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Study Guide available! Web site (dusk2.geo.orst.edu/oceans) Go to the syllabus page and click on the Study Guide for Test#1
Lecture 9: Marine Sediments Lecture 9: Marine Sediments What’s all that muck at the bottom of the ocean, and what’s it good for?
Marine Sediments are: F Particles of various sizes derived from a variety of sources that are deposited on the ocean floor F A vast “library” recording geologic, oceanographic and climatic conditions F Remarkably complete compared to land
Where do these come from? F Inputs are: -- rivers -- atmosphere -- surface waters -- volcanoes (both on land and submarine) -- deep ocean water -- outer space
Classifications F By Size Clay -- Silt -- Sand -- Pebble -- Cobble mm 1 mm 100 mm F Effects of water velocity on transport: rivers and near-shore vs open ocean
Sediment Transport n Fluid velocity determines the size of the particles that can be moved
Classifications F By Origin Biogenous Terrigenous Hydrogenous Cosmogenous
Terrigenous sediments (from land) F Rivers F Winds (eolian) F Glaciers (ice-rafted debris, IRD) F Turbidites F Sea level changes
River sediment loads (10 6 tons/yr)
Glacial (Ice-rafted debris)
Turbidites u Rapidly-accumulated terrestrial sediments u Earthquake-triggered submarine avalanches u High velocity (~50 mph!), erosive events u Good examples preserved on Mary’s Peak
Sea Level Changes
Biogenous sediments (from living things) F Calcareous (CaCO 3 ) Foraminifera -- animals Coccolithophores -- plants F Siliceous (SiO 2 ) Radiolaria -- animals Diatoms -- plants
m = micron = millionth of a meter!
Productivity = skeletons and soft tissue u Accumulation depends on production and preservation u SiO 2 is preserved everywhere u CaCO 3 is variable, depending on P, T, pH
Carbonate Compensation Depth
F The depth at which carbonate input from the surface waters is balanced by dissolution in corrosive deep waters F In today’s ocean this depth (CCD) varies between 3 km (polar) and 5 km (tropical) F Thus, accumulation rates vary a lot!
Accumulation Rates for Oozes F Productivity –reproduction of planktonic organisms F Preservation –silica dissolves only very slowly –calcium carbonate varies with depth F Rates are variable: <1 to 15mm/1000 yr
Coastal waters are often highly productive, with abundant planktonic organisms thriving in the surface waters. Why then are biogenous oozes rarely found nearshore?? F Do biogenous sediments dissolve readily at shallow depths on the continental shelf? NO F Do plankton species in coastal waters lack skeletons? NO F Are planktonic organisms consumed by large organisms, preventing deposition of skeletons? NO
the large input of terrigenous sediment to the continental margin overwhelms the biogenous component in the sediment. YES the large input of terrigenous sediment to the continental margin overwhelms the biogenous component in the sediment. YES
Hydrogenous (from sea water) F Metalliferous sediments at spreading ridges F Manganese nodules F Evaporites -- Salt deposits
baseball to bowling ball size!
Cosmogenous (from outer space) F Meteorites and comets