarch species abundance (after Zang, 1994, 1995b).

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Acritarchs from the upper Younghusband Conglomerate, a possible equivalent of the Pindyin Sandstone, in Manya 5.A Amadeusphaeridium sp. B Acritarch with a prominent process. C Trachyhystrichosphaera aimika Hermann, 1976 emend. Butterfield, Knoll and Swett,1994.Acritarchs from the Alinya Formation in Giles 1.D Comasphaeridium tonium Zang, 1995. E Lomentunella sp. F Trachyhystrichosphaera sp.Acritarchs from the Meramangye Formation in Meramangye 1.G ? Vandalosphaeridium sp. H Acritarch with a prominent process. I Pterospermella sp.Scale bar (in F) is 20 µm for D, G, H, I; 25 µm for B; 32 µm for C, E, F; and 80 µm for A.

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Acritarchs from the Dey Dey Mudstone in Lake Maurice West 1. A Tanarium sp. B Comasphaeridium sp. C Unnamed species.

Acritarchs from the Tanana Formation in Giles 1. D Multifronsphaeridium pelorium Zang in Zang and Walter, 1992. E Hocosphaeridium scaberfacium Zangin Zang and Walter, 1992. F Acritarchs with a prominent process and numerous conical spines.

Acritarchs from the Munyarai Formation in Munyarai 1. G Goniosphaeridium sp. H Trachyhystrichosphaera sp. I Gyalosphaeridium sp.

Scale bar (in I) is 20 µm for B, H, I; 32 µm for C, G; 50 µm for F; 63 µm for E; and 125 µm for A, D.

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Acritarchs from the Narana Formation in Munta 1 (A) and Lairu 1 (B, C). A Comasphaeridium sp. B Brevitrichoides sp. C Leiosphaeridia sp.

Acritarchs from the Early Cambrian Ouldburra Formation in Manya 6. D Ceratophyton sp. E Ceratophyton sp.

Miospores from the Devonian Mimili Formation in Munyarai 1. F Ancyrospora sp. G Ancyrospora sp. H Punctatisporites sp. I Retusotriletes sp.

Scale bar (in I) is 20 µm for A, B; 25 µm for C, D, E; 32 µm for F, G, I; and 40 µm for H.

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variations in isotopic signatures within and even betweenbasins, so providing another correlation tool. TheNeoproterozoic of the Officer Basin has few carbonate-richunits but nevertheless preliminary δ13C measurements havebeen made and tentative correlations suggested. A slightcontrast (~3‰ ) between the 13C-enriched Karlaya Limestonein Murnaroo 1 and the negative to moderately positiveTanana–Narana Formations in Ungoolya 1 was noted byJenkins et al. (1992), and attributed to the different sampleages with some contribution from facies effects.

Pell et al. (1993) presented a preliminary carbon isotopecurve for the South Australian late Marinoan stage based onvalues from the Wonoka and Billy Springs Formation of theAdelaide Fold Belt, augmented by data from ObservatoryHill 1 and Ungoolya 1. This curve displays consistentlynegative values (-6 to -8.5‰ ) through 360 m of WonokaFormation in Bunyeroo Gorge, implying low rates of burialof organic carbon and hence poor source rocks from thisinterval. In contrast, total organic carbon of the slightly olderDey Dey Mudstone (=Bunyeroo Formation) in Lake MauriceWest 1 and Karlaya 1 is ~0.8 to 1.5% (see Ch. 8), which ismoderately rich. These wells are on the Murnaroo Platformwhich subsided at one quarter the rate of the MunyaraiTrough (Moussavi-Harami and Gravestock, 1995), and thuseven richer source rocks are anticipated there. These shouldequate to strongly positive 13C values. Clearly, the isotopicresults from the limited data set in the Officer Basin are verypreliminary and it is likely that facies effects will loom largein any interpretation.

The magnetostratigraphic characteristics of cores fromObservatory Hill 1 and Lake Maurice West 1 have beendocumented by Chamalaun et al. (1990). The remanentmagnetisation of ~400 samples was measured with a spinnermagnetometer through the lower Karlaya Limestone, DeyDey Mudstone and upper Murnaroo Formation aftercarefully fitting the core together. Since the cores are verticaland not orientated with respect to azimuth, an arbitraryfiducial line was scribed and directions were measuredrelative to it.

Two magnetic events are represented within the Dey DeyMudstone in both wells. Magnetic inclination values are

more variable in the lower event which may represent anepoch of magnetic field excursions rather than a reversal.The upper event is sharp and probably a true reversal. Asshown on Figure 7.3, both events are within theComasphaeridium magnum acritarch assemblage zone(AAM 2, Table 7.1), which suggests that magneto-stratigraphy holds promise for more detailed correlationswithin acritarch zones. The two events are 75 m apart and,assuming a subsidence rate of 15 m per million years

Fig. 7.3 Lake Maurice West 1 Neoproterozoic lithostratigraphy,acritarch assemblages, and depths of magnetic field excursions andthe Acraman impact layer.

Fig. 7.2 Rb–Sr isochrons of the Neoproterozoic Munyarai Forma-tion, Ordovician Indulkana Shale and Devonian Mimili Formation.See text for details.

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(Moussavi-Harami and Gravestock, 1995), they areseparated in time by about five million years.

Lithology and event stratigraphy

It should have been obvious at the time of drilling that thetracheidal wood fragments claimed to have been recoveredfrom total depth in Munyarai 1 did not come from the hard,laminated dolomitic siltstone characteristic of the Dey DeyMudstone intersected in that well. The lithologic successionis now sufficiently well known to enable wireline logcorrelations to be carried out with some confidence. It is onlyin the Marla Overthrust Zone where Proterozoic intersectionsare few, and at the Rodda beds type section which exceeds 3km in thickness (Preiss and Krieg, 1992), that correlationremains a problem within the basin. Correlation with otherbasins is still a matter of debate. On a sequence stratigraphicbasis, Sukanta et al. (1991) correlated the Marinoan in theOfficer Basin with the Adelaide Fold Belt. A key argumentfor this is a set of submarine canyon incisions common toboth regions which suggested correlation from the NaranaFormation in the Officer Basin to the Wonoka Formation inthe Adelaide Fold Belt. However, from acritarch studies,Zang (1995b) correlated the canyon surface at the base of theNarana Formation with the disconformity at the base of theRawnsley Quartzite and not the Wonoka Formation which isstratigraphically older.

One key horizon for interbasinal correlation is low in theDey Dey Mudstone in the Officer Basin and low in theBunyeroo Formation of the Adelaide Fold Belt. This is the‘Acraman impact layer’, a bed of ejecta which resulted froma bolide impact on the Gawler Craton. The impact crater ismodern Lake Acraman and impact debris was spread over awide area to form a unique marker bed. The bed has beenidentified in cores from Observatory Hill 1 and Lake MauriceWest 1, and comprises medium to coarse-sand-sized acidvolcanic clasts. A thin, pale green alteration halo is evidentin the surrounding red-brown mudstone. The preservation ofthe layer suggests that the Dey Dey Mudstone is a deep waterdeposit (Wallace et al., 1990). The impact layer is a fewmetres above the magnetic polarity excursion in both wells(Fig. 7.3) which lends weight to magnetostratigraphy as acorrelation tool.

CAMBRIAN STRATIGRAPHY AND AGE

As no Cambrian body fossils have been found inoutcrops, correlation prior to their discovery in a drillhole in1978 was by lithological comparison with the well-knownsuccession of the Flinders Ranges (e.g. Wopfner, 1969). Apossible hyolith conch (?Biconulites) was reported from floatin a modern claypan near the Observatory Hill Formationtype section (Gatehouse, 1976). However, the ooliticlithology which encloses the specimen does not occur in thisformation and the specimen is presumed to have beentransported. Biostratigraphic and lithological correlations ofCambro-Ordovician strata are shown on Figure 7.4.

Invertebrate fossils

Marine invertebrates have been found in the OuldburraFormation which, prior to stratigraphic revision (Brewer et

al., 1987), had been incorporated within the Observatory HillFormation. Fragments of two small trilobites in a core from87.85 m in Marla 1 were identified as belonging to a genusof redlichiids, and are therefore Early Cambrian in age (Jagoand Youngs, 1980). One further specimen from this depth,and other trilobite remains from 333 m in the adjacentMarla 1B, remained unidentified.

Well-preserved trilobites from 967.7 to 970.1 m inManya 6 also came from the Ouldburra Formation. Thesebelong to a new species of Abadiella and indicate an EarlyCambrian (Atdabanian) age (Jago et al., 1994). Trilobitefragments have been recorded over a 394 m interval(889–1263 m) in this well by Dunster (1987a). He also notedthe lowest fossils (sponge spicules) at 1391 m. Detailed corelogging by him also revealed trilobites between 357.8 and385 m in Manya 3; this interval is in sequence C1.3,considered Early Cambrian (Botomian) in age (Gravestockand Hibburt, 1991). Possible archaeocyaths recorded at1207 m in Manya 6 are calcite pseudomorphs of aragonitefan cements from a reworked bioherm.

Dunster (1987a) has documented archaeocyath–calcimicrobe biohermal buildups between 399 and 654 m inMarla 6, as well as wackestones with fossil hyoliths(suggesting a provenance for Gatehouse’s (1976) sample),sponges and ostracods. This fauna indicates an EarlyCambrian age of the Ouldburra Formation even though fossilpreservation is too poor to permit identification to genuslevel.

Fig. 7.4 Cambro–Ordovician lithostratigraphy, fossils and geo-chronology.

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The presence of chitinophosphatic shelly fossilfragments, reported from Wilkinson 1 by Kantsler (inGatehouse, 1979), could not be verified from thin sectionexamination.

Acritarchs

An impoverished assemblage of acritarchs was reportedfrom between 314.5 and 512.2 m in Wilkinson 1 by Muir (inGatehouse, 1979), an interval now correlated with theOuldburra Formation. At that time, Muir considered theTommotian Stage to be latest Proterozoic, whereas it isregarded now as the second stage of the Early Cambrian. Inany event, the stratigraphic range of the four species reportedby her can only be regarded as Neoproterozoic to MiddleCambrian and better age resolution is not possible.Re-examination of the same interval in Wilkinson 1 failed tofind any microfossils, although sheet-like or granular organicmatter was found to be fairly common (van Neil, 1984).Acritarchs have been suggested as possible source organismsfor dinosterane which occurs in samples from the OuldburraFormation in Karari 1 (Kamali, 1995a,b).

Cambrian acritarchs recovered from the Early Cambrianof the Manya Trough and Marla Overthrust Zone are poorlypreserved and of low diversity in comparison to coevaldeposits in the Arrowie and Stansbury Basins (W-L. Zang,MESA, unpublished data, 1996). Only one assemblage hasbeen assigned (AAC 1, Table 7.1), and the characteristicallyCambrian genus Skiagia has not yet been recognised.

Geochronology

An outcropping silty shale in the Chambers Bluff area,and reported as ‘apparently conformable beneath the MtChandler Sandstone’, had a calculated Rb–Sr age of574±34 Ma (Webb, 1978). The shale was thought to beObservatory Hill Formation but, if this was the case, thecontact would not be conformable. Given the magnitude ofthe associated error, this age does not improve correlation.Still less accurate ages of 524±68 and 660±60 Ma wereobtained from the Observatory Hill Formation inByilkaoora 1 (Webb, 1978) and Cadney Park Member inByilkaoora 3 (Henry and Brewer, 1984). In the OuldburraFormation in Wilkinson 1, strontium levels are too high forreliable age determination by the Rb–Sr method (Webb,1978), and it may be that the Observatory Hill Formation andCadney Park Member are unsuitable for the same reason.

Lithology

Diagnostic lithologies have been employed todemonstrate or reinforce correlations in the absence of fossildata. The most widely correlated lithology is chert, whichoccurs abundantly as concretions, sheets and breccias at twokey levels of the Observatory Hill Formation — the MoylesChert Marker Bed and the Parakeelya Alkali Member.Brewer et al. (1987) considered the chert lags and concretionsfound at the type section near Observatory Hill (Wopfner,1969) to correlate with the Parakeelya Alkali Member.

As part of their objective of correlating Munyarai 1 withUngoolya 1, Womer et al. (1987) employed three keylithologies associated with the Observatory Hill Formation

— chert, calcite-after-trona pseudomorphs and green garnet.The first two correlate with the Moyles Chert Marker andParakeelya Alkali Member respectively, and the green garnetis a common accessory in lag gravel at the disconformablebase of the formation in both wells. This disconformity iscurrently known only in the Ungoolya area and on theMunyarai structure; no garnets have been noted where thelower boundary of the Observatory Hill Formation isconformable.

Fine-grained, centimetre-thick crystal tuff bands havebeen recognised in the Cadney Park Member which isdominantly a gypsiferous redbed suite. The tuff bands (at545.2 and 562.3 m in Manya 2; 436.2 m in Manya 4; 625.9and 636.6 m in Byilkaoora 3) are buff-grey and composed ofsubhedral, partly sericitised feldspar crystals and relict shardsin a glassy groundmass. Henry and Brewer (1984) noted thistuffaceous component and suggested a tentative correlationbetween the Cadney Park Member and the basalticCadlareena Volcanics (their Welbourn Volcanics). Thesebasalts are now known to be Proterozoic and unrelated, butthat does not lessen the correlation potential of the tuffswithin the Cambrian succession. Pontifex (1984, p.190)commented that ‘The source of this fine tuffaceousmaterial...is uncertain, but seems likely to be deposited fromhigh-level drifting clouds from a volcanic centre, maybe1000 plus kilometres away’. Their presence supportscorrelation of the Cadney Park Member with formations ofthe upper Hawker Group and/or Billy Creek Formation in theArrowie Basin (sequences C1.3 and C2.1 of Gravestock andHibburt, 1991), where tuff beds up to 1.5 m thick attest toactive rift volcanism. It is possible that the Officer Basin tuffsrepresent fallout from the same volcanic complexes on thepalaeo-Pacific margin of Gondwana.

ORDOVICIAN STRATIGRAPHY AND AGE

Ordovician strata are interpreted in Munyarai 1 between1018 and 1355 m depth, based on lithological similarity withoutcrops of Blue Hills Sandstone, Indulkana Shale andMount Chandler Sandstone in the EVERARD 1:250 000 maparea. These outcrops have been correlated with theOrdovician succession in the Amadeus Basin, relyingstrongly on ‘similarities of the lithology, sequence andtectonic setting’ (Krieg, 1973, p.14). No body fossils havebeen found and acritarchs have not been recovered from thefew, mainly sandy well intersections. The Ordovicianacritarch assemblages shown in Table 7.1 are in theWarburton Basin.

Ichnology

Trilobite resting traces (Rusophycus) and Skolithos andDiplocraterion burrows in the Mount Chandler Sandstonesuggested equivalence with the Pacoota Sandstone, althoughsome differences were noted (Packham and Webby, 1969;Krieg, 1973; Benbow, 1982). Trace fossils are usuallyconsidered to be good facies and palaeoenvironmentalindicators, and as most types have long time ranges they arenot often used for stratigraphic correlation and age dating.However, the exception to this rule are the trace fossilsassociated with trilobites in early Palaeozoic rocks. Thesetrace fossil types include Rusophycus, Cruziana, and

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Diplichnites. There are 19 species of Cruziana that haverestricted ranges in the Cambrian and Ordovician (Crimes,1975). In the Mount Johns Range adjacent to the MarlaOverthrust Zone, trilobite trace fossils are common, and thereis potential for stratigraphic correlation of the Marla andMunda Groups based on trace fossils. Although bioturbationhas been recorded in drill cores, diagnostic trace fossils havenot been found.

Geochronology

Six samples were collected from outcrops 2 kmeast-northeast of Chambers Bluff to determine the age of theIndulkana Shale. Rb–Sr analysis produced the ratios plottedon Figure 7.2, which represents a Late Ordovician isochronof 460±15 Ma (Webb, 1978). An additional surface samplewas collected some years later and its age determined as438±10 Ma (Early Silurian) using the K–Ar method (Womeret al., 1987). Webb’s (1978) age is preferred because of theconsistency of data from the six samples. No fossils havebeen found in the Blue Hills Sandstone and the age of thisunit may well range into the Silurian.

Lithology

The Mount Chandler Sandstone, besides containing tracefossils, is distinctive by virtue of its clean, well-sorted,mature quartzose lithology, which contrasts with other morefeldspathic or micaceous units in the basin (Krieg, 1973). Itis an attribute that can be used for correlation in the absenceof other data. The Mount Chandler Sandstone in Manya 5has been identified in this manner. The Blue Hills Sandstoneis the only other lithologically similar formation.

Detailed aeromagnetic maps show a distinctive magneticmarker bed which is clearly associated with continuousoutcrops of Indulkana Shale on the eastern rim of theMunyarai Trough. Shallow subcrops having the samemagnetic character occur northeast of the Marla OverthrustZone and, though undrilled, have been correlated confidentlywith the Indulkana Shale by Hamer (1994). The magneticsource, presumably magnetite, has not been identified.

DEVONIAN STRATIGRAPHY AND AGE

Devonian fossils occur in situ in the Mimili Formationand comprise vertebrate remains and spores (Fig. 7.5).

Vertebrate fossils

Cuttings between 816.9 and 823.0 m in Munyarai 1yielded scales from thelodont, acanthodian and ganoid(osteichthyan) fish (Gilbert-Tomlinson in Conoco, 1969),indicating a maximum age of Early Devonian for this part ofthe section. The fossiliferous interval was extended to liebetween 738 and 860 m (J. Hibburt, MESA, pers. comm.,1987) and the fossils were examined by Long et al. (1988).These authors identified scales of thelodonts, an acanthodian,teeth, plates and bone fragments, and correlated thisassemblage with the early Middle Devonian (Eifelian)Wuttagoonaspis fish fauna of the Georgina and AmadeusBasins. The Munyarai fauna is not large enough to determinewhether the host strata are marine or non-marine.

Fig. 7.5 Munyarai 1 Devonian lithostratigraphy, fossils and geo-chronology.

Rusophycus sp. in Apamurra Formation siltstone, Mount Johns Range.Photo courtesy of Dr J.B. Jago. (Photo 44430)

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Palynomorphs

Palynomorphs were not recovered from the fish-bearingstrata by Long et al. (1988) and, despite preparation of largequantities of material, only two spores were recovered fromcore 3 by Harris (in Conoco, 1969). The specimens (cf.Leiotriletes) only indicate a Devonian or younger age.Fragments of tracheidal wood reported from the bottom coreand as high as core 3 are now known to be contaminants, butit was these that stood for many years as testimony to thesupposed Devonian age of the Munyarai 1 succession belowthe fish scale zone.

Further sampling was carried out by Vlierboom (1973)who was the first to report palynomorphs from core 2, at adepth of 548.6 m (189 m above the top of the fish fauna).Vlierboom carried out two preparations on this sample toimprove the microfossil yield; he stated ‘In the first samplepreparation several well-preserved Triassic sporomorphswere found but as the samples were previously determinedas Siluro-Devonian it was suspected that the samples hadbeen contaminated’. The first preparation yielded only sevenspecimens, two of which — Platysaccus queenslandi andAlisporites sp. — indicated a Triassic age. The secondpreparation yielded 34 specimens, all of which wereconcluded by Vlierboom to indicate a Late Devonian(probably Famennian) age. Further work is planned toexamine the Triassic question.

More recently, Eames and Miller (in Womer et al., 1987)identified well-preserved miospores in three samples from640.1 to 853.5 m. The good preservation of this assemblagecontrasted strongly with the very poor preservation of eightsamples recovered from the much deeper interval(1652.0–2225.1 m) in Munyarai 1. Although the lowersamples were regarded as ‘probably Middle Devonian’, theyare now known to be Neoproterozoic in age. The upperassemblage of miospores was confidently assigned a LateDevonian (Frasnian) age because of similarity to a Frasnianassemblage from the Carnarvon Basin in Western Australia.The stratigraphic position of the Devonian assemblage isshown on Figure 7.5, which indicates an overlap of 116 mthat may be either Middle Devonian (based on fish fossils)or Late Devonian (based on spores). The interval which maybe positively correlated with Devonian strata based on fossilcontent comprises only 30% of the top 1000 m drilled. Atleast half the drilled section, from the surface to 548.6 m, maybe considerably younger than Devonian, but this section ismainly sandy and lacks fossils. A sample of core 1(249.3–253.0 m) has been submitted to Geotrack inMelbourne for assessment of its zircon fission track age.

