Marine Sedimentation

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Marine Sedimentation
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Classification of marine sediments can be based
upon size or origin.
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Sediment in the Sea

• Size classification divides sediment by grain
  size into gravel, sand and clay.
• Mud is a mixture of silt and clay.
• Origin classification divides sediment into five
  categories Terrigenous sediments, Biogenic
  sediments, Authigenic sediments, Volcanogenic
  sediments and Cosmogenic sediments.

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Factors that control sedimentation include
particle size and the turbulence of the
deposition environment.
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Sediment in the Sea

• Terrigenous sediments strongly reflect their
  source and are transported to the sea by wind,
  rivers and glaciers.
• Rate of erosion is important in determining
  nature of sediments.
• Average grain size reflects the energy of the
  depositional environment.
• Hjulstroms Diagram graphs the relationship
  between particle size and energy for erosion,
  transportation and deposition.

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Based upon water depth, the ocean environment can
be divided into the shelf, which is shallow and
near a terrigenous source, and the deep ocean
basin, which is deep and far from a terrigenous
source.
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Sedimentation in the Ocean

• Seaward, water becomes deeper and more distant
  from a terrigenous source.

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Shelf sedimentation is strongly controlled by
tides, waves and currents, but their influence
decreases with depth.
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Sedimentation in the Ocean

• Shoreline turbulence prevents small particles
  from settling and transports them seaward where
  they are deposited in deeper water.
• Particle size decreases seaward for recent
  sediments.
• Past fluctuations of sea level has stranded
  coarse sediment (relict sediment) across the
  shelf including most areas where only fine
  sediments are deposited today.

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Worldwide distribution of recent shelf sediments
by composition is strongly related to latitude
and climate.
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Sedimentation in the Ocean

• Calcareous biogenic sediments dominate tropical
  shelves.
• River-supplied sands and muds dominate temperate
  shelves.
• Glacial till and ice-rafted sediments dominate
  polar shelves.

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Geologic controls of continental shelf
sedimentation must be considered in terms of a
time frame.
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Sedimentation in the Ocean

• For a time frame up to 1000 years, waves,
  currents and tides control sedimentation.
• For a time frame up to 1,000,000 years, sea level
  lowered by glaciation controlled sedimentation
  and caused rivers to deposit their sediments at
  the shelf edge and onto the upper continental
  slope.
• For a time frame up to 100,000,000 years, plate
  tectonics has determined the type of margin that
  developed and controlled sedimentation.

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If influx of terrigenous sediment is low and the
water is warm, carbonate sediments will dominate.
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Sedimentation in the Ocean
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Deep-sea Sedimentation has two main sources for
sediment terrigenous material from the land and
biogenic and authigenic from the sea.
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Sedimentation in the Ocean

• Major sedimentary processes in the deep sea
  include, Bulk emplacement, Debris flows,
  Turbidity currents
• Major pelagic sediments in the ocean are red clay
  and biogenic oozes.
• Authigenic deposits are chemical and biochemical
  precipitates that form on the sea floor and
  include ferromanganese nodules and phosphorite.

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The distribution of sediments in the deep ocean
varies greatly, but is strongly controlled by the
compensation depth.
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Sedimentation in the Ocean

• Surface Deposits are the sediments found exposed
  on the sea floor.
• Deep-sea stratigraphy refers to the broad-scale
  layering of the sediments of the sea floor. It
  strongly reflects the sediment types deposited as
  the sea floor

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