Minnelusa Sandstone

A study of stratigraphic and depositionalenvironments related to hydrocarbon

distribution in the Minnelusa Formation

Powder River Basinof the

Minnelusa Sandstone of the Powder River Basin Overview

GeoDigital Information's Minnelusa Formation study is designed to enhance both exploration and development efforts that are directed at Minnelusa reservoirs. These reservoirs occur within eolian sequences at multiple stratigraphic horizons. GDI has created an extensive stratigraphic framework that documents the extent of these reservoir-potential intervals. The mapping of these intervals is essential in the exploration for Minnelusa reservoirs.

The Minnelusa Formation study represents twelve man-years of geologic research which affords explorationists significant time savings in assimilating data and developing exploration strategies. The study area covers over 5,100 square miles in northeastern Wyoming and southeastern Montana. It spans Crook Campbell and Weston counties in Wyoming and portions of Powder River and Carter counties in southeastern Montana.

Correlations of 4,332 wells were made by defining 29 geologic markers throughout the

study area. In addition, porosity limits were defined for all wells with suitable log suites. Minnelusa depositional models and lithofacies reservoir potential are determined through the integration of core, thinsection, and log analyses. Eight representative field studies are incorporated with a focus on Minnelusa reservoir characteristics, trap types, and deliverability.

The Minnelusa study contains descriptions of 221 cores. Additionally, more than 400 thinsections were examined to define the diagenetic sequence of events that affect reservoir quality. These core and thinsection descriptions are essential for understanding the geologic history of the Minnelusa in the Powder River Basin.

The study components include an extensive summary text and figures, maps and cross sections, core and thinsection descriptions, and stratigraphic data appendices. These components provide the client with a presentation format that is concise and readily useable.

Database

4,332 - Study Wells

29 - Regional Stratigraphic Markers Correlated

24 - Measured Outcrop Section Described

221 - Cores Described

400+ - Thinsections

24,444’ - Crossplot Cores

2,343 - DST Data Wells

24 - Rock Types Described in the Rock Guide

Maps

Regional Maps (1:250,000) (1:96,000) (1:48,000)

Interval Isopach Maps

Structure Maps

Sandstone Maps

Porosity-Feet Maps

Field Maps (1:24,000)

Interval Isopach Maps

Sandstone Maps

Porosity-Feet Maps

Structure Maps

Facies Distribution Maps

Cross Sections

8 - Regional Stratigraphic Sections

1 - Regional Outcrop Cross Section

17 - Field Cross Sections

Field Studies

Bonepile, Camp Creek, Jewel, South Jewel, Corral Creek, Maysdorf, Swartz Draw, and Rourke Gap

Report Contents

TEXT AND FIGURES - An extensively illustrated report includes discussions, figures, and color plates on: Executive Summary, History of Study, Stratigraphy, Tectonic Framework, Depositional Facies, Petrography, Depositional Setting, Modern Analogs, Field Studies, Synthesis, and Exploration Potential.

CORE AND OUTCROP DESCRIPTIONS - This appendix contains descriptions of 221 cores from northeast Wyoming, and southeast Montana.

STRATIGRAPHIC DATA - This file contains the stratigraphic data (29 formation tops and stratigraphic markers, and net sandstone

values) and isopach values, as well as information on well name, operator, location, API number, completion date, datum, and production status for the 4,332 study wells.

MAPS AND CROSS SECTIONS - This appendix contains 47 regional maps at scales of 1:48,000, 1:96,000, and 1:250,000 and 32 field maps at a scale of 1:24,000. This includes isopach maps, structure maps, gross and net sandstone maps, and a study well map.

CROOK

WESTON

CAMPBELL

JOHNSON WYO

MIN

G

SO

UTH

D

AKO

TA

Gillette

Newcastle

MONTANA

POWDER RIVERCARTER

SHERIDAN

Study Boundary

Minnelusa Sandstonesof the Powder River Basin

MILES

240 N

R 48 ET7S

R 56 ET7S

R 67 WR 74W

T44N

T44N

StudyTable of Contents

Minnelusa Sandstones

Powder River Basinof the

ii

TABLE OF CONTENTS

Page Preface

Table of Contents ……………………………………………………………….... ii List of Maps ………………………………………………………………….…… vi List of Cross Sections ………………………………………………………….. viii List of Figures ……………………………………………………….………........ ix List of Tables ……………………………………………………………….…… xvi Acknowledgements ……………………………………………………….…….xvii

