Reading MaterialDistribution of Marine SedimentsSea-Level ChangeHolocene Rise in Sea LevelContinental-Margin Sedimentation during Low Sea LevelContinental-Margin Sedimentation during High Sea LevelReading MaterialOn reserve in:Undergrad Library – hard copiesClass websiteUW library site - www.lib.washington.edu“Sediments”, from “Oceanography”M.G. Gross, Prentice-HallDistribution of Marine SedimentsLithogenic sedimentdominates near continents (shelf, slope, rise)because source from landglacial at high latitudes, fluvial at all latitudesBiogenic sedimentdominates away from lithogenic sediments, usually away from continents(exception: calcareous sediment can dominate some low-latitude beaches) calcareous sediment (foraminifera) found on flanks of mid-ocean ridgesbecause it dissolves in water >4000 m deepsiliceous sediment found where nutrient supply is greatnutrients stimulate marine productivity (diatoms, radiolarians)Authigenic sediment and red claydominates away from continents, in water depths >4000 m, not high prodbecause they are overwhelmed everywhere else by lithogenic and biogenicSea-Level ChangeTime scales of ~10,000 yearsSea level fluctuates due to climate changeCold periodsmore precipitation as snow (not rain)more snow remains for multiple years, ice sheets form miles thickevaporation continues from oceans, but return as runoff reducedcold temperatures cause sea water to contractsea level dropsWarm periodsless precipitation as snowglaciers meltwarm temperatures cause sea water to expandsea level risesSea-Level Change Past 40,000 yHolocene = past 20,000 y, when sea level was risingTransgression = transfer of shoreline landwardSea-Level Rise Past 10,000 yRecent Sea-Level RiseExample of step-wise sea-level riseFlooded 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 riseThis is a bathymetric chart, cool colors are deep, warm colors are shallow~35 m deep~65 m deepHolocene Rise in Sea LevelCold period (ice age) ends ~20,000 years agoSea level stood ~130 m below present sea levelat edge of continental shelf (shelf break)Global sea level rose quickly (~10 mm/y) until ~7000 years agoRate of global rise has been slow (~2 mm/y) since thenSea-level change along any particular coast depends also upon land movementplate tectonicssediment consolidation (e.g., deltas sink)glacial rebound (weight of glaciers removed, land rises)Continental-Margin Sedimentation during Low Sea LevelRivers and glaciers cross continental shelf to shelf breakMuch sediment supplied at top of steep slopecreates unstable sedimentLarge storms or earthquakes trigger underwater landslidesSlurry of sediment moves down continental slopeknown as “turbidity currents”Erodes seabed on continental slopeforms submarine canyonsDeposits sediment on continental rise and abyssal plainscreates layers known as “turbidites”Turbidity Current and resulting Turbidite1929 Grand Banks turbidity currentContinental-Margin Sedimentation during High Sea LevelFluvial and glacial valleys floodedSediments trapped in river-mouth estuaries and fjordsIf much sediment supplied, estuaries and fjords are filleddeltas formedSediment can escape to continental shelfmud winnowed by wavesleaving sand nearshoremud transported to middle shelfOn collision margins (narrow, steep shelf)sediment can escape to continental slopeHolocene deposits (<20,000 y) on continental shelvesNote: boundary between modern inner-shelf sand and modern mid-shelf mud depends on waves41o00’40o50’40o40’124o40’124o30’700600500400350300250200150100908070605040302010Eel River Drainage BasinEel River Drainage BasinEel River Drainage Basin~9000 km2Study Area0 m3501400ElevationCaliforniaEel marginEel Canyon, northern CaliforniaMultiple entrants that are presently receiving sediment and experience many turbidity currents each yearCore Depth051015202530Core Depth30354045505560L1C12DUPLICATE DUPLICATE CORESCORESL1C13L1C13 L1C12LarryChannelThalwegΖ = 137 mSepik Canyon enters the mouth of SepikRiver (north coast of New Guinea)Sediment from the river supplies many turbidity currents each yearSepik Canyon
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