Sedimentary RocksInterpretations

What do Sedimentary Rocks Record?

• Source of sediment• Erosion and Transport Agent• Distance of Transport• Depositional Environment• Paleogeography/Tectonic Setting

Interpretation of Composition

Detrital Rocks:• Source of sediment• Exposure to Weathering (Distance of Transport) (Type of Climate)

Note About Detrital Rock Color & Composition

•Grain SizeSmaller is often darker

•CompositionCarbon - black or brownQuartz - tan, clear, whiteOrthoclase - orange

•Depositional EnvironmentIron on land - redIron in deep, oxygen poor water - green

Interpretation: Grain Size

• Gravel

• Sand

• Silt

• Clay

• River, Beach

• River, Beach, Desert

• Delta, Shallow Ocean

• Deep Ocean, Lake, Swamp

• High Energy

• Low Energy

Detrital Rock Names

(Based Primarily on Grain Size)

Sand Sized: Sandstone

Gravel Sized:Conglomerate

Siltstone Shale

Mud Sized:Mudstone

Interpretation: Sorting

Interpretation:Poorly SortedWell Sorted

Transport AgentGravity and Glaciers (and Rivers)Water and Wind

Clast Supported

Conglomerate(River

Deposits)

Matrix Supported Conglomerate

(Glacial/Landslide Deposits)

“Modern”Glacial Sediments

2.2 Gyr Conglomerate

Interpretation:Distance of TransportShort Far

Interpretation: Grain Roundness

Limestone

CrystallineLimestone

Chalk

Fossiliferous Limestone

Formation of Limestone

Calcite Precipitates inWarm WaterWater Under Low Pressure (Shallow)

Or

It is secreted by biological organismsClams, Mussels, Scallops, etc.CoralsForaminifera

Limestone Represents:

Shallow Tropical Ocean

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Black Sea

Travertine(Limestone

)

Chert (Flint, Jasper, Agate…)

Diatom Steletons

Chert Represents

Deep Ocean

Evaporites:Bonneville Salt Flats, Utah

RockGypsum

Rock Salt

Isolated,Arid,Salty

Sea/Lake

Peat and Coal

Swamp, Bog

Intermission: QuizWhat can you say about the history

of this rock?

Quartz Sandstone

Deposited in a beach/river or desert,

very far from the source of the sediment.

Intermission: QuizWhat can you say about the history

of this rock?

Shale

Deposited in a quiet water environment (deep ocean, lake,

lagoon). Dark color implies oxygen-poor environment, rich in

organic material.

Intermission: QuizWhat can you say about the history

of this rock?

Limestone

Deposited in a shallow tropical ocean.