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Continental Margins and Ocean Basins. Continental Margins Three Main Divisions. Continental shelf. Continental slope. Continental rise. Continental Shelf. Submerged part of the continent. Slopes gently toward ocean basin (<1 °). Composed of continental crust.

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continental margins three main divisions
Continental MarginsThree Main Divisions
  • Continental shelf
  • Continental slope
  • Continental rise
continental shelf
Continental Shelf
  • Submerged part of the continent
  • Slopes gently toward ocean basin (<1°)
  • Composed of continental crust
  • Shelf ends at shelf break – boundary between shelf and steeper slope
continental slope
Continental Slope
  • Boundary between continental and oceanic crust
  • Extends from shelf break to rise
  • Steeply sloping compared to shelf (5-25°)
  • Submarine canyons are major features
submarine canyon
Submarine Canyon
  • Origin of submarine canyons:
  • river erosion
  • turbidity currents
submarine canyon turbidity currents
Submarine CanyonTurbidity Currents
  • Turbidites are layered and exhibit graded bedding (decrease in sediment grain size from bottom to top)
  • Downslope movement of dense mixture of clay, silt, sand and water
  • Deposits are called turbidites
monterey canyon hudson canyon
Monterey Canyon & Hudson Canyon
  • extends about 95 miles,
  • terminates at Monterey fan
  • reaching depths of 3,600 m (11,800 ft).
  • canyon is about 1 mile deep
  • 2,200 m (7,217 ft) deep at base of continental slope.
  • As much as 12 km (7.5 miles) wide (from east rim to west rim)
continental rise
Continental Rise
  • At base of continental slope
  • Slope angle decreases
  • Caused by the accumulation of sediment
continental margins types
Continental MarginsTypes
  • Passive Margin
  • Active Margin
continental margin aseismic passive
Continental MarginAseismic (Passive)
  • No plate boundary
  • Wide continental margin
  • Thick sediment accumulation
  • Little tectonic activity
continental margin seismic active
Continental MarginSeismic (Active)
  • Convergent plate boundary
  • Trenches are boundaries
  • Narrow continental margin
  • Thin accumulation of sediments
  • Tectonically active
continental margin passive vs active
Continental MarginPassive vs. Active
  • Passive Margins
  • Major rivers drain into ocean
  • Sediment transported by river builds out shelf
  • Active Margins
  • Large rivers uncommon
  • Irregular shelves
southern california seafloor
Southern California Seafloor
  • Extensive, complex
  • Consist of basins & ridges
  • Widest shelf in California
  • NW-SE structural grain
ocean basin floor features
Ocean Basin FloorFeatures
  • Seamounts and Guyots
  • Abyssal Plain
  • Trenches
  • Ridges and Rises
  • Coral Reefs and Atolls
ocean basin floor
Ocean Basin Floor
  • Covers about 30% of Earth’s surface
  • Begins at base of continental rise
  • Sedimentation: Passive and turbidity currents
  • Contain abyssal plains, deep sea trenches, and seamounts
ocean basin floor abyssal plain
Ocean Basin FloorAbyssal Plain
  • Flat, deep ocean floor
  • Depth may be 2-3 miles or more
  • Thick sediment accumulation covers oceanic crust
ocean basin floor deep sea trenches
Ocean Basin FloorDeep Sea Trenches
  • Occur at subduction zones where oceanic crust is forced downward into mantle
  • Associated with earthquakes and volcanoes
  • Deepest is Mariana Trench (11,020 m)
  • Longest is Peru-Chile trench (5,900 km)
ocean basin floor ridges and rises
Ocean Basin FloorRidges and Rises
  • Underwater volcanic mountain chain
    • Extends for 65,000 km
    • 1,000 km wide
    • 1,000-2,000 m high

Ridges = steep slopes

Rises = gentle slopes

  • Contain central rift valleys
    • 15-50 km wide
    • 500-1,500 m deep
  • Offset by fractures
ocean basin floor seamounts and guyots
Ocean Basin FloorSeamounts and Guyots
  • Seamounts are underwater volcanoes formed along ocean ridges or over hot spots
  • May emerge as an island
  • May be eroded flat on top and called Guyots
ocean basin floor coral reefs and atolls
Ocean Basin FloorCoral Reefs and Atolls
  • Volcanic islands (from seamount) form in warm latitudes
  • Fringing coral reefs form in shallow, sunlit waters
  • Dormant volcano subsides and flattens (becomes a guyot)
  • Actively-growing reef becomes a barrier reef and then an atoll