Geochronology

Whole-rock samples of core in the depth range632.5–634.3 m and 2133.6–2136.4 m were analysed forRb–Sr age information by Compston (in Conoco, 1969).Compston showed clearly that the shallower samplesoccupied a distinct field with a lower gradient and anequivalent age between 300 and 400 Ma, i.e. Carboniferousto Devonian (Fig. 7.2). Interpreted simply as an isochron, theslope of the well-aligned deeper samples gave an equivalentage of 650 Ma, clearly Neoproterozoic as was concludedmuch later.

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INTRODUCTION

One key attribute, namely the association of Proterozoicand Cambrian source rocks and evaporites, is shared betweenthe Officer Basin, Persian Gulf and southwest SiberianPlatform. In these regions, halite and anhydrite areassociated at two main stratigraphic levels with argillaceousdolomite (the chief source rock) and sandstone. These wereoriginally interbedded sabkha–lagoonal deposits but theyhave been extensively altered by halokinesis. Mobile saltoccurs in the early Neoproterozoic (~800 Ma) AlinyaFormation of the Officer Basin, Bitter Springs Formation ofthe Amadeus Basin, and Hormuz Series of the Persian Gulfregion where salt diapirs have become major oil traps(Edgell, 1991).

The evaporite association also occurs in younger strata oflate Proterozoic and early Cambrian age (~650–518 Ma) insouthwestern Siberia (Kuznetsov et al., 1992), Oman and theManya–Tallaringa Trough region of the eastern OfficerBasin. The salt has remained largely immobile in the OfficerBasin and Siberia.

Despite major oil and gas production from Siberia and thePersian Gulf, and numerous in situ oil bleeds (e.g.Byilkaoora 1), the Proterozoic–Cambrian hydrocarbonpotential of the Officer Basin has been perceived as low, aperception shared with rocks of similar age in the AmadeusBasin (e.g. Summons and Powell, 1991). Currentinterpretations emphasise that Mereenie and Palm Valley oiland gas migrated from source facies of the Ordovician HornValley Siltstone, whereas oil generated in the Proterozoic orCambrian migrated prior to trap development (e.g. Jacksonet al., 1984). This assumption, based mainly on thestratigraphic range of the cyanobacterium Gloeocapsa-morpha prisca, is weakened by several factors. Theseinclude the dry gas composition at Palm Valley, the presenceof gas but not oil at West Walker 1 (Jackson et al., 1984), wetgas in the Bitter Springs Formation at Magee 1 (Wakelin-King, 1994), and the discovery of G. prisca in the EarlyCambrian Ouldburra Formation in the Officer Basin (Kamali,1995a; Michaelsen et al., 1995). On the basis of this andother evidence, the Amadeus Basin oil and gas may have beengenerated from formations as old as the Bitter SpringsFormation, a play that was actively explored by Pacific Oiland Gas Pty Ltd and resulted in the Magee 1 discovery(Wakelin-King, 1994).

A lack of knowledge of pre-Ordovician source rocksshould not be a deterrent to exploration in the Officer Basin.As McKirdy (1993) pointed out, the eastern Officer Basin isremarkably well endowed with oil shows in Neoproterozoic

and Cambrian rocks, the oils representing four geneticallydistinct families. Potential source rocks appear to beorganically lean on average but this is largely due to thepyrolysis technique being not well suited to treatment of thecarbonate-dominated lithologies. Most samples comprisevertical portions of core, even though the organic-richmaterial is horizontally laminated. Pyrolysis is carried outon powdered rock samples which thus comprise perhaps 90%matrix and must be considered minimal because samples arepre-digested in ~30% HCl, which is harsh treatment. TheTotal Organic Carbon (TOC) content of Officer Basinsamples is usually quite low (<0.5%) but, where organic-richlayers are specifically sampled, the TOC may be >4.5%(McKirdy et al., 1983).

Figure 8.1 provides a stratigraphic summary of both thesource potential of the Officer Basin and oil shows.

FORMATION DESCRIPTION

Alinya Formation

Source richness

Six samples of the Alinya Formation analysed fromGiles 1, and nine from Manya 5, revealed that the sourcerichness is very poor to poor (average TOC = 0.24, range0.02–0.62). However, samples are from thin black shale bedsat the base of upward-shallowing evaporite cycles (Zang andMcKirdy, 1994) in Giles 1 and redbeds in Manya 5, and maynot be representative of the more basinal parts of the unit.Given the very limited sampling from only two wells, it ispremature to dismiss the unit as too organically lean forhydrocarbon generation. Available Rock-Eval data for theAlinya are summarised in Table 8.1.

Kerogen type and source potential

Hydrogen Index (HI) values are commonly low (0–106),indicating gas-prone Type IV to III kerogen (Fig. 8.2). Thesamples in Manya 5 have near zero genetic potential; theseare overmature and contain intertinite or sub-graphitickerogen (McKirdy in Weste, 1984). Samples from Giles 1indicate poor genetic potential up to 0.91 kg hydrocarbon pertonne of source rock, but an almost identical molecularbiomarker assemblage to the Alinya Formation is found inthe correlative Gillen Member of the Bitter SpringsFormation (Amadeus Basin; McKirdy in Zang and McKirdy,1993), which also contains an oil-prone black, pyritic shale(in Bluebush 1, Mount Charlotte 1; Jackson et al., 1984).Thus, oil-prone kerogens may be found in the AlinyaFormation. Confirmation of this potential is provided by oil

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Fig. 8.1 Summary stratigraphic column of the Officer Basin, showing potential and proven source units, and oil shows.

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shows recorded from the Relief Sandstone in ObservatoryHill 1, and from the Murnaroo Formation in Lake MauriceEast and West wells. The source for this oil has beenunequivocally determined as Alinya Formation based onbiomarker distributions (McKirdy, 1993).

Origin and organic petrology

McKirdy (in Zang and McKirdy, 1994) has identified adiverse assemblage of molecular biomarkers from the Giles 1evaporitic facies association, which indicates derivation fromprecursor eucaryotic algae and eubacteria.

The tidal flat facies of the Alinya Formation in Giles 1contains abundant mats of the cyanobacteriumEoentophysalis gilesis (Zang, 1995a), which may formstratiform stromatolites 1–8 mm thick. The thinly bedded tolaminated tidal flat evaporite association is very similar tothat described from Shark Bay by Ferguson and Skyring(1995, fig. 5d), despite the 800 million year age difference

between the two occurrences. Such cyanobacterial mats arecapable of transforming into oil-prone kerogens under anoxicconditions.

Coominaree Dolomite

The Coominaree Dolomite is restricted to the eastern partof the basin, and has been intersected only in Manya 5. It ismore widespread in the Peake and Denison Ranges, 200 kmto the southeast. Contrary to Gravestock and Sansome(1994), no samples have been analysed for source rockquality, but the presence of stromatolites in the unit mayindicate a minor source potential. However, the oxygenatedenvironment may have resulted in the organic matter beingconsumed by aerobic bacteria.

Meramangye Formation

Only two samples (Marla 9) from the marineMeramangye Formation have been analysed for TOC, and

Fig. 8.2 HI versus Tmax plot, Alinya Formation.

Table 8.1 Rock-Eval source rock data, Alinya Formation.

Well Depth TOC Genetic potential Oxygen Hydrogen Tmax

(m KB) (%) (kg/t) Index Index (°C)

Giles 1 1243.0 0.62 0.91 29 106 4451256.0 0.40 0.26 8 58 4751265.5 0.62 0.47 0 60 439

Manya 5 1266.4 0.26 0.00 158 0 4271283.9 0.28 0.01 64 0 3231300.6 0.26 0.01 50 50 2181314.2 0.46 0.01 61 0 271

Photomicrograph of algal mats in the Alinya Formation in Giles 1:Top: intertidal anhydrite; cross-polars, width of view is 5.7 mm.(Photo 44405) Bottom: subtidal shale; plane polarised light, width ofview is 2.2 mm. (Photo 44406)

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indicate a very poor source with TOC ranging from 0.07 to0.09%. No Rock-Eval analyses have been performed

Dey Dey Mudstone

Source richness

Fifty-one samples of the Dey Dey Mudstone analysedfrom Giles 1, Karlaya 1, Munta 1, Munyarai 1, andUngoolya 1 indicate source richness ranging from very poorto poor (average TOC = 0.11%, range 0.03–0.81%). Thesource potential improves towards the top of the formation,where the depositional environment changes from fluvial to

marine. Rock-Eval data for the Dey Dey Mudstone aresummarised in Table 8.2.

Kerogen type and source potential

HI values are moderate (100–382), indicating oil-proneType II kerogen (Fig. 8.3), with poor to fair genetic potentialup to 2.92 kg hydrocarbon per tonne of source rock. The oilpotential of the upper Dey Dey Mudstone is confirmed by thepresence of oil shows in thin sandstone beds in Karlaya 1 andMarla 9. This is discussed further in Chapter 9.

Origin and organic petrology

The potential source beds are thin but contain oil-pronelamalginite which was probably derived from acritarchs andcyanobacterial mats (McKirdy, 1993). Sterane distributionssuggest a green algal source (see Tanana Formation).

Karlaya Limestone

Source richness

The Karlaya Limestone is widely distributed over theMurnaroo Platform and in the Munyarai Trough, and is alsoprobably present in the Birksgate Sub-basin. Twenty-eightsamples have been analysed for TOC from Karlaya 1,Munyarai 1, Murnaroo 1 and Giles 1, which indicate a poorsource with an average TOC of 0.20% (range 0.02–0.72%);this is, however, significantly better than the overlyingTanana Formation. Rock-Eval analyses are summarised inTable 8.3.

Kerogen type and source potential

HI values are moderate (173–194, two samples only),indicating oil-prone Type II kerogen (Fig. 8.4), with poorgenetic potential up to 1.54 kg hydrocarbon per tonne ofsource rock. Given that the Karlaya Limestone containsisotopically heavy shelf carbonate indicative of organicmatter burial (Jenkins et al., 1992; Pell et al., 1993), thesource potential might be expected to be better than the datawould suggest. Oil shows, which may have been sourcedfrom the underlying Dey Dey Mudstone, have been recordedfrom Karlaya 1.

Fig. 8.3 HI versus Tmax plot, Dey Dey Mudstone.

Table 8.3 Rock-Eval source rock data, Karlaya Limestone.

Well Depth TOC Genetic potential Oxygen Hydrogen Tmax

(m KB) (%) (kg/t) Index Index (°C)

Murnaroo 1 182.3 0.40 0.22 417182.4 0.72 1.54 98 194 426185.4 0.60 1.18 116 173 424

Table 8.2 Rock-Eval source rock data, Dey Dey Mudstone.

Well Depth TOC Genetic potential Oxygen Hydrogen Tmax

(m KB) (%) (kg/t) Index Index (°C)

Karlaya 1 2093.7 0.81 2.92 34 285 4322094.9 0.40 2.10 50 382 4312096.2 0.21 0.32 119 109 4222099.2 0.23 0.30 126 100 4242101.0 0.31 0.48 61 119 426

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Tanana Formation

Source richness

One hundred and seven samples of the Tanana Formation,analysed from Giles 1, Karlaya 1, Lairu 1, Marla 9, Munta 1,Munyarai 1 and Ungoolya 1, indicate source richness rangingfrom very poor to moderate (average TOC = 0.14%, range

0.02–1.11%). The richest samples occur in Marla 9, althoughthe highest value was from Lairu 1. Rock-Eval data for theTanana Formation are summarised in Table 8.4.

Kerogen type and source potential

HI values are low (3–100), indicating gas-prone Type IIIkerogen (Fig. 8.4), with a poor genetic potential of up to0.67 kg hydrocarbon per tonne of source rock. However, oilbleeds from fractures in Marla 9 suggest that oil has beengenerated.

Origin and organic petrology

The Marla 9 (Tanana Formation) and Karlaya 1 (Dey DeyMudstone) oils have distinctive sterane distributions similarto those in Neoproterozoic oils and source rocks from Omanand Siberia. Primitive green algae appear to be the precursors(McKirdy, 1993).

Munyarai Formation

Four samples were analysed from the MunyaraiFormation in Munyarai 1, with TOC ranging from 0.08 to0.20%. No Rock-Eval analyses were performed. The unit ispredominantly fine grained and the environment isinterpreted to be marine prodelta and outer shelf. Thisformation may have source potential but further drilling isrequired to obtain samples for analysis.

Narana Formation

Source richness

Fifty-one samples of the Narana Formation analysedfrom Byilkaoora 1, Karlaya 1, Lairu 1, Munta 1 andUngoolya 1 indicate source richness ranging from very poorto moderate (average TOC = 0.16, range 0.04–0.57%).Rock-Eval data for the Narana Formation are summarised inTable 8.5.

Table 8.4 Rock-Eval source rock data, Tanana Formation.

Well Depth TOC Genetic potential Oxygen Hydrogen Tmax

(m KB) (%) (kg/t) Index Index (°C)

Marla 9 218.9 0.92 0.05 11 3269.3 0.53 0.67 28 100 438

Ungoolya 1 1623.1 0.20 0.16 140 75 3501930.6 0.20 0.12 75 60 362

Table 8.5 Rock-Eval Source rock data, Narana Formation

Well Depth TOC Genetic potential Oxygen Hydrogen Tmax

(m KB) (%) (kg/t) Index Index (°C)

Karlaya 1 1424.6 0.21 0.08 347 38 4211435.7 0.32 0.29 262 81 4181594.57 0.21 0.10 319 47 423

Ungoolya 1 1287.2 0.57 0.09 26 16 3271287.6 0.30 0.06 40 20 2761299.9 0.20 0.08 140 40 3351325.1 0.20 0.27 180 120 4211345.1 0.34 0.21 91 56 4231450.1 0.21 0.20 171 86 4191499.8 0.21 0.42 171 171 4211523.6 0.22 0.38 209 145 4211525.0 0.21 0.33 186 129 421

Fig. 8.4 HI versus Tmax plot, Karlaya Limestone and TananaFormation.

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Kerogen type and source potential

HI values are low to moderate (16–171), indicating gasprone Type III kerogen (Fig. 8.5), with poor genetic potentialof no more than 0.42 kg hydrocarbon per tonne of sourcerock.

Origin and organic petrology

No organic petrology has been carried out. The NaranaFormation comprises a lower canyon fill succession which isorganically lean and an upper limestone–mudstone successionwhich contains the richest source rocks. The latter arepresumed to derive from algal–cyanobacterial precursors.

Ouldburra Formation

Source richness

More than 260 TOC measurements have been made onsamples from the Ouldburra Formation, including Marla 1A,1B, 3, 6, 7 and Manya 3, 6 in the Marla Overthrust Zone andManya Trough, and Wallira West 1, Wilkinson 1 and Karari 1,2A in the Tallaringa Trough. The average TOC of all samplesis 0.29% but may be much higher (up to a very good 4.56%in Marla 1A) in thin, organic-rich layers that are only reliablydetected by close sample spacing. A profile of part of theOuldburra Formation in Manya 6 (Fig. 8.6) shows thedownhole variation in TOC (Kamali, 1995a). Between 680and 850 m depth there are frequent high TOC ‘spikes’ againsta low background, while from 1050 to 1450 m, spikes aremore sporadic but the background TOC level rises to 0.3%.

Fig. 8.6 Manya 6 TOC and copper profile (after Kamali, 1995b).Fig. 8.5 HI versus Tmax plot, Narana Formation.

Fluorescing Gloeocapsamorpha prisca and lamalginite in the Ould-burra Formation at 263.35 m in Karari 1, Tallaringa Trough (fromKamali, 1995a). (Photo 44404)

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Kamali (1995a) related the organic matter distribution inManya 6 to five ‘organic matter preservation cycles’separated by exposure surfaces. In the two lower cycles(1035–1500 m), organic matter is in laminae of algal–cyanobacterial origin interbedded with halite which indicatesa hypersaline environment. Organic matter in the upper threecycles (635–1035 m) is associated with limestone ordolomite interbedded with anhydrite and thin silty layers.The high frequency of organic-rich versus organic-pooralternations is suggested by Kamali (1995a) to stem fromperiodic flooding events and lowstands. This cyclicity is bestdeveloped in transgressive and highstand tracts of sequenceC1.2 (703–849 m; Gravestock and Hibburt, 1991), whichmay correlate with a global relative sea-level maximum inEarly Cambrian (Botomian) time. Rock-Eval data for theOuldburra Formation are summarised in Table 8.6.

Kerogen type and source potential

There is a problem with Rock-Eval pyrolysis data forsamples from the Manya Trough. The very low HI (0–91)suggests the presence of poor quality gas prone Type III orIV kerogen and an associated mineral matrix effect inargillaceous samples, even though their n-alkane profilesindicate an algal source (McKirdy et al., 1984). Theseauthors also pointed out the contrast between organic-richlaminae (TOC = 4.56%) and the dolomitic host rock (TOC =0.18%). Ill-defined S2 peaks also result in anomalously lowTmax values, and oxygen indices (OI) are variable.

Samples from the Ouldburra Formation in the TallaringaTrough are in complete contrast, even though the organicmatter–carbonate–evaporite association is the same. Thiscontrast is clearly demonstrated on Figure 8.7 which shows

Table 8.6 Rock-Eval source rock data, Ouldburra Formation.

Well Depth TOC Genetic potential Oxygen Hydrogen Tmax

(m KB) (%) (kg/t) Index Index (°C)

Manya Trough

Manya 3 246.7 0.37 0.02 75 2 419360.4 0.45 0.02 75 2 440418.0 0.37 0.02 64 2 221

Manya 6 657.9 0.36 0.03 139 0 249691.7 0.97 0.75 69 41 307698.0 0.68 0.57 56 38 436698.6 0.82 0.81 52 61 476732.7 0.93 0.13 41 9 359773.8 0.34 0.04 126 0 279780.0 0.48 0.10 48 6 333785.8 0.34 0.04 115 0 279807.9 0.63 0.10 11 5 317810.5 0.43 0.04 49 2 279826.2 0.69 0.09 57 6 317899.8 0.91 0.07 11 3 279999.4 0.34 0.01 27 0 279

1057.0 0.31 0.00 39 0 2791127.0 0.63 0.01 24 0 2791229.7 0.64 0.03 30 2 2411231.9 0.22 0.01 49 0 2661247.9 0.32 0.00 44 0 2411267.5 0.43 0.00 86 0 2661277.1 0.42 0.21 214 36 4661279.1 0.52 0.15 133 12 3041279.8 0.64 0.01 92 0 2411302.1 0.38 0.00 121 0 2051312.7 0.61 0.00 80 0 2211332.3 0.33 0.03 312 0 2811386.6 0.37 0.04 86 3 2411392.4 0.31 0.01 155 0 2321419.3 0.36 0.17 86 31 2411459.2 0.32 0.08 88 19 241

Marla 1B 136.7 0.64 0.15 87 12 440138.6 0.48 0.13 137 10 432

Marla 6 416.0 1.34 1.44 30 91 422671.2 1.13 0.27 15 11 341700.2 0.47 0.08 87 0 237

Marla 7 392.8 0.53 0.43 47 60 403

Tallaringa Trough

Karari 1 263.3 1.18 5.18 455 388 427275.4 0.20 1.27 150 510 435

Karari 2A 211.8 0.34 1.12 91 285 430285.5 0.73 3.69 652 438 427298.0 0.59 2.90 567 372 425

Wilkinson 1 344.4 0.72 1.91 79 243 422344.6 0.78 1.64 69 193 424462.1 0.58 1.74 63 227 431480.9 1.10 5.35 50 409 433

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the consistently high HI of samples from the TallaringaTrough. Kamali (1995a) ascribed this contrast in the organicmatter to a lower degree of oxidation, less bacterialdegradation and less compaction compared to the ManyaTrough. Michaelsen et al. (1995) suggested that theOuldburra Formation in the Manya Trough was depositedunder ‘dysoxic’ conditions (pristane–phytane ratio =1.0–2.6), compared to ‘anoxic’ conditions in the TallaringaTrough (pristane–phytane ratio ≤1.2). It is here suggestedthat these differences are due to the over maturity of theManya Trough samples (supported by burial historymodelling and MPI maturity data, see Chapter 9), and that inother areas not presently sampled, suitable OuldburraFormation facies (transgressive tracts, evaporiteassociations) are likely to have fair to good source potential.Genetic potential of the Tallaringa Trough samples ismoderately good, with values up to 5.18 kg hydrocarbon pertonne of source rock.

Origin and organic petrology

Examination of the base-metal assays routinely carriedout on Comalco cores from mineral drillholes (Brewer, 1984)showed that copper and zinc display elevated values at depthscomparable with those corresponding to some of theorganically rich layers. A profile for copper illustrates thiseffect and suggests reducing conditions in the depositionalenvironment (Fig. 8.6). Elevated base-metal values arecommonly associated with organically rich sedimentsincluding sabkhas rich in cyanobacterial mats (Demaison andMoore, 1980; Ferguson and Skyring, 1995).

