Ocean Sediments

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Ocean Sediments
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Importance of Sediments

• Economic Value
• Oil, fossil fuels
• Salt Phosphorus deposits
• Determine shape structure of Ocean bottom
• Strongly affect distribution of Benthic Organisms
• Chronological record of Earths history
• Tectonic history
• Climate history
• Evolutionary history

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Sediment Thickness
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Topographic profiles
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Law of Superposition

• Younger sediments over Old sediments
• YOUNG
• ----------------------
• OLD

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Sediment Classification

• By Grain Size
• By Origin

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Sediment Classification

• Grain Size
• Clay lt4 µm
• Silt 4-62 µm
• Sand 62-2000 µm
• Gravel gt2000 µm

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Table 3.1
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Basic Sediment Transport(READ CC4)
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Sediment Sorting

• Well-sorted sediments are those of similar size
  class
• Beach well sorted (far from source)
• Glacier not sorted (close to source)

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Sediment Angularity

• Sediment weathering during transport induces loss
  in angularity
• Angular grains (close to source)
• Rounded grains (far from source)

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Sediment Classification

• Origin
• Lithogenous or Terrigenous (75)
• Biogenous (20)
• Hydrogenous
• Cosmogenous

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Lithogenous Sediments

• Fragments of rocks broken, weathered and eroded
  form lithogenous sediments

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http//images.google.com
Frost Wedging
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Wind Rain erosion
www.naturalphotos.com
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Lithogenous Sediments

• Transport of sediments by
• Rivers
• Glaciers
• Waves
• Wind
• Landslides
• Humans

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www.southalabama.edu
http//earthobservatory.nasa.gov
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Sediment Discharge by Rivers

• Ganges 1700 million Tm/year
• Amazon 900 million Tm/year
• Mississippi 260 million Tm/year
• (Figure 6-2)

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• http//www.pbs.org/harriman/images/

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• http//www.pbs.org/harriman/images/

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walrus.wr.usgs.gov/elnino/coastal/ images/
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http//earthobservatory.nasa.gov
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Aerial dust transport

• Winter

• Summer

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St Helens
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• http//geohazards.cr.usgs.gov/

• http//web.umr.edu/rogersda

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• http//www.hihwnms.nos.noaa.gov/graphics/

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Biogenous Sediments

• Composed of planktonic organism remains
• Calcareous skeletons (CaCO3)
• Siliceous skeletons (SiO2)
• Accumulation rate controlled by
• Primary productivity
• Rate of dissolution
• (Importance of fecal pellets)

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Figure 3.21a
Diatoms (siliceous high latitudes) Coccololithosp
heres (calcareous mid latitides)
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Figure 3.21b
Radiolarians (siliceous low latitudes)
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Foraminifera (calcareous all latitides)
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Pteropods (calcareous all latitudes)

• http//www.mbari.org/expeditions/

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Dissolution Biogenous Particles

• Silica
• Ocean is UNDERSATURATED with silica
• Dissolution highest in surface waters
• Low Pressure
• High Temperature
• Accumulation in sediments occurs in
• Areas of very high productivity
• Poles and upwelling zones (diatoms)
• Tropics (Radiolarians)

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Dissolution Biogenous Particles

• Carbonates
• Foraminifera (Calcite) less soluble
• Pteropods (Aragonite) More soluble
• Dissolution is highest in Deep Waters
• High pressure
• Low temperatures
• Low pH (high C02)
• Carbonate Compensation Depth (CCD)

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Carbonate Compensation Depth

• CCD varies with Latitude
• CCD varies between Oceans
• North Pacific 1000m
• South Pacific 2500m
• Atlantic 4000m

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Carbonate Compensation Depth

• New Deep Waters have low CO2 conc.
• Old Deep Waters have high CO2 conc.
• Animal respiration
• Decomposer activities
• Pacific Deep Waters are older than Atlantic Deep
  Waters

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Global Thermohaline Circulation
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Carbonate Compensation Depth Greenhouse Effect?

• CO2 atmosphere, seawater sediments are
  interrelated!
• Will increase in atmospheric CO2 cause increase
  in dissolved seawater CO2?
• Consequences of a shallow CCD?
• Release into atmosphere of dissolved carbonate
  sediments?

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Hydrogenous Sediments

• Lower concentrations than Lithogenous and
  Biogenous sediments
• Ocean water usually is UNDERSATURATED, but..
• Hydrothermal Vent Minerals (metal rich sedim.)
• Manganese Nodules (areas of low sedimentation)
• Carbonate banks - CaCO3 precipitates at
• High Temperature
• Low Pressure
• High pH (low CO2)
• Caused by high productivity - photosynthesis

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Bahamian Bank
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Carbonate Sediments
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Figure 3.23
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Chicxulub crater
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End
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