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Origin and Distribution of Marine Sediments

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

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Origin and Distribution of Marine Sediments

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  1. Origin and Distribution of Marine Sediments What’s all that squishy muck at the bottom of the ocean? What can we learn from it?

  2. 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

  3. Where do these come from? • Inputs are:-- rivers-- atmosphere-- surface waters-- volcanoes (both on land and submarine) -- deep ocean water-- outer space

  4. Classifications • By SizeClay -- Silt -- Sand -- Pebble -- Cobble 0.001 mm 1 mm 100 mm • Effects of water velocity on transport: rivers and near-shore vs open ocean

  5. Sediment Transport • Fluid velocitydetermines thesize of theparticles thatcan be moved

  6. Size Sorting

  7. Classifications • By OriginTerrigenous -- from landBiogenous -- from life in the oceansHydrogenous -- precipitated from waterCosmogenous -- extraterrestrial

  8. Terrigenous sediments (from land) • Rivers • Winds (eolian) • Glaciers (ice-rafted debris, IRD) • Turbidites • Sea level changes

  9. River sediment loads (units 106 tons/yr)

  10. Glacial (Ice-rafted debris)

  11. Turbidites • Rapidly-accumulated terrestrial sediments • Earthquake-triggered submarine avalanches • High velocity (~50 mph!), erosive events • Good examples preserved on Mary’s Peak

  12. Turbidites (submarine avalanches)

  13. Sea Level Changes

  14. Biogenous sediments (from living things) • Calcareous (CaCO3)Foraminifera -- animalsCoccolithophores -- plants • Siliceous (SiO2)Radiolaria -- animalsDiatoms -- plants

  15. mm = micron = millionth of a meter!

  16. mm = micron = millionth of a meter!

  17. mm = micron = millionth of a meter!

  18. mm = micron = millionth of a meter!

  19. Productivity = skeletons and soft tissue • Accumulation depends on production and preservation • SiO2 is preserved everywhere • CaCO3 is variable, depending on P, T, pH

  20. Carbonate Compensation Depth South North

  21. 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!

  22. Accumulation Rates for Oozes • Productivity • reproduction of planktonic organisms • Preservation • silica dissolves only very slowly • calcium carbonate varies with depth • Ratesare variable: <1 to 15mm/1000 yr

  23. Coastal waters are often highly productive, with abundant planktonic organisms thriving in the surface waters.Why then are biogenous oozes rarely found nearshore??

  24. the large input of terrigenous sediment to the continental margin overwhelms the biogenous component in the sediment.

  25. Hydrogenous (from sea water) • Metalliferous sediments at spreading ridges -- “black smokers” • Manganese nodules • Evaporites -- Salt deposits

  26. baseball to bowling ball size!

  27. Cosmogenous (from outer space) • Meteorites and comets

  28. Sediment Accumulation

  29. Sediment succession

  30. Distribution of Marine Sediments

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