6SEDIMENTARY ROCKS

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6SEDIMENTARY ROCKS
Goosenecks of the San Juan River
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San Juan Goosenecks
The sinuous black ribbon of the San Juan River
cuts deep into the sandstone-pink landscape of
southeastern Utah. The image shows Goosenecks
State Park, where the river is surrounded by
canyon walls more than 1,000 feet high. Light
gray, pink, and white striations (parallel lines)
on the canyon walls mark where the river has
eaten away at the ancient landscape to reveal 16
layers of geology, the oldest of which is well
over 300 million years old.
Form when loose sediment (mud, sand, gravel) or
organic material consolidates, or when ions in
solution precipitate.
The ancient San Juan River flows out of the San
Juan Mountains in southwestern Colorado. Early in
its history, the river flowed over a flat
landscape where swirling water wandered freely in
ever-changing loops. Over time, the river wore
away at the earth, cutting the deep canyons seen
here, until its course was fixed into a groove.
At the same time, the land of southern Utah and
northern Arizona was being pushed up, making the
groove even deeper. The resultthe chasms of
Goosenecks State Parkis one of the best examples
of an entrenched river meander in the world.
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DIAGENESIS LITHIFICATION
Ripples in beach sand , such as those in the
upper photograph (A) may someday become a rock
like the sandstone in the lower photograph (B).
This sandstone was part of a beach over 200
million years ago in the Triassic period. Images
courtesy of Windows to the Universe,
http//www.windows.ucar.edu
DIAGENESIS all the chemical, physical and
biological changes that affect sediments after
deposition occurs near/at surface at low
temperatures (lt150-200C) recrystallization lit
hification compaction, cementation
Sediment (A) may someday become a clastic rock
(B) if compacted and cemented together. Images
courtesy of Windows to the Universe,
http//www.windows.ucar.edu
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TYPES of SEDIMENTARY ROCKS
DETRITAL consolidation of solid
particles CHEMICAL precipitation of dissolved
substances inorganic (evaporation) organic
(biochemical)
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DETRITAL SEDIMENTARY ROCKS
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DETRITAL SEDIMENTARY ROCKS
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DETRITAL SEDIMENTARY ROCKS
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CHEMICAL SEDIMENTARY ROCKS
Inorganic (evaporation)
travertine limestone
oolitic limestone
chert
rock salt
rock gypsum
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CHEMICAL SEDIMENTARY ROCKS
organic (biochemical)
fossiliferous limestone
coquina limestone
chert
bituminous coal
chalk
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CHEMICAL SEDIMENTARY ROCKS
Two Groups Inorganic limestone chert rock
salt rock gypsum organic (biochemical) limestone c
hert coal
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SEDIMENTARY ENVIRONMENTS
Continental Transitional Marine
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SEDIMENTARY FACIES

• Deposits of sediment that have distinctive
  physical, chemical, or biological attributes
• Coarse-grained deposits in a high-energy
  depositional environment are adjacent to
  finer-grained sediments that are deposited in
  quieter water

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SEDIMENTARY FACIES
Transgression Rise in sea level relative to land,
results in offshore facies being deposited over
nearshore facies Regressions Fall in sea level
relative to land, results in nearshore facies
being deposited over offshore facies.
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SEDIMENTARY STRUCTURES
Strata or beds Graded bedding Cross-bedding Ripple
marks current vs. wave Mudcracks Fossils
Strata or beds layers of sedimentary rocks
distinguished based on composition, texture
(grain size), color reflect changes in source
material, flow velocity, cementation
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SEDIMENTARY STRUCTURES
Strata or beds Graded bedding Cross-bedding Ripple
marks current vs. wave Mudcracks Fossils
Cross bedding layers of sediment deposited at an
angle reflects current flow in dunes, stream
channels, deltas
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Origin of CROSS BEDDING
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CROSS BEDDING
Cross bedding Layers are arranged at an angle to
the deposition surface can interpret flow
direction (wind, water) Sand dunes in deserts and
along shorelines, stream channels, shallow marine
environments
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GRADED BEDDING
Single bed shows an upward decrease in grain
size form by turbidity currents (underwater
landslides) deposit called a turbidite
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RIPPLE MARKS
Small ridges with intervening troughs Current
ripples are asymmetric (stream channels,
dunes) Wave (oscillation) ripples are symmetric
(shallow marine waves)
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MUD CRACKS
Clay-rich sediment dries, shrinks and
cracks Periodic drying (river floodplain,
lakeshore, tidal flats)
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FOSSILS
Remains or traces of prehistoric life Most
organisms are uniquely adapted to their habitat
and lived at specific times during the geologic
past
trilobite
T. rex
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RESOURCES
Petroleum and Natural Gas Hydrocarbons that
originate from the microscopic remains of marine
organisms They migrate upward through porous rock
until they encounter a structural or
stratigraphic trap
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RESOURCES
Source rock organic rich shale, generates oil
or gas Reservoir rock porous and permeable,
store petroleum (sandstone) Cap rock or seal
impermeable to allow oil or gas to collect
(shale) Trap structure to prevent oil or gas
from leaking away (anticline)
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RESOURCES

• Uranium
• Most uranium used in North American nuclear
  reactors comes from carnotite, a mineral found in
  sedimentary rocks
• K2(UO2)2(VO4)2- 1-3H2O
• Hydrated Potassium Uranyl Vanadate.
• An important ore of uranium and vanadium and as
  mineral specimens.

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RESOURCES
Banded Iron Formation Layers of chert with iron
oxide (hematite) All over 2 b.y.