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…