siliciclastic_marine_c10_part2

siliciclastic_marine_c10_part2 - 10.3 The Oceanic...

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10.3 The Oceanic (Deep-water) Environment • Deep-water environments =>seaward of shelf edge – constitutes majority of planet’s surface • Not much of the preserved sedimentary record – generally low sedimentation rates – Destroyed by subduction • Deep-sea research stimulated by drilling programs – Deep Sea Drilling Program DSDP in 1968 – Ocean Drilling Program ODP in 1984 – Integrated Ocean Drilling Program IODP – Many 1000s shallow gravity-driven piston cores • Regional-scale seismic-stratigraphic investigations
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Principal elements of continental margins
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Oceanic Environment: Continental-slope setting • Slope = region from shelf break to continental rise – Active margins (Pacific-rim) • Irregular folds and terraces due to active compressional tectonics – Passive margins (Atlantic-rim) • Relatively smooth and convex up with extensional tectonics • Relatively narrow – 10 to 100 km wide • 4° average slope – More shallow slope off major deltas – Steeper slopes (>45°) adjacent to some coral islands
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Schematic of an active margin
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Oceanic Environment: Continental-slope setting • Submarine slope canyons of various scales – Oriented normal to shelf break – Most have their heads near shelf break – few extend past shelf break and cross the shelf – Some extend basinward pass the continental rise – Passageway for turbidity currents moving downslope • Originate by two related mechanisms – Downcutting rivers during sea-level lowstands – Local slope failure by slumping followed by headward and sidewall erosion
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• Two physiographic components beyond base of slope Ocean floor – Abyssal plains – Abyssal hills – mid-ocean ridges • Rise 2.5 km above abyssal plain Continental rise – Off passive margins – Gently sloping surface – leads to deep ocean floor – Some canyon incision – Generally absent on active margins with subduction-zone trench Oceanic Environment: continental-rise and deep ocean setting
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Transport and depositional processes to and within deep water • Most deep water sediment originates on shelf • Various mechanisms transport sediment from shelf to deep- ocean environments • Some sediment arrives from eolian transport
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Sediment-plume transport to deep ocean • Freshwater-surface plumes can deliver considerable quantities of fine-sediment across continental shelves – 100 km basinward transport of fine sediment – Mixing and flocculation causes clay to settle
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This note was uploaded on 02/20/2010 for the course GEOL 3032 taught by Professor Bouma,a during the Fall '08 term at LSU.

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siliciclastic_marine_c10_part2 - 10.3 The Oceanic...

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