Reading MaterialMaterials filling ocean basinsClassification of marine sedimentsSlide 4Slide 5Slide 6Slide 7Slide 8Distribution of Marine SedimentsSlide 10Slide 11Slide 12Sea-Level ChangeSlide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Holocene Rise in Sea LevelContinental-Margin Sedimentation during Low Sea LevelSlide 25Slide 26Slide 27Continental-Margin Sedimentation during High Sea LevelSlide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Reading MaterialSee class website“Sediments”, from “Oceanography”M.G. Gross, Prentice-HallMaterials filling ocean basinsDissolved chemicalsespecially 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 source90% mud (silt, clay), 10% sandglaciers (glacial) – greatest impact at high latitudes supplies wide range of sizes (boulders to rock flour)Classification 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)Biogenic Sediments, microscopic in size(single-celled plants and animals)Classification 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)Authigenic Sediments(manganese nodules)and red clayClassification 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)Cosmogenic Sedimentstektites (micrometeorites)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 factorsSea-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 landward Needed for sea-level curve1)Age date2)Indicator of sea level3)No vertical land motionSea-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 (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 currentContinental-Margin Sedimentation during High Sea LevelFluvial and glacial valleys floodedSediments trapped in river-mouth estuaries and fjordsIf much sediment supplied, estuaries and fjords
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