New molecular biomarkers found in the TallaringaTrough include 24-Isopropylcholestanes, possibly fromfossil sponges (McCaffrey et al., 1993), and dinosterane, adinoflagellate indicator (Michaelsen et al., 1995). Ofperhaps the greatest importance is the discovery of telalginitecomposed of the cyanophyte G. prisca in the Early CambrianOuldburra Formation (Kamali, 1995a,b; Michaelsen et al.,1995). This organism had hitherto been identified only inOrdovician oil-prone source rocks (e.g. Summons andPowell, 1991).

In this context it is interesting to note the observations ofDow (in Womer et al., 1987) on a whole rock extract fromthe Observatory Hill Formation in Ungoolya 1. Dow stated:

The whole extract gas chromatogram reveals a distinctodd carbon predominance in the C14-C20 carbon numberrange . . . . ascr ibed . . . to a part icular organismGloeocapsamorpha prisca. The high pristane and phytanecontent of the subject sample (from 1208.3 m) and thenumerous extraneous peaks, however, are uncharacteristicof Ordovician oils and may be due to contamination,possibly from the drilling fluid.

As an alternative to contamination, this extract issuggested to represent oil which has migrated from theOuldburra Formation and may have mixed with oil from aNeoproterozoic source sharing the same migration pathway.This implies that the Ouldburra Formation occurs downdipof Ungoolya 1, as indicated by Moussavi-Harami andGravestock (1995) on their restored isopach map.

Observatory Hill Formation

Source richness

Nearly 150 samples have been analysed from theObservatory Hill Formation from Byilkaoora 1, 2, 3, Emu 1,Giles 1, Karlaya 1, Munyarai 1, Murnaroo 1 and Ungoolya 1.The TOC of the Observatory Hill Formation is higher in theMarla Overthrust Zone ( average 0.42%, maximum 2.29%)than on the Murnaroo Platform (average 0.20%, maximum0.49%) where the alkaline playa facies was either not welldeveloped or deep weathering has leached the shallow toexposed beds. There is no record of the Observatory HillFormation in the Tallaringa Trough; strata originally ascribedto this formation in wells such as Wallira West 1, Wilkinson 1,and Karari 1 and 2A have since been assigned to theOuldburra Formation (e.g. Stainton et al., 1988).

A TOC profile of the Observatory Hill Formation inByilkaoora 1 is shown on Figure 8.8. Most of the elevatedvalues are from the Moyles Chert Marker bed and ParakeelyaAlkali Member, although values are variable due to stainingby migrated oil (McKirdy et al., 1984). Copper assays areelevated and these also partly correspond to the organic-richlevels (data in Brewer, 1984). Rock-Eval data for theObservatory Hill Formation are summarised in Table 8.7.

Kerogen type and source potential

A plot of HI versus Tmax (Fig. 8.9) shows that theObservatory Hill Formation has moderate to good oil sourcepotential, and suggests Type II kerogen, but high H/C andC/N atomic ratios are consistent with an origin from Type Ikerogen (McKirdy and Kantsler, 1980; McKirdy et al.,1983).Fig. 8.7 HI versus Tmax plot, Ouldburra Formation.

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Genetic potential is best in the Marla Overthrust Zonewith potential yield up to 7.34 kg hydrocarbon per tonne ofsource rock, and the abundant oil shows (including oil

bleeding from vugs in core from Byilkaoora 1) confirms theoil potential of this formation.

Origin and organic petrology

The discovery of oil bleeding from vugs and fractures incore from Byilkaoora 1 first drew attention to thehydrocarbon potential of the Officer Basin. The oil wasgenerated in situ from halotolerant algae and bacteria in thenon-marine playa lake facies of the Parakeelya AlkaliMember of the Observatory Hill Formation (McKirdy andKantsler, 1980; Pitt et al., 1980; Brewer et al., 1987), anargillaceous dolomitic mudrock with pseudomorphs of theevaporites trona and shortite. Organic petrographicexamination has revealed abundant lamalginite which forms‘a web of organic matter such as might be expected from analgal mat’ (McKirdy and Kantsler, 1980, p.84).

The importance of cyanobacterial mats as oil-pronekerogen precursors has been discussed by Zhmur et al. (1994)for settings ranging from lagoonal to marine. Zhmur andcolleagues from the Paleontological Institute, RussianAcademy of Sciences, are currently studying cyanobacterialmats from the Officer Basin, including those from the

Table 8.7 Rock-Eval source rock data, Observatory Hill Formation.

Well Depth TOC Genetic potential Oxygen Hydrogen Tmax

(m KB) (%) (kg/t) Index Index (°C)

Byilkaoora 1 200.7 0.76 1.79 28 211 428202.3 0.67 2.43 35 298 427204.3 0.58 1.80 50 281 420254.9 0.83 2.88 27 310 425259.4 0.68 2.51 52 301 420286.5 0.58 1.90 55 260 419

Byilkaoora 2 660.9 0.44 0.65 77 134 434670.0 0.50 1.41 100 240 417677.4 0.53 2.16 94 362 416680.5 0.77 3.43 42 412 422688.5 0.39 1.22 64 254 415699.6 2.29 7.34 27 257 439703.3 0.20 0.37 120 160 420705.7 0.13 0.02 146 15 404711.9 0.62 1.99 46 283 416720.1 0.28 0.62 86 200 418720.3 0.39 1.30 146 303 423727.4 0.31 1.05 139 284 410728.0 0.39 1.80 110 395 415728.5 0.34 1.00 91 262 414729.1 0.68 2.64 57 350 412729.7 0.27 0.79 156 241 415738.0 0.43 1.41 105 263 431

Byilkaoora 3 343.0 0.73 3.59 18 386 423346.2 0.61 2.66 18 364 413346.8 0.56 2.47 54 355 414348.4 0.35 1.09 123 289 416365.2 0.55 3.64 13 600 426368.7 0.50 1.98 80 370 420373.2 0.81 3.69 86 417 423

Giles 1 212.6 0.47 0.50 57 98 424213.3 0.42 0.54 40 124 426

224.4 0.56 0.99 14 173 430

Munyarai 1 1692.9 0.12 0.02 200 0 433

Ungoolya 1 1203.6 0.43 1.51 33 333 4221203.8 0.50 1.48 50 276 4181207.5 0.26 0.74 50 262 4261243.8 0.21 0.07 33 29 4321245.6 0.27 0.14 170 44 345

Fig. 8.8 Byilkaoora 1 TOC and copper profile.

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alkaline playa facies of the Observatory Hill Formation.Results of this study will be available in 1998.

Apamurra Formation

Four samples from Byilkaoora 1 were analysed for TOC,and results ranged from 0.33 to 0.64%. No Rock-Evalanalyses have been performed. The unit is widespread overthe eastern Officer Basin and is of shallow marine origin; itwarrants further analysis to determine the source potential.

Indulkana Shale

No source rock analyses have been performed on theOrdovician Indulkana Shale because the unit has only beenintersected in the subsurface in a few wells and has not beencored. The formation may have source potential as it is aprobable correlative of the marine, organic-rich Horn ValleySiltstone in the Amadeus Basin. A distinctive aeromagneticsignature is associated with the Horn Valley Siltstone(Hamer, 1994) which may be caused by an oxidisedpyrite-rich layer indicative of formerly reducing conditions.

Fig. 8.9 HI versus Tmax plot, Observatory Hill Formation.

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INTRODUCTION

Excitement followed the discovery of oil in fractures andvugs in core from Byilkaoora 1 (Benbow and Pitt, 1979; Pittet al., 1980; McKirdy and Kantsler, 1980), but it was thepresence of calcite pseudomorphs of trona and shortite thatled initially to extensive mineral exploration in thenortheastern Officer Basin. Comalco drilled 20 cored holesin the Marla area, nine of which displayed oil shows. Mostof these were from the Observatory Hill Formation but oilwas also found bleeding from calcite veins in the upperRodda beds (?Tanana Formation) in Marla 9, and oil wasrecovered from the mud pit in Byilkaoora 2. A review of oilshows from mineral wells is provided by Hibburt et al.(1995). Woodhouse (in Weste, 1984) suggested the mud pitoil, though similar to extracts from oil-impregnated core, hadmigrated ‘much further’.

These are clear, macroscopic indications of oil generationand migration in Neoproterozoic and Cambrian rocks. Thereare also microscopic indications of oil migration from bothCambrian and Neoproterozoic strata. These are reviewedbelow with an assessment of the thermal maturity of sourcerocks and the timing of hydrocarbon migration.

OIL-SOURCE CORRELATION AND

MATURITY

The thermal maturity of hydrocarbon source rocks isgenerally assessed from reflectance measurements ofvitrinite phytoclasts. However, in pre-Devonian rocksdevoid of higher plant material, the distribution of triaromatichydrocarbons can be exploited as a measure of the maturityof oils and source rock extracts. The aromatic maturity ofOfficer Basin source rocks has been reviewed by McKirdyand Michaelsen (1994), and available data are presented inTable 9.1. Oil shows and oil-source correlations arediscussed briefly below, from the stratigraphically youngestto the oldest occurrences.

Trainor Hill Sandstone

The youngest Extractable Organic Matter (EOM) is in theTrainor Hill Sandstone, only metres below its eroded top inMarla 10. Cryptomelane (KMn8O16) was identified as thesource of a black stain in the sandstone. A trace of organicmatter was extracted but has not been identified (Watson,1994a). The EOM–cryptomelane association suggestssecondary hydrocarbon migration due to hot groundwatermovement and may be a Tertiary to Recent (50–0 Ma)phenomenon (see ‘Apatite fission track analysis’).

Observatory Hill Formation

Oil in the Early Cambrian Observatory Hill Formationhas been described in detail by McKirdy and Kantsler (1980)and McKirdy et al. (1983, 1984), and a review of all easternOfficer Basin oils is provided in McKirdy (1993). TheObservatory Hill Formation oil is mainly in the ParakeelyaAlkali Member and Moyles Chert Marker Bed in the MarlaOverthrust Zone; it is non-marine, algal-sourced and partlybiodegraded.

In Byilkaoora 1, the Observatory Hill source rockmaturity, expressed as calculated vitrinite reflectance (VRcalc)from the methylphenanthrene index (MPI), is VRcalc =0.99–1.09%, which is at or just past peak maturity for Type Ikerogen (McKirdy and Michaelsen, 1994). However, steraneand hopane distributions in Byilkaoora 1 oil suggestexpulsion from a marginally mature source, and VRcalc of theoil is 0.49% (McKirdy et al., 1984; McKirdy, 1993). TheByilkaoora 2 mud pit oil is biodegraded as is the EOM in thehost rock, and shows evidence of short distance migration(Woodhouse in Weste, 1984).

There is thus sufficient information to show that presentday maturity of the Observatory Hill Formation in the MarlaOverthrust Zone is in the middle oil window. However, theindigenous oil was generated at a much lower maturity leveland has migrated short distances within the formation. Thiscan only have been achieved via a fracture network. InByilkaoora 1 and 2, bitumen is also present in theconformably underlying Wallatinna Member.

Organic matter was extracted from the Observatory HillFormation in stratigraphic well Observatory Hill 1, drilled atthe type section on the Murnaroo Platform. The aromaticmaturity of the sample yielded a VRcalc of 0.94% (McKirdyet al. in Gatehouse and Hibburt, 1987). The maturity of thisextract is comparable to that of the source rocks in the MarlaOverthrust Zone and suggests that most of the ObservatoryHill Formation is now at peak oil generation.

The identification of ?G. prisca in Ungoolya 1 by Dow(in Womer et al., 1987) has been mentioned in Chapter 8. Theorganism was identified by its C14–C20 odd carbon numberpredominance. G. prisca, or a precursor, has also beenidentified from petrographic examination of telalginite fromthe Early Cambrian Ouldburra Formation (Kamali, 1995a).Assuming the Ouldburra Formation to be the only G. priscarich source rock in the eastern Officer Basin, the Ungoolya 1occurrence is particularly significant because the extract wastaken from the Observatory Hill Formation in an interval(1201–1215 m) with poor shows in ‘vugs and very smallvertical fractures in chert laminae displaying light brown to

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Table 9.1 Aromatic maturity data for the Officer Basin (after McKirdy and Michaelsen ,1994; Kamali, 1995a).

Formation Well Sample MPI MPR VRcalc VRcalc VRcalc

depth type % % %

(m) (a) (a1) (b)

DevonianMimili Munyarai 1Formation 633.00 extract 1.43 2.78 1.26 1.22 0.98

CambrianObservatory Byilkaoora 1Hill Formation 262.95 extract 0.98 1.15 0.99 0.91 1.00

285.00 extract 1.16 0.87 1.09 1.03 0.88293.17 oil 0.38 0.25 0.63 0.49 0.34

Observatory Hill 134.14 extract 0.90 0.88 0.94 0.85 0.89

Ouldburra Wilkinson 1Formation 333.07 extract* 0.58 0.64 0.75 0.63 0.75(Tallaringa 390.08 extract 0.83 0.45 0.90 0.80 0.60Trough) 461.87 extract* 0.52 0.55 0.71 0.58 0.68

Karari 1263.35 extract 0.38 0.46 0.63 0.49 0.60

Karari 2A285.50 extract 0.46 0.60 0.68 — 0.72298.0 extract 0.30 0.47 0.58 — 0.62298.13 extract* 0.34 0.38 0.60 0.46 0.52

(Manya Trough) Marla 3619.60 extract 1.00 1.24 1.00 0.92 1.03

Marla 6416.0 extract 1.43 1.76 1.26 1.22 1.18671.25 extract 2.13 4.98 1.68 1.71 1.63

Marla 7392.85 extract 1.30 1.92 1.18 1.13 1.22

Manya 6698.60 extract 1.11 2.34 1.07 1.00 1.31

1279.15 extract* 0.85 1.33 0.91 0.82 1.06

Relief Observatory Hill 1Sandstone 155.35 oil 1.32 1.46 1.19 1.15 1.10

NeoproterozoicTanana Munyarai 1Formation 2289.81 extract 1.63 — 1.38 1.36 —

Marla 9209.75 extract 0.66 0.90 0.80 — 0.89234.83 extract 0.68 0.73 0.81 0.70 0.81269.93 extract 0.71 0.94 0.83 — 0.92

Karlaya Munyarai 1Limestone 2611.83 extract 1.67 — 1.40 1.39 —

Murnaroo 1183.90 extract 0.64 0.85 0.78 — 0.87190.95 extract 0.70 1.0 0.82 — 0.94

Dey Dey Karlaya 1Mudstone 2093.73 extract 0.66 0.75 0.79 — 0.82

2345.15 extract 0.37 0.90 0.62 — 0.89

Lake Maurice West 1417.7 extract 0.28 0.63 0.57 — 0.74418.20 extract 0.29 0.82 0.57 — 0.86

Murnaroo Lake Maurice West 1Formation 534.14 oil 1.03 — 1.02 0.94 —

Lake Maurice East 1540.83 oil 1.40 — 1.24 1.20 —

Alinya Giles 1Formation 1237 extract 0.43 1.27 0.66 0.52 1.04

* stained by oil(a) VRcalc = 0.60 MPI+0.40 (0.65≤ VR ≤1.35%)

VRcalc = -0.60 MPI+2.30 (VR >1.35%)(a1) VRcalc = 0.7 MPI + 0.22 (0.5≤ VR ≤1.7%)(b) VRcalc = 0.99 log10 MPR + 0.94 (0.4≤ VR ≤1.7%)

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Oil bleeds from the Observatory Hill Formation in Byilkaoora 1; core width is 41 mm: (a) alkaline playa sequence, 219.75 m (Photo 44388)(b) 277.0 m (Photo 44390) (c) 293.0 m (Photo 44391) (d) 295.5 m (Photo 44392) (e) 278.9 m (Photo T15624) (f) 219.45 m (Photo 44389).

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dc

fe

ba

yellow-gold fluorescence, pale straw cut and slow streamingbright yellow cut’ (Henry, 1986). Thus at Ungoolya 1 on theedge of the Murnaroo Platform, the Observatory HillFormation contains traces of live oil, some of which hasmigrated from the Early Cambrian Ouldburra Formation, orsome other G. prisca-bearing (?Ordovician) source rock.

Ouldburra Formation

No shows have been recorded from the OuldburraFormation during drilling operations. Kamali (1995b)reported live oil from Marla 6 and Manya 6 in the ManyaTrough, and Karari 1 and 2A in the Tallaringa Trough. Theseare microscale shows from organic petrographic studies.Dead oil and bitumen have been recorded in Marla 3 (Hibburtet al., 1995) and illustrated by Kamali et al. (1995) who notedthat such material indicates oil migration paths.

Calculated vitrinite reflectances show that the OuldburraFormation in the Manya Trough is late mature to overmatureand generally gas-generative (VRcalc = 1.0–1.68%; McKirdyand Michaelsen, 1994). However, one sample from 1279 min Manya 6 is stained by migrated hydrocarbons and has anMPI-derived VRcalc of 0.82–0.91% (Kamali et al., 1993;Kamali, 1995b; Table 9.1). Interestingly, the stain is inlimestone ~4 m above the top salt bed in this well, thus theoil can only have migrated laterally.

MPI-derived maturities of Ouldburra Formation samplesfrom the Wilkinson and Karari wells in the Tallaringa Troughare significantly lower (VRcalc = 0.58–0.68%, Table 9.1) andthe unit is mature for oil generation. As a result of their lowermaturity, organic macerals are more readily distinguished, inparticular lamalginite and talalginite, which display evidenceof active oil expulsion into microfractures and veinlets(Kamali, 1995a,b). These samples are from present depths<300 m, whereas samples from the Ouldburra Formation inWilkinson 1 (65 km northeast) at similar depths are slightlymore mature (VRcalc = 0.71–0.90%; Table 9.1).

McKirdy and Michaelsen (1994) have suggested thatregional maturity of the Ouldburra Formation increasessouthwest towards Hughes 2 on the Murnaroo Platform(VRcalc = 0.99% at 243 m in Hughes 2). However, it is morelikely that the maturity of the Ouldburra Formation increasesin the opposite direction in the Tallaringa Trough (i.e. towardsthe northeast), and also increases in a generally northwards

direction into the Manya and Munyarai Troughs (Fig. 9.1).New seismic data indicate that the Cambrian is eroded on thesouthern Murnaroo Platform (Lindsay, 1995; Lindsay andLeven, 1996), and the formations intersected in the Hugheswells are Neoproterozoic.

Relief Sandstone

No shows have been recorded while drilling the EarlyCambrian Relief Sandstone. Giles 1, when drilled, wasthought to be located on an anticline with the ReliefSandstone inside closure. Re-mapping by Mackie (1994)suggested, however, that the southeastern flank of the Gilesstructure is faulted and the anticline is open to the east.Consequently there have been no valid structural tests of theRelief or any other sandstone reservoir under seal in theeastern Officer Basin.

Bitumen was identified in thin section from the ReliefSandstone in Observatory Hill 1 (Gatehouse and Hibburt,1987), with VRcalc from an oil extract of 1.15% (McKirdy andWatson, 1989). This occurrence is highly significant. Theoil is in a basal Cambrian sandstone but molecularbiomarkers identify the oil with a specific Proterozoic source,namely the Al inya Formation (see below). The oil is clearlya product of post-Petermann Ranges Orogeny hydrocarbonmigration from a source rock at peak levels of oil generation.

Cambrian maturity mapping

A preliminary iso-reflectance map of Cambrian aromaticmaturity is shown on Figure 9.1. Potential source rocks inthe Ouldburra and Observatory Hill Formations are restrictedto the eastern part of the basin. Based on available data, twoareas, the Munyarai and Manya Troughs, are overmature andare therefore in the gas zone. A region south of the WatsonHigh on the Murnaroo Platform is designated as ‘immature’and seismic data show that Cambrian strata have not beenpreserved to the southwest (Lindsay, 1995). Sparse datasuggest that the Birksgate Sub-basin, west of the NurraiRidge, is relatively immature (McKirdy and Kantsler, 1980,p.83, fig. 15).

The bulk of the eastern Officer Basin ranges from initiallymature in the southern Tallaringa Trough to mature on thesouthwestern margin of the Munyarai Trough. Althoughthere is not much evidence, the region between Emu 1 and

Oil staining in Relief Sandstone at 161.5 m in Observatory Hill 1: Left: UV fluorescence (Photo 44386) Right: transmitted white light (Photo44387). Field of view for both images is 0.5 mm.

