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SedimentaryRocks and

Sedimentary

Basins

Reading

Stanley, S.M., 1998, Sedimentary Environments, Ch.5. Earth Systems History

Get it from the class website:

http://www.geo.wvu.edu/~jtoro/Petroleum/index.htm

Sedimentary Rocks

Intro

Origin of sedimentary rocks

Clastic Rocks

Chemical and Biochemical Sedimentary Rocks

Interpreting Sedimentary Rocks

Environment of deposition

Sedimentary structures

What is a Sedimentary Basin?

A thick accumulation of sediment

Necessary conditions:

1. A depression (subsidence)

2. Sediment Supply

Where are the Sedimentary Basins?World Map of Sed. Basins


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Our Peculiar Planet:

Liquid Water and Plate Tectonics

Tectonics

Hydrologic Cycle

SEDIMENT

Unconsolidatedproducts of Weathering & Erosion

Loose sand, gravel, silt, mud, etc. Transported by rivers, wind, glaciers, currents, etc.

Sedimentary Rock:

Consolidated sediment

Lithified sediment

3 Basic Types of Sedimentary

Rocks Detrital ( = Clastic)

Made of Rock Fragments

Biochemical

Formed by Organisms

Chemical

Precipitated from Chemical Solution

Detrital Material Transported by a River

Formation of a Sedimentary

Rocks1. Weathering

mechanical & chemical

2. Transport by river, wind, glacier, ocean, etc.

3. Deposition

in a point bar, moraine, beach, ocean basin,etc

4. Lithification

loose sediment turns to solid rock


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Processes during Transport

1. Sorting

Grain size is related to energy of transport

Boulders high energy environment

Mud low energy

Significance for Petroleum System?

Black shales Source rocks

Porous Sandstones Reservoirs

Processes during Transport

2. Rounding

abrasion is progressive

angular grains near source

rounded grains long transport


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Sorting and

Rounding

Well rounded

Well sorted

Quartz sandstone

Bimodal rounding

Poorly sorted

Lithic sandstone

Many depositional

environments with particularcharacteristics

Lithification

Compaction Decrease inpore space

Due to increasing pressure with burial

Cementation Pores filled

quartz or calcite cements

Recrystallization No porosity left

Beginning of metamorphism

Lithification

Determines the nature of the reservoir

Critical for economic viability

Highly variable

Hard to predict ahead of the drill


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Lithification of Shale

Dewatering of shale

Overpressure?

Expulsion of hydrocarbons?

Classification of Clastic Sediments

Based on Particle size

Gravel (more than 2 mm) Pebbles (small) (Driveway gravel)

Cobbles (medium) (Plum to melon size)

Boulders (large) (Melon to bus size)

Sand (2 mm - 1/16 mm)

Silt (1/16 - 1/256 mm)

Clay (< 1/256 mm)

Detrital Rock Names 1

Gravel Conglomerate

Naming of Sedimentary Rocks 2

Sand Sandstone

Quartz sandstone, Arkose sandstone (with

feldspar)

Fine Grain Detrital Rocks

Silt Siltstone

Mud Mudstone or Shale

Shalewith

plant

fossils


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Biochemical Sedimentary Rocks

Carbonate Rocks Limestone calcite (CaCO3 )

Dolostone dolomite (Ca,Mg (CO3 )2)

Coal

CARBONATE SEDIMENTARY

ROCKS

Made of Calcium Carbonate or Mg -Ca Carbonate Precipitated from seawater

Mostly by organisms (biochemical)

algae, shells, corals

In some cases chemically (inorganic)

Chalk- Microscopic algae

Chalk

White Cliffs of Dover, UK


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Carbonate Bank-

Bahamas

Coral Reef

Coral Reef Carbonates

Sedimentary Section of the Grand

Canyon

> 1.5 b.y.

250 m.y.

Unconformity550 m.y.

History of Sedimentation 1

History of Sedimentation 2North Slope Basin, AK


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Sedimentary Environments of

Deposition Sedimentary Environments

Type and geometry of sedimentary rocks Key to paleogegraphy

Prediction of distribution of source rocks and

reservoirs

Non-Marine Environments

Glacial

Lakes

Deserts

Alluvial Fans

Braided Streams

Meandering Streams

How do we recognize them?

Rock Types

Sedimentary Structures

Fossils

Geometry

Deserts

Perfect sorting

Great reservoirs

Rarely preserved

Alluvial Fans

Conglomerates

Poorly sorted

Not so great!


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Types of River

Mountain

Braided?

Meandering

Fluvial Environments (Rivers)

Braided StreamMeandering Stream

Meandering StreamDevelopment of Meanders

Time

Sandstone

Mudstone


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Channel Sandstone

Conglomerate

Sandstone

Well Log Response

Sea level

and the

Stacking

of Rocks

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