Module 6: Marine Sediments • Terrigenous Sediments: • Comprised of land-derived materials. • Settling rates of sediment particles. • Deposition on continental margins aided by turbidity currents. What are Today’s Key Concepts • Understanding Ocean Sediments and Sedimentation Processes: • Transport of terrigenous sediments to the ocean. • Role of turbidity currents as mechanism for deposition & redeposition on continental margins.Oceans & Global EnvironmentG131 Oceans & Global EnvironmentMuddy sediments in canyon Two Approaches Size or Origin • Origins of constituent materials: • Terrigenous: materials derived from land • Biogenic: sourced from living organisms. • Hydrogenous: chemical precipitate. • Volcanogenic: volcanic materials (e.g. ash. • Cosmogenic: derived from space. Classifying Marine SedimentsG131 Oceans & Global EnvironmentDeep sea cores: mud with ash layerVolcanic ash layerDeep sea cores: carbonate oozesMn nodule in clay from Pacific Terrigenous SedimentsG131 Oceans & Global EnvironmentLand-derived Materials on Ocean Floor • Physically weathered & eroded rock fragments from land, altered by chemical weathering. • Transported by rivers & water, by wind (dust storms), and by ice (glacial sediments).Classification of Marine Sediments by Source of Particles Relative proportions of continental margins within area of the ocean Continental margin profile illustrating origins of both terrigenous & biogenic components of marine sediments via a combination of settling from surface waters and bottom transport.Continental MarginG131 Oceans & Global EnvironmentVertical scale exaggeratedShelf, Slope, RiseShelf & Deep Seathin layer of sedimentthick layer of sediment Terrigenous Sediments G131 Oceans & Global Environment Settling Rates for Particles • Larger particles settle (sink) faster. • Smaller particles take longer to settle and can therefore be transported further from their source (e.g. dust or river inputs). Particle Sizes and Settling Rates
Turbidites & Deep-Sea FansContinental Margin SedimentsG131 Oceans & Global EnvironmentTurbidity currents can transport coarse sands and gravel down to the continental rise via submarine canyonsDeposits formed by turbidity currents include graded beds where pelagic muds are scoured and overlain by sands and gravel with larger particles at the base (graded beds). Continental Shelf Shelf Sediments • Land-derived clastic sediments deposited on continental shelves. • Shelf sediments are redistributed downslope by turbidity currents to produce graded beds with finer muds traveling further. Graded beds Turbidite deposition Deposition in submarine fans G131 Oceans & Global Environment Graded beds
Sediment Accumulation RatesG131 Oceans & Global EnvironmentRates of sediment accumulation are a function of the supply of material to the ocean. Hence, they tend to be higher in regions that receive large fluxes of terrigenous materials and lower in regions that are remote from land.Rates range from < 1 cm/ky to > 5cm/ky Distribution of CarbonatesG131 Oceans & Global EnvironmentCoastal Carbonates & Reefs • Favored by low influx of terrigenous sediment and by warm water. • Predominately low latitude deposits formed in shallow, warm waters.Tropical & subtropical settingsCarbonate & coralsOccur in regions without major terrigenous inputs Distribution of Ocean Sediments G131 Oceans & Global Environment Surface sediment types
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