Geology of the Oceans

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Geology of the Oceans
Week 2 Geology of the Oceans
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Structure of the Earth
MOHOROVICIC DISCONTINUITY
LITHOSPHERE
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Silica-Aluminum (SIAL)
Silica-Magnesium (SIMA)
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Types of Plate Boundary

• Divergent where plates form, such as at
  mid-ocean ridges
  
• Convergent where plates are destroyed
• Transform where plates slide past each other

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Divergent Boundaries
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Magnetic Field Reversals and the Age Of the Sea
Floor

• The Earth experiences random reversals in the
  polarity of its magnetic field
  
• These reversals result in a characteristic
  alignment of magnetic minerals as they cool from
  a liquid state
  
• Thus, reversals have been recorded at sites
  where new crust is created, such as along oceanic
  ridges

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Convergent Boundaries
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Transform Boundaries
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Types of Continental Margins

• Passive (Divergent/Atlantic Type) these face
  divergent boundaries but are not
  tectonically-active themselves
  
• Active (Convergent/Pacific Type) these form at
  boundaries between two converging plates
  
• Translational these are sites where plates slide
  past each other

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Convergent Continental Margins
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Multi-Beam Sonar Images of Continental Margins
(courtesy of Scientific American www.sciam.com)
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Sonar Imagery of an Active (Convergent) Margin
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Sonar Imagery of a Passive Margin
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Sonar Imagery of a Passive Margin (Northeastern
U.S.)
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Sonar Imagery of a Translational Boundary
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Geo-Marine Environments
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Turbidity Currents
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Hot Spots

• Occur at the interior of plates where heat and
  pressure have gradually built up
  
• Result in release of magma at the surface and
  formation of volcanic features
  
• Are fairly stationary through time

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Seamounts and Guyots
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Hydrothermal Vents

• Release hot, mineral-laden water with great
  force
  
• Form predominantly along oceanic ridges
• Create chimneys, often tens of meters in height,
  as a result of mineral precipitation

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Bathymetry of the Oceans
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Sediments Classification

• By size
• By mineralogy
• By source

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Sediment Size Classification
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Sediment Thickness in the Oceans
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Distribution of Marine Sediments
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Sediment Classification by Source

• Terrigenous
• Biogenous
• Hydrogenous
• Cosmogenic

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Terrigenous Sediment

• From erosion of land, volcanic eruptions, blown
  dust
  
• Dominant around continental margins and in polar
  oceans
  
• Cover 45 of ocean floor, although they have the
  greatest volume of all types
  
• e.g. quartz sands, clays

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Biogenous Sediment

• Hard parts of some marine organisms
• Covers 55 of ocean floor and is dominant in
  deep ocean
  
• e.g. calcareous oozes from foraminifera,
  pteropods, and coccolithophores siliceous oozes
  from radiolarians and diatoms phosphatic
  components from fish bones and teeth

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Foraminifera
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Coccolithophores
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Radiolarians
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Diatoms
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Hydrogenous Sediment

• From precipitation of dissolved material in
  seawater by bacteria or through evaporation
  
• Covers found only with other sediments
  
• e.g. manganese nodules

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Cosmogenous Sediment

• From spacedust and meteorite debris
• Very small proportion of sediment
• e.g. tektite spheres, glassy nodules

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Biogenous Sediments Include Calcareous And
Siliceous Oozes ----------- Red clay, Glacia
l-Marine Sediments And Continental Shelf Deposi
ts Are Essentially Terrigenous
Global Distribution of Sediment Types