2.8

• Ocean basin


  A depression of the earth's surface in which an ocean lies
• Ocean basins have developed as plate tectonics continued and date back to 2 billion years ago
• Pangea


  The supercontinent that began to break up a little less than 200 million years ago
• The Atlantic Ocean has formed when the Pangean continent began to separate


  200 million years ago
• North America separated from South America and Africa

  180 million years ago
• Laurasia


  The landmass formed when North America joined Eurasia
• South America began to separate from Africa


  135 million years ago
• Evolution of the ocean basins through tectonic plate movements


  1. Tectonic activity has led to the shrinking of the Pacific Basin at the expense of the growth of the Atlantic and Arctic basins

  2. Opening of the Tethys Seaway surrounding the globe in tropical latitudes and subsequent closure

  3. Opening of the Southern Ocean

  4. Southern continents moved north, away from Antarctica
• Ocean basin


  • It is one of many vast undersea regions that together cover nearly three-quarters of the earth's surface
  • It contains the vast majority of all the water on the planet and has an average depth of nearly 4 km (about 2.5 miles)
  • Ocean basins vary in size, shape, and characteristics due to the movement of the earth's crust (lithosphere)
• Main types of tectonic activity that shape ocean basins


  • Seafloor spreading (e.g. Atlantic Basin)
  • Subduction (e.g. Pacific Basin)
• Major ocean basins


  • Pacific basin
  • Atlantic basin
  • Indian basin
  • Arctic basin
  • Southern basin
• Smaller basins


  • North Aleutian Basin, between the Pacific and Arctic Oceans
• Continental shelf


  A shallow submerged margin of the continents that lies between the edge of the shoreline and the continental slope
• Continental slope


  A steeply sloping portion of continental crust found between the continental shelf and continental rise
• Continental rise


  Thick layers of sediment found between the continental slope and the ocean floor
• Ocean floor


  A flat plain found at the bottom of the ocean. The ocean floor represents the surface of the oceanic crust. The ocean floor lies between the mid-oceanic ridges and the trenches, usually 5,000 to 7,000 meters below the ocean surface. Also called the abyssal plain.
• Mid-oceanic ridges


  A chain of submarine mountains where oceanic crust is created from rising magma plumes and volcanic activity. Also associated with this feature is plate divergence which creates a rift zone.
• Stages of ocean basin formation (Wilson cycle)


  1. As the crust thins as a result of extensional tectonics, an ocean basin forms and sediments accumulate along its margins

  2. Subduction is then initiated at one of the margins of the ocean basin and the ocean basin is closed

  3. When the crust starts to thin again, a new cycle begins