Executive Summary

Executive Summary …..…………………………………………………………………E-1

Chapter 1 Introduction ……………………………………………………………………………… 1-1

Chapter 2 History of Study - Previous Work ………………………………………………….…. 2-1 Geologic Mapping and Introduction of Stratigraphic Nomenclature ………. 2-2 Correlation of Stratigraphic Units ………………………………………..……. 2-4 Modern Stratigraphic Studies …………………………………………..…….. 2-7

Chapter 3 Stratigraphy …………………………………………………………….………………. 3-1 Lower Member of the Minnelusa Formation ………………………………… 3-2 Middle Member of the Minnelusa Formation ………………………………… 3-4 Upper Member of the Minnelusa Formation ………………………………… 3-6 Goose Egg Group ……………………………………………………………… 3-7 Detailed Stratigraphy of the Upper Member of the Minnelusa Formation …3-9 Potential Source Beds and Hydrocarbon Migration ………………………. 3-13

Chapter 4 Tectonic Framework …………………………………………………….……………… 4-1

Chapter 5 Depositional Facies …………………………………………………….……….……… 5-1 Marine Facies …………………………………………………………………… 5-2

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Open-Marine Carbonate Deposits …………………………………… 5-3 Open-Marine Siliciclastic Deposits …………………………………… 5-3 Transitional Facies ……………………………………………………….….… 5-4 Restricted-Marine Carbonate Deposits ……………………………… 5-4 Restricted-Marine Evaporite Deposits …………………………….… 5-4 Algal-laminated Carbonate Deposits ………………………………… 5-5 Storm Deposits ……………………………………………..……….… 5-5 Sabkha Facies ……………………………………………………………….… 5-5 Coastal Sabkhas (interdune) ……………………………….………… 5-6 Terrestrial Sabkhas (interdune) …………………………….…….….. 5-6 Dunes ………………………………………………………………..…….…… 5-6 Vertical Facies Relationships …………………………………………………. 5-8

Chapter 6 Petrographic Analysis …………………………………………………………………… 6-1 General Description of Subsurface Sandstones ……………………….…… 6-3 Framework Constituents ……………………………………………… 6-3 Authigenic Constituents ………………………………………….…… 6-4 Compaction ……………………………………………….…………… 6-6 Porosity …………………………………………………………………. 6-6 General Description of Outcrop Samples …………………………………… 6-7 Diagenesis of the Upper Minnelusa Strata ………………………….………. 6-8 Early Stage Diagenesis ……………………………………….……… 6-8 Middle Stage Diagenesis ……………………………………………… 6-10 Development of Secondary Porosity ………………………………… 6-11 Hydrocarbon Migration …………………………………………..…… 6-11 Late Stage Diagenesis ……………………………………….……….. 6-12 Discussion of the Petrographic Results …………………………….…….….. 6-12 Petrographic Evidence for the Depositional Environment ……..….. 6-13 Effects of Diagenesis on Outcrops …………………………….…….. 6-14 Diagenetic Controls of Porosity in Producing Fields ………….……. 6-14 Using Petrographic Evidence to Aid in the Determination of Lithologies in Uncored Wells ……………………………………. 6-15 Effects of Texture, Compaction, and Authigenic Clay on Permeability in Different Lithologies ……………..…………….…. 6-16 Potential Problems in Well Completion and Stimulation ……….….. 6-17 Petrographic Supplement ……………………………………………………………… 6-18 General Description of the Middle Minnelusa Sandstones ………………… 6-18 General Description of the Subsurface Dolomite Lithologies ……………… 6-19 General Description of Unconsolidated Sediments from the Killpecker Dunes, Southwestern Wyoming ………………….…………… 6-20 X-ray Diffraction Analysis ……………………………………………………… 6-21 SEM Analysis …………………………………………………………………… 6-21

Chapter 7 Depositional Setting ……………………………………………………..……………… 7-1 Basin Configuration …………………………………………….……………… 7-2

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Sea Level …………………………………………………………..…………… 7-3 Paleoclimate ……………………………………………………………..……… 7-4 Hydrographic Regime …………………………………………………..……… 7-4 Waves and Currents …………………………………………………… 7-5 Tidal Range …………………………………………………..………… 7-5 Discussion of Dune Accumulation ……………………….…………………… 7-5 Adhesion ………………………………………………………..……… 7-6 Cementing ……………………………………………………………… 7-6 Preservation of Dunes ……………………………………………………….… 7-7 Regional Paleogeographic Reconstructions ………………………………… 7-8

