Download Sedimentology = Study of Marine Sediments

Sedimentology = Study of
Marine Sediments
Marine Sediments =
particles that have accumulated on
seafloor
 Describe different types of sediments by:
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source
 how transported
 chemical make-up
 particle size
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Sorting: measure of the uniformity of
grain sizes
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Larger particles only travel as far as water
has energy to keep them suspended
(Think where we see sand)
Smaller can carry further before settling
out
Unsorted = Mix of sizes
Well-Sorted = all one size
Classification of Sediments by Origin
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Four main types:
terrigenous aka lithogenous
 biogenous
 hydrogenous
 cosmogenous
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1. Terrigenous Sediments
(Lithogenous Sediments)
Source: derived from existing rocks that
weather and erode; particles are carried
to sea by wind, water, and ice
 Location Found: Mostly Continental
Margin - near rivers
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1. Terrigenous Sediments
(Lithogenous Sediments)
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Types:
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Muds = very fine clay
Glacial = mixed sizes of particles
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Icebergs break off, carry stuff with them
Volcanic = usually dust & ash unless close to
volcano
Type of rock: quartz (SiO2 –sand), clay,
volcanic ash
 Amount: 22 billion tons of terrigenous
sediment is added to the continental margin
each year
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2. Biogenous Sediments
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Source: hard remains of organisms
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Shells and skeletons of dead organisms
Diatoms, foraminiferans, radiolarians, and others
(TINY)
 Most live at surface, get eaten and eliminated,
and clumps of skeletons sink
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Made of either Calcium Carbonate (CaCO3)
or Silica (SiO2)
Location Found: Continental Margin
and Pelagic Sea (open ocean)
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Types:
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Types of rock formed:
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Often fine grained Oozes (contain 30 %
microscopic biogenous material)
Shell/coral fragments
Diatomaceous earth (used in toothpaste, filters,
medicines, paint, etc.)
Chalk (used for many things including chalkboards)
Limestone (Missouri rock)
Amount: Form at rate of 1-5 cm/1000 years
3. Hydrogenous Sediments
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Source: dissolved material in water
Chemical reactions cause dissolved
material to precipate
 Usually caused by change in temperature or
pressure
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Location Found: Continental Margin
and Pelagic Sea
3. Hydrogenous Sediments
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Types (wide variety):
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Amounts: not very much – only when conditions are
right
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metals
carbonates
phosphates
salts
Often found as nodules of iron or manganese
Round blobs about size of baseball
Or slabs
Form around small object such as shark tooth
May be very important economically one day
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Minerals for industry, fertilizer
4. Cosmogenous Sediments
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Source: from outer space
Space dust
 meteors
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Location Found: Continental Margin
and Pelagic Sea
4. Cosmogenous Sediments
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Composition of meteorites:
silicate rock material
 iron and nickel
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Amount: not very common
 Importance: determine large scale
cataclysmic changes such as dinosaur
extinction (KT boundary - layer of
Iridium)
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“Missing” Sediments
When drilling of seafloor began,
scientists didn’t find as much as they
expected.
 Why?
 The older sediments have been
subducted back into the mantle
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Why Study Sediments?
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Sediments Studies Reveal Earth’s
History
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Examples:
Past climate
 Plate motions
 Age of seafloor
 Fossil evolution and extinction
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