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Giles 1 appears more mature than the Ammaroodinna Ridgeand its extension into the Marla Overthrust Zone. Faults inthe latter region were reactivated by the Devonian AliceSprings Orogeny, whereas the Giles structure is a product ofthe older Petermann Ranges Orogeny. Whether this maturitycontrast is related to the age difference between thesestructures, or due to greater uplift and erosion of the MarlaOverthrust Zone after the Alice Springs Orogeny, is not clear.

Tanana Formation, Karlaya Limestone andDey DeyMudstone

Oil shows have been recorded in the Tanana Formation,Karlaya Limestone and upper Dey Dey Mudstoneimmediately beneath. Since most of these shows span the

Karlaya–Dey Dey boundary, both formations are regarded aspart of the same source rock package.

Bleeds from small, disconnected vugs with patchy to pinpoint bright yellow fluorescence were recorded in KarlayaLimestone core from Karlaya 1 (Dunster, 1987b).Fluorescence was also noted in very thin sandstone beds inthe upper Dey Dey; extracts from the upper Dey Dey (depth2094–2345 m) gave VRcalc = 0.82–0.89%. In Lake MauriceWest 1 (depth 418 m), the Dey Dey Mudstone yielded VRcalc

= 0.74–0.86%, and the Karlaya Limestone in Murnaroo 1(depth 184–191 m) gave VRcalc = 0.87–0.94% (Table 9.1).

These values indicate that the Karlaya–Dey Dey sourcerock package is early mature on the Murnaroo Platform.Maturity increases into the Munyarai Trough, since VRcalc in

Fig. 9.1 Eastern Officer Basin Cambrian aromatic maturity. Contours represent vitrinite reflectance calculated from methylphenanthreneindex.

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the Devonian Mimili Formation is 0.98% and in the KarlayaLimestone (depth 2612 m) is 1.4% in Munyarai 1 (McKirdyand Michaelsen, 1994; Table 9.1).

A Proterozoic oil show was recorded while drillingMarla 9 in the Marla Overthrust Zone over an intervaltentatively correlated with the Tanana Formation (depth245–287 m). The show comprises oil bleeds from fracturespartly cemented by calcite. VRcalc of extracts from 210 to270 m depth is 0.81–0.92%. Weak bleeds were also reportedfrom the Dey Dey Mudstone (depth 328 m). Marla 9 is notin the Manya Trough as McKirdy and Michaelsen hadassumed, hence its maturity is not anomalously low, althoughit is somewhat lower than nearby Cambrian values.Byilkaoora 1 is the only other well to have intersected theNeoproterozoic in the Marla Overthrust Zone; no shows wererecorded in this part of the section.

The Karlaya–Dey Dey oil is marine and its distinctivesterane distribution links it to green algal precursors. Similarsterane distributions are found in Neoproterozoic oils fromOman and Siberia (McKirdy, 1993).

Murnaroo Formation

The Proterozoic Murnaroo Formation is a potentialreservoir, not a source rock. As with the Cambrian ReliefSandstone, thin sections from Lake Maurice West 1 (depth534–576 m) were oil stained and small quantities of oil weresubsequently extracted from drillcore. VRcalc of the EOM is0.94–1.20% and it has a similar maturity and composition toresidual hydrocarbon from the Relief Sandstone inObservatory Hill 1 (McKirdy and Watson, 1989). Thus, twowells 60 km apart on the Murnaroo Platform contain oil froma common source in sandstone reservoirs of Proterozoic andEarly Cambrian age.

The Murnaroo and Relief shows are perhaps the mostsignificant in the Officer Basin.

Alinya Formation

It was McKirdy (1993) who recognised that biomarkerdistributions (hopane–sterane and diasterane–sterane ratios;McKirdy and Watson, 1989) point unequivocally to theAlinya Formation as the source of the Murnaroo–Relief oilshows. This constitutes a second family of Neoproterozoicoil, as confirmed from extracts of the Alinya Formation inGiles 1. VRcalc from core in this well (depth 1237–1266 m)yields a value of 1.04% (McKirdy and Michaelsen, 1994;Table 9.1). The calculated maturity is comparable tomaturities calculated for extracts from the Relief Sandstone(1.15%) and Murnaroo Formation (0.94–1.20%), suggestingthat the Alinya Formation was the source of this oil, whichmust have migrated after deposition of the Relief Sandstone.Moussavi-Harami and Gravestock (1995) suggested that oilmigration took place after burial beneath thick Ordoviciansediments.

Because the same biomarker assemblage has been foundin the Bitter Springs Formation of the Amadeus Basin (Zangand McKirdy, 1994), the oil source facies was probably verywidespread and was certainly far richer organically than themeagre Giles 1 data would suggest.

Proterozoic maturity mapping

A preliminary iso-reflectance map of Neoproterozoicaromatic maturity is shown on Figure 9.2. No source rocksexist in the easternmost parts of the basin whereMesoproterozoic basement underlies Neoproterozoic orCambrian sedimentary rocks at shallow depths. Like theCambrian map, it is a hybrid of VRcalc values from twodistinct oil families in samples taken over a wide depth range.Both maps are thus highly interpretive.

Overmature, gas-prone conditions are indicated for theManya and Munyarai Troughs and the Ammaroodinna andMiddle Bore Ridges. Iso-reflectance contours are displacedto the south and west compared to Cambrian contours, thusthe northern Murnaroo Platform is at a peak stage of oilgeneration. No maturity data exist for the BirksgateSub-basin or Tallaringa Trough. Basement from refractionseismic investigation could be 800 m below the drilledCambrian section in the Tallaringa Trough (Milton, 1975).The Cambrian aromatic maturity values suggest that anyunderlying Proterozoic source rocks are likely to be withinthe oil window. The Neoproterozoic samples from Marla 9indicate that the Marla Overthrust Zone is within the oilwindow. Similarly, results from Hughes 2 suggest that thesouthwestern Murnaroo Platform is oil mature.

THERMAL MATURITY

There are few usable bottom-hole temperature recordsfrom eastern Officer Basin wells. Drillstem test temperaturesfrom Lairu 1 (40.6°C at 1090 m) and Munta 1 (73.3°C at1981 m) indicate a low to average present-day geothermalgradient ranging from 14 to 24°C/km. However, this basinhas had a complex history of subsidence and uplift, andpresent-day geothermal gradients may not apply toconditions prior to the Neogene.

To better understand the thermal history of the easternOfficer Basin, apatite fission track analysis (AFTA) and fluidinclusion geothermometry have been carried out on a smallsample population. In addition, vitrinite reflectances weremeasured on Permian phytoclasts from several wells in orderto provide some constraints on Palaeozoic thermal history.The results presented below have far-reaching consequencesfor geohistory modelling.

Permian vitrinite reflectance

In their search for economic coal deposits, Comalcodrilled eight holes in the Permo-Carboniferous ArckaringaBasin near the northwestern margin of the BoorthannaTrough (Bourke and Senapati, 1983). Cuttings from two ofthese holes, 42 km southeast of Manya 2 (Fig. 9.1), weresampled for coal from the Permian Mount ToondinaFormation at depths ranging from 187 to 216 m. Measuredvitrinite reflectance (VRmeas), organic petrology and VRcalc

from MPI were recorded (Watson, 1994b). Further measuredVR and petrographic descriptions were obtained from coresamples of the Mount Toondina and Boorthanna Formations(255–497 m) in Manya 2, and the Cretaceous Bulldog Shaleand Mount Toondina Formation (62 and 360 m, respectively)in Mount Willoughby 1 (Tingate, 1994).

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In Manya 2, measured VR varies from 0.35 to 0.51%,which is inconsistent with the present depth of the samples.The degree of gelification of telovitrinite in samples from theMount Toondina Formation suggests a cover of not less than1.2–1.5 km since Permian deposition (Keiraville Konsultantsin Tingate, 1994), pointing to a greater depth of burial inMesozoic time.

Measured vitrinite reflectance in the two Comalco coaldrillholes ranges from 0.29 to 0.50%. In these holes and inManya 2, the Mount Toondina Formation containsfluorescing telalginite composed of Reinschia andBotryococcus-related genera, as well as Tasmanites. Oildrops are also present. Of greatest interest, however, is thecalculated vitrinite reflectance of 0.85%, corresponding to a

methylphenanthrene index of 0.75. This is considerablyhigher than the measured vitrinite reflectance of 0.33–0.50%on adjacent samples, pointing to suppression of vitrinitereflectance due to the presence of hydrogen-rich macerals(Hutton and Cook, 1980; Keiraville Konsultants in Tingate,1994). Reflectance suppression of fluorescent lamalginite byas much as 0.4–0.5%, compared to VRcalc from MPI, isevident in source rocks from the Proterozoic McArthur Basin(Crick, 1992), and a similar problem is encountered in theTriassic of the North West Shelf (Beardsmore andO’Sullivan, 1995).

As a result of this phenomenon, the Permian vitrinitereflectances should be regarded as minimum values andpost-Early Permian burial may have been as high as 2 km in

Fig. 9.2 Eastern Officer Basin Neoproterozoic aromatic maturity. Contours represent vitrinite reflectance calculated from methylphenan-threne index.

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the vicinity of these wells. It would also appear that thematurity of Permian source rocks in the Boorthanna Troughhas been underestimated. A technique developed by CSIRODivision of Petroleum Resources which examinesfluorescence alteration of multiple macerals (FAMM;Wilkins et al., 1992) will be applied in this region.Preliminary results indicate VR suppression of 0.1% (N.Sherwood, CSIRO, pers. comm., 1997). It is noteworthy thatvan Neil (1984) first documented fluorescence alteration ina sample from the Ouldburra Formation in Wilkinson 1.

Fluid inclusion microthermometry

Fluid inclusions were studied in three samples from theOuldburra Formation in Manya 6 in the Manya Trough(Kamali, 1995b). Microthermometry was performed oninclusions from ‘early’ calcite cement, ‘late’ calcite cement,‘early’ dolomite and saddle dolomite in an attempt todetermine palaeotemperature history. The sampled depthswere 889.5, 896.5 and 956.8 m, with the deepest yielding themajority of inclusions in ‘late’ calcite and saddle dolomite.

Saddle dolomite from the deepest sample contained fluidinclusions with four or more homogenisation temperaturesranging from 163 to 332°C, which significantly exceed thetemperature of dolomite crystal formation, and thus havere-equilibrated.

Such high temperatures suggest the passage ofhydrothermal brines, but calculated vitrinite reflectancevalues of 1.07% (from 698.6 m depth) and 0.91% (from1279.15 m; oil stained) argue against this hypothesis and alsonegate a widespread thermal event (Kamali, 1995b).Furthermore, salt in this well has not been mobilised, thus thehigh temperature data must be treated with caution.

Homogenisation temperatures for ‘early’ calcite(31–50°C) and ‘early’ dolomite ‘60–68°C’ are consistentwith the entrapment of primary fluid inclusions withincreasing burial. ‘Late’ calcite (homogenisationtemperature 132–170°C) may have been precipitated at adepth exceeding 4 km from a more saline brine which isconsistent with burial beneath a thick Ordovician–Devoniansection prior to the Alice Springs Orogeny. Gravestock andSansome (1994) suggested that the Relief Sandstone inManya 6 may have been buried to a depth approaching 6 kmbeneath an advancing thrust front to account for the degreeof compaction of the sandstone. Modelling (see below)suggests that a depth of 4.6 km would be sufficient to accountfor present-day maturity values.

The absence of hydrocarbons from Ouldburra Formationfluid inclusions in Manya 6 does not downgrade the sourcepotential of this unit. Instead, it points to their migration atsome time between the relatively early low-temperaturecements and the relatively late high-temperature cement.

Two-phase fluid inclusions were also examined by theBaas Becking Geobiological Laboratory (1983) from theParakeelya Alkali Member of the Observatory HillFormation in the Byilkaoora wells. These inclusions are incarbonate pseudomorphs of shortite (an indicator of alkalineplaya environments), and have homogenisation temperaturesin the range 60–108°C. Even though this is in the thermal

window for oil generation, oil was not noted in theseinclusions either, oil in vugs and fractures notwithstanding.

It is possible that homogenisation temperatures in theByilkaoora samples are related to a much younger (≤100 Ma)thermal event revealed by apatite fission track data. All thefluid inclusions analysed to date are from the structurallycomplex Marla Overthrust Zone (Byilkaoora wells) and theadjacent Manya Trough (Manya 6), and these interpretationsshould thus be regarded as preliminary.

Apatite fission track analysis

Apatite fission track analysis was carried out by Geotrack(1994) on sandstone samples from five wells in threestructurally contrasting regions. Wells in the MarlaOverthrust Zone and Manya Trough were predicted to havethermal histories dominated by the Alice Springs Orogeny,whereas an older thermal history was expected from ‘cooler’,shallower wells on the Murnaroo Platform. Sandstones inthe Tallaringa Trough were not analysed.

Apatite yield was excellent from all but the oldest andyoungest samples. The yield from the oldest (PindyinSandstone in Giles 1) was very poor and the Pindyin wastherefore not analysed. Yield was also poor from the LateJurassic Algebuckina Sandstone in Manya 2, but goodinformation was obtained nevertheless. Analytical andpalaeotemperature data (Table 9.2) were interpreted byTingate (1994) based on a geothermal gradient of 25°C/km,which was assumed in the absence of measured temperaturedata.

One unexpected outcome of this analysis was the totalthermal annealing of tracks associated with the Alice SpringsOrogeny, regardless of location. Maximum palaeo-temperatures in excess of 110°C were experienced by theRelief Sandstone and Murnaroo Formation in Lake MauriceWest 1 during the Late Devonian and Carboniferous, yet thiswell is 200 km south of the Musgrave Block. Similarly,apatites analysed from early Palaeozoic strata beneath thePedirka Basin, up to 160 km east of the Musgrave Block,have experienced the same effect (Tingate in Alexander et al.,1996). The uraniferous granites beneath the Cooper Basinwere intruded during the Early to Middle Carboniferous andother thermal events have been recorded as far south as theFlinders Ranges (Gatehouse et al., 1995). The Alice SpringsOrogeny was evidently associated with high heat flow overa wide area of northern South Australia, and this is taken intoaccount for geohistory modelling (see below).

Permian and Jurassic apatites from Manya 2, and olderapatites from other wells (Table 9.2), were heated to 90°Cprior to cooling during the Cretaceous (110–70 Ma). Tingate(1994) correctly associated this higher temperature with LatePermian to Cretaceous burial, and suggested a cover of1.5 km would be enough to provide conditions suited to theelevated temperature. Based on measured vitrinitereflectance suppression, and assuming a lower geothermalgradient, the interpreted depth of burial is now closer to 2 km,at least for the Manya Trough and Marla Overthrust Zone.

There is also consistent evidence that palaeotemperaturewas elevated during the last 50 million years, partly due to

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thicker Tertiary cover, since eroded. Tingate (1994)considered the main reason to be hot water flow. Support forthe existence of heated aquifers in Tertiary time comes fromthe presence of abundant kaolinite in the AlgebuckinaSandstone (which probably caused the poor apatite yield).The presence of Liesegang rings in Permian strata also pointsto circulation of warm water and suggests the aquifers werenot confined solely to the Jurassic sandstones.

The apatite fission track data are consistent and uniformenough to constrain palaeotemperatures in the eastern OfficerBasin over the past 300 million years. However,measurement of thermal events in the preceding 800 millionyears of the basin’s history is elusive, and analysis of thisperiod is a best guess.

GEOHISTORY MODELLING

Geohistory and maturity modelling of the eastern OfficerBasin has been undertaken using version 2.05 of Winbury®,

a modular software program developed by Paltech Pty Ltd.Modelling was undertaken on three wells, each of which hasundergone a differing tectonic history and is located in adistinct structural setting:

• Manya 6 (Manya Trough)

• Giles 1 (Ammaroodinna Ridge)

• Byilkaoora 1 (Marla Overthrust Zone).

Considerable difficulty was experienced in constrainingmaturity models for all wells, with the possible exception ofManya 6. This has arisen as a result of inadequatetemperature, maturity and kinetic data. Whilst estimates ofthe amount and timing of erosion have been addressed byMoussavi-Harami (1994) and summarised in Table 9.3, anaccurate estimate of the original Rock-Eval properties forprincipal source rocks, in particular TOC and HI, has beenhampered largely as a consequence of the complex structuralhistory and great depths of burial.

Table 9.2 Sample analytical and palaeotemperature data (after Geotrack, 1994; Tingate, 1994).

Formation Well Strat. Fission Mean track Standard Present 1 Maximumdepth age track age length deviation temp. palaeotemperature 2

360-300 Ma 50-0 Ma110-70 Ma

(m) (Ma) (Ma) (µm) (µm) (°C)

Manya 2Algebuckina 245.5–247.7 150–130 201.2±17.6 11.59±0.34 1.47 31 — 90 60Sandstone

Boorthanna 492.9–494.3 290–280 279±16.2 11.76±0.15 1.54 37 — 90 60Formation

Cadney Park 510–516 525–518 237.2±16.8 11.35±0.25 2.57 38 ≥110 90 70Formation

Manya 6Cadney Park 448.2–448.8 525–518 236.2±11.8 11.43±0.19 1.70 36 ≥110 90 60Formation

Relief 1699.6–1701.2 540–520 231.0±15.9 11.21±0.64 2.92 68 >110 90 70Sandstone

218.8±26.9

Manya 5Relief 455.1–455.5 540-520 216.6±14.5 11.92±0.15 1.57 36 ≥110 90 60Sandstone

Murnaroo 459–459.6 615-600 192.1±13.1 12.22±0.28 2.00 37 >110 90 60Formation

195.6±20.8

Tarlina 1054.5–1055.8 650-640 238.4±18.7 11.23±0.21 2.12 51 >110 90 70Sandstone

Lake Maurice West 1Relief 217.7–218.7 540–520 323.6±19.9 12.12±0.22 2.32 30 100 90 60Sandstone

Murnaroo 488.2–488.8 615–600 240.2±14.2 11.98±0.16 1.68 37 ≥110 90 60Formation

Giles 1Relief 416.6–416.9 540–520 299.3±17.4 11.95±0.18 1.79 35 100 90 60Sandstone

Tanana 422.3–422.6 585–575 251.6±15.5 12.10±0.18 1.74 36 ≥110 90 60Formation

233.5±22.3

Tarlina 1063.4–1063.8 640–615 148.2±12.6 11.16±0.19 1.87 51 >110 100 90Sandstone

139.6±22.8

1 Calculated assuming a geothermal gradient of 25°C/km.2 Palaeotemperature estimates have an error of approximately 10°C.Underlined ages are central ages used when sample single grain age data have chi squared probabilities of <50% (see Geotrack (1994) forfurther details).

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Source rock packages modelled for the three wells are theCambrian Observatory Hill and Ouldburra Formations, andthe Neoproterozoic Karlaya Limestone and Dey DeyMudstone. The Alinya Formation was not considered due toa lack of data. All Rock-Eval parameters for the EarlyCambrian Ouldburra Formation, the most prospective sourceunit, are extrapolated from Karari 1 and 2A wells in theTallaringa Trough, which still display active oil expulsion.

Manya Trough

The thermal and burial history of the Manya Trough isrepresented by Manya 6. Modelling of this well is fairly wellconstrained by fission track data and a detailed temperature

log. One attribute of the latter is temperature suppressionthrough the salt zone in the lower Ouldburra Formation andupper Relief Sandstone. For the purposes of more accuratelymodelling the richest source rock units, the 1 km thickOuldburra Formation has been divided into three informalunits, of which the richest source quality is found in the upperunit (average TOC = 0.82%). Present day maturity zones aresummarised on Figure 9.3 and Table 9.4.

Formations below the Relief Sandstone (in which the wellreached total depth) are reconstructions based on data fromManya 5.

Source rocks of the upper and middle Ouldburra appearto have entered the oil window (VRcalc = 0.65%) at ~370 Ma,just prior to the Alice Springs Orogeny, and the wet gaswindow shortly thereafter (~360 Ma). They have remainedin the wet gas window to the present day. Structures whichwere in place as a result of the Petermann Ranges andDelamerian Orogenies could be expected to be charged. Bycomparison, the lower Ouldburra Formation source unitentered the oil window just prior to the Delamerian Orogenyat ~510 Ma and remainded there until 460 Ma before enteringthe wet gas window (VRcalc = 1.0%) just prior to the AliceSprings Orogeny (~370 Ma). This unit has been in the drygas window since the Carboniferous (~315 Ma).

Fig. 9.3 Geohistory plot, Manya 6.

Table 9.3 Interpreted amount of sediment lost, selected wells,Officer Basin (m).