Chapter 8 Modern Analogs ………………………………………………………………………… 8-1 Modern Coastal Sabkha - Dune Environments – Qatar Peninsula………… 8-2 Sand Seas - Rub al Khali ………………..………………………….………… 8-4 Modern Analogs to Upper Minnelusa ………..………….…………………… 8-4 Sand Seas & Coastal Dunes …………………………..……………………… 8-5 Cuestas in Southeastern Colorado …………………………………………… 8-5

Chapter 9 Studies of Selected Oil Fields ………………………………………………………… 9-1 Bonepile ………………………………………………………………….……… 9-2 Camp Creek ……………………………………………………….…………… 9-5 Jewel, South Jewel, Corral Creek ……………………………….…………… 9-7 Maysdorf ………………………………………………………………….….…9-10 Swartz Draw ……………………………………………….……………..….…9-11

Conclusions ………………………………………………………..……….…..9-13

Chapter 10 Synthesis ………………………………………………………………………………… 10-1 Depositional Models …………………………………………………………… 10-2 Exploration Concepts ……………………………………………………..…… 10-3 Exploration in the "A" Sandstones …………………………………….……… 10-4 Exploration in the "B" Sandstones ……………………………………….…… 10-5 Exploration in the "C" Sandstones …………………………………………… 10-5 Exploration in the "D" Sandstones ………………………………………….… 10-6 An "AO " Sandstone ? ………………………………………………………….. 10-7

BIBLIOGRAPHY Bibliography ………………………………………………………………………….…. B-1

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Additional Supplements to this Study

Rock Guide Supplement Appendix I – Core Descriptions Appendix II – Measured Outcrop Sections Appendix III – Crossplots Appendix IV – DST Recovery Data Database Maps and Cross Sections Update 1

vi

LIST OF MAPS

1:48,000 (4 Sections) and 1:96,000 (3 Sections) Scale Maps

Interval Isopach - Top of Goose Egg Formation All 7 sheets to Top of Minnekahta Limestone Interval Isopach - "C" Dolomite of the Upper Member, All 7 sheets Minnelusa Formation Structure Contour - Top of Minnekahta Limestone All 7 sheets Facies Distribution - "A" Unit of the Upper Member, Sheets 1 & 2 only Minnelusa Formation (1:96,000 only) Facies Distribution - "B" Unit of the Upper Member, Sheets 1 & 2 only Minnelusa Formation (1:96,000 only) Facies Distribution - "C" Unit of the Upper Member, Sheets 1, 2, & 3 only Minnelusa Formation (1:96,000 only) Net Sandstone - "D" Unit of the Upper Member, Sheets 1, 2, & 3 only Minnelusa Formation (1:96,000 only)

1:250,000 Scale Maps

Limit of "A" Unit Sandstone (showing "A" Production) Limit of "B" Unit Sandstone (showing "B" Production) Limit of "C" Unit Sandstone (showing "C" Production) Location of Regional Cross Sections

1:24,000 Scale Field Maps

Bonepile

Interval Isopach - Opeche Formation Net Sandstone - "A" Unit of the Upper Member, Minnelusa Formation Porosity Feet (10% Cutoff) - "A" Unit Sandstone of the Upper Member, Minnelusa Formation Structure Contour - Top of "A" Interval Sandstone of the Upper Member, Minnelusa Formation Structure Contour - Top of "B" Interval Dolomite of the Upper Member, Minnelusa Formation

Camp Creek

Interval Isopach - Opeche Formation Net Sandstone - "B2" Interval of the Upper Member, Minnelusa Formation Porosity Feet (10% Cutoff) - "B2" Sandstone Interval of the Upper Member, Minnelusa Formation

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Structure Contour - Top of "B2" Sandstone Interval of the Upper Member, Minnelusa Formation Structure Contour - Top of "C" Interval Dolomite of the Upper Member, Minnelusa Formation Structure Contour – Top of Minnekahta Limestone

Jewel, Jewel South, and Corral Creek

Structure Contour - Top of Minnekahta Limestone Interval Isopach - Opeche Formation Porosity Feet (10% Cutoff) - "B" Unit Sandstone of the Upper Member, Minnelusa Formation Structure Contour - Top of "C" Interval Dolomite of the Upper Member, Minnelusa Formation

