Reading Material See class website Sediments from Oceanography M G Gross Prentice Hall Materials filling ocean basins Dissolved chemicals especially from rivers and mid ocean ridges volcanic eruptions some remain dissolved e g producing salt water some precipitate inorganically e g producing Manganese nodules some precipitate organically e g producing biogenic oozes Solid particles from winds aeolian dust blown from land only important in deepest ocean forms red clay rivers fluvial most important source 90 mud silt clay 10 sand glaciers glacial greatest impact at high latitudes supplies wide range of sizes boulders to rock flour Classification of marine sediments Lithogenic from disintegration of rock on land aeolian FLUVIAL and glacial sources Biogenic organic precipitation of dissolved components dominated by single celled plants and animals create oozes calcium carbonate limestone calcareous silicon dioxide opal siliceous Authigenic inorganic precipitation of dissolved components seawater becomes supersaturated with regard to some chemicals Cosmogenic from outside Earth meteorites usually very small tektites Biogenic Sediments microscopic in size Classification of marine sediments Lithogenic from disintegration of rock on land aeolian FLUVIAL and glacial sources Biogenic organic precipitation of dissolved components dominated by single celled plants and animals create oozes calcium carbonate limestone calcareous silicon dioxide opal siliceous Authigenic inorganic precipitation of dissolved components seawater becomes supersaturated with regard to some chemicals Cosmogenic from outside Earth meteorites usually very small tektites Authigenic Sediments manganese nodules and red clay Classification of marine sediments Lithogenic from disintegration of rock on land aeolian FLUVIAL and glacial sources Biogenic organic precipitation of dissolved components dominated by single celled plants and animals create oozes calcium carbonate limestone calcareous silicon dioxide opal siliceous Authigenic inorganic precipitation of dissolved components seawater becomes supersaturated with regard to some chemicals Cosmogenic from outside Earth meteorites usually very small tektites Cosmogenic Sediments tektites micrometeorites Distribution of Marine Sediments Lithogenic sediment dominates near continents shelf slope rise because source from land glacial at high latitudes fluvial at all latitudes Biogenic sediment dominates away from lithogenic sediments usually away from continents exception calcareous sediment can dominate shallow low latitude areas calcareous sediment foraminifera found on flanks of mid ocean ridges because it dissolves in water 4000 m deep siliceous sediment found where nutrient supply is great nutrients stimulate marine productivity diatoms radiolarians Authigenic sediment and red clay Deep sea sediments Trailing Edge Margin Sea Level Change Time scales of 10 000 years Sea level fluctuates due to climate change Cold periods more precipitation as snow not rain more snow remains for multiple years ice sheets form miles thick evaporation continues from oceans but return as runoff reduced cold temperatures cause sea water to contract sea level drops Warm periods less precipitation as snow glaciers melt warm temperatures cause sea water to expand sea level rises Likely Cause of Natural Climatic Changes Cyclical variations in orbital and rotational factors Sea Level Change Time scales of 10 000 years Sea level fluctuates due to climate change Cold periods more precipitation as snow not rain more snow remains for multiple years ice sheets form miles thick evaporation continues from oceans but return as runoff reduced cold temperatures cause sea water to contract sea level drops Warm periods less precipitation as snow glaciers melt warm temperatures cause sea water to expand sea level rises Sea Level Change Past 40 000 y Needed for sea level curve 1 Age date 2 Indicator of sea level 3 No vertical land motion Holocene past 20 000 y when sea level was rising Sea Level Rise Past 10 000 y Recent Sea Level Rise Example of step wise sea level rise Flooded river valley on the continental shelf in the Gulf of Papua between Australia and New Guinea 35 m deep This is a bathymetric chart cool colors are deep warm colors are shallow This valley might have been flooded quickly by stepwise sea level rise 65 m Holocene Rise in Sea Level Cold period ice age ends 20 000 years ago Sea level stood 130 m below present sea level at edge of continental shelf shelf break Global sea level rose quickly 10 mm y until 7000 years ago Rate of global eustatic rise has been slow 2 mm y since then Sea level change along any particular coast depends also upon land movement plate tectonics sediment consolidation e g deltas sink glacial rebound weight of glaciers removed land rises Continental Margin Sedimentation during Low Sea Level Rivers and glaciers cross continental shelf to shelf break Much sediment supplied at top of steep slope creates unstable sediment Large storms or earthquakes trigger underwater landslides Slurry of sediment moves down continental slope known as turbidity currents and debris flows Erodes seabed on continental slope forms submarine canyons Deposits sediment on continental rise and abyssal plains creates layers known as turbidites Trailing Edge Margin Turbidity Current and resulting Turbidite 1929 Grand Banks turbidity current Continental Margin Sedimentation during High Sea Level Fluvial and glacial valleys flooded Sediments trapped in river mouth estuaries and fjords If much sediment supplied estuaries and fjords are filled deltas formed Sediment can escape to continental shelf mud winnowed by waves leaving sand nearshore mud transported to middle shelf On collision margins narrow steep shelf sediment can escape to continental slope Holocene deposits 20 000 y on continental shelves Note boundary between modern inner shelf sand and modern mid shelf mud depends on waves Washington continental shelf Continental Margin Sedimentation during High Sea Level Fluvial and glacial valleys flooded Sediments trapped in river mouth estuaries and fjords If much sediment supplied estuaries and fjords are filled deltas formed Sediment can escape to continental shelf mud winnowed by waves leaving sand nearshore mud transported to middle shelf On collision margins narrow steep shelf sediment can escape to continental slope Eel River Drainage Basin 60 50 40 30 10 20 90 100 80 70 500 350 400 250 300 150 200
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