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
 

      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 turbidites are deposited by turbidity currents.

      Abyssal Plain

      Part of the deep ocean basin (see below)

Deep Ocean Basins

Contain abyssal plains, deep sea trenches, and seamounts
Cover about 30% of Earth's surface

      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 surrounding lagoon over now-submerged volcanic peak)