Origin and Distribution of Marine Sediments

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Origin and Distribution of Marine Sediments

• Whats all that squishy muck at the bottom of the
  ocean?
• What can we learn from it?

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Marine Sediments are

• Particles of various sizes derived from a variety
  of sources that are deposited on the ocean floor
• A vast library recording geologic,
  oceanographic and climatic conditions
• Remarkably complete compared to land

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Where do these come from?

• Inputs are-- rivers-- atmosphere-- surface
  waters-- volcanoes (both on land and submarine)
  -- deep ocean water-- outer space

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Classifications

• By SizeClay -- Silt -- Sand -- Pebble -- Cobble
  0.001 mm 1 mm
  100 mm
• Effects of water velocity on transport rivers
  and near-shore vs open ocean

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Sediment Transport

• Fluid velocitydetermines thesize of
  theparticles thatcan be moved

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Size Sorting
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Classifications

• By OriginTerrigenous -- from landBiogenous --
  from life in the oceansHydrogenous --
  precipitated from waterCosmogenous --
  extraterrestrial

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Terrigenous sediments
(from land)

• Rivers
• Winds (eolian)
• Glaciers (ice-rafted debris, IRD)
• Turbidites
• Sea level changes

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River sediment loads (units 106 tons/yr)
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Glacial (Ice-rafted debris)
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Turbidites

• Rapidly-accumulated terrestrial sediments
• Earthquake-triggered submarine avalanches
• High velocity (50 mph!), erosive events
• Good examples preserved on Marys Peak

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Turbidites (submarine avalanches)
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Sea Level Changes
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Biogenous sediments (from living
things)

• Calcareous (CaCO3)Foraminifera --
  animalsCoccolithophores -- plants
• Siliceous (SiO2)Radiolaria -- animalsDiatoms --
  plants

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mm micron millionth of a meter!
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mm micron millionth of a meter!
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mm micron millionth of a meter!
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mm micron millionth of a meter!
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Productivity skeletons and soft tissue

• Accumulation depends on production and
  preservation
• SiO2 is preserved everywhere
• CaCO3 is variable, depending on P, T, pH

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Carbonate Compensation Depth
South
North
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Carbonate Compensation Depth

• The depth at which carbonate input from the
  surface waters is balanced by dissolution in
  corrosive deep waters
• In todays ocean this depth (CCD) varies between
  3 km (polar) and 5 km (tropical)
• Thus, accumulation rates vary a lot!

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Accumulation Rates for Oozes

• Productivity
• reproduction of planktonic organisms
• Preservation
• silica dissolves only very slowly
• calcium carbonate varies with depth
• Rates are variable lt1 to 15mm/1000 yr

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Coastal waters are often highly productive, with
abundant planktonic organisms thriving in the
surface waters. Why then are biogenous oozes
rarely found nearshore??
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• the large input of terrigenous sediment to the
  continental margin overwhelms the biogenous
  component in the sediment.

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Hydrogenous (from sea water)

• Metalliferous sediments at spreading ridges --
  black smokers
• Manganese nodules
• Evaporites -- Salt deposits

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baseball to bowling ball size!
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Cosmogenous (from outer space)

• Meteorites and comets

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Sediment Accumulation
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Sediment succession
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Distribution of Marine Sediments