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Continental Margins and Ocean Basins

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 and Ocean Basins

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  1. Continental MarginsandOcean Basins

  2. Continental MarginsThree Main Divisions • Continental shelf • Continental slope • Continental rise

  3. 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

  4. 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

  5. Submarine Canyon • Origin of submarine canyons: • river erosion • turbidity currents

  6. 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

  7. 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)

  8. Continental Rise • At base of continental slope • Slope angle decreases • Caused by the accumulation of sediment

  9. Continental MarginsTypes • Passive Margin • Active Margin

  10. Continental MarginAseismic (Passive) • No plate boundary • Wide continental margin • Thick sediment accumulation • Little tectonic activity

  11. Continental MarginSeismic (Active) • Convergent plate boundary • Trenches are boundaries • Narrow continental margin • Thin accumulation of sediments • Tectonically active

  12. 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

  13. Southern California Seafloor • Extensive, complex • Consist of basins & ridges • Widest shelf in California • NW-SE structural grain

  14. Active Continental MarginSouthern California 3-D shaded relief map

  15. Seafloor instability – Santa Barbara Basin

  16. Active Continental MarginSouthern California

  17. Southern California Borderland--Origin

  18. Ocean Basin FloorFeatures • Seamounts and Guyots • Abyssal Plain • Trenches • Ridges and Rises • Coral Reefs and Atolls

  19. 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

  20. Ocean Basin FloorAbyssal Plain • Flat, deep ocean floor • Depth may be 2-3 miles or more • Thick sediment accumulation covers oceanic crust

  21. 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)

  22. Marianas Trench

  23. 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

  24. 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

  25. 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

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