Marine sedimentary processes and the deep ocean

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Forces that act upon the continental shelf have much less effect on the deep sea environment

Deep sea= v.still. Some light currents- but v. different sedimentary regimes.

On the continental shelf:

  • Turbulence prevents particles from settling + transports them seaward where they are deposited in deeper water.
  • Particle size decreases seaward for geologically recent sediments.
  • Past fluctuations of sea level may have stranded coarse sediment (relict) across the continental shelf. 

Globally- we get different varieties of sea sediments at different latitudes

  • Tropical shelves- we get calcareous biogenic sediments.
  • Temperate shelves- sands and muds from river estuaries.
  • Polar shelves- glacial till + ice rafted sediments.
  • Thickness of sediment vary widely- v. thick near to large estuaries e.g. Ganges delta, missippi river, Amazon etc. - deep sea sediment fans e.g. Bengal fan.- large sources of terrestrial sediments.
  • Upwelllings-promote plankton growth- produces thick sediments of biogenic oozes.

Deep sea sedimentation

External- terrigenous material from land

Internal- biogenic and authignenic (formed where found)

Major sedimentary processes:

  • Bulk emplacement- slumps + earthquakes, debris flows, turbidity currents.
  • Red clay=forms when dust is blown far out to sea and sink.  Dust from deserts=important-provides Iron for plankton growth.
  • Authigenic deposits- (in-situ)chemical and biochemical precipitates that form on the seafloor- e.g. ferromanganese nodules + phosphorite. 
  • Pelagic (open water)= any sediment that forms out at sea
  • Biogenic oozes
  • Calcareous oozes- above calcium carbonate compensation…

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