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FROM SEDIMENT INTO

SEDIMENTARY ROCK

Objectives

• Identify three types of sediments.

• Explain where and how chemical and biogenic

sediments form.

• Explain three processes that lead to the lithification of

sediments.

• Explain how features such as ripples, cracks, and

fossils tell geologists about the environment in which a

rock originated.

• Identify plate tectonics that are favorable for the

accumulation of sediments.

Sediments and Sedimentation

• Deposition

– The laying down of sediment

• Sediment separated into three broad categories

– Clastic

– Chemical

– Biogenic

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Sediments and Sedimentation

Sediments and Sedimentation

• Clastic sediment

– Sediment formed from fragmented rock and mineral

debris

– Produced by weathering and erosion

– Described by particle shape, angularity, and size

• Clastic sediment

– Volcaniclastic

sediments

• Volcanic in

origin

• Pyroclasts

– Distinguished

by size

» Bombs

» Lapilli

» Ash

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Clastic sediment

Clastic sediment

Clastic sediment

Glacial till: poorly sorted Well sorted, well rounded,

quartz sand

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Sediments and Sedimentation• Chemical sediment

– Sediment formed by the

precipitation of minerals

dissolved in lake water,

river water, or sea water

– Plants and animals alter

chemical balance

• Limestone

– Shallow sea water

evaporation causes

dissolved salts to

precipitate

Sediments and Sedimentation

• Biogenic sediment

– Sediment that is

primarily composed of

plant or animal remains

• Shells, bones, teeth

• Wood, roots, leaves

– Or, precipitates as a

result of biologic

processes: foraminifer in

the head of a pin

Sedimentary Rocks• Lithification

– The processes by which

loose sediment is

transformed into

sedimentary rock

• Bedding

– The layered arrangement

of strata in

sediment/sedimentary rock

• Bedding surface

– The top or bottom surface

of a rock stratum or bed

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Lithification Processes

Lithification Processes

Lithification Processes

• Compaction

– Reduction of pore space

in a sediment as a result

of the weight of overlying

sediments

• Cementation

– Substances dissolved in

pore water precipitate out

and form a matrix in

which grains of sediments

are joined together

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Lithification

Processes

• Recrystallization

– The formation of

new crystalline

mineral grains

What kind of sediment?

• How do you know? • How do you know?

Compare textures of a sedimentary rock with

an igneous rock (granite)

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Types of Sedimentary Rocks

• Clastic sedimentary rock

– Conglomerate

• Has large fragments in a finer grained matrix

– Sandstone

• Medium grained, where clasts are typically, but not necessarily,

dominated by quartz grains

– Mudstone

• A very fine grained sedimentary rock of the same composition as

shale but without fissility

– Shale

• A very fine grained fissile or laminated sedimentary rock,

consisting primarily of clay sized particles

Conglomerate

Figure 7.6

Quartz sandstone

Figure 7.4

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Breccia

Figure 7.7

Shale with plant remains

Figure 7.2

Types of Sedimentary Rocks

• Chemical sedimentary rocks

– Evaporite

• Formed by the evaporation of lake water or sea water, followed by

lithification of the resulting salt deposit

– Banded iron formation

• A type of chemical sedimentary rock rich in iron minerals or silica

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Evaporites

Bedrock geology of Lower Michigan

http://www.deq.state.mi.us/documents/deq-glm-rcim-geology-

1987_Bedrock_Geology_Map.Pdf

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Travertine-Mammoth Hot Springs, Yellowstone NP

Banded Iron Formation (BIF)

Types of Sedimentary Rocks

• Biogenic sedimentary rocks

– Limestone

• A sedimentary rock that consists primarily of the mineral calcite

– Peat• Formed from the accumulation and compaction of plant remains

– Coal• A combustible rock formed from the lithification of plant-rich sediment

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Coquina

Figure 7.9

Chalk

White Cliffs of Dover

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Depositional Environments

• Interpreting

environmental clues

– Patterns formed by air

and water moving over

sediments

• Preserved and later

exposed

– Ripple marks

– Fossils

– Mud cracks

Ripple marks

Characteristics-fossils

Fossiliferous limestone

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Mud cracks

Depositional Environments on Land

Depositional Environments on Land

• Streams

• Lakes

– Delta

• A sedimentary deposit,

commonly triangle shaped,

that forms where a stream

enters a standing body of

water

– Glacier

– Wind

• Eolian sediment

– Sediments that are

carried and deposited

by the wind

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Depositional Environments on Land

Delta Old Lake bed

Lacustrine sediments-Lake

Michigan Bluffs

Depositional environments in and

near the ocean• Delta

• Estuary

– Semi-enclosed body of

coastal water, in which

fresh water mixes with

sea water

• Beaches

• Shelves

• Carbonate platforms and

reefsGreen beach

due to olivine

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Chesapeake Bay:

An Estuary

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Great Barrier Reef

Depositional environments in and

near the ocean

Carbonate platform in the Bahamas

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Depositional environments in and

near the ocean

• Turbidites

– A turbulent, gravity driven flow consisting of a mixture of

sediment and water,

– Conveys sediment from the continental shelf to the deep

sea

• http://www.youtube.com/watch?v=tfNLI2JW7mg&NR=1

• Seafloor

– Rich in nutrients

• Calcareous ooze

• Siliceous ooze

Deep sea sediments deposited

by turbidity current (turbidite)

How Plate Tectonics Affect

Sedimentation

• Divergent plate boundaries

– Rift valleys

• A linear, fault-bounded valley along

a divergent plate boundary or

spreading center

• Convergent plate boundaries

– Collisional type

– Subduction type

• Back-arc basin

• Accretionary wedges

• Ophiolites (slabs of oceanic

lithosphere)