Reading Material See class website Sediments from Oceanography M G Gross Prentice Hall 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 dominates away from continents in water depths 4000 m not high prod because they are overwhelmed everywhere else by lithogenic and biogenic Deep sea sediments 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 Holocene past 20 000 y when sea level was rising Transgression transfer of shoreline landward 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 step wise sea level rise 65 m deep 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 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 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 Eel River Drainage Basin 6 50 0 40 30 10 20 90 100 80 70 500 350 40 0 250 300 150 200 600 700 40o50 40o40 124o40 124o30 Study Area Eel River Drainage Basin 9000 km2 Elevation 0m 350 1400 ia rn lifo Ca Eel margin 41o00 Eel Canyon northern California Multiple entrants that are presently receiving sediment and experience many turbidity currents each year 0 30 DUPLICATE CORES 5 35 40 Core Depth Core Depth 10 15 Larry Channel Thalweg 20 25 30 137 m L1C12 L1C13 45 50 55 60 L1C12 L1C13 Sepik Canyon enters the mouth of Sepik River north coast of New Guinea Sediment from the river supplies many turbidity currents each year Sepik Canyon turbidites
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