Maysdorf

Structure Contour - Top of Minnekahta Limestone Interval Isopach - Opeche Formation Structure Contour - Top of "A" Interval Sandstone of the Upper Member, Minnelusa Formation Porosity Feet (10% Cutoff) - "A" Unit Sandstone of the Upper Member, Minnelusa Formation Net Sandstone - "A" Unit Sandstone of the Upper Member, Minnelusa Formation Structure Contour - Top of "B1" Interval Sandstone of the Upper Member, Minnelusa Formation 7 Structure Contour - Top of "B" Unit Dolomite of the Upper Member, Minnelusa Formation Net Sandstone - "B" Unit of the Upper Member, Minnelusa Formation Porosity Feet (10% Cutoff) - "B" Unit Sandstone of the Upper Member, Minnelusa Formation

Swartz Draw

Interval Isopach - Opeche Formation Net Sandstone - "C1" Interval of the Upper Member, Minnelusa Formation Porosity Feet (10% Cutoff) - "C" Sandstone Interval of the Upper Member, Minnelusa Formation Structure Contour - Top of "C" Interval Sandstone of the Upper Member, Minnelusa Formation Structure Contour - Top of "D" Unit Dolomite of the Upper Member, Minnelusa Formation

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The following is a l ist of maps that were updated from the original regional Minnelusa

study, as well as several new detailed sub-unit map sequences (see Additional Supplement

“Update 1” for more information). The scales are the same as utilized originally, both 1:96,000

and 1:48,000. Note that not all maps contain all seven sheets. Some of the sandstone units

and sub-units did not exist in all geographic areas; thus, those map areas were not included.

The enclosed diagram illustrates the breakdown and nom enclature for the various map

sections. An additional field study was also created as a section of “Update 1”, the Rourke Gap

Field. The maps for that field study are at a scale of 1:24,000.

1:48,000 (4 Sections) and 1:96,000 (3 Sections) Scale Maps

Interval Isopach - Opeche Formation All 7 sheets

Net Sandstone "A" Unit of the Upper Member, 6 sheets-no sheet 1 Minnelusa Formation

Net Sandstone "B" Unit of the Upper Member, All 7 sheets Minnelusa Formation

Net Sandstone "C" Unit of the Upper Member, All 7 sheets Minnelusa Formation

Porosity Feet (10% cutoff) "A" Sandstone 6 sheets-no sheet 1 of the Upper Member,' Minnelusa Formation

Porosity Feet (10% cutoff) "B" Sandstone All 7 sheets of the Upper Member, Minnelusa Formation

Porosity Feet (10% cutoff) "C" Sandstone All 7 sheets of the Upper Member, Minnelusa Formation

Sandstone "A1" Sub-unit of the Upper Member, 5 sheets-no sheet 1 or D Minnelusa Formation

Sandstone "A2" Sub-unit of the Upper Member, 6 sheets-no sheet 1 Minnelusa Formation

Sandstone "B1" Sub-unit of the Upper Member, All 7 sheets Minnelusa Formation

Sandstone "B2" Sub-unit of the Upper Member, All 7 sheets Minnelusa Formation

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Sandstone "C1" Sub-unit of the Upper Member, All 7 sheets Minnelusa Formation

Sandstone "C2" Sub-unit of the Upper Member, All 7 sheets Minnelusa Formation

Porosity Feet (10% cutoff) "A1l" Sub-unit Sandstone 5 sheets-no sheets 1 or D of the Upper ,Member, Minnelusa Formation

Porosity Feet (10% cutoff) "A2" Sub-unit Sandstone 6 sheets-no sheet 1 of the Upper Member, Minnelusa Formation

Porosity Feet (10% cutoff) "B1" Sub-unit Sandstone 6 sheets-no sheet 1 of the Upper Member, Minnelusa Formation

Porosity Feet (10% cutoff) "B2" Sub-unit Sandstone All 7 sheets of the Upper Member, Minnelusa Formation

Porosity Feet (10% cutoff) "C1" Sub-unit Sandstone All 7 sheets of the Upper Member, Minnelusa Formation

Porosity Feet (10% cutoff) "C2" Sub-unit Sandstone All 7 sheets of the Upper ,Member, Minnelusa Formation

Structure Contour Top of "C" Dolomite of the All 7 sheets Upper Member, Minnelusa Formation

