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Ocean Sediments

Ocean Sediments. Importance of Sediments. Economic Value Oil, fossil fuels Salt & Phosphorus deposits Determine shape & structure of Ocean bottom Strongly affect distribution of Benthic Organisms Chronological record of Earth’s history Tectonic history Climate history

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Ocean Sediments

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  1. Ocean Sediments

  2. Importance of Sediments • Economic Value • Oil, fossil fuels • Salt & Phosphorus deposits • Determine shape & structure of Ocean bottom • Strongly affect distribution of Benthic Organisms • Chronological record of Earth’s history • Tectonic history • Climate history • Evolutionary history

  3. Sediment Thickness

  4. Topographic profiles

  5. Law of Superposition Younger sediments over Old sediments YOUNG ---------------------- OLD

  6. Sediment Classification • By Grain Size • By Origin

  7. Sediment Classification • Grain Size • Clay <4 μm • Silt 4-62 μm • Sand 62-2000 μm • Gravel >2000 μm

  8. Table 3.1

  9. Basic Sediment Transport(READ CC4)

  10. Sediment Sorting Well-sorted sediments are those of similar size class • Beach: well sorted (far from source) • Glacier: not sorted (close to source)

  11. Sediment Angularity Sediment weathering during transport induces loss in angularity • Angular grains (close to source) • Rounded grains (far from source)

  12. Sediment Classification • Origin • Lithogenous or Terrigenous (~75%) • Biogenous (~20%) • Hydrogenous • Cosmogenous

  13. Lithogenous Sediments • Fragments of rocks broken, weathered and eroded form lithogenous sediments

  14. http://images.google.com Frost Wedging

  15. Wind & Rain erosion www.naturalphotos.com

  16. Lithogenous Sediments • Transport of sediments by: • Rivers • Glaciers • Waves • Wind • Landslides • Humans

  17. www.southalabama.edu http://earthobservatory.nasa.gov

  18. Sediment Discharge by Rivers • Ganges: 1700 million Tm/year • Amazon: 900 million Tm/year • Mississippi 260 million Tm/year (Figure 6-2)

  19. http://www.pbs.org/harriman/images/

  20. http://www.pbs.org/harriman/images/

  21. walrus.wr.usgs.gov/elnino/coastal/ images/

  22. http://earthobservatory.nasa.gov

  23. Aerial dust transport Winter Summer

  24. St Helens

  25. http://geohazards.cr.usgs.gov/ http://web.umr.edu/~rogersda

  26. http://www.hihwnms.nos.noaa.gov/graphics/

  27. Biogenous Sediments • Composed of planktonic organism remains • Calcareous skeletons (CaCO3) • Siliceous skeletons (SiO2) • Accumulation rate controlled by: • Primary productivity • Rate of dissolution (Importance of fecal pellets)

  28. Figure 3.21a Diatoms (siliceous high latitudes) Coccololithospheres (calcareous – mid latitides)

  29. Figure 3.21b Radiolarians (siliceous – low latitudes)

  30. Foraminifera (calcareous – all latitides)

  31. Pteropods (calcareous – all latitudes) http://www.mbari.org/expeditions/

  32. Dissolution Biogenous Particles • Silica • Ocean is UNDERSATURATED with silica • Dissolution highest in surface waters • Low Pressure • High Temperature Accumulation in sediments occurs in: • Areas of very high productivity • Poles and upwelling zones (diatoms) • Tropics (Radiolarians)

  33. Dissolution Biogenous Particles • Carbonates • Foraminifera (Calcite) – less soluble • Pteropods (Aragonite) – More soluble • Dissolution is highest in Deep Waters • High pressure • Low temperatures • Low pH (high C02) Carbonate Compensation Depth (CCD)

  34. Carbonate Compensation Depth • CCD varies with Latitude • CCD varies between Oceans • North Pacific: 1000m • South Pacific: 2500m • Atlantic: 4000m

  35. Carbonate Compensation Depth • New Deep Waters have low CO2 conc. • Old Deep Waters have high CO2 conc. • Animal respiration • Decomposer activities Pacific Deep Waters are