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Marine Sediments are:Particles of various sizes derived from a variety of sources that are deposited on the ocean floor.A vast “library” recording geologic, oceanographic and climatic conditions Remarkably complete compared to land Effects of water velocity on transport: rivers and nearshore vs open ocean. | Origin and Distribution of Marine Sediments What’s all that squishy muck at the bottom of the ocean? What can we learn from it? Marine Sediments are: Particles of various sizes derived from a variety of sources that are deposited on the ocean floor A vast “library” recording geologic, oceanographic and climatic conditions Remarkably complete compared to land Where do these come from? Inputs are: -- rivers -- atmosphere -- surface waters -- volcanoes (both on land and submarine) -- deep ocean water -- outer space Classifications By Size Clay -- Silt -- Sand -- Pebble -- Cobble 0.001 mm 1 mm 100 mm Effects of water velocity on transport: rivers and near-shore vs open ocean Sediment Transport Fluid velocity determines the size of the particles that can be moved Size Sorting Classifications By Origin Terrigenous -- from land Biogenous -- from life in the oceans Hydrogenous -- precipitated from water Cosmogenous -- extraterrestrial Terrigenous sediments (from land) Rivers Winds (eolian) Glaciers (ice-rafted debris, IRD) Turbidites Sea level changes River sediment loads (units 106 tons/yr) Glacial (Ice-rafted debris) Turbidites Rapidly-accumulated terrestrial sediments Earthquake-triggered submarine avalanches High velocity (~50 mph!), erosive events Good examples preserved on Mary’s Peak Turbidites (submarine avalanches) Sea Level Changes Biogenous sediments (from living things) Calcareous (CaCO3) Foraminifera -- animals Coccolithophores -- plants Siliceous (SiO2) Radiolaria -- animals Diatoms -- plants mm = micron = millionth of a meter! mm = micron = millionth of a meter! mm = micron = millionth of a meter! mm = micron = millionth of a meter! Productivity = skeletons and soft tissue Accumulation depends on production and preservation SiO2 is preserved everywhere CaCO3 is variable, depending on P, T, pH Carbonate Compensation Depth South North Carbonate Compensation Depth The depth at which carbonate input from the surface waters is balanced by dissolution in corrosive deep waters In today’s ocean this depth (CCD) varies between 3 km (polar) and 5 km (tropical) Thus, accumulation rates vary a lot! Accumulation Rates for Oozes Productivity reproduction of planktonic organisms Preservation silica dissolves only very slowly calcium carbonate varies with depth Rates are variable: Coastal 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) Metalliferous sediments at spreading ridges -- “black smokers” Manganese nodules Evaporites -- Salt deposits baseball to bowling ball size! Cosmogenous (from outer space) Meteorites and comets Sediment Accumulation Sediment succession Distribution of Marine Sediments
