LLC Marginal Marine Depositional Environments Core …cloud1.activelearner.com/.../GEO-MMD/MMD_01_Slides.pdf · Marginal Marine Depositional Environments Core Deltas and Deltaic Deposits

Marginal Marine Depositional Environments Core

Deltas and Deltaic Deposits

Processes and examples from modern and ancient environments with oil field examples

Subaerial– Alluvial fan– Fluvial braided and meandering– Aeolian – wind and desert

Marine– Offshore Bars– Submarine fan – channel-levee complex, Bouma sequence– Carbonates – limestone, dolomite

• Reef, platform, pinnacle, pelagic• Diagenesis

Marginal Marine– Delta – river, wave, tide dominated, fan delta, braid delta– Beach and barrier island

Processes and examples from modern and ancient environments with oil field examples

Subaerial– Alluvial fan– Fluvial braided and meandering– Aeolian – wind and desert

Marine– Offshore Bars– Submarine fan – channel-levee complex, Bouma sequence– Carbonates – limestone, dolomite

• Reef, platform, pinnacle, pelagic• Diagenesis

Marginal Marine– Delta – river, wave, tide dominated, fan delta, braid delta– Beach and barrier island

Depositional Environments


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Learning Objectives

By the end of this lesson, you will be able to:

Define what a ‘Delta’ is

Understand the processes which result in the formation of distributary channels, distributary mouth bars, bar fingers and crevasse splays

Relate delta morphology to the slope of the shelf

Describe what controls reservoir shape, size and orientation of deltaic deposits by sediment input, wave energy, and tidal range

Explain variations in delta type as it relates to sediment input environments: Alluvial Fan, Braided Rivers, and common deltas

Selected Major Deltas in the World


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What is a “Delta”?

A River Delta is a landform that is created by deposition of

sediment carried by a river as the flow leaves its mouth and

enters slower-moving or standing water.

This occurs where a river enters an ocean, sea, estuary, lake,

reservoir, or (more rarely) another river that cannot transport

away the supplied sediment.

A Delta Forming in a Mountain Lake



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End Members of Delta Types

The Mississippi Delta Over the Last 7–8,000 Years

Over the past ~7000–8000 years there havebeen seven delta lobes ofthe Mississippi

Delta switching every~1000 years or so.

Bed load of Mississippionly about 5%. Mostsediment is suspended.


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Delta Mouth Deposition

An Example:

60 foot (18.2 m) channel depth

50 foot (14.2 m) thick distributary mouth bar

Aerial View of Mississippi Delta Mouth Deposition

A breach in the levee during flood can result in a sub-delta or “crevasse splay”



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Aerial View of Delta Mouth Deposition

West Bay —A short-lived Crevasse Splay

Development of a Crevasse Splay


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West Bay Crevasse Splay in Late 1980s

Crevasse splay ismostly submerged

Example of a Productive Crevasse Splay

Admire 650 sandstone –25+ foot (~8m) sands with up to 24% porosity and 1500 millidarcies

400+ mmbor

15x9 mile (24x15 km) near Wichita, Kansas

In 1915, it represented10% of world production



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Profiles of Shelves Off Seven Deltas


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Nile Delta: Wave Dominated

Nile Delta: Wave Dominated



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Niger Delta: Wave and Tidal Dominated

Niger Delta: Wave Dominated Portion

Smooth NigerDelta coastlineEscravos, Nigeria

Would you know you were on a delta?


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NNE–SSW Cross Section Through the Niger Delta




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Tidal Delta Features

Fly River Delta: Tide Dominated

Fly River Delta, Paupua New Guinea

Tidal delta 5–6 m tides

Good reservoir potential


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Deltaic Structural Styles

SW Iceland: 50 miles wide, 30 mile long braid plain (80x48km)



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Close-up of Vertical Section of Braid Delta

Braid/Fan Delta, Peyto Lake, Alberta, Canada


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Fan Delta Prograding into Indian Ocean, Betty’s Bay, South Africa

Concave upwardprofile of alluvial fan

Fan Delta, Atlantic Ocean Side Capetown South Africa

Notice the effect of relatively high energy wave action on poorly sorted alluvial fan sediments

Potentially good reservoir rock



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Brae Field, North Sea: Productive Example of a Fan Delta

Brae Field, North Sea: Structure Map


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Brae Field, North Sea: Geologic Cross Section

Brae Field, North Sea: Stratigraphic Column



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Brae Field, North Sea: Geologic Model

Fan Delta, Modern Day Analogue for Brae Field

Laguna Salida, NWMexico


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Learning Objectives

By the end of this lesson, you will be able to:

Define what a ‘Delta’ is

Understand the processes which result in the formation of distributary channels, distributary mouth bars, bar fingers and crevasse splays

Relate delta morphology to the slope of the shelf

Describe what controls reservoir shape, size and orientation of deltaic deposits by sediment input, wave energy, and tidal range

Explain variations in delta type as it relates to sediment input environments: Alluvial Fan, Braided Rivers, and common deltas

You now can:



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Documents

LLC Marginal Marine Depositional Environments Core …cloud1.activelearner.com/.../GEO-MMD/MMD_01_Slides.pdf · Marginal Marine Depositional Environments Core Deltas and Deltaic Deposits