Objectives

1. List and describe the main subdivisions of the continental margin (continental shelf, continental slope, continental rise).
   
2. Discuss ocean waves, their formation, their parts (wave length, wave height, crest, trough), and their mechanism (breakers, wave base, velocity, period of the wave).
   
3. Discuss tides and their causes, including spring tides and neap tides.
   
4. Discuss ocean currents (Coriolis effect, long-shore current, rip current).
   
5. Discuss wave depositional features and erosional features along the shoreline.
   
6. Recognize the effects of coastal processes on manmade structures in the coastal zone.
   

Continental Margins

• Continental Shelf
  Submerged part of the continent
  Gently sloping (less than one tenth of a degree)
  Up to 1500 km wide; averages 80 km wide
  Water depth at seaward edge averages 130 m (about 400 feet)
  Locally cut by canyons (eroded by rivers during the Ice Age low sea level stand)

• Continental Slope
  Boundary between continental and oceanic crust
  Steeply sloping compared to shelf (averages about 5 degree slope, up to 25 degrees)
  May be about 20 km wide

• Continental Rise
  At base of continental slope; slope angle decreases
  May be hundreds of km wide
  Thick accumulation of sediment transported downslope from continental shelf

  At mouths of submarine canyons, deep-sea fans are present
  May be carved by turbidity currents - bottom-currents carrying suspended sediment downslope
  As the currents slow, the suspended sediments begin to settle out; larger and heavier grains settle first.
  Graded beds called turbidities are deposited by turbidity currents.

• Abyssal Plain
  Part of the deep ocean basin (see below)

Deep Ocean Basins

• Abyssal Plain
  Flat, deep ocean floor.
  Depth may be 2 - 3 miles or more
  Thick accumulations of sediment bury topography of oceanic crust

  Types of sea floor sediments:

  • Terrigenous sediment
    Mineral grains from weathered continental rocks
    Fine-grained sediment (clay, mud)
    Accumulates slowly (5000 to 50,000 years to deposit 1 cm)
    Color may be black, red or brown

  • Biogenous sediment
    Biological origin - primarily shells and skeletons of microscopic plankton
    
    • Calcareous oozes
      Remains of foraminifera and coccolithophores
      May form chalk

    • Siliceous oozes
      Remains of radiolarians and diatoms
      May form diatomite or chert

    • Phosphatic material
      From bones, teeth and scales of fish

  • Hydrogenous sediment
    (Authigenic or diagenetic minerals)
    Minerals that precipitate from sea water by chemical reactions.
    Example: manganese nodules

• Deep Sea Trenches
  The deepest part of the oceans
  May exceed 10,000 m deep (30,000 feet, or nearly 5 miles)
  Deepest is Mariana trench in Pacific Ocean (more than 11,000 m or 33,000 ft)
  Occur at subduction zones where oceanic crust is forced downward into the mantle
  Associated with earthquakes (Benioff Zones) and volcanoes

• Seamounts
  Undersea volcanic peaks which formed along mid-ocean ridges or over hot spots
  May be eroded flat on top and called guyots
  Subsidence occurs after volcanic activity ceases; crust moves away from ridge or off hot spot.
  May be ringed by coral reefs called atolls (circular reef surounding lagoon over now-submerged volcanic peak)
  

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This page created by Pamela J. W. Gore
Georgia Perimeter College, Clarkston, GA

Page created May 27, 1996
Modified March 5, 1997
Modified November 19, 1998
Last modified July 17, 1999