Reading MaterialClassification of marine sedimentsDistribution of Marine SedimentsSlide 4Slide 5Slide 6Sea-Level ChangeSlide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Holocene Rise in Sea LevelContinental-Margin Sedimentation during Low Sea LevelSlide 20Slide 21Slide 22Reading MaterialSee class website“Sediments”, from “Oceanography”M.G. Gross, Prentice-HallClassification of marine sedimentsLithogenic – from disintegration of rock on landaeolian, FLUVIAL, and glacial sourcesBiogenic – organic precipitation of dissolved components dominated by single-celled plants and animals (create oozes) calcium carbonate (limestone) = calcareous silicon dioxide (opal) = siliceousAuthigenic – inorganic precipitation of dissolved components seawater becomes supersaturated with regard to some chemicalsCosmogenic – from outside Earth meteorites, usually very small (tektites)Distribution 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 shallow low-latitude areas) 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 biogenicDeep-sea sedimentsTrailing-Edge MarginSea-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 risesLikely Cause of Natural Climatic Changes Cyclical variations in orbital and rotational factorsHolocene sea-level changeConstructing sea-level curves indicator of sea level, not transported(e.g., oyster beds, marsh peats) age dates,14C good for Holocene stable land surface108 years106 yearsPleistocene104 yearsLast high-stand106 yearsbroad fall in slHolocene eustatic sea-level riseLGM = Last Glacial Maximum130 m lower, 18-20 kybprose rapidly until ~7 kybpStep-wise rise in sea leveldue to pulses of meltwaterFlooded 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 deep“Local” sea-level risePuget SoundTectonic UpliftDeltasubsidenceLast ~7000 yearsPast CenturyThe futureHolocene 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 (eustatic) 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” and “debris flows”Erodes seabed on continental slopeforms submarine canyonsDeposits sediment on continental rise and abyssal plainscreates layers known as “turbidites”Trailing-Edge MarginTurbidity Current and resulting Turbidite1929 Grand Banks turbidity
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