Continental Margins and Ocean Basins
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Transcript of Continental Margins and Ocean Basins
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
Boundary between continental and oceanic crust
Steeply sloping compared to shelf (5-25°)
Submarine canyons are major features
Extends from shelf break to rise
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
•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)
•extends about 95 miles,•terminates at Monterey fan•reaching depths of 3,600 m (11,800 ft). •canyon is about 1 mile deep
Continental Rise
At base of continental slope Slope angle decreases
Caused by the accumulation of sediment
Continental MarginAseismic (Passive)
No plate boundary
Little tectonic activity
Thick sediment accumulation
Wide continental margin
Continental MarginSeismic (Active)
Convergent plate boundary
Trenches are boundaries
Tectonically active
Thin accumulation of sediments
Narrow continental margin
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
Extensive, complexConsist of basins & ridgesWidest shelf in CaliforniaNW-SE structural grain
Ocean Basin FloorFeatures
Seamounts and Guyots
Coral Reefs and Atolls
Ridges and Rises
Abyssal Plain
Trenches
Ocean Basin Floor
Covers about 30% of Earth’s surface
Contain abyssal plains, deep sea trenches, and seamounts
Begins at base of continental rise Sedimentation: Passive and turbidity currents
Ocean Basin FloorAbyssal Plain
Flat, deep ocean floor
Depth may be 2-3 miles or more
Thick sediment accumulation covers oceanic crust
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 FloorRidges and Rises
Contain central rift valleys• 15-50 km wide• 500-1,500 m deep
Offset by fractures
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
Ocean Basin FloorOcean Basin FloorSeamounts and GuyotsSeamounts and Guyots
Seamounts are underwater volcanoes formed along ocean ridges or over hot spots
May be eroded flat on top and called Guyots May emerge as an island