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Sedimentary Rocks

Weathering

Erosion

Transport

Deposition

Sediments

Lithification

http://www.teachnet-lab.org/ps101/bglasgold/rocks/EFCycleP2.gif

WeatheringThe sediments that make up sedimentary rocks are produced by:

Mechanical & Chemical Weathering

Mechanical Weathering

Types of mechanical aka physical

weathering

• unloading – rx expand when overburden lessened

• frost wedging – H2O expands 9% to ice

• insolation – solar heating � expansion

• salt crystals

• root wedging

• seismic deformation

Chemical Weathering

hydrolysis, oxidation,

dissolution, dehydration,

solutioning, bio-chemical

weathering

Mineral

Stability

big point: some

minerals are more

stable than others…

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Products of Weathering

• Lithic (Rock) Fragments(granite, basalt,schist, etc.)

• Dissolved Ions(Calcium, Potassium, Sodium, etc.)

• Rust Minerals (Hematite, Goertite, etc.)

• Clay Minerals(Bentonite, Montmorillonite, etc.)

• Residual Minerals(Quartz, Orthoclase, Muscovite, etc.)

Erosion & Transport

Water

Wind

Ice

Gravity

Common Depositional Environments Marine shoreline and near-shore

environments

Lithification

Sediment

Rock

Cementation

Typical Cements:

•Calcite

•Quartz

•Iron oxide

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Sedimentary Rocks

Identification

Note: Use many of the same terms to describe

sediments & sedimentary rocks.

Only difference is lithification!

Types of Sedimentary Rocks

Detrital or clastic Rocks Chemical Rocks

vs.

Difference: Texture

Detrital (Clastic Texture)

vs.

Chemical (Crystalline Texture)

Detrital Rock Composition

Detrital Rocks

• Lithic Fragments

• Quartz

• Clay Minerals

• Fossil Fragments

• Rust Minerals

• Orthoclase

• Muscovite / Biotite

Detrital Rock Texture

Clastic Texture

• Grain Size

• Grain Sorting

• Grain Rounding

• Sediment Maturity

Grain Size

•Gravel

2mm

•Sand

1/16 mm

•Mud - Silt

1/256 mm

•Mud - Clay

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Detrital Rock Names(Based Primarily on Grain Size)

Sand Sized: Sandstone

Gravel -Sized:

Conglomerate

Siltstone Shale

Mud-Sized:

Mudstone

Sorting

Gravel Sized Detrital Rocks(Subdivided Based on Grain Roundness)

Breccia

Conglomerate

Maturity

Mature

•Well Sorted

•Well Rounded

•All Quartz

Immature

•Poorly Sorted

•Angular grains

•Mixed Composition

including clay

Sandstones(Subdivided based

on maturity)

Quartz SandstoneArkose (Sandstone)

Lithic Sandstone Greywacke

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Sandstones Under a Scope

Detrital Sedimentary Rock ID

Chemical Rock Texture

Crystalline Texture

• Coarse

• Fine

Chemical Sedimentary Rocks(Names based primarily on composition)

Basic Rock Name

• Limestone

• Chert

• Rock Salt

• Rock Gypsum

• Peat or Coal

Composition

• Calcite

• Quartz (silica)

• Halite

• Gypsum

• “Carbon” / Plant

Remains

Chemical Rocks(Names based mainly on composition)

LimestonesCrystalline

Limestone

Chalk

Fossiliferous Limestone

Chemical Rocks (cont.)Evaporites

Rock

Gypsum

Rock Salt

Coal

Chert

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Chemical Sedimentary Rock ID

Sedimentary Rocks

Interpretations

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 brown

Quartz - tan, clear, white

Orthoclase – orange or pink

• Depositional EnvironmentIron on land - red

Iron in deep, oxygen poor water - green

Detrital Rock Names(Based Primarily on Grain Size)

Sand Sized: Sandstone

Gravel -Sized:

Conglomerate

Siltstone Shale

Mud-Sized:

Mudstone

Interpretation: Grain Size

• Gravel

• Sand

• Silt

• Clay

• River, Beach

• River, Beach, Desert

• Delta, Shallow Ocean

• Deep Ocean, Lake,

Swamp

• High Energy

• Low Energy

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Interpretation: Sorting

Interpretation:

Poorly Sorted

Well Sorted

Transport Agent

Gravity 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

Crystalline

Limestone

Chalk

Fossiliferous Limestone

Formation of Limestone

Calcite Precipitates in

Warm Water

Water Under Low Pressure (Shallow)

Or

It is secreted by biological organisms

Clams, Mussels, Scallops, etc.

Corals

Foraminifera

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Limestone Represents:

Shallow Tropical Ocean

Chalk

(Foraminifera)

Black Sea

Black Sea

Travertine

(Limestone)

Chert (Flint, Jasper, Agate…)

Chemical sed. rk formed

via silicious ooze in the

deep sea. Source of silica

= tests (tiny shells) of

radiolarians and diatoms

(which are made of silica)

Diatom Skeletons

Radiolarians

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Chert

Represents

Deep Ocean

Evaporites:Bonneville Salt Flats, Utah

Rock

GypsumRock Salt

Isolated,

Arid,

Salty

Sea/Lake

Peat and Coal

Swamp, Bog

Coal beds in Puget Group sedimentary rocks near Ashford

Sedimentary features and

structures

• beds

• crossbeds

• ripple marks

• graded beds

• fossils

• mud cracks

• raindrop imprints

• etc

Channel fill Sharon Conglomerate, Cuyahoga River valley,

Ohio

~315 Ma

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Crossbedded sandstone

Zion National Park. Festooned cross beds deposited by wind.

dune deposition

by wind!

Planar cross bedsSharon Conglomerate,

lower Pennsylvanian

Age (~315 Ma),

Cuyahoga River valley,

Ohio; interpreted as a

braided stream

sedimentary

environment (lens cap

~52 mm) – dune

deposition by water!

How crossbeds form—migrating dunes!

Turbidity currents

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Modern mud

cracks

modern mud cracks,

Ceres Road 2007

flood-deposited muds

Ancient mud

cracks in shale

Current ripples in wet sediment,

Baja CA

Ripple marks in sandstone, Capitol

Reef National Park, Utah

Ripple marks in tilted Puget Group sedimentary rocks

of Eocene age near Wilkeson WA

Pat Pringle, photo

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Fossil fish from Eocene Green River Shale in western

Wyoming

Fossil shells in sandstone, CA

Fossil metasequoia leaf from rocks

several miles east of Packwood,

Oligocene age

Lithologic Indicators of Climatehttp://www.scotese.com/

legend.htm

dipping beds in Centralia

Coal Mine, view to south

fossils from Skookumchuck

Formation

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http://orerockon.com/For_sale.htm

<= Portunites triangulum Crab,

Eocene, Wahiakum Co., Washingtonhttp://www.geo-tools.com/fossils.htm

More WA fossils!

Dinosaur footprint, Tuba City, AZ

Misc. Sedimentary Features

• Sorting

• Roundness

• Orientation: random vs. preferred

• Color

Sorting

Preferred orientationImbrication = strong current

Current direction is

right to left

Color

• Black = reducing conditions (ex: pyrite,

MnO2, organic matter)

• Green = near oxidation/reduction margin

(ex: glauconite, chlorite)

• Red = oxidation (ex: hematite, “red beds”—

most of these are subaerial)

Color is a function of size and composition

Finer grained = truer colors

Weathering & matrix cement also influence

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http://www.ci.tenino.wa.us/TeninoQuarry1_small.jpg

Eocene McIntosh Formation:

Tenino Sandstone

Photo donated by Larry McMIllan

outcrop along rr tracks near Chehalis R., Galvin WA

Rock Units

• FORMATION-

– Extensive enough to show on a map

– Distinctive from neighboring rock units

– Named locally

• CONTACTS

– Sedimentary contacts – bounding surfaces

between two sedimentary units

Grand Canyon – an awesome place to see strata! Monument Creek

Grand Canyon

Bob Webb, photo, 1986

Track of 1984 debris flow

The great unconformity

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Granite Rapid, Grand Canyon

Bob Webb, photo, 1986volcanologist for scale