Chapter%204%20Marine%20Sedimentation

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Marine Sedimentation
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Streams Rivers
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Glaciers
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Landslide (Gravity)
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Marine Sedimentation
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Learning Objectives
1. Understand the origin and classification of
marine sediments. 2. Use Hjulstroms diagram to
explain the erosion, transportation, and
deposition of sediments. 3. Explain the factors
controlling origin and deposition of sediment on
the continental shelf and in the deep ocean. 4.
Calculate the rate of sedimentation in the deep
sea.
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Classification of marine sediments can be based
upon size or origin.
Sediment in the Sea
4-1

• Size classification divides sediment by grain
  size into gravel, sand, silt 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
depositional environment.
4-1
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.

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Hjulstroms Diagram

• Hjulstroms Diagram graphs the relationship
  between particle size and energy for erosion,
  transportation and deposition.

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ocean environment can be divided intothe shelf
(is shallow and near a terrigenous source) the
deep ocean basin (is deep and far from a
terrigenous source)
4-2
Sedimentation in the Ocean
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Shelf Versus Basin Depths
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Shelf sedimentation is strongly controlled by
tides, waves and currents, but their influence
decreases with water depth.
4-2
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 have stranded
  coarse sediment (relict sediment) across the
  shelf including most areas where only fine
  sediments are deposited today.

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Model Prediction of Shelf Sediments
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Influence of Past Sea Level
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Relict Sediment
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Worldwide distribution of recent shelf sediments
by composition is strongly related to latitude
and climate.
4-2
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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Shelf Sedimentation Model
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Geologic controls of continental shelf
sedimentation must be considered in terms of a
time frame.
4-2

• 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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Case study The Atlantic Passive Margin
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Case study Pacific Destructive/Subduction Margin
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Carbonate Shelves
If influx of terrigenous sediment is low and the
water is warm, carbonate sediments and reefs will
dominate.
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Deep-sea Sedimentation has two main sources of
sediment external- terrigenous material from the
land and internal-biogenic and authigenic from
the sea.
4-2
Sedimentation in the Ocean
Red Clays Kaolinite Chlorite Quartz Feldspar
Sedimentation in the Deep Sea
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4-2
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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Ice Rafting
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Deep-sea Sedimentation has two main sources of
sediment external- terrigenous material from the
land and internal-biogenic and authigenic from
the sea.
4-2
Sedimentation in the Ocean
Red Clays Kaolinite Chlorite Quartz Feldspar
Sedimentation in the Deep Sea
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Biogenic Deposits
Carbonate
Silica
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Figure 5-14
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Figure 5-15
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Figure 5-16
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Figure 5-17
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Authigenic Deposits
from precipitation of metal oxides
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1) latitude2) distance from landmasses3) CCD
(carbonate compensation depth)
4-2
Distribution of sediments in the deep ocean

• Glacial marine sediments occur in the high
  latitudes.
• Pelagic clays occur far from land and in the
  deepest water.
• Calcareous oozes occur above the calcium
  carbonate composition depth.
• The rate of sedimentation depends on the type of
  sediment in deep sea.

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4-2
Sedimentation in the Ocean

• Deep-sea stratigraphy refers to the broad-scale
  layering of sediments that cover the basaltic
  crust. The stratigraphy of the deep sea is
  strongly influenced by sea-floor spreading.

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The Atlantic basin contains a two-layer-cake
stratigraphya thick basal layer of carbonate
ooze overlain by a layer of mud.
4-2
Sedimentation in the Ocean
Stratigraphy of the Atlantic Basin
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The Pacific basin contains a four-layer-cake
stratigraphy, because unlike the Atlantic its sea
floor as it spreads crosses the equator where the
CCD is lowered to the ocean bottom.
4-2
Sedimentation in the Ocean
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Stratigraphy and Model of Pacific Basin
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There are a number of sampling techniques for
obtaining sediment from the ocean bottom.
4-3
Collecting Marine Sediment

• Bottom dredges scrape the sediment and collect
  material in a wire or canvas bag.
• Grab samplers take a bite out of the sediment
  covering the bottom.
• Gravity and piston corers use a weight to drive a
  core barrel into a soft bottom. A piston corer
  takes a much longer core than a gravity corer
  because of the piston in the core barrel.

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The Drying Up of the Mediterranean Sea
4-4

• The Mediterranean basin is located where plates
  are colliding as Africa moves northward relative
  to Europe.
• Anhydrite and stromatolites of Miocene age
  indicate that the Mediterranean sea dried out
  between 5 and 25 million years ago.
• Two models have been suggested to account for
  this emptying of the Mediterranean Sea of its
  water.
• The Uplift Model
• The Drying-Out Model

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Refilling the Mediterranean Sea

• After drying out, seawater from the Atlantic
  Ocean cascaded down the face of the Gibraltar
  Sill, refilling it in about 100 years.

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