1:24,000 Scale Field Maps

Rourke Gap Field Maps

Interval Isopach-Opeche Formation Sandstone Isopach ,"A2" Sub-unit of the Upper Member, Minnelusa Formation Porosity Feet (10% cutoff) "A2" Sub-unit Sandstone of the Upper Member, Minnelusa Formation Interval Isopach "B" Dolomite Sub-unit of the Upper Member, Minnelusa Formation Sandstone Isopach "B1" Sub-unit of the Upper Member, Minnelusa Formation Interval Isopach "B” Dolomite Sub-unit of the Upper Member, Minnelusa Formation Sandstone Isopach "B2" Sub-unit of the Upper Member, Minnelusa Formation Porosity Feet (10% cutoff) "B2" Sub-unit Sandstone of the Upper Member, Minnelusa Formation Interval Isopach "C" Dolomite Sub-unit of the Upper Member, Minnelusa Formation Sandstone Isopach "C1 " Sub-unit of the Upper Member, Minnelusa Formation Interval Isopach "C’ ” Dolomite of the Upper Member, Minnelusa Formation Sandstone Isopach "C2" Sub-unit of the Upper Member, Minnelusa Formation Porosity Feet (10% cutoff) "C2" Sub-unit Sandstone of the Upper Member, Minnelusa Formation Structure Contour Top of "C" Dolomite of the Upper Member, Minnelusa Formation

x

Structure Contour Top of the Porosity "C2" Sub-unit Sandstone of the Upper Member, Minnelusa Formation

LIST OF CROSS SECTIONS Regional Cross Sections

A- A' (2 Sections)

B- B' (2 Sections)

C- C' (2 Sections)

D-D’

E- E' (2 Sections)

F- F' (2 Sections)

G- G' (2 Sections)

H- H' (3 Sections) Outcrop Transect - Eastern Flank of Bighorn Mountains

Field Cross Sections - All stratigraphic unless marked

Bonepile A - B C - D E - F (2 Sections)

Camp Creek

A - B C - D

Corral Creek

A - B C - D

Jewel, Jewel South

A - B C - D E - F

xi

Maysdorf A - B C - D

Rourke Gap

A – A’ B – B’

Swartz Draw

A - B C - D C - D (Structural)

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LIST OF FIGURES Figure 1.1. Block diagram of Powder River Basin showing study area Figure 1.2. Minnelusa study area, including township and range grid Figure 1.3. Location map showing Laramide outcrops in vicinity of Powder River Basin Figure 1.4. Correlation diagram of eastern Wyoming and northeastern Colorado Figure 1.5. Correlation diagram of Powder River Basin Figure 2.1. Correlation diagram of Permo-Pennsylvanian strata as named by previous authors Figure 3.1. Subcrop map of Pennsylvanian rocks Figure 3.2. Photo of Mississippian/Pennsylvanian contact Figure 3.3. Photo of Mississippian/Pennsylvanian contact illustrating the unconformity Figure 3.4. Photo showing detail of Mississippian/Pennsylvanian unconformity Figure 3.5. Representative log of the Lower Member of the Minnelusa Formation Figure 3.6. Photo illustrating contact between the Lower and Middle Members of the Minnelusa Formation Figure 3.7. P hoto of red conglomeratic sandstones of the Lower Member of the Minnelusa Formation Figure 3 .8. P hoto i llustrating M adison, A msden, and Tensleep For mations al ong the M iddle Fork of the Powder River Basin Figure 3.9. Isopach map of Lower Pennsylvanian strata Figure 3.10. Representative log of the Middle Member of the Minnelusa Formation Figure 3.11. Diagram of tenfold division of the Middle Member of the Minnelusa Formation Figure 3.12. Photo of Leo I and II eolian sandstones Figure 3.13. Photo of Leo I (Meng) sandstone Figure 3.14. Location of Pennsylvanian - Permian contact/ unconformity on geophysical logs Figure 3.15. Representative log illustrating the subdivision of the four Upper Member units Figure 3.16. Photo of breccia collapse feature in Upper Member strata

