from sediment into sedimentary rockhomepages.wmich.edu/~kehew/geos1000/ch08_sedimentary...
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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)