Tectonic event Manya 6 Giles 1 Byilkaoora 1

Continental uplift 1300 200 1000Alice Springs Orogeny 2750 100 500Rodingan Event 450 255 1735Delamerian Orogeny 1250 625 450Petermann Ranges Orogeny 770 2400 1675Sturtian uplift not reached 500 1000

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Ammaroodinna Ridge

The thermal and burial history of the AmmaroodinnaRidge is represented by Giles 1. Modelling of this well ispoorly constrained and draws heavily on heatflowconstructed for Manya 6. Present-day maturity zones aresummarised on Figure 9.4 and Table 9.5.

The entire Precambrian succession at the Giles 1 locationentered the oil window at ~570 Ma, prior to the PetermannRanges Orogeny, and has stayed there until the present day.The Dey Dey Mudstone–Karlaya Limestone source rockpackage is presently just within the oil window (VRcalc =0.7%). By comparison, the Cambrian succession remains

immature largely as a result of significantly reduceddepositional rates on the Ammaroodinna Ridge.

Marla Overthrust Zone

The thermal and burial history of the Marla OverthrustZone is represented by Byilkaoora 1. There is no bottom holetemperature data for this well and a regional geothermalgradient of 25°C/km is assumed. Only one VRcalc value wasavailable (1.0% at 200 m) and heatflow modelling has beendrawn from Manya 6; the pre-Narana Formation stratigraphy

Fig. 9.4 Geohistory plot, Giles 1.

Table 9.5 Hydrocarbon maturity, Giles 1, Ammaroodinna Ridge.

Formation VRcalc Maturity Depth(%) window (m subsea)

Observatory Hill Formation, <0.65 ImmatureCadney Park Member, (oil) SurfaceRelief Sandstone, 0.65 Mature ~123Tanana Formation, (oil)Karlaya Limestone Member,Dey Dey Mudstone,Murnaroo Formation,Meramangye Formation,Tarlina Sandstone,Alinya Formation,Pindyin Sandstone,Tarlina Sandstone

Table 9.4 Hydrocarbon maturity, Manya 6, Manya Trough.

Formation VRcalc Maturity Depth(%) window (m subsea)

Post-Devonian <0.65 Immature (oil) SurfaceCadney Park Member,upper and middle 1.0 Wet gas ~175Ouldburra FormationLower Ouldburra Formation, 1.6 Dry gas ~944Relief Sandstone,Murnaroo Formation*,Tarlina Sandstone*

* Not penetrated.

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is a reconstruction below total depth. Present-day maturityzones are summarised on Figure 9.5 and Table 9.6.

The Dey Dey Mudstone–Karlaya Limestone source rockpackage entered the oil window at ~570 Ma, and the wet gaswindow at ~550 Ma before passing into the dry gas windowbetween ~490 and 475 Ma during the Delamerian Orogeny.More significantly, source rocks of the Observatory HillFormation appear to have remained within the oil windowfrom ~450 Ma (i.e. post Delamerian Orogeny) until thepresent day which may account for the highly degradednature of the oil recovered from bleeds in the core.

Fig. 9.5 Geohistory plot, Byilkaoora 1.

Table 9.6 Hydrocarbon maturity, Byilkaoora 1, Marla OverthrustZone.

Formation VRcalc Maturity Depth(%) window (m subsea)

Trainor Hill Sandstone, <0.65 Mature SurfaceApamurra Formation, (oil)Arcoeillinna Sandstone,Observatory Hill Formation,Cadney Park Formationupper Narana Formation 1.0 Wet gas ~100lower Narana Formation, 1.6 Dry gas ~700Tanana Formation*,Karlaya Limestone*,Dey Dey Mudstone*,Murnaroo Formation*,Meramangye Formation*,Tarlina Sandstone*

* Not penetrated.

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INTRODUCTION

The Officer Basin contains a number of reservoirs withexcellent porosity and permeability. These are generallysandstones of fluvial or aeolian origin, and were originallyfeldspathic, but dissolution of the feldspars has led toextensive secondary porosity development, in some caseswith permeabilities over 8 darcys (8000 md). Reservoirpotential also exists in carbonates (vuggy porosity). The onlyprevious core analysis for reservoir properties carried out byindustry was for Comalco in the early 1980s, whichconcentrated on the Ungoolya Group reservoirs (Weste,1984), but MESA has since obtained data from all availablecored sandstone reservoirs as part of the South AustralianExploration Initiative (106 samples; Sansome andGravestock, 1993). In addition, some analytical work wasinitiated by university student projects (Gaughan, 1989;Kamali, 1995b).

FORMATION DESCRIPTION

Pindyin Sandstone

Distribution

Pindyin Sandstone crops out in the Birksgate Sub-basinbut in the subsurface it has only been intersected by Giles 1.The formation is, however, presumed to be widespread in thedeeper, undrilled parts of the basin. The thickness rangesfrom 100 to 200 m.

Petrophysics

Twelve samples from Giles 1 range from 3.8 to 22.5%porosity with an average of 11.8%, and permeability valuesreach 1538 md. The porosity–log permeability (phi log k)plot is linear (Fig. 10.1). Calculated shale volume (Vshale)

rarely exceeds 5% and the Gamma Ray is generally between20 and 40 API units (Fig. 10.2). Wireline log porosity isreadily calculated from the density log using a quartz matrixdensity of 2.65 g/cm3. The Pindyin Sandstone aeolian faciesis the cleanest potential reservoir in the basin.

Seal

Siltstone and evaporites of the Alinya Formation may actas a semi-regional seal for the Pindyin Sandstone on thenorthern margin of the Murnaroo Platform.

Tarlina Sandstone

Distribution

Tarlina Sandstone is distributed over the MurnarooPlatform, Manya Trough and may possibly extend to the

Aeolian sandstone of the Pindyin Sandstone at 1291.36 m in Giles 1.Quartz grains are evenly coated with haematite. Porosity is col-oured blue; core porosity from a nearby sample was 22.6% andpermeability was 1538 md. Plane polarised light; field of view is1.6 mm. (Photo 44393)

Fig. 10.1 Porosity–log permeability plot, Pindyin Sandstone; Mur-naroo Platform depth range 1291–1326 m. Fig. 10.2 Vshale versus Gamma Ray for Giles 1, Pindyin Sandstone.

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Tallaringa Trough. The formation is up to 183 m thick to thesouth of the basin on the Murnaroo Platform, but may be upto 373 m in Manya 5. It may not be present on the northernmargin of the basin due to facies changes.

A section corresponding to the Murnaroo Formation inManya 5, as originally interpreted by Gravestock andSansome (1994), has been revised. Moussavi-Harami (1994)and Moussavi-Harami and Gravestock (1995) now considerthat the Murnaroo Formation is underlain by the TarlinaSandstone. This interpretation better fits the burial history ofthis well.

Petrophysics

Twenty-one samples from Giles 1 and Manya 5 haveporosities ranging from 9 to 19.6% with low permeabilitieswhich average 1.0 md. The porosity–log permeability plot isclustered and there is no discernible difference betweenMurnaroo Platform and Manya Trough samples of the TarlinaSandstone, supporting the reinterpretation of Manya 5stratigraphy as discussed above (Fig. 10.3).

Calculated Vshale in Giles 1 is mainly 10–20% with fewvalues exceeding 30%. Gamma Ray (Fig. 10.4) is generally60–90 API units in Giles 1, reflecting the feldspar content.Scattered high values to 150 API are attributed to slumpedmudclast horizons. Porosity from the wireline density log(quartz matrix) correlates reasonably well with measuredvalues (Fig. 10.5). The relatively low permeability values,despite good porosity, suggest that pore-bridging clays maybe responsible.

Seal

Mudstone of the Meramangye Formation may act as aseal for the Tarlina Sandstone in the northern MurnarooPlatform where it reaches a thickness of 195 m in Giles 1.The Meramangye Formation may disappear towards thebasin margins, resulting in stacked reservoirs. The TarlinaSandstone is overlain by Murnaroo Formation in LakeMaurice East (southern Murnaroo Platform) and Manya 5(Manya Trough).

Murnaroo Formation

Distribution

The Murnaroo Formation is a key petroleum reservoirtarget. The formation is widespread on the MurnarooPlatform (maximum thickness 391 m) and extends to theManya Trough where it was fully cored in Manya 5 (246 mthick). In Marla 9, however, the formation is represented bya thin condensed section. It underlies the Dey Dey Mudstone(Murnaroo Platform and Marla Overthrust Zone) andCambrian Relief Sandstone (Manya Trough), and overlies theMeramangye Formation or Tarlina Sandstone.

Fig. 10.4 Vshale versus Gamma Ray for Giles 1, Tarlina Sandstone.

Fig. 10.3 Porosity–log permeability plot, Tarlina Sandstone; Mur-naroo Platform depth range 1064–1230 m; Manya Trough depthrange 715–1053 m.

Fig. 10.5 Core porosity versus porosity calculated from the densitylog, Tarlina Sandstone.

Pindyin Sandstone aeolianite at 445.4 m in Watson Siding 1a. Planepolarised light; field of view is 3.2 mm. (Photo 44429)

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Petrophysics

The reservoir quality is variable, ranging from 3 to 20%in the three sampled wells (Giles 1, Munta 1, Manya 5;n = 28). The porosity–log permeability plot shows thatpermeability can reach 200 md and is generally greater than1 md (Fig. 10.6). Slightly higher porosity but lowerpermeability values in Manya 5 near the Marla OverthrustZone may be related to early cementation by illitic clay priorto burial.

On average, however, there is no great difference inporosity distribution between Manya 5 (Manya Trough) andthe other two wells (Murnaroo Platform; Fig. 10.7). In Giles1, the Gamma Ray varies from 20 to 200 API probably dueto the feldspar, mica, heavy mineral and glauconitecomposition. Vshale ranges up to 40% but is predominantly20% or less (Fig. 10.8).

Water saturation

Three samples from Manya 5 were submitted forair–mercury capillary pressure curve analysis. Two curvesfrom the Murnaroo are very similar, whilst the one TarlinaSandstone sample indicates that a higher injection pressureis required for the same saturation. Calculations fromcapillary pressure data (assuming a 100 000 ppm brine)indicate that, for the Murnaroo Formation, a 120 m verticalheight above an oil–water contact yields an irreducible watersaturation (Swirr) of 22%. In contrast, the Tarlina Sandstonewould yield an Swirr of 43% under similar conditions. This

result is consistent with the low permeability measurementsfor the Tarlina (Fig. 10.3).

Seal

On the Murnaroo Platform and in the Marla OverthrustZone, the Murnaroo Formation is sealed by the Dey DeyMudstone. Thickness of the Dey Dey Mudstone ranges from86 m to possibly 900 m, in the Munyarai Trough. In theManya Trough, seals are absent, resulting in stackedreservoirs, with the Cambrian Relief Sandstone overlying theMurnaroo Formation.

Relief Sandstone

Distribution

The Relief Sandstone has been intersected on theMurnaroo Platform and in the Manya Trough (thickness~100 m). It is overlain conformably by, and intertongueswith, the Ouldburra Formation (transitional, with haliteinterbeds), and is overlain conformably to disconformably bythe Observatory Hill Formation. In Manya 5, however, theRelief Sandstone is overlain by the Ordovician MountChandler Sandstone due to Delamerian erosion.

Petrophysics

Porosity is secondary; Gaughan and Warren (1990) citedone sample from Observatory Hill 1 with a permeability of4839 md. Gravestock and Sansome (1994) reported a samplefrom Giles 1 with a permeability of 8033 md. Five samplesfrom Giles 1 (40 m interval) exceed 1400 md and fivesamples from Meramangye 1 (17 m interval) are in the2607–6297 md range. In contrast, the Relief Sandstone inManya 6 rarely exceeds 0.08 md (Gravestock and Sansome,1994).

The porosity histogram shown on Figure 10.9 (three wellsfrom the Marla Overthrust Zone and Manya Trough, n =19;two wells from the Murnaroo Platform, n =25) clearlyillustrates the bimodal porosity distribution pointed out byGaughan and Warren (1990). The porosity–log permeabilityplot illustrates the marked difference between the two regions(Fig. 10.10). Two trends are evident — one related to highsecondary porosity and low compaction in the MarlaOverthrust Zone and Manya Trough, the other related to lowsecondary porosity and high compaction on the Murnaroo

Fig. 10.8 Vshale versus Gamma Ray for Giles 1, Murnaroo Forma-tion.

Fig. 10.7 Porosity histogram of pore distribution, Murnaroo For-mation.

Fig. 10.6 Porosity–log permeability plot, Murnaroo Formation;Murnaroo Platform depth range 593–1985 m; Manya Trough depthrange 458–686 m.

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Platform and related to Carboniferous depth of burial(Gravestock and Sansome, 1994).

The Gamma Ray (Giles 1) ranges from 20 to 80 API withscattered higher readings to 200 API. Vshale remains generallybetween 10 and 30% (Fig. 10.11). Vshale from neutron logsrun in Marla, Manya and Byilkaoora wells are unreliablebecause of uncalibrated substandard readings. Core to logcorrelation is poor (Fig. 10.12).

The Relief Sandstone reservoir quality is superb on theMurnaroo Platform due to high dissolution and lowcompaction effects. Porosity in the Marla Overthrust Zone

and Manya Trough should not be written off as it is only poorin deeply buried footwall situations. In hanging wallstructures, porosity reaches 13% and permeability reaches124 md. In Manya 5 (Manya Trough), porosity reaches10.9% with a permeability of 0.44 md. Commercialreservoirs may be found in all areas (Gravestock andSansome, 1994).

Seal

The Ouldburra and Observatory Hill Formations may actas seals for the Relief Sandstone. The Relief Sandstoneintertongues with the Ouldburra Formation, possibly due torelative sea-level changes. At low relative sea level, theRelief Sandstone progressed basinwards over the Ouldburra

Fig. 10.9 Porosity histogram of pore distribution, Relief Sandstone.

Fig. 10.11 Vshale versus Gamma Ray for Giles 1, Relief Sandstone.

Fig. 10.10 Porosity–log permeability plot, Relief Sandstone; Mur-naroo Platform depth range 304–447 m; Marla Overthrust Zoneand Manya Trough depth range 405–1755 m.

Relief Sandstone at 416 m in Emu 1. (Photo 44384)

Fig. 10.12 Core porosity versus porosity calculated from the densitylog, Relief Sandstone.

Relief Sandstone at 178.9 m in Observatory Hill 1. Porosity, col-oured blue, is ~20%. Plane polarised light; field of view is 6.8 mm.(Photo 44385)

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Formation, while high relative sea level led to flooding of thehinterland, causing carbonate buildup (OuldburraFormation) thus forming a seal to the Relief Sandstone(Gravestock and Hibburt, 1991). In the Marla OverthrustZone, the Cadney Park Member of the Observatory HillFormation might provide a seal to the Relief Sandstone.

Ouldburra Formation

Distribution

The Ouldburra Formation has been intersected in theMarla Overthrust Zone and Manya and Tallaringa Troughs.The maximum thickness is in the Manya Trough (987 m inManya 6). However, the Ouldburra is absent on the easternmargin of the Manya Trough in Manya 5. The maximumthickness in the Tallaringa Trough is 486 m in Wilkinson 1.Magnetic data suggest that the formation in the TallaringaTrough thickens towards the Karari Fault, which isinterpreted as a reverse or thrust fault (Milton, 1974).

The Ouldburra is predominantly carbonate but it doescontain sandstone reservoir potential. As an example, inManya 3 (Middle Bore Ridge) there are 30 stacked sands(Dunster, 1987a) with an average thickness of 3.8 mcomprising 100 m of sandstone in 639 m of section (16%).The average separation between the stacked sands is 17.8 m(Gravestock and Hibburt, 1991).

The Ouldburra Formation is overlain conformably by theObservatory Hill Formation. It overlies and intertongueswith the Relief Sandstone (Gravestock and Hibburt, 1991).In Wilkinson 1, the Ouldburra is underlain by ReliefSandstone and unconformably overlain by Permian StuartRange Formation. Hence, the true thickness of the Ouldburrais unknown in the Tallaringa Trough.

Petrophysics

Reservoir quality in the Ouldburra Formation is variablewith porosity ranging from 3 to 27% and permeabilityranging from 0.005 to 1640 md. Dolomitisation has resultedin substantial secondary porosity in the carbonates (Kamaliet al., 1995). Carbonate reservoir porosity averages 15.0%while the clastic reservoirs average 13.8%. The porosity–logpermeability plot has a poor correlation, with significantscatter for carbonate reservoirs, whilst the sandstones are ingood agreement and plot on a semi-log trend with minorscatter (Fig. 10.13). In this respect, the intra-Ouldburrasandstones behave like other siliciclastic reservoirs in theOfficer Basin. Kamali (1995b) identified that the bettercarbonate reservoirs are composed of sucrosic dolomite withintercrystalline porosity. Subaerial exposure in the earlystages of diagenesis of the carbonates has largely contributedto the Ouldburra’s good reservoir quality. The extent anddistribution of these higher quality carbonate reservoirs is yetto be determined.

While no samples have been taken from Wilkinson 1, a3 m sandstone described as very porous and vuggy wasintersected at a depth of 460 m. Another ~1 m thicksandstone with a visual porosity of 10% was intersected at704 m. The carbonates have been described as mainlymicritic and have no visible porosity (Gatehouse, 1979).

Seal

Halite is an effective stratigraphic seal across theOuldburra–Relief interface, while intraformational seals areprovided by micritic carbonates. In Manya 3, for example,these carbonates average 17.8 m in thickness, while thethinnest carbonate beds are 1 m thick. Locally, thin brecciabeds may lower the seal efficiency of some carbonates butare not considered a major risk.

Arcoeillinna Sandstone

Distribution

The Arcoeillinna Sandstone is a southwest-thickeningunit (60–172 m) which extends through the Manya andMunyarai Troughs. It reaches a maximum thickness inMunta 1 on the Murnaroo Platform. The ArcoeillinnaSandstone occurs between the Observatory Hill Formation(source rock) and the dolomitic mudstone seal of theApamurra Formation.

Petrophysics

As with the older Relief Sandstone, the porositydistribution between the Marla Overthrust Zone–ManyaTrough areas and the Murnaroo Platform is bimodal, the latterhaving a very high average porosity value of 21%. However,the Arcoeillinna in the Marla Overthrust Zone and ManyaTrough has quite high porosity values averaging 13.7% andranging up to 19% (Fig. 10.14).

Fig. 10.13 Porosity–log permeability plot, Ouldburra Formation;Marla Overthrust Zone and Manya Trough depth range 187–1471 m (raw data from Kamali, 1995b).

Fig. 10.14 Porosity histogram of pore distribution, ArcoeillinnaSandstone.

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The porosity–log permeability plot (Fig. 10.15) isremarkably linear, with Marla Overthrust Zone and ManyaTrough permeability values ranging between 0.1 and 50 md,and Murnaroo Platform permeabilities averaging 291 mdwith a maximum exceeding 1700 md.

Gamma Ray and Vshale values are very high (Fig. 10.16)but two fields can be distinguished on the porosity–logpermeability plot. One, which comprises mostly sandstone(with muddy laminae), has a ‘low’ Gamma Ray and very highVshale. Abundant mica may be responsible. The other, whichcomprises mostly mudstone, has a very high Gamma Ray andlow to moderate Vshale. These observations must be takenwith caution because of the poor quality logging in the basin.Because of its abundant thin muddy interbeds, theArcoeillinna Sandstone is not a high quality reservoir butcould be considered a potential secondary target.

The formation is a fine to medium-grained, immaturemicaceous arkose with numerous muddy laminae andmudstone interbeds. Benbow (1982) provided the followingsandstone composition: quartz (50%), K-feldspar (35%),minor plagioclase, lithic grains (10%), and muscovite andbiotite (5%). His interbedded siltstone and claystonecomposition is: quartz and feldspar (35%), muscovite andbiotite (35%), and chlorite (30%). This heterogeneouscomposition is confirmed by XRD data (Gravestock andSansome, 1994).

Seal

The widespread, seismically mappable ApamurraFormation (Benbow, 1982; Stainton et al., 1988) is a potentialregional seal above the Arcoeillinna Sandstone or olderreservoirs.

Trainor Hill Sandstone

Distribution

The Trainor Hill Sandstone was originally widespread butwas thinned and locally removed in the Marla OverthrustZone by Delamerian erosion. Maximum thickness inMarla 10 is 316 m but exceeds 440 m on the MurnarooPlatform, reaching a maximum preserved thickness of 520 min Lairu 1. Where preservation is more complete it thus rivalsthe Murnaroo Formation in thickness.