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Figure 3.17. Photo of breccia collapse feature in Upper Member strata Figure 3.18. Photo of brecciated strata in Upper Member of the Minnelusa Formation Figure 3.19. Photo illustrating detail of brecciation in Upper Minnelusa sandstone Figure 3.20. Diagram illustrating lithologic correlations from outcrop to subsurface Figure 3.21. Isopach map of Leonardian, Wolfcampian, and Pennsylvanian rocks Figure 3.22. Map illustrating distribution of the four units in the Upper Member with overlying drainage pattern developed on unconformity at top of Minnelusa Figure 3.23. Representative log of Goose Egg Group Figure 3.24. Photo of Upper Minnelusa - Opeche Formation contact Figure 3.25. Photo of Opeche Formation - Minnekahta Limestone contact Figure 3.26. Photo of Upper Minnelusa - Opeche Transition Zone contact Figure 3.27. Photos from core of Opeche Transition Zone conglomerate Figure 3.28. Photo of gypsum beds in Opeche Formation Figure 3.29. Photo of Opeche Formation Shale Figure 3.30. Diagram of structural lineaments in the northern Rocky Mountain region Figure 3.31. Diagram comparing the subdivision of the Upper Member from outcrop to well-log response Figure 3.32. Diagram showing the breakdown of Upper Member units Figure 3.33. Photo of the chemical rock at top of the "B" Unit Figure 3.34. Photo of lower dune cross-stratification in lower portion of "B" sandstone Figure 3.35. Photo of slipface cross-stratification in "A" Unit sandstones Figure 4.1. Tectonic map illustrating ancient and modern features Figure 5.1. Photo of oscillation ripples Figure 5.2. Photo of shell lag on dolomite bedding surface Figure 5.3. Photo of marine Tensleep sandstones Figure 5.4. Photo of burrow structure in marine sandstone

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Figure 5.5. Photo of skolithos in marine sandstone Figure 5.6. Photo of polygonal desiccation cracks Figure 5.7. Photo of modern algal mat illustrating desiccation features Figure 5.8. Photos from core, outcrop, and modern environment illustrating algal laminations Figure 5.9. Photos comparing interdune bedding in core, outcrop, and modern interdune environments Figure 5.10. Diagram illustrating sedimentary features common in modern coastal environments Figure 5 .11. P hotos o f w ater es cape s tructures i llustrated i n c ore, outcrop, and m odern environment Figure 5.12. Photos showing soft sediment deformation features in core, outcrop, and modern environment Figure 5.13. Photo of box core from modern interdune environment Figure 5.14. Photo of box core from modern interdune environment Figure 5.15. Photos of algally laminated sandstones Figure 5.16. Photo of stoss slope of modern barchan dune Figure 5.17. Photo of peel illustrating stoss slope bedding Figure 5.18. Photos of wind deflation lags seen in core and outcrop Figure 5.19. Photos of desiccation cracks seen in outcrop and modern mud flat environment Figure 5.20. Photo of microfaults in core Figure 5.21. Photo of microfaults in trench of modern dune Figure 5.22. Photo of peel from dune crest area Figure 5.23. Photo illustrating high-angle foreset-bedding in dune crest area Figure 5.24. Photos illustrating dune slipface bedding Figure 5.25. Photo of contact between a dune slipface and interdune bedding Figure 5.26. Photo of outcrop showing dune/interdune contact Figure 5.27. Photo of outcrop showing dune/interdune contact Figure 5.28. Photo comparison of bounding plane surfaces in core, outcrop, and modern dune

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Figure 5.29. Photo of bounding planes in dune sandstone outcrops Figure 5.30. Photo showing multiple bounding planes in outcrop Figure 5.31. Photo of modern dune example of multiple bounding planes Figure 5.32. Photo of dolomite interdune deposits on outcrop Figure 5.33. Photo of lateral pinchout of interdune bedding on outcrop Figure 5.34. Block diagrams of common dune types Figure 5.35. Photo of barchan dune - Wyoming Figure 5.36. Diagram of facies relationship common in the Minnelusa Formation Figure 5.37 (RG-27). Rock Guide-Tan Churned Dolomite, Burrowed Figure 6.1. Location map of Upper Minnelusa sandstone petrographic core samples Figure 6.2 (RG-6). Cross-Bedded Quartz Arenite Figure 6.3 (RG-11). Flat-Bedded Quartz Arenite Figure 6.4 (RG-13). Wavy-Bedded Quartz Arenite Figure 6.5 (RG-15). Massive Quartz Arenite Figure 6.6. Photomicrographs of representative cross-bedded sandstones Figure 6.7. Photomicrograph of representative flat-bedded sandstone, photomicrograph of algal dolomite Figure 6.8. Photomicrographs of representative wavy-bedded sandstones Figure 6.9. Photomicrographs of representative massive sandstones Figure 6.10 (RG-16). Churned Quartz Arenite Figure 6.11. Classification of the subsurface sandstones Figure 6.12. Photomicrographs showing the replacement of a quartz overgrowth with anhydrite cement Figure 6. 13. P hotomicrographs s howing di ssolution por osity dev eloped w ithin a f ramework feldspar grain Figure 6.14. P hotomicrograph showing the variable deg rees to which f ine-grained authigenic dolomite infills the intergranular areas

