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Chapter 4 Marine Sedimentation

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Classification of marine sediments can be based ... latitude 2) distance from landmasses 3) CCD (carbonate compensation depth) Glacial marine sediments occur in the ... – PowerPoint PPT presentation

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Title: Chapter 4 Marine Sedimentation


1
  • SEDIMENTS
  • Text Book Chapter 5
  • Why do we care about oceanic
  • sediments?
  • Continents are sites of erosion
  • Oceans are sites of depositions
  • Therefore oceans retain a more-nearly complete
    and organized record of Earth history.

2
Learning Objectives Ocean Sediments
  • 1. Understand the origin and classification of
    marine sediments.
  • 2. Explain the factors controlling origin and
    deposition of sediment on the continental shelf
    and in the deep ocean.
  • Questions
  • Why don't the oceans have more sediment in them?
    Where does it all go? Earth is 4.6 billion years
    old and the oceans should have more sediment in
    them.
  • Salt composition of the oceans has not changed
    for the last 1.5 billion years. Explain why?

3
Marine Sedimentation
4
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older
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Classification of marine sediments can be based
upon size or origin.
Sediments in the Sea
  • 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 four
    major categories

6
  • The 4 main types of sediment
  • Lithogenous/terrigenous composed of fragments
    of pre-existing rock material
  • Biogenous composed of hard remains of
    once-living organisms
  • Hydrogenous formed when dissolved materials
    come out of solution (precipitate)
  • Cosmogenous derived from outer space

7
Factors that control sedimentation include
particle size and the turbulence of the
depositional environment.
Sediments in the Sea
  • Terrigenous sediments strongly reflect their
    source and are transported to the sea by wind,
    rivers and glaciers.

8
Streams Rivers
9
Glaciers
10
Landslide (Gravity)
11
ocean environment can be divided intothe shelf
neritic deposits(shallow areas and near a
terrigenous source) the deep ocean basin
pelagic deposits (deep areas and far from a
terrigenous source)
Sedimentation in the Ocean
12
Shelf Versus Basin
13
Shelf sedimentation is strongly controlled by
tides, waves and currents, but their influence
decreases with water depth.
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.

14
Worldwide distribution of recent shelf sediments
by composition is strongly related to latitude
and climate.
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.

15
Shelf Sedimentation Model
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17
Geologic controls of continental shelf
sedimentation must be considered in terms of a
time frame.
  • 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.

18
Influence of Past Sea Level
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20
Case study The Atlantic Passive Margin
21
Case study Pacific Destructive/Subduction Margin
22
Carbonate Shelves
If influx of terrigenous sediment is low and the
water is warm, carbonate sediments and reefs will
dominate.
23
Ice Rafting
24
Deep-sea Sedimentation has two main sources of
sediment external- terrigenous material from the
land and internal-biogenic and authigenic from
the sea.
Sedimentation in the Ocean
Sedimentation in the Deep Sea
25
Sedimentation in the Ocean
  • Major pelagic sediments in the ocean are red clay
    and biogenic oozes.
  • Authigenic deposits are formed in situ (at place)
    by precipitation of submarine weathering (e.g.
    hydrothermal areas, ridges) metal rich sediments
    and manganese nodules

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Biogenic Deposits
Calcium Carbonate (e.g. mollusks, corals,
foraminifers, some algae)
Silica (e.g. diaotms, radiolaria)
28
Tiny animals with calcite shells (CaCO3)
29
Coccoliths
Tiny plants with a calcite skeleton (CaCO3)
30
Diatoms
SiO2
Radiolaria
31
Silica Sedimentation
Siliceous ooze found where it accumulates faster
than it dissolves
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33
Calcium carbonate Sedimentation
CCD Calcite dissolves beneath the calcite
compensation depth (CCD) at 4.5 km
34
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35
Nodules Deposits hydrogenous sediment
from precipitation of metal oxides
36
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37
1) latitude2) distance from landmasses3) CCD
(carbonate compensation depth)
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 depth (CCD) while siliceous ooze occur
    below
  • The rate of sedimentation depends on the type of
    sediment in deep sea.

38
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.

39
The Atlantic basin contains a two-layer-cake
stratigraphya thick basal layer of carbonate
ooze overlain by a layer of mud.
Sedimentation in the Ocean
Stratigraphy of the Atlantic Basin
40
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.
Sedimentation in the Ocean
41
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42
Stratigraphy and Model of Pacific Basin
43
There are a number of sampling techniques for
obtaining sediment from the ocean bottom.
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.

44
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45
1243 sites
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49
The Drying Up of the Mediterranean Sea
  • 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.

50
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.

51
04_T04
52
Learning Objectives
1. Understand the origin and classification of
marine sediments. 2. Explain the factors
controlling origin and deposition of sediment on
the continental shelf and in the deep ocean.
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