Petrophysics

Like the preceding Arcoeillinna and Relief Sandstones,porosity distribution of the Trainor Hill is bimodal(Fig. 10.17). Mean porosity values are very good — 15% inthe Marla Overthrust Zone and Manya Trough and 22% inthe Murnaroo Platform. Permeability values on theporosity–log permeability plot (Fig. 10.18) are high, usuallytens to hundreds of millidarcies in the Marla Overthrust Zoneand up to 5249 md on the Murnaroo Platform (Ungoolya 1,depth 667 m). Core-log porosity correlation (calcite matrixdensity) is good (Fig. 10.19). Gamma Ray values reach 300

Fig. 10.15 Porosity–log permeability plot, Arcoeillinna Sandstone;Murnaroo Platform depth range 959–1200 m; Marla OverthrustZone depth range 106–566 m.

Fig. 10.16 Vshale versus Gamma Ray for Marla 4, ArcoeillinnaSandstone.

Fig. 10.17 Porosity histogram of pore distribution, Trainor HillSandstone.

Fig. 10.18 Porosity–log permeability plot, Trainor Hill Sandstone;Murnaroo Platform depth range 472–907 m; Marla OverthrustZone depth range 105–459 m.

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API and Vshale is predominantly in the range 5 to 80%. Values>100% on Figure 10.20 are spurious and related to acorrection factor for poor logs.

Upper levels of the Trainor Hill Sandstone in outcrop arecalcareous and dolomitic, but the abundant kaolin reportedfrom outcrops (Benbow, 1982) is not matched by the XRDdata from cores (Gravestock and Sansome, 1994). Thenear-surface kaolin results from a Tertiary weathering eventwhich affected sandstones as young as Jurassic (AlgebuckinaSandstone) and is evident in most of the upholes drilled forvelocity data in the region. Feldspar content is usually lowbut in outcrop it ranges up to 35%; biotite is lacking incontrast to the Arcoeillinna (Benbow, 1982).

Seal

The Trainor Hill Sandstone is usually overlaindisconformably by the Ordovician Mount ChandlerSandstone. The Delamerian unconformity at the top of theTrainor Hill Sandstone is a moderate reflector but due tomuting and near-surface noise, coupled with the weight-droptechnique, picking the reflector in the basin is quite difficult(Mackie, 1994; Rudd, 1995). The overlying Mount ChandlerFormation is sandy and does not provide a stratigraphic seal.However, in Devonian thrust zones, there is a good chanceof fault seal and of juxtaposition against potential Cambriansource rocks. In this scenario, the Trainor Hill Sandstonewould be in the footwall and sealed by rocks in the hangingwall.

Mount Chandler Sandstone

Distribution

This Ordovician sandstone is widespread and oncethickened northwards over the Musgrave Block before beingeroded during the Alice Springs Orogeny. Maximum drilledthickness ranges from 212 m in the Marla Overthrust Zone(Byilkaoora 2) to 472 m on the Murnaroo Platform(Karlaya 1) but may be >600 m thick in outcrop (Benbow,1982).

Petrophysics

There are too few samples from the Murnaroo Platformto compare porosity distribution but the porosity–logpermeability plot (Fig. 10.21) indicates consistently highporosity (up to 25.4%) and permeability (up to 238 md). Logporosity data agree well with core data (Sansome andGravestock, 1993) using a quartz matrix density of2.65 g/cm3 (not calcite — this was an error in the aboveabstract). Gamma Ray and Vshale values are correspondinglylow.

Seal

The Mount Chandler Sandstone is locally sealed in thenorthern Munyarai Trough–Mount Johns region by theIndulkana Shale. The shale reaches a thickness of 60 m inthe Indulkana Range (Krieg, 1973) and may be quitewidespread east of the Marla Overthrust Zone based onaeromagnetic evidence (Hamer, 1994). However, in theMarla Overthrust Zone, the sandstone requires hanging wallfault structures for seal. The Mount Chandler andstratigraphically younger Blue Hills Sandstone (not studied)also run the risk of being breached by Permian erosion.Despite its excellent reservoir qualities, the Mount ChandlerSandstone is thus unlikely to be a major target for petroleum.

Fig. 10.19 Core porosity versus porosity calculated from the densitylog, Trainor Hill Sandstone.

Fig. 10.20 Vshale versus gamma ray for Lairu 1, Trainor HillSandstone.

Fig. 10.21 Porosity–log permeability plot, Mount Chandler Sand-stone; Murnaroo Platform depth range 323–400 m; Marla Over-thrust Zone and Manya Trough depth range 63–192 m.

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128

INTRODUCTION

An understanding of the range of structural styles andtheir causes increases with the density of seismic and drillingdata. In the 100 000 km2 Officer Basin in South Australia,~6250 km of seismic have been recorded and 40 wells drilleddeeper than 400 m. Understandably there have been as manystructural interpretations as interpreters, with models rangingfrom extensional to compressional.

A compressional style is now clearly evident and isparticularly well expressed on the 1993 seismic surveys

conducted by MESA and AGSO (Mackie, 1994; Gravestockand Lindsay, 1994; Lindsay, 1995; Lindsay and Leven, 1996;Hoskins and Lemon, 1995). Seismic recorded on thesoutheastern flank of the Munyarai Trough has also revealedstructures associated with salt movement (Badley, 1988;Stainton et al., 1988; Thomas, 1990) and palaeoreliefsassociated with a canyon-cutting event (Thomas, 1990;Sukanta et al., 1991). Seismic surveys are listed inTable 11.1, and seismic line coverage of the basin is shownon Figure 1.2 (Ch. 1).

Table 11.1 Eastern Officer Basin seismic surveys.

Survey Survey name Operator Contractor Year Line coverage MESA referencecode (km) *refraction

53OF01 1953 atomic test deep British Atomic Weapons BMR 1953 — BMR Record 1954/64refraction survey Research Establishment

62OF01 Mabel Creek area Exoil Pty Ltd Namco International Inc. 1962 137, 27* Env. 224, 225 seismic survey (1, A–C), 214

66OF01 Serpentine Lakes Continental Oil Co. Seismograph Services Ltd 1966 944 Env. 501 (1–22), reconnaissance (Aust.) Ltd 603 (1–2)seismic survey

66OF02 1966 Eastern Officer Continental Oil Co. SADME 1966 106, 58* Env. 697, 692; Basin seismic reflection, (Aust.) Ltd Report 64/27refraction and gravity survey

67OF01 Eastern Officer Basin Continental Oil Co. Namco Geophysical Co. 1967 169 Env. 747, 795, 829seismic and gravity (Aust.) Ltdsurvey

74OF01 Northern margin of the SADME SADME 1974 475 Report 73/31, 73/181eastern Officer Basin 86*and Wintinna Trough seismic survey

74OF02 Everard seismic survey Shell Development (Aust.) GES Pty Ltd 1974 168 Env. 2509 (1–3)

78OF01 OF78 seismic survey SADME SADME 1978 94 —

80OF01 Mini-sosie seismic Comalco Aluminium Ltd Velocity Data Pty Ltd 1980 53 Env. 6259 (19–20)reflection survey in EL 699 (Manya)

83OF01 1983 PEL 23 seismic Comalco Aluminium Ltd Petty Ray Geophysical 1983 257 Env. 5805 (1–3, 5–6)survey (Marla)

83OF02 Marla seismic survey Comalco Aluminium Ltd Geosystems Pty Ltd 1983 36 Env. 5805 (1–3)1983 PEL 23

84OF01 1984 seismic survey Comalco Aluminium Ltd Petty Ray Geophysical 1984 1278 Env. 5923, 6165PEL 23

85OF01 1985 seismic survey Comalco Aluminium Ltd Petty Ray Geophysical 1985 706 Env. 6993PEL 23, 30

86OF01 Comalco 1986 seismic Comalco Aluminium Ltd Petty Ray Geophysical 1986 496 Env. 6902survey

87OF01 1987 Amoco Officer Amoco Australia Petty Ray Geophysical 1987 235 Env. 6766Basin seismic survey Petroleum Co.

AGS93 NGMA transect AGSO AGSO 1993 550 Lindsay (1995)

OF93 Wallatinna seismic MESA Geosystems 1993 379 Env. 8812survey

Total coverage 6252 km

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PREVIOUS UNSUCCESSFUL TESTS

Despite identification of an array of trap types andmultiple sandstone reservoirs under seal, there have been fewon-structure tests of effectively trapped sands. Table 11.2lists the six key wildcat wells and five sealed sandstonereservoirs (Birksgate 1 is omitted due to its remoteness). Notone well in Table 11.1 is from the Marla Overthrust Zonewhich remains untested despite oil bleeds in nine mineralexploration drillholes (Fig. 11.8). This area is now underlicence.

Each of the six wells listed in Table 11.1 had four chancesof hitting a sealed reservoir, totalling 24 chances. The ReliefSandstone is not included because it is present only in Giles1 and was not drilled in closure according to Mackie’s (1994)interpretation. Of the 24 chances, 14 missed the opportunityto reach the target. There were only five intersections of asandstone reservoir under seal, and four of these comprise theArcoeillinna Sandstone. Each of the five intersections isdiscussed below.

Arcoeillinna Sandstone in Munyarai 1

In Munyarai 1, the Arcoeillinna Sandstone wasintersected at a depth of 1484 m (4869 ft KB) beneath theApamurra Formation which forms the seal. The Apamurrais represented by core 7 (2.8 m recovery), a brick-redmudrock with granules of quartz, feldspar and heavyminerals in bands or floating in a dolomitic matrix. From thisdescription the Apamurra Formation is probably an effectiveseal. The lack of hydrocarbon shows suggests that theArcoeillinna was isolated from Cambrian and Proterozoichydrocarbon migration pathways. The only oil showrecorded in Munyarai 1 was trace yellow and rare bluefluorescence in the Karlaya Limestone.

Arcoeillinna Sandstone in Ungoolya 1

In Ungoolya 1, the Arcoeillinna Sandstone wasintersected at 956 m depth beneath 39 m of ApamurraFormation. The latter is described as a red-brown, slightly

dolomitic siltstone with disturbed anhydrite laminae andabundant dewatering structures. The common dewateringstructures suggest an ineffective seal despite the presence ofanhydrite. Minor gas shows recorded in the Apamurra andnear the base of the overlying Trainor Hill support the lackof seal rather than unfavourable location with respect tomigrating hydrocarbons as the well was in closure at theApamurra level (Henry, 1986). However, Mackie’s (1994)mapping suggests that the structure may have been breachedby faulting.

Arcoeillinna Sandstone in Karlaya 1

The Arcoeillinna Sandstone in Karlaya 1 was intersectedat a depth of 1037 m beneath 78 m of Apamurra Formation(Fig. 6.22). The Apamurra is described as red-brownsiltstone, sandy near the top, with 0.15 m of dolomite nearthe base (Dunster, 1987b). Recent seismic mapping (Mackie,1994) suggests that Karlaya 1 was off-structure at this level.No Cambrian shows were recorded in Karlaya 1; the highestrecorded show (1430 m) was from the Narana Formation.

Arcoeillinna Sandstone in Lairu 1

The Arcoeillinna Sandstone in Lairu 1 was intersected at1091 m beneath 36 m of Apamurra Formation, the latterlithologically similar to the Karlaya 1 occurrence. The wellwas deliberately sited off-structure (Dunster, 1987c: Staintonet al., 1988) and no significant shows were recorded.

Murnaroo sandstone in Munta 1

Sandstone of the Murnaroo Formation was intersected ata depth of 1973 m beneath nearly 300 m of Dey DeyMudstone. The basal 50 m of the latter unit are composed ofslightly calcareous and dolomitic siltstone grading toclaystone, which suggests that the Dey Dey is an effectiveseal. Traces of gas were recorded in the Tanana Formationand Karlaya Limestone but not in the Murnaroo. Althoughthe well was sited ‘to test structural closure in theMurnaroo–Giles–Tarlina package’ (Cucuzza, 1987), detailedmapping (Thomas, 1990) suggests that salt withdrawal has

Table 11.2 Opportunities to test sandstone reservoirs and reasons for failure. Mount Chandler, Blue Hills and Trainor Hill Sandstones areomitted due to lack of seal or erosion. Numbers 1 to 5 refer to sandstones intersected under seal.

Well Reservoir sandstoneYear drilledTrap Pindyin Tarlina Murnaroo Relief Arcoeillinna

Munyarai 1 Not reached Not reached Not reached Not present 11968Anticline

Giles No closure No closure No closure No closure At surface1985Anticline

Ungoolya 1 Not reached Not reached Not reached Not present 21985Anticline

Karlaya 1 Not reached Not reached Not reached Not present 31987Faulted anticline

Lairu 1 Not reached Not reached Not reached Not present 41987Anticlinal flank

Munta 1 Not reached Not reached 5 Not reached No closure1987Sub-unconformity tilted fault block

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deformed the Murnaroo and underlying formations into aseries of tilted fault blocks and, as a result, Munta 1 isoff-structure at this level (Fig. 11.5). Mackie (1994) alsomapped this location outside closure (Fig. 11.3).

POTENTIAL TRAP TYPES

A great variety of structural traps exists in the OfficerBasin, most of which have been identified but not drilled.They include:

• foreland basement thrusts (Steenland, 1965)

• detached thrusts with hanging wall and footwallrollovers (Stainton et al., 1988)

• simple anticlines with at least two generations offolding (Petermann Ranges and Alice SpringsOrogenies; Stainton et al., 1988)

• tilted fault blocks associated with salt withdrawal(Badley, 1988; Stainton et al., 1988; Thomas, 1990)

• salt walls and diapirs (Badley, 1988; Thomas, 1990)

• palaeoreliefs (‘buried hills’) which originated with thecanyon-cutting event (Stainton et al., 1988; Thomas,1990). Subcrop unconformities also have astratigraphic component.

Purely stratigraphic traps, for example porous sandstoneor dolomite beds sealed within the Ouldburra Formation(Dunster, 1987a; Gravestock and Hibburt, 1991; Kamali,1995b) or vuggy Moyles Chert Marker Bed in theObservatory Hill Formation, also have hydrocarbonpotential.

POTENTIAL TRAP VOLUMES

Many potential leads and prospects were identified byseismic mapping in the Munta and Marla areas by Thomas(1990) and Mackie (1994). Some additions and/ormodifications were made in the Marla area — Figures 11.1and 11.2 illustrate all closures mapped at the base Cambrianand top basement horizons. Four prospects were selected toillustrate the potential volumes of oil that the various typesof Officer Basin traps could contain. Average porosities,water saturations, net to gross ratios and formation volumefactors used to calculate these estimates are the averagevalues used for the various plays summarised in Chapter 13(‘Undiscovered resources’). All potential reserve estimatesare unrisked to maximum closure and are of oil in place.Source richness and maturity will determine the extent towhich these structures are filled; this is likely to beconsiderably less than 100%, given the large trap sizes.

Prospect A

Prospect A (Fig. 11.3) was identified by Mackie (1994)in the vicinity of Munta 1. The trap is a probable salt wallpiercement structure with reservoir horizons abutting thesides of the salt wall (Fig. 11.4). The Relief Sandstone andOuldburra Formation were not deposited in this area,although potential may exist in the Arcoeillinna Sandstone.Seismic quality is not good, but Munta 1 appears to have beendrilled outside closure and did not penetrate the two lower

reservoir horizons (Tarlina and Pindyin Sandstones). Intensefaulting is probable at the Tarlina and Murnaroo horizons dueto the salt flowage (Fig. 11.5). The structure map on Figure11.3 shows an area of closure of 65 km2 (16 000 acres) and amaximum vertical closure of 69 m (226 feet). The unriskedpotential oil in place of the structure in the Pindyin Sandstoneis ~67 million kilolitres (420 million barrels), and similarpotential would also exist in the Arcoeillinna Sandstone,Murnaroo Formation and Tarlina Sandstone.

Prospect B

Prospect B (Fig. 11.6) is a combination stratigraphic andstructural trap. It comprises a subcrop pinchout on acompressive fault-bounded anticline (Fig. 11.7). Seismicquality is reasonable, but there is insufficient seismiccoverage to the north to prove closure. The ArcoeillinnaSandstone is not likely to be sealed at this location. Thestructure map on Figure 11.6a shows an area of closure for atrap in the Cambrian (Ouldburra Formation or ReliefSandstone ) of 54 km2 (13 350 acres) and a maximum verticalclosure of 48 m (157 feet). The unrisked potential oil in placeof the structure in the Relief Sandstone is ~45 millionkilolitres (290 million barrels), but with the possibility ofstacked sand reservoirs, the potential for the Ouldburra isover 1 billion barrels (165 million kilolitres). The structuremap on Figure 11.6b shows an area of closure for a trap nearbasement (Pindyin Sandstone) of 130 km2 (32 000 acres) anda maximum vertical closure of 103 m (338 feet). Theunrisked potential oil in place of the structure in the PindyinSandstone is ~120 million kilolitres (750 million barrels).Significant potential would also exist in the TarlinaSandstone as an unconformity play beneath the erosionalbase of the Narana Formation, but this has not been estimated.

Prospect C

Prospect C (Fig. 11.8) is a probable detached fold-thrusttrap (Fig. 11.9). Seismic quality is poor but there isreasonable seismic coverage. Ten wells have been drilled inthe vicinity of the prospect, most of which had numerous oilshows in the Observatory Hill Formation and, in the case ofMarla 9, in the Tanana Formation and Dey Dey Mudstone(Hibburt et al., 1995). Most of these wells did not reach theOuldburra Formation and Relief Sandstone, with theexception of Marla 3 which may have been drilled close tothe closure for the prospect, but considerable up-dip potentialexists. The Proterozoic sequence has been interpreted to bethin or absent (Mackie, 1994), but the section intersected inMarla 9 to the west of the prospect suggests that at least theMurnaroo target may be present. The main Cambrian targethorizons are the Arcoeillinna Sandstone, OuldburraFormation and Relief Sandstone. The structure map onFigure 11.8 shows an area of closure for a trap in theCambrian of 146 km2 (38 550 acres) and a maximum verticalclosure of 241 m (790 feet). The unrisked potential oil inplace of the structure in the Relief Sandstone up dip fromMarla 3 is ~900 million kilolitres (5.7 billion barrels).

Prospect D

Prospect D (Fig. 11.10) is a foreland basement upthrusttrap (Fig. 11.11). Seismic quality is reasonable but further

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Fig. 11.1 Cambrian (Arcoeillinna Sandstone, Ouldburra Formation, Relief Sandstone) prospects and leads (after Mackie, 1994; base Cambrian time horizon). Contour interval 50 ms.

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Fig. 11.2 Proterozoic (Pindyin and Tarlina Sandstones, Murnaroo Formation) prospects and leads (after Mackie, 1994; crystalline basement time horizon). Contour interval 100 ms.

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seismic coverage is required in the southern area. Manya 2and 3 were drilled just outside closure. Middle Bore 1 waspossibly drilled on closure just to the north of Prospect D.None of these wells reached the Relief Sandstone and inMiddle Bore 1 it was faulted out. The main Cambrian targethorizons are the Arcoeillinna Sandstone, OuldburraFormation and Relief Sandstone. Potential also exists inProterozoic reservoirs, although these and some of the otherCambrian targets may not be present due to faulting. Thestructure map on Figure 11.10 shows an area of closure for atrap in the Cambrian of 299 km2 (73 900 acres) and amaximum vertical closure of 207 m (680 feet). The unriskedpotential oil in place of the structure in the Relief Sandstoneis ~2200 million kilolitres (13.7 billion barrels).

Fig. 11.4 Seismic line 86-106 through Prospect A, showing probable abutment of reservoirs against a salt pillar.

Fig. 11.3 Time structure map, crystalline basement, Prospect A(after Mackie, 1994). Contour interval 100 ms.

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0 5

KILOMETRES97-0205 MESA

97-0255 MESAKILOMETRES

20

SALT

INTRA UNGOOLYA GPUNCONFORMITY

BASE TARLINAUNCONFORMITY

BASEMENT

BASE CAMBRIAN

Fig. 11.5 Time structure map, top Murnaroo Formation, ProspectA (after Thomas, 1990). Contour interval 20 ms.

Fig. 11.6 (a) Time structure map, base Cambrian, Prospect B.Contour interval 50 ms. (b) Time structure map, crystalline base-ment, Prospect B. Contour interval 100 ms. (after Mackie, 1994).

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Fig. 11.7 Seismic line 86-0044 through Prospect B.

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97-0253 MESAKILOMETRES

20

BASE CAMBRIAN

INTRA UNGOOLYA GPUNCONFORMITY

BASE TARLINAUNCONFORMITY

BASEMENT

Fig. 11.8 Time structure map, base Cambrian, Prospect C (light shading; after Mackie, 1994); additional closures are shaded darker.

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Fig. 11.9 Seismic line 85-0096 through Prospect C.

138

97-0254 MESA

BASE CAMBRIAN

BASEMENT

BASEMENT

BASE PERMIAN

BASE

FMCADNEY PARK

CAMBRIANBASE

KILOMETRES

20

Fig. 11.10 Time structure map, base Cambrian, Prospect D (lightshading; after Mackie, 1994); additional closures are shaded indarker.

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Fig. 11.11 (a) Seismic line 84-0060 through the northern part of Prospect D. (b) Seismic line 85-0080 through the southern part of ProspectD.

140

97-0257 MESA

BASEMENT

BASE CA MBRIAN

KILOMETRES

20

97-0256 MESA

BASEMENT

CAMBRIAN

BASE

KILOMETRES

20

INTRODUCTION

MESA has developed an economic model for oilexploration and development in the Marla region as a guideto potential explorers in the Officer Basin region. Althoughthe Officer Basin has gas potential, gas discovery economicshave not yet been modelled as development is dependent onfuture links between gas reserves in the northwest ofAustralia and markets on the eastern seaboard (Fig. 4.1). Ifsufficient reserves are discovered, a pipeline to either theAdelaide or eastern Australian markets (via Moomba) maybe economic.

Development of oil reserves is generally less capitalintensive than gas. Two scenarios were examined:

• The ≤30 mmbbl OOIP (original oil in place) case, inwhich oil is trucked from Marla and the infrastructurerequired is a trunkline from the field to the StuartHighway, storage tank, yard, office and workshop atMarla, basic surface facilities and truck loadingfacilities.

• The 100–200 mmbbl OOIP case, in which oil is pipedto Port Bonython and the infrastructure required is thesame apart from a larger storage tank and trunkline.

In both cases, a single oil pool in a single field has beenmodelled on a stand-alone basis — it is likely that more thanone oil pool and field would be discovered.

Marla has diesel generated power, water andcommunication infrastructure available, and the fully sealedStuart Highway runs through the area. It is currentlyuneconomic for oil from a new discovery in Central Australiato be transported via rail to Adelaide even though the railwayruns through the region. Trucking oil to the Port Stanvacrefinery near Adelaide using two or three tank road trains isthe alternative. Privatisation of the rail freight network mayimprove rail transport economics in the future.

METHODOLOGY

Two Microsoft Excel spreadsheets were used to developthe economic model. The first spread sheet modelled oilproduction for a range of field sizes and permeabilitythickness kh (which determines the flow capacity of a well;in millidarcy feet (md.ft)), and results were placed into theeconomic model adapted from the Cooper Basin gas model(McDonough, 1996, in press). Reservoir properties werebased on the early Palaeozoic P3 Pacoota Sandstone reservoirin the Mereenie Oilfield as this information is very limited inthe Officer Basin. It is likely that the Mereenie case is more

conservative and that Officer Basin reservoirs may havebetter reservoir characteristics.

The second spreadsheet determines the net present valueof the project by calculating exploration, capital andoperational costs, royalty and revenue for a range of fieldsizes, enabling minimum economic field size in the region tobe determined. A high oil price of US$25/bbl and a low oilprice of US$18/bbl were used. This covers variations in oilprice forecasts for 1997, which range from US$19 toUS$25/bbl (Bell, 1997). Appendix 12.1 is a summary ofinformation used in the model. Other sources of informationused were GPA Engineering Pty Ltd (GPA, 1996) and Bureauof Resource Sciences (BRS, 1996).

EXPLORATION SUCCESS RATIOS

The Australian historical base case success ratio for awildcat well to discover an economic field is ~1:12.5; thesuccess ratio over the period 1978–87 was 1:8.3, reflectingmodern techniques and knowledge (MacKenzie and Cai,1993). A total of eight petroleum exploration wells have beendrilled in the entire Officer Basin, but none of these are in theMarla area.

In the economic model, oil is discovered by the fifthexploration well of the hypothetical drilling program, or thethirteenth petroleum exploration well in the Officer Basin, a1:13 success ratio — comparable to the historical Australiancase and more conservative than the modern Australian case.A pessimistic case where oil is discovered in the eighthexploration well was examined as part of the case studybelow.

EXPLORATION AND DEVELOPMENT

SCENARIOS

An exploration program, based on the combined programfor PEL 61 and 63, was used up to the discovery of a singleoil field in Year 3. The development program was thenapplied and run until either production ceased due todepletion or until one PPL term (21 years) had elapsed. Asingle Murnaroo Formation oil pool was modelled but thereis a good possibility of multiple stacked hydrocarbon poolsin the Officer Basin. In the Marla area, stacked pools in theArcoeillinna, intra-Ouldburra, Relief and Murnaroo arepossible. In the Munta area, stacked pools in theArcoeillinna, Relief, Murnaroo, Tarlina and Pindyin arepossible. It is also likely that more than one field would bediscovered in a particular area (Mackie, 1994). Table 12.1shows the field sizes that were modelled using US$18/bbl

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Table 12.1 Field sizes used for the economic model, in imperial andmetric units.

Field size Field size(million barrels) (kilolitres)

CASE 1 (<30 million barrels)

5 794 94010 1 589 87515 2 384 81020 3 179 75030 4 769 630

CASE 2 (>30 million barrels)

50 7 949 380100 15 898 760200 31 797 510

and US$25/bbl for the oil price and for a range of reservoirproperties.

Case 1 was used to determine the minimum economicfield size; Case 2 was used to determine a conservative upsidepotential. Much larger field sizes are possible in the OfficerBasin (see Ch. 11). Facilities required for Case 1 and 2 areshown on Figure 12.1.

Case 1

The first exploration and development scenario, for fields≤30 mmbbl OOIP, was as follows:

Year 0

Apply for PEL, negotiate access agreement with AnanguPitjantjatjara.

Year 1 — exploration

Construct access roads and, using existing seismic grid,drill two exploration wells.

Year 2 — exploration

Construct access road and drill one exploration well;acquire and interpret 320 km of seismic.

Year 3 — exploration and discovery of oil

Construct access road and drill two exploration wells;acquire and interpret 250 km of seismic. The secondexploration well discovers oil and is completed. Apply for aPPL, and initially limit oil production to 330 bopd

(52 m3/day); commence trucking oil to Port Stanvac nearAdelaide. Pay petroleum royalty.

Year 4 — development

Conduct geological and geophysical data review,estimate oil reserves, and plan development drilling. A totalof five wells will be used to produce from the field. Thedevelopment drilling program is determined from theproduction profiles. The maximum field production rate isset at 1000 bopd (158.9 m3/day), with a limit of five wells;higher volumes of oil could not be handled by trucking toAdelaide (Appendix 12.1).

For the purpose of modelling flowlines, the field isassumed to be circular (radius = 5 km; area = 75 km2); thediscovery well is assumed to be near the field centre anddevelopment wells are sited halfway between the edge andcentre of the field. As the reservoir is assumed to be a solutiongas drive, it is assumed that there will be no water productionand therefore no associated disposal requirements. Site a10 000 bbl (1589 m3) storage tank at the field.

Year 5 onwards — development

Construct a 50 km pipeline to the Stuart Highway,establish a truck loading facility on the highway and truck oilto Adelaide. Acquire and interpret 100 km of developmentseismic. Drill development wells as required by theproduction model.

Case 2

The second exploration and development scenario, forfields in the 50–200 mmbbl OOIP range, was as follows:

Year 0

Apply for PEL, and negotiate access agreement withAnangu Pitjantjatjara.

Year 1 — exploration

Construct access roads and, using the existing seismicgrid, drill two exploration wells.

Year 2 — exploration

Construct an access road and drill one exploration well;acquire and interpret 320 km of seismic.

Year 3 — exploration and discovery of oil

Construct an access road and drill two exploration wells;acquire and interpret 250 km of seismic. The secondexploration well discovers a large oil field and is completed.Apply for a PPL; initially limit oil production to 3300 bopd(520 m3/day), and commence trucking to Port Stanvac. Sitea 100 000 bbl (15 898 m3) storage tank at the field.Commence a feasibility study and construction of a 740 kmtrunkline to Port Bonython (the Moomba–Port Bonythontrunkline was used as model; McDonough, 1996).

Year 4 — development

Conduct geological and geophysical data review,estimate oil reserves, plan development drilling with a

Fig. 12.1 Case 1 and 2 schematic of facilities.

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maximum of 10 wells and limit field production to10 000 bbl/day (1589 m3/day). Complete the construction ofa trunkline to Port Bonython. The development model is notentirely realistic as the amount of oil produced daily duringYears 3 and 4 while the trunkline is being constructed couldnot be handled by trucking alone. However, this is somewhatoffset by the capacity of the trunkline (33 000 bbl/day or5250 m3/day).

Year 5 onwards — development

Acquire, process and interpret 200 km of developmentseismic. Drill development wells as required by theproduction model.

Royalty and licence fees

Guidelines for the payment of petroleum royalty wereapplied to these scenarios. Licensees pay royalty at a rate of10% of the value of the petroleum at the wellhead minus allexpenses (capital and operating costs) actually incurred intreating, processing or refining the petroleum downstream ofthe wellhead. PEL application fees were included for the firstfive years of the model (one PEL term). PPL application,rental and renewal fees were applied from the year thatproduction commenced and continued for 21 years (one PPLterm) or until the field ceased production.

RESULTS

For each field size, the following kh values were used fora 60 m thick pay zone within the Murnaroo Formation:

• 250 md.ft — the most pessimistic case wherepermeability = 0.787 md (based on averagepermeability data for the early Palaeozoic PacootaSandstone P3 reservoir, Mereenie oil field, NorthernTerritory).

• 1000 md.ft — calculated using arithmetic averagepermeability (5.371 md) from the MurnarooFormation, Marla region (Ch. 10).

• 9200 md.ft — geometric average permeability fromthe Murnaroo Formation (46 md), Marla region (Ch.10).

• 17 700 md.ft — geometric average permeability fromthe Murnaroo Formation (86 md), Munta region (Ch.10).

20 mmbbl OOIP case study

Results for a 20 mmbbl OOIP field (kh = 9200 md.ft) aresummarised on Figure 12.2 as an example of how each OOIPand kh scenario was modelled. Oil production and the timingof development drilling was calculated for this field size andkh, and input into the economic model. Explorationexpenditure, capital expenditure (CAPEX), operatingexpenditure (OPEX), revenue and petroleum royalty weremodelled over a 20-year period and the net present value(NPV) of the project calculated at a discount rate of 12.5%.All calculations are before tax.

A breakdown of the net present value (Fig. 12.2) revealsthat OPEX is the most significant component of the NPV,profit is next, while royalty, CAPEX and exploration

expenditure are relatively minor components. A reduction inthe price of oil from US$25 to US$18/bbl results in a majorreduction of profit and hence royalty (Table 12.2).

Table 12.2 Net present value of profit and expenses for a 20 mmbblOOIP field (kh = 9200 md.ft).

Cash flow NPV($ million)

US$18/bbl US$25/bbl

Exploration 5.3 5.3CAPEX 3.5 3.5OPEX 22.2 22.2Profit before tax and royalty 5.8 18.5Royalty 1.9 3.4Revenue 21.9 7.27

A breakdown of OPEX (Fig. 12.3) indicates that transportcosts (i.e. trucking oil from Marla to Port Stanvac) are themost significant operating expense. PEL application fees andrent averaged under $5000/year and were applied over thefirst five years of the model (one PEL term). PPL application,rental and renewal fees were ~$20 000/year for case 1 and$94 000/year for case 2. Other land access costs are:

• payment of compensation of a minimum of $20 000per annum to AP when exploration is carried out and,

Fig. 12.2 Net present value analysis over the life of the project;revenue versus costs (20 mmbbl OOIP field, kh = 9200 md.ft).

Fig. 12.3 Net present value analysis of operating expenditure(20 mmbbl OOIP field, kh = 9200 md.ft).

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• payment of production royalties to AP of 1–3% on asliding scale based on the quantity of oil and gasproduced, following an economic discovery.

CAPEX has been divided into road construction andvehicles, development drilling and seismic, and surfaceequipment (trunkline, flowlines, pumps) on Figure 12.4.Surface equipment makes up nearly half of the CAPEX dueto construction costs of a trunkline from the field to the StuartHighway. Seismic and drilling costs are the other significantcomponent of CAPEX.

The net present value of the before tax cash flows for theproject is $21.9 million for an oil price of US$25/bbl,representing an internal rate of return of 44.5% (a realdiscount rate of 12.5% was used in all cases). The cashflowsover the life of the project are shown on Figure 12.5. Theimpact of exploration and capital expenditure during the firstthree years of the project are obvious. Once the pipeline iscommissioned, production generates revenue and positivecashflows commence. Operating costs total~$4.9 million/year. Wells were drilled in Years 1 (discoverywell), 2, 14 and 15 (two wells).

The discovery of oil was delayed until Year 10 for thiscase study to see what effect lack of initial explorationsuccess would have on overall project economics. A delaymeans that a more expensive exploration program is requiredand that generation of revenue from production occurs later.If the discovery of oil is delayed until Year 10 of theexploration licence after the drilling of eight explorationwells, a 20 mmbbl OOIP sized field is not economic. This

implies that a successful exploration strategy is to drill wellswithin the first five years to bring forward possiblediscoveries.

Discussion

Tables 12.3–12.6 summarise the NPVs and IRR (internalrate of return) of all scenarios modelled with a real discountrate of 12.5 %.

Table 12.3 NPV for all field sizes and kh; oil price = US$25/bbl.

Field size kh (md.ft)(million barrels) 250 1000 9200 17 700

Case 1

5 -2.1 -1.9 6.5 6.510 5.5 6.7 12.5 13.415 11.0 12.2 18.1 17.620 14.9 16.8 21.9 22.130 19.7 22.1 23.2 23.2

Case 2

50 -14.9 35.6 80.2 —100 28.3 110.4 129.2 135.4200 120 199.4 219.6 223.4

Table 12.4 NPV for all field sizes and kh (oil price = US$18/bbl).

Field size kh (md.ft)(million barrels) 250 1000 9200 17 700

Case 1

5 -7.2 -6.9 -1.6 -1.610 -3.1 -2.3 1.9 2.815 -0.2 0.6 5.1 5.220 2.2 3.4 7.3 7.630 5.1 6.9 7.6 7.6

Case 2

50 -57.5 -29.6 80.2 —100 -33.1 11.5 25.68 29.43200 14.8 60.2 74.63 76.30

Table 12.5 IRR as a percentage, for all field sizes and kh (oil price= US$25/bbl).

Field size kh (md.ft)(million barrels) 250 1000 9200 17 700

Case 1 IRR (%)

5 -1.5 -4.7 43.9 43.910 29.8 32.2 42.1 42.815 35.9 37.0 44.4 44.420 39.0 41.1 44.4 45.030 41.0 42.0 42.1 42.1

Case 2 IRR (%)

50 5.7 66.1 118.9 —100 21.91 93.67 100.46 101.42200 70.50 99.93 101.76 101.76

Table 12.6 IRR as a percentage, for all field sizes and kh (oil price= US$18/bbl).

Field size kh (md.ft)(million barrels) 250 1000 9200 17 700

Case 1 IRR (%)

5 — — 2.0 2.010 -1.6 3.5 18.4 20.315 11.9 13.9 23.5 23.720 17.0 19.8 24.9 25.530 21.0 23.1 23.4 23.4

Case 2 IRR (%)

50 — — 10.9 —100 -0.6 18.4 25.8 27.3200 16.2 31.0 33.7 33.7

Fig. 12.4 Net present value analysis of capital expenditure(20 mmbbl OOIP field, kh = 9200 md.ft).

Fig. 12.5 Net present values (before tax cash flow) for 20 mmbblOOIP field over the life of the project (kh = 9200 md.ft, US$25/bbloil price, discount rate = 12.5%).

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Minimum economic field size

NPV results for high (US$25/bbl) and low (US$18/bbl)oil prices at a real discount rate of 12.5% have been plottedfor Case 1 field sizes versus NPV for each individual kh (Figs12.6–9).

The 250 md.ft case (Fig. 12.6) represents the mostconservative scenario with the poorest reservoir quality. Theworst case minimum economic field size (note: original oilin place, not recoverable oil) ranges from 15 mmbbl forUS$18/bbl oil down to 6 mmbbl for US$25/bbl oil. Betterreservoir quality in the 1000 md.ft case means that theminimum economic field size drops slightly to 14 mmbbl forUS$18/bbl oil; there is little change in the US$25/bbl case(Fig. 12.7). The profitability increases with the improvementin reservoir quality. Increases in kh extend the number of

years that maximum production is achieved and influencesthe timing of development wells.

The 9200 and 17 700 md.ft cases show a dramaticincrease in profitability from the low end cases, and theminimum economic field size drops to 7 mmbbl forUS$18/bbl and <5 mmbbl OOIP for US$25/bbl (Figs 12.8,12.9). There is little difference between the two, as fieldproduction is limited to 1000 bbl/day (158.9 m3/day) by oiltransport constraints, and both models achieve the productionlimit for a similar period of time. The only variation betweenthe two is in the timing and number of development wells,which produces minor variations in NPV.

Further increases in kh or field size above 30 mmbblOOIP would necessitate modification of the developmentscenario as alternative oil transport scenarios would becomeeconomic and the production limit could be removed orincreased.

Upside potential

Three large field sizes (50, 100 and 200 mmbbl OOIP)were modelled as Case 2 to explore the upside economicpotential of Officer Basin oil and the feasibility of a trunklineto Port Bonython. The production limit was increased to 10000 bbl/day (15 898 m3/day) and NPV calculated for thestandard kh values used in Case 1. Figure 12.10 shows NPVsfor all scenarios modelled at an oil price of US$25/bbl. Theminimum economic field size for Case 2 (kh = 250 md.ft) is~70 mmbbl OOIP for an oil price of US$25/bbl.

Fig. 12.7 Net present value of before tax cash flows (discount rate= 12.5%) versus Case 1 field sizes for kh = 1000 md.ft.

Fig. 12.6 Net present value of before tax cash flows (discount rate= 12.5%) versus Case 1 field sizes for kh = 250 md.ft.

Fig. 12.9 Net present value of before tax cash flows (discount rate= 12.5%) versus Case 1 field sizes for kh = 17 700 md.ft.

Fig. 12.8 Net present value of before tax cash flows (discount rate= 12.5%) versus Case 1 field sizes for kh = 9200 md.ft.

Fig. 12.10 Net present value of before tax cash flows (discount rate= 12.5%) for each kh versus Case 1 and Case 2 field sizes.

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146

INTRODUCTION

Estimating undiscovered petroleum reserves of theOfficer Basin in South Australia provides some quantitativeexpression of the potential, and a basis for comparison withother basins. As the basin is clearly oil prone, onlyundiscovered oil resources are calculated; however, gasdiscoveries may also be possible although it is unlikely thatsmall gas discoveries would be economic.

As the Officer Basin has had only minimal explorationeffort, with no economic discoveries so far, estimates ofundiscovered resources are best carried out by a method thatuses available geological data and Monte Carlo typestatistical techniques to estimate, as a probabilitydistribution, the undiscovered potential for each play(Morton, 1992, 1995, 1996b). This chapter presents a revisedestimate of the undiscovered potential of the basin thatreflects new knowledge of potential reservoirs and sourcerocks acquired since 1992.

In total, the average estimate of the potential of the OfficerBasin plays in South Australia is ~400 million kilolitres(2.5 billion barrels) of recoverable oil. The increase from the1992 estimate of ~300 million kilolitres is due mainly to therecognition of additional source rocks and reservoirs,particularly two new Neoproterozoic plays (Pindyin andTarlina Sandstones), and the potential for stacked reservoirsin the Ouldburra Formation. These estimates may appear tobe large in comparison to other, geologically younger,Australian petroleum basins, but are comparable togeologically more analogous (Proterozoic–Cambrian)petroleum provinces elsewhere in the world. TheLena–Tunguska province in the Siberian Platform has apredicted potential of 318 million kilolitres (2 billion barrels)of oil and gas liquids, with 2417 billion cubic metres(85 trillion cubic feet) of gas (Meyerhoff, 1982), the MoscowBasin has a potential of 2353 million kilolitres (16 billionbarrels) of liquid hydrocarbons (V. Gorbachev, NEDRA,pers. comm., 1997) and, from geochemical evidence in oilsfrom Oman, Proterozoic sediments are now believed to be avery significant source for the prolific oil and gas fields ofthe entire Persian Gulf area (Edgell, 1991). The proven oilreserves in Oman alone are 795 million kilolitres (nearly5 billion barrels; Feld, 1997).

Potential (undiscovered) ‘resources’ should not becompared to traditional Proved, Probable and Possiblereserves in known discoveries. Undiscovered resources arecalculated to give a quantitative indication of the potential ofthe basin, and require considerable exploration to establishtheir existence.

METHOD

For a commercial petroleum field to exist in the easternOfficer Basin, four essential components are required:

• A mature ‘source’; a rock unit that contains sufficientorganic matter and which has been subjected tosufficient heat and pressure over time to haveproduced significant quantities of hydrocarbons butnot to have destroyed them through excessive heat andpressure.

• A ‘reservoir’ horizon; a rock unit that accumulates thegenerated oil or gas. A reservoir rock must be porousand have sufficient permeability to produce fluidseconomically.

• A ‘seal’ horizon; a rock unit that traps petroleum in thereservoir and prevents further migration.

• A structure over the reservoir horizon that willconcentrate the petroleum in economic quantities andthat was present at the time of petroleum expulsionfrom the source rock. This is usually an anticline, butstratigraphic traps can also be important, e.g. theOuldburra Formation.

When all four of these occur together, a petroleum ‘play’or a potential target for exploration exists.

The method of estimating undiscovered resourcesconsists of identifying all of the ‘plays’ that may exist, eitherby discoveries made so far or by analysis of the available data(e.g. drillhole, geophysical, or outcrop). The oil potential foreach play is then calculated using the following formula:

Pt = Ap*AB*h*NG*FF*Por*S h*FVF*SR*RF

Where:

Pt Total potential recoverable oil reserves of the play

Ap Prospective area of the basin

AB Anticline to total basin area ratio

h Average gross reservoir thickness.

NG Net to gross pay ratio

FF Anticline fill factor

Por Porosity (fraction)

Sh Hydrocarbon saturation (1 - water saturation)

FVF Formation volume factor

SR Exploration drilling success ratio

RF Recovery factor.

None of the above parameters is known with certainty butmost can be estimated from available data to within at least

147

broad limits. The most common method of combining andexpressing the uncertainty associated with this type ofequation is to use Monte Carlo simulation techniques (Whiteand Gehman, 1979). A frequency distribution for eachparameter is assumed, which is converted to a cumulativeprobability distribution, and a random number between 0 and1 (corresponding to 0 to 100% probability) is used to sampleeach of the distributions; these are combined as in theequation above to give one estimate of the potential of theplay. The process is repeated many times (in this case at least1000 times) to produce multiple estimates of the potential ofeach play. These are then used to produce a probabilityversus petroleum potential distribution for each play and forthe basin as a whole. Because this is computationallyintensive, the calculation is carried out by computer using acommercially available simulator (‘@RISK’, a MicrosoftEXCEL spreadsheet add in). This uses a more advancedstratified sampling technique called ‘Latin Hypercube’ thatwill converge in fewer iterations than with the traditional‘Monte Carlo’ technique.

DISCUSSION OF PARAMETERS

Prospective area (Ap)

This is the area of the basin that is believed to contain thethree essential components of source, reservoir and seal, andwhere the reservoir is at an economically drillable depth(assumed to be <4500 m). This is a critical factor indetermining the potential of the basin but can be mapped withreasonable accuracy from the available drillhole, source rockand regional depth to basement seismic mapping data(Lindsay, 1995). It is entered as a uniform distribution (equalprobability between minimum and maximum limits). Mapsfor each play, taking into account distribution of source, sealand reservoir, are shown on Figures 13.1 to 13.4.

Anticline to basin area ratio (AB)

This is the proportion of the prospective area that is withinan anticlinal trap. It was extrapolated from seismic structuremapping in the Marla and Munta areas (Mackie andGravestock, 1993; Mackie, 1994). The top crystallinebasement depth horizon was used for the Pindyin, Tarlina andMurnaroo plays, and the basal Cambrian depth horizon forthe Relief, Ouldburra and Arcoeillinna plays. Although theseismic coverage in this area is the best available in theOfficer Basin, it is still poor compared to that required to

Fig. 13.1 Pindyin, Tarlina Sandstone and Murnaroo Formationprospectivity, Officer Basin. Fig. 13.3 Ouldburra Formation prospectivity, Officer Basin.

Fig. 13.2 Relief Sandstone prospectivity, Officer Basin.

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identify all of the smaller prospects, and may not be typicalof trap styles elsewhere in the basin, hence the values used inthis assessment may be conservative. This parameter isentered as a truncated lognormal distribution.

Gross reservoir thickness (h)

This is the maximum vertical closure of the trap. Allreservoirs are modelled as a cone (‘h’ is reduced to one-thirdthe volume of a cone = 1/3 x area x height) with the exceptionof the Ouldburra reservoirs, which are modelled as a slab and‘h’ is not reduced. The parameter is modelled as a truncatedlognormal distribution.

Net to gross pay ratio (NG)

The net to gross ratio reduces the maximum reservoirthickness to the anticipated pay (permeable reservoir)thickness. This has been estimated using core data. Atruncated normal distribution is used.

Anticline fill factor (FF)

In oil or gas basins with commercial fields, anticlines canrange from filled to spill to near 0% fill (0% = dry wells).The average fill is therefore less than one, and it is assumedthat the richer the source rock the greater the average fill.This critical parameter is subjective and has been assumed toaverage 50% for the Officer Basin, although it would beexpected to be greater for plays with rich source potential. Atriangular distribution is used.

Porosity (Por)

The average porosity of the reservoir was estimated fromavailable routine core analysis data (Ch. 10). A truncatednormal distribution is used.

Hydrocarbon saturation (Sh)

The average hydrocarbon saturation is partly dependenton the average porosity and the pay thickness, and thedistributions are linked in the Monte Carlo simulator so thatwhen a low value of porosity and/or pay thickness is chosena low hydrocarbon saturation is also chosen. The range hasbeen determined from capillary pressure data from theMurnaroo Formation, but modified for the betterpermeability reservoirs. A truncated normal distribution isused.

Formation volume factor (FVF)

The volume of oil in a reservoir decreases when broughtto the surface due to the drop in pressure, and consequent lossof volatiles. The value for this factor was estimated fromEromanga Basin data (Morton, 1996b).

Success ratio (SR)

This is an estimate of the proportion of prospects to bedrilled that will contain oil (i.e. the drilling success ratio).Like the fill factor (FF) above, this ratio is related in part tothe richness of the source rocks, but other factors such as thedegree of structural complexity, trap integrity and quality ofseismic data are also important. A value was estimated fromAustralian and world average drilling results, and a truncatednormal distribution is used.

Recovery factor (RF)

The recovery factor converts petroleum in-place reservesto recoverable oil, and is mostly dependent on the degree ofmobility of the underlying aquifer and height of the oilcolumn. Estimates were derived from averages in the CooperBasin. A truncated normal distribution is used.

Fig. 13.4 Arcoeillinna Sandstone prospectivity, Officer Basin.

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POTENTIAL PLAYS

There are six major plays that have potential for discoveries:

1. Pindyin Sandstone

Reservoir: Pindyin Sandstone. Seal: Alinya Formation.Source: overlying Alinya Formation or the underlying, undrilled, possibly pre-Adelaidean sequence.

Summary of Monte Carlo input parameters:

Minimum Mean Maximum

Prospective area of the basin (km2) 15 620 65 874 116 070Anticline to total basin area ratio 0.02 0.06 0.15Average gross reservoir thickness (m) 13 69 192Net to gross pay ratio 0.30 0.60 0.91Anticline fill factor 0.01 0.5 0.99Porosity (fraction) 0.10 0.12 0.14Water saturation 0.2 0.3 0.45Formation volume factor 0.85 0.89 0.91Exploration drilling success ratio 0.04 0.10 0.17Recovery factor 0.18 0.25 0.32

2. Tarlina Sandstone

Reservoir: Tarlina Sandstone. Seal: Meramangye Formation.Source: Alinya Formation

Summary of Monte Carlo input parameters:

Minimum Mean Maximum

Prospective area of the basin (km2) 15 667 65 874 116 108Anticline to total basin area ratio 0.02 0.06 0.17Average gross reservoir thickness (m) 17 69 194Net to gross pay ratio 0.30 0.55 0.84Anticline fill factor 0 0.5 0.99Porosity (fraction) 0.13 0.15 0.17Water saturation 0.35 0.41 0.50Formation volume factor 0.85 0.89 0.91Exploration drilling success ratio 0.04 0.10 0.18Recovery factor 0.01 0.18 0.30

3. Murnaroo Formation

Reservoir: Murnaroo Formation sand. Seal: Dey Dey Mudstone.Source: Alinya Formation and Dey Dey Mudstone

Summary of Monte Carlo input parameters:

Minimum Mean Maximum

Prospective area of the basin (km2) 15 696 65 874 116 059Anticline to total basin area ratio 0.02 0.06 0.16Average gross reservoir thickness (m) 14 69 194Net to gross pay ratio 0.55 0.87 1.00Anticline fill factor 0.01 0.5 0.98Porosity (fraction) 0.13 0.15 0.18Water saturation 0.25 0.35 0.45Formation volume factor 0.85 0.89 0.91Exploration drilling success ratio 0.03 0.10 0.17Recovery factor 0.18 0.25 0.32

4. Relief Sandstone

Reservoir: Relief Sandstone. Seal: Ouldburra Formation or Observatory Hill Formation.Source: Alinya Formation (as shown from oil extracts), Dey Dey Mudstone, Karlaya Limestone, Ouldburra Formation and Observatory HillFormation.

Summary of Monte Carlo input parameters:

Minimum Mean Maximum

Prospective area of the basin (km2) 3459 25 711 47 963Anticline to total basin area ratio 0.01 0.05 0.16Average gross reservoir thickness (m) 15 69 195Net to gross pay ratio 0.28 0.60 0.94Anticline fill factor 0.02 0.5 0.98Porosity (fraction) 0.09 0.18 0.25Water saturation 0.15 0.25 0.44Formation volume factor 0.85 0.89 0.91Exploration drilling success ratio 0.04 0.11 0.16Recovery factor 0.18 0.25 0.32

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Additional potential may exist in carbonate reservoirs ofthe Ouldburra Formation (Kamali et al., 1995b), and sand ofthe Tanana and Narana Formations. The Trainor Hill andMount Chandler Sandstones (sealed by Indulkana Shale) arealso a possible play, but seal and source are significant risks.

The table below summarises the assessment of theundiscovered recoverable oil potential of the Officer Basinin South Australia at various probabilit y levels.

5. Ouldburra Formation

Reservoir: Ouldburra Formation sand. Seal: intra-Ouldburra Formation shale and micrite.Source: Ouldburra Formation, with possible contribution from Dey Dey Mudstone, Karlaya Limestone.

Summary of Monte Carlo input parameters:

Minimum Mean Maximum

Prospective area of the basin (km2) 10 860 19 626 28 389Anticline to total basin area ratio 0.01 0.05 0.21Average gross reservoir thickness (m) 45 99 171Net to gross pay ratio 0.25 0.35 0.64Anticline fill factor 0.01 0.50 0.98Porosity (fraction) 0.12 0.14 0.16Water saturation 0.20 0.30 0.40Formation volume factor 0.85 0.89 0.91Exploration drilling success ratio 0.03 0.10 0.17Recovery factor 0.01 0.18 0.3

6. Arcoeillinna Sandstone

Reservoir: Arcoeillinna Sandstone. Seal: Apamurra Formation.Source: Observatory Hill Formation and Ouldburra Formation.

Summary of Monte Carlo input parameters:

Minimum Mean Maximum

Prospective area of the basin (km2) 5387 13 134 20 893Anticline to total basin area ratio 0.01 0.05 0.16Average gross reservoir thickness (m) 25 50 92Net to gross pay ratio 0.31 0.65 0.96Anticline fill factor 0.02 0.5 0.99Porosity (fraction) 0.16 0.175 0.19Water saturation 0.25 0.35 0.50Formation volume factor 0.85 0.89 0.91Exploration drilling success ratio 0.03 0.10 0.17Recovery factor 0.01 0.18 0.3

Play Probability that the ult imate potentialwill exceed the stated va lue

million kilolitres (million barrels)90% 50% 10%

Arcoeillinna 3.3 (20.6) 10.8 (68.1) 27.8 (174.9)Ouldburra 29.4 (185.1) 85.1 (535.5) 209.9 (1320.4)Relief 6.3 (39.8) 30.3 (190.7) 95.0 (597.8)Murnaroo 21.7 (136.7) 69.1 (434.6) 210.4 (1323.7)Tarlina 18.6 (117.2) 63.7 (400.6) 186.1 (1170.7)Pindyin 18.0 (113.2) 62.6 (394.1) 172.9 (1087.4)

Total 236.4 (1486.9) 399.0 (2510.0) 674.0 (4239.6)

151

152

Appendix 1.1 Abbreviations used throughout the text

Organisations and projects

AGSO Australian Geological Survey Organisation

AP Anangu Pitjantjatjara

BMR Bureau of Mineral Resources (now AGSO)

GPA Glen Parkinson and Associates

MESA Mines and Energy Resources South Australia

MT Maralinga Tjarutja

NGMA National Geoscience Mapping Accord

SAEI South Australian Exploration Initiative

SASE South Australian steel and energy project

General

BIF banded iron formation

CEF Code of Environmental Practice

DEF Declaration of Environmental Factors

LPG Liquefied Petroleum Gas

OEL Oil Exploration Licence

OOIP original oil in place

OPL Oil Production Licence

PEL Petroleum Exploration Licence

PPL Petroleum Production Licence

TD total depth

XRD X-ray diffraction mineral analysis

ZOCA zone of cooperation (Timor Sea)

Measurement

°C degrees Celsius (temperature)

API gamma ray log units

BOPD barrels of oil per day

ha hectare (area; = 104 m2)

kL kilolitre (volume; = 1 m3)

kPa kilopascal (pressure; = 1 kg/m.s2)

L/s Litres per second

Ma million years before present

md millidarcies

mmbbl million barrels

ms milliseconds

µ/ft microseconds per foot

ppm parts per million (= milligrams per litre)

rb reservoir barrels

SCF standard cubic feet (gas)

stb stock tank barrel (oil)

Conversions

°C = ((°F - 32).5)/9

1 Petajoule (PJ) = 9.4781 1011 BTU

US$1 = A$0.75

1 cubic metre (m3) = 1 kilolitre (kL)

1 standard cubic metre of gas (m3) = 5.6154 standard cubic feet ofgas

1 kilolitre (kL) = 6.29 US barrels

1 kilopascal (kPa) = 0.1450 pound-force per square inch (psi)

Radiometric dating

K–Ar Potassium 40–Argon 40

Rb–Sr Rubidium 87–Strontium 87

U–Pb Uranium 235, 238–Lead 207, 206

Source rock and maturity parameters

EOM extractable organic matter

HI Hydrogen Index

MPI methylphenanthrene index

MPR methylphenanthrene ratio

OI Oxygen Index

VRcalc calculated equivalent vitrinite reflectance

Tmax temperature of maximum generation of S2 hydrocarbons

TOC total organic carbon

Reservoir, engineering and financial parameters

CAPEX capital expenditure

FVF formation volume factor (stb/rb)

k permeability (md)

kh reservoir flow capacity

NPV net present value

OPEX operating expenditure

OWC oil-water contact

Swirr irreducible water saturation

Sequence stratigraphy

HST high stand system tract

IVF incised valley fill

LST low stand system tract

MFS maximum marine flooding surface

TST transgressive system tract

153

Appendix 3.1 Sections of the Pitjantjatjara Land Rights Act 1981 relevant to petroleumexploration in the Officer Basin

154

155

156

157

158

Appendix 3.2 Sections of the Maralinga Tjarutja Land Rights Act 1984 relevant topetroleum exploration in the Officer Basin

159

160

161

162

163

164

APPENDIX 12.1 Economic model data and assumptionsCosts

The following assumptions have been made (all cash values below are Australian dollars unless indicated):

Conversion from US$ to A$: $0.79 (December 1996–January 1997).

Crude oil price: High case of US$25/bbl (January 1997) and low case of US$18/bbl were selected.

Real discount rate: 12.5% (before tax).

ExplorationPEL area in model: 4297 km2.

Cost of exploration well: $1.015 million.

Cost of seismic: $3500/km.

Seismic data: Existing regional seismic grid = 1808 km;New exploration seismic = 570 km.

Seismic per exploration well: 475 km.

Capital expenditureCost of development well: $0.832 million.

Road construction: The Department of Transport provided rough estimates for road construction costs in outback South Australia (1997). Total cost = $21 500/km which includes:

• $20 000 forming and sheeting road

• $25 000 per water bore with four bores per 100 km of road

• $50 000 per 100 km Aboriginal and environmental clearances.

For the model, wells are located on or within 20 km of the existing MESA seismic grid, which was left as tracks at the request of the landholder.

Road tanker capacity: 30 m3/tank (190 bbl/tank; GPA, 1996), up to a maximum of three tanks.

Flowlines (100 mm): $70/km (GPA 1996).

Trunkline (150 mm): $94/m (GPA, 1996); trunkline capacity = 790 bbl/day (125.6 m3/day).

Trunkline (300 mm): $187/m (capital costs for Moomba–Port Bonython trunkline; McDonough, 1996; Section 5.0); trunkline capacity = 33 000 bbl/day (5250 m3/day).

Completion cost per well: $350 000 (BRS, 1996).

Pumps: $102 000 (GPA, 1996).

Wellhead: $150 000 (GPA, 1996).

Oil storage tanks: US$18.75/bbl (BRS, 1996).

Vehicle: $50 000 (typical 4WD), replaced every three years.

Operating costsTrucking cost: $10.80/bbl (McDonough, 1996).

Downhole well maintenance: $45 000/well/year (R. McDonough, MESA, pers. comm., 1996).

Pump maintenance: 8% CAPEX/year (GPA, 1996).

Pump fuel cost: $1500/hp/year (GPA, 1996).

Flowline maintenance: 3% CAPEX (GPA, 1996).

Trunkline maintenance: 2.5% CAPEX (GPA, 1996).

Marla operation: $50 000/year.

Head office: $150 000/year.

Road maintenance: $1100 average cost of patrol grading to suitable standard for heavy vehicles (Department of Transport, 1997); the range is $800–1400/km/year, depending on weather conditions.

165

Reservoir engineering data

The spreadsheet Oil_prod.xls calculates total production rate, annual and cumulative production, wells needed and the recovery factor.

Max. wells: Five (discovery well and four development wells).

Max. field rate: 1000 bopd (158.9 m3/day).

Field area: Case 1: 75 km2 , Case 2: 150 km2 (the average area of prospects and leads delineated by Mackie (1994) is 97 km2; area ranges from 16 to 299 km2). The field is assumed to be circular.

Pay thickness: 60 m (average closure mapped by Mackie (1994) is 173 m, closure ranges from 125 to 750 m).

Original Oil in Place: Two cases were modelled: Case 1 = 5–30 mmbbl, Case 2 = 50–200 mmbbl. Note that original oil in place is referred to throughout the text, not recoverable oil.

Recovery factor: Oil recoveries did not exceed 25%.

Reservoir depth: 1750 m (5743 ft), primary reservoir Murnaroo Formation (D. Gravestock, MESA, pers. comm., 1996).

Reservoir pressure: 17 427 kPa (2527 psia), based on hydrostatic gradient.

Bottomhole pressure: 3250 kPa (500 psia), assumed.

Reservoir kh: 250, 1000, 9200 and 17 700 md.ft were selected.

Water gradient: 0.44 psi/ft (assumed).

Temperature gradient: 20°C/km.

Surface temperature: 25°C.

Reservoir temperature: 60°C (140°F, 600 R).

Oil API gravity: 50 (based on Mereenie Pacoota P3).

GOR: 800 scf/stb (based on Mereenie Pacoota P3).

Gas gravity: 0.76 (based on Mereenie Pacoota P3).

Initial Oil FVF: 1.42 rb/stb (calculated from correlation). The Marla region is overmature and oil here is likely to be more gas-rich than other parts of the Officer Basin.

Rock compressibility 4x10-6.psi-1 (assumed).

Water compressibility 3x10-6.psi-1 (assumed).

Water saturation 50% (assumed).

Oil production above the bubble point is calculated using the material balance equation. Oil production below the bubble point is calculatedusing the Tracy Material Balance Method (Smith and Tracy, 1986). For a given pressure decrement, the oil production volume is calculated.Individual well flow rates are determined based on reservoir pressure and flowing bottomhole pressure. The number of wells required (up toa maximum of five) to produce at the target field flow rate is then calculated. Based on the total rate, the time to produce the oil volume forthe pressure decrement is calculated to develop a oil production profile with time.

Oil properties are based on Mereenie Field data, (oil gravity, gas gravity, GOR). Correlations are then used to calculate bubble pointpressure, oil formation volume factor, oil viscosity, etc.

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