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Figure 6 .15. A bundant authigenic dol omite totally oc cludes s ome of t he por es i n t his s andy dolomite Figure 6.16. Two different sizes of authigenic dolomite are common Figure 6.17. Anhydrite cement (bright blue) surrounds well-compacted quartz grains Figure 6 .18. The lath-like projections o f anhydrite ( center) are the result o f the dissolution of anhydrite cement along cleavage Figure 6.19. Photograph showing well-developed quartz overgrowth cement surrounding center grain Figure 6.20. Photomicrograph showing well-developed overgrowth on rounded quartz grain Figure 6.21. Authigenic illite clay (brown) coating detrital quartz grains Figure 6.22. The fine-grained platelets in the center of the photomicrograph are authigenic kaolinite clay Figure 6.23. Mixed-layer clay completely fills the intergranular areas in this sandstone Figure 6.24 (RG-24). Cross-Bedded Quartz Arenite Figure 6.25 (RG-25). Cross-Bedded Quartz Arenite Figure 6.26. Sutured grain-to-grain contacts Figure 6.27. Possible effects of secondary porosity on permeability Figure 6.28. Schematic diagram showing the destruction of primary porosity and the generation of secondary porosity with increasing depth of burial Figure 6.29. Diagrammatic chart of the diagenetic history of the Upper Minnelusa sandstones Figure 6.30. Anhydrite cement selectively cements the coarser-grained laminae Figure 6.31. The slightly rounded, corroded nature of the authigenic dolomite rhombs Figure 6.32. Relationship of dolomite cement in sandstones to adjacent dolomite lithologies Figure 6.33. "Dead oil" (black) lines the pores and penetrates anhydrite cement along cleavage planes Figure 6.34. Floating and tangential grain contacts within the anhydrite cemented area Figure 6.35. Location of photomicrograph of anhydrite rehydrating to gypsum Figure 6.36. Relationship of the sonic log response to the amount of anhydrite cement Figure 6.37. Cementation trends in the different sandstone intervals

xvii

Figure 6.38. Ternary diagrams of the relative percentages of framework grains, porosity, and cement plus matrix Figure 6.39. Comparison of porosity and grain size in cross-bedded and wavy-bedded sandstones Figure 6.40. Comparison of the degree of compaction and rock-type Figure 6.41. Location of unconsolidated samples taken from a modern barchan dune Figure 6.42. Photomicrograph of an unconsolidated sand from a modern eolian dune Figure 6.43. Low magnification scanning electron photomicrograph of a clay-coated sample Figure 6.44. Low and high magnification scanning electron photomicrograph of a well-cemented sandstone Figure 6.45. Low and high magnification scanning electron photomicrograph of a sandstone Figure 6.46. Low and high magnification view of a clay coated sandstone Figure 7.1. Generalized sea-level curve - world wide Figure 7.2. Generalized sea-level curve for study area - Permo-Pennsylvanian Figure 7.3. Generalized sea-level curve for study area -Wolfcampian time Figure 7.4. Lower Permian global paleogeography diagram Figure 7.5. Lower Permian paleowind direction diagram Figure 7.6. Diagram illustrating groundwater table in dunes Figure 7.7. Diagram illustrating possible dune preservation sequence Figure 7.8. Diagram illustrating early cementation processes in dunes Figure 7.9. Schematic diagram showing coastal alignment of dunes Figure 7.10. Diagram showing dune stacking mechanism Figure 7.11. Paleogeographic reconstruction o f t he s tudy ar ea during " C" U nit s andstone deposition Figure 7.12. Paleogeographic reconstruction of study area during "B" Unit chemical rock deposition Figure 7.13. Paleogeographic reconstruction of study area during "B" Unit sandstone deposition

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Figure 7 .14. P aleogeographic r econstruction o f t he s tudy ar ea showing pos t-Minnelusa erosional topography developed during Late Wolfcampian sea-level lowstand Figure 7.15. Paleogeographic reconstruction of study area during Lower Leonardian during eustatic sea level rise Figure 8.1. Location map of Qatar coast Figure 8.2. Landsat image of Qatar coast Figure 8.3. Photo mosaic of the UM Said Sabkha in southeastern Qatar Figure 8.4. Photo of eolian dune, Qatar coast Figure 8.5. Photo of eolian dune, Qatar coast Figure 8.6. Photo of isolated barchan dune, Kiawah Island, South Carolina Figure 8.7. Aerial photo of barchan dunes, Baja, California Figure 8.8. Location map of Rub al Khali desert Figure 8.9. False color image aerial photo of Rub al Khali Dune Figure 8.10. Landsat photo of Rub al Khali dunes Figure 8.11. Location map of Lake Chad Figure 8.12. Landsat image of northeast shore of Lake Chad Figure 8.13. Location map of aerial photo coverage area southeast of Pueblo, Colorado Figure 8.14. Aerial photo of isolated cuesta remnants, southern Colorado Figure 8.15. Close-up of net sandstone map displaying morphology of drainage patterns Figure 8.16. Aerial photo of cuesta drainage morphology, southern Colorado Figure 8.17. Close-up of net sandstone map illustrating cuesta drainage morphology Figure 8.18. Aerial photo of cuesta drainage patterns Figure 9.1. Location map of field studies Figure 9.2. Comparison of aerial photo and net sandstone map illustrating "field-scale" cuesta drainage patterns Figure 9.3. Paleogeographic reconstruction of study area during "C" Unit sandstone deposition

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Figure 9.4. Paleogeographic reconstruction of study area during "B" Unit sandstone deposition Figure 10.1. Paleogeographic reconstruction of the study area during the time of "C" sandstone Figure 10.2. Paleogeographic reconstruction of the study area during the time of "B" sandstone Figure 10.3. Paleogeographic reconstruction of the study area during early Leonardian (Permian) time Figures RG-1 Thru RG-37 - Core Photographs - Rock Guide Supplement

LIST OF TABLES Table 6.1. Location of Outcrop Thin Section Samples Table 6.2. List of Upper Minnelusa Subsurface Samples Table 6.3. List of Porosities by Lithologic Type Table 6.4. Data from X-ray Diffraction Analogs Table 9.1. Porosity vs. authigenic cements and rock type in Camp Creek

Selected Figuresfrom the Study

Powder River Basinof the

Minnelusa Sandstones

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Figure 3.12. Outcrop photo of Leo I and II eolian sandstones of the upper portion of the Middle Member of the Minnelusa Formation in the northern Black Hills. Within the slope (covering carbonates and shales) that overlies the "Leo" sandstones is the Pennsylvanian-Permian boundary. The upper cliffs in the photo are Upper Minnelusa sandstones. Location: Ranch A, Sec 13, T52N, R61W.

Figure 3.13. Outcrop photo of Leo I (Meng Sandstone) eolian sandstone of the upper portion of the Middle Member of the Minnelusa Formation in the Black Hills. Pennsylvanian-Permian boundary occurs in the slope in the middle of the outcrop. Upper cliffs in the photo are Upper Minnelusa deposits. Location: Hot Brook Canyon, Sec 10, T7S, R5E.

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Figure 5.27. View of the contact between the slipface of a

migrating dune and the underlying interdune from the

Tensleep Formation (far right). Note the slight deformation

of the interdune due to loading pressure. Location: Outlaw

Cave, Wyoming.

Figure 5.26. Outcrop example of the contact

between dune and interdune in Tensleep

sandstone. Note the change in orientation

and thickness of bedding. Location: Outlaw

Cave, Wyoming, Sec 18, T42N, R84W.

Figure 5.25. Modern example of the

contact between a slipface and interdune

bedding. Soft sediment deformation is

almost non-existent here because there

was little interstitial water present at the

time of deposition. Location: Killpecker

Dune field, north of Rock Springs,

Wyoming.

Enlargement of area C showing cluster of authigenic kaolinite crystals filling a pore

(arrow). 286X.

High magnification view of the center of the top photo (arrow) showing the stacked

hexagonal platelets or "books" that are the typical crystal habit of kaolinite. 1,368X.

Figure 6.45.

D

C

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Figure 9.4. A modern drainage system in southern Colorado has formed erosional

remnants of flat-lying Tertiary sandstones. The modern landforms are very similar to those

created by pre-Opeche erosional valleys. The isopach map of the "B" sandstone shows

erosional remnants of "B" sandstone downdip from an erosional valley at least 115 feet

deep. The valley is filled by fine-grained sediments of the Opeche Formation, which

constitute an updip seal for oil production from the erosional sandstone remnants. Situated

on the southwest side of a single erosional valley are, from south to north, Jewel South,

Jewel, and Corral Creek fields. The fields are separated by smaller valleys that have

incised into the "B" sandstone.

Yellow indicates the presence of "B" sandstone and beige represents areas of complete

truncation of "B" sandstone. The drainage pattern, which formed the valleys, is shown by

blue lines. Return to Text

Example of a Core Description

Example of a Measured Outcrop Section