Reading Material See class website Sediments from Oceanography M G Gross Prentice Hall 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 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 Holocene sea level Constructingchange sea level curves indicator of sea level not transported e g oyster beds marsh peats age dates 14C good for Holocene stable land surface 108 years 106 years Pleistocene 104 years Last high stand 106 years broad fall in sl Holocene eustatic sea level rise LGM Last Glacial Maximum 130 m lower 18 20 kybp rose rapidly until 7 kybp Step wise rise in sea level due to pulses of meltwater Flooded river valley on the continental shelf in the Gulf of Papua between Australia and New Guinea This valley might have been flooded quickly by step wise sea level rise 35 m deep This is a bathymetric chart cool colors are deep warm colors are shallow 65 m Local sea level rise Puget Sound Tectonic Uplift Delta subsidence Last 7000 years Past Century The future 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
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