Mudrocks, Organic Deposits, and other

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Mudrocks, Organic Deposits, and other Rare
Sediments
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MudrocksSilts and Clays

• Formed from weathering of primary
• Minerals
• Accounts for 60 of all siliclastic
• sedimentary rocks
• Most form from in soils upon continents
• Some form from alteration by ground-
• And marine waters

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Silts Eolian Deposition
Air-borne Silts in a Dust Storm
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Dust Storm
Stratford, TX 1935 The Dust Bowl Era
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Extended periods of Dust Storm events can lead to
significant
accumulation of silts, especially in low areas
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Pleistocene-age accumulation of silts in the
central U.S.A.
Requires fairly dry climate, wind, and a lot of
silt size material
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When Silt size dust accumulates as sediment, it
is called LOESS.
Loess in Nepal
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Pleistocene Loess mantles the landscape in parts
of Iowa, U.S.A.
Loess Layer
River Gravels, See the Channel?
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Early Permian Halgaito Fm., Southeastern Utah,
U.S.A. Is made mostly of silt, so it may be a
loessite
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Late Pennsylvanian-age Maroon Fm. Colorado, U.S.A.
Loessite
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Bentonites
Altered volcanic ash-fall deposits
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Bentonites
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Bentonites
Bentonites are mostly preserved in low areas
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Bentonites
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• Alteration of Volcanic Ashes releases silica
• Into solution, leaving montmorillonite
• Toothpaste
• Paint
• Filler
• Drilling Muds

What becomes of the free silica?
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Some of the free silica is used to
form DIATOMITES AND DIATOMACEOUS EARTH
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DIATOMS are single-celled photosynthesizers that
use silica in solution to make a skeleton
DIATOM skeletons are made of a mineralloid
called opal-A.
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Opal-A is amorphous silica with lots of Waters
of hydration SiO2nH2O
Although soft and not chemically stable Opal-A
is beautiful and used in jewelery
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When Opal-A is buried, put under pressure From
overlying sedi- ments and heated, waters of
hydration are expelled to form Microcrystalline
quartz, or chert SiO2
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ORGANIC MATTER IN THE SEDIMENTARY RECORD

• Of all Siliciclastics, mudrocks hold the largest
  amount of O.M.
• Most Mudrocks have 2 O.M. by weight
• 3 kinds of Organic Matter
• Humus soil organic matter
• Peat organic matter accumulated in fresh or
  brackish H2O
• Sapropel low-oxygen environments, finely
  disseminated

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Black Shales 3 to 10 weight Organic
matter Incorporate sapropellic organic matter
Black Shales accumulate in sluggish, poorly
circulated marine Environments (anoxia).
Abundant in Earths Past.
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Epieric Seas
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Oil Shales

• 25 weight organic matter
• Almost all of the O.M. is kerogen, derived from
  ALGAE
• Cracks to give petroleum at 350 degrees
  Celcius
• Not all are shales because many deposits are
  formed in
• Fine-grained carbonate
• Important source of Energy around the world

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The Most Famous Oil Shale you might know Is the
Eocene-age Green River Formation
A big lake system in Colorado, Wyoming, and Parts
of Utah. Alternating periods of algal Blooms and
carbonate precipitation from the Water column.
Anoxic bottom water resulted In exquisitely
preserved fossil fish and plants
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Coals
Coals Have greater than 70 organic
Carbon Derived almost entirely of plant O.M, so
it is Dominantly Peat-type organic matter
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Coal Ranking
Peat No Rank, unconsolidated, semi-carbonized
plant remains with high moisture content. Not
Coal Lignite lowest rank. Brown to
brownish-black coals with high water content and
commonly reatins much of the structures of the
woody plant fragments. Subbituminous coals
between lignite and bituminous coal Bituminous
coals hard, black coals with very little water
and high C content. Alternating brown and black
bands.
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Anthracite Hard, black, glassy and dense coal
with gt90 Carbon. Exhibits conchoidal fracture.
Typically only found in very ancient coals
(Carboniferous-age).
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Banded Iron Formations
Preserve record of important event in Earth
history Important source of industrial iron.
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Banded Iron Formations
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