Sediment and Sedimentary Rocks
Chapter 6
Eroded sandstone formations from ancient sand dunes – Colorado Plateau
Omo River basin – Ethiopia
- hot, dry, inhospitable
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Sedimentary Rocks
Chapter 6
• Produced from weathering products of pre-existing
rocks or accumulated biological matter
– Detrital rocks produced from rock fragments
– Chemical rocks produced by precipitation of dissolved
ions in water
– Organic rocks produced by accumulation of biological
debris, such as in swamps or bogs
Relationship to Earth’s Systems
• Atmosphere
– Most sediments produced by weathering in air
– Sand and dust transported by wind
• Hydrosphere
– Water is a primary agent in sediment production,
transportation, deposition, cementation, and formation of
sedimentary rocks
• Biosphere
– Biological activity key to formation of sedimentary rocks
– Petroleum and coal resources have biological origin
From Sediment to Sedimentary Rock
Deposition
– Environment of deposition is the location in which
deposition, settling, accumulation occurs
•
•
•
•
•
Deep sea floor
Beach
Desert dunes
River channel
Lake bottom
From Sediment to Sedimentary Rock
• Preservation
– Sediment must be preserved, as by burial with additional
sediments, in order to become a sedimentary rock
• Lithification
– General term for processes converting loose sediment into
sedimentary rock
– Combination of compaction and cementation
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Lithification
AND/OR
3. RECRYSTALLIZATION
Shells made of aragonite
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Shells made of calcite
From clasts to rocks
SEDIMENT
ROCK
Figure 8.1
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Conglomerate
Sandstone
From clasts to rocks
SEDIMENT
ROCK
Figure 8.1
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Siltstone
Shale or Mudstone
Types of
Sedimentary Rocks
• Detrital sedimentary rocks
– Form from cemented sediment grains
that come from pre-existing rocks
• Chemical sedimentary rocks
– Form by precipitation of minerals from
solution
– Have crystalline textures
•Organic sedimentary rocks
– Accumulate from remains of organisms
Clues to a bed’s origin
Sediment-laden flood water
carries a wide range of clasts.
As velocity of flow drops,
the largest clasts settle first.
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Clues to a bed’sClues
originto a bed’s origin
As velocity of flow drops,
the largest clasts settle first.
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Cross Bedding
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Cross-bedding
SORTING
Very poorly sorted
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Moderately sorted
Very well sorted
Sorting and Roundness
ROUNDNESS
High sphericity
High sphericity
High sphericity
Low sphericity
Low sphericity
Low sphericity
Angular
Intermediate
Rounded
Grains which have traveled the farthest will be more rounded.
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Examples of Sediment Sorting
Glacial till is typically poorly sorted.
sorted
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Sand grains are well
From Sediment to Sedimentary Rock
• Transportation
– Movement of sediment away from its source, typically by
water, wind, or ice
– Rounding of particles occurs due to abrasion during transport
– Sorting occurs as sediment is separated according to grain size
by transport agents, especially running water
– Sediment size decreases with increased transport distance
V = D/T
D1 = 10 cm
D2 = 5 cm
D3 = 2 cm
T1 = 2 sec
T2 = 2 sec
T3 = 2 sec
V2
V3
Find: V1
Water velocity
Chemical Biogenic Sediments
Utah's Bonneville Salt Flats
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Foraminifera
One-celled plankton
Banded Iron Formation - Australia
Black layers are
rich in reduced iron
(Fe2+)
Red layers are rich in
oxidized iron (Fe3+)
White layers are
rich in silica.
* Iron dissolved in seawater formed chemical sediments.
* Today iron content in seawater is lower, because it reacts with oxygen in atmosphere
* Algea bacteria, the early photosynthesizers, may have oxygenated our atmosphere.
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Biogenic Sedimentary Rocks
Limestone
A sedimentary rock that consists
primarily of the mineral calcite.
Peat
A biogenic sediment formed from the
accumulation and compaction of
plant material.
Coal
A combustible rock formed from the
lithification of plant-rich sediment.
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Two of these rocks are sedimentary, one is igneous.
Can you identify them?
Plate Tectonics and Sedimentary Rocks
• Tectonic setting plays
key role in the
distribution of
sedimentary rocks
• Occurrence of specific
sedimentary rock types
can be used to
reconstruct past platetectonic settings
• Erosion rates and
depositional
characteristics give clues
to each type of tectonic
plate boundary
Sites of sedimentation
Figure 8.16
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Divergent plate boundaries
Sites
Sitesof
ofsedimentation
sedimentation
Figure 8.16
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Convergent plate boundariesCollisional-type
Sites
Sitesof
ofsedimentation
sedimentation
Figure 8.16
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Convergent plate boundariesSubduction-type
Amazing Places: The Navajo Sandstone
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Sedimentary Rocks (?) on Mars
In all the craters, the walls expose subsurface sedimentary rock (fine-grained
sandstones) up to ten meters thick. The deeper the crater, the more layers are
visible; no underlying rock has yet been seen. The whole of Meridiani
Planum, hundreds of kilometers wide, appears underlain by sedimentary rock
to a depth that is still unknown.
Pancam photo mosaic, approximately true color: NASA/JPL/Cornell
Sedimentary Rocks (?) on Mars
Fractured and apparently layered rock on Mars.
Credit: NASA/JPL-Caltech/MSSS
Sedimentary Rocks (?) on Mars
More than four years after Mars rover Spirit visited the Comanche
outcrop in Gusev Crater's Columbia Hills, scientists armed with a new
instrument calibration have discovered the rocks are rich in long-sought
carbonate minerals. Comanche (left) and Comanche Spur (right) appear
reddish-brown in this false-color image from Spirit's Pancam. (The
bluish-wite rocks in the foreground belong to an unrelated outcrop.)
Credit: NASA/JPL/Cornell University
Read more at: http://phys.org/news/2010-06-mars-rover-instrumentoutcrop-long-sought.html#jCp
Sedimentary Rocks (?) on Mars
NASA/JPL
* Pancam image of rover tracks cutting through fields of blueberries.
* “Blueberries” may be hematite.
Sedimentary Rocks (?) on
Mars
This Mars Global
Surveyor
Image reveals the layered
floor of western Candor
Chasma in the great
martian canyon Valles
Marinaris. The uniform
pattern -- beds of similar
properties and thickness
repeated over a hundred
times -- suggest that
deposition was interrupted
at regular or episodic
intervals. Patterns like
this, when found on Earth,
usually indicate the
presence of sediment
deposited in dynamic,
energetic, underwater
environments.
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© 2008, John Wiley and Sons, Inc.