Lecture 7 Marine Sediments講座7海洋沉積物

1、 Origin and Distribution of Marine SedimentsWhats all that squishy muck at the bottom of the ocean? What can we learn from it?Marine Sediments are:FParticles of various sizes derived from a variety of sources that are deposited on the ocean floorFA vast “l(fā)ibrary” recording geologic, oceanographic an

2、d climatic conditionsFRemarkably complete compared to landWhere do these come from?FInputs are:- rivers- atmosphere- surface waters- volcanoes (both on land and submarine) - deep ocean water- outer spaceClassificationsFBy SizeClay - Silt - Sand - Pebble - Cobble 0.001 mm 1 mm 100 mmF Effects of wate

3、r velocity on transport: rivers and near-shore vs open oceanSediment TransportFluid velocitydetermines thesize of theparticles thatcan be movedSize SortingClassificationsFBy OriginTerrigenous - from landBiogenous - from life in the oceansHydrogenous - precipitated from waterCosmogenous - extraterres

4、trialTerrigenous sediments (from land)FRiversFWinds (eolian)FGlaciers (ice-rafted debris, IRD)FTurbiditesFSea level changesRiver sediment loads (units 106 tons/yr)Glacial (Ice-rafted debris)TurbiditesuRapidly-accumulated terrestrial sedimentsuEarthquake-triggered submarine avalanchesuHigh velocity (

5、50 mph!), erosive eventsuGood examples preserved on Marys PeakTurbidites (submarine avalanches)Sea Level ChangesBiogenous sediments (from living things)FCalcareous (CaCO3)Foraminifera - animalsCoccolithophores - plantsFSiliceous (SiO2)Radiolaria - animalsDiatoms - plantsmm = micron = millionth of a

6、meter!mm = micron = millionth of a meter!mm = micron = millionth of a meter!mm = micron = millionth of a meter!Productivity = skeletons and soft tissueuAccumulation depends on production and preservationuSiO2 is preserved everywhereuCaCO3 is variable, depending on P, T, pHCarbonate Compensation Dept

7、hCarbonate Compensation DepthFThe depth at which carbonate input from the surface waters is balanced by dissolution in corrosive deep watersFIn todays ocean this depth (CCD) varies between 3 km (polar) and 5 km (tropical)FThus, accumulation rates vary a lot!Accumulation Rates for Oozes FProductivity

8、wreproduction of planktonic organismsFPreservationwsilica dissolves only very slowlywcalcium carbonate varies with depthFRates are variable: 1 to 15mm/1000 yrCoastal waters are often highly productive, with abundant planktonic organisms thriving in the surface waters. Why then are biogenous oozes rarely found nearshore?the large input of terrigenous sediment to the continental margin overwhelms the biogenous component in the sediment. Hydrogenous (from sea water)FMetalliferous sediments at spreading ridges - “black smokers”FManganese nodulesFEvaporites - Salt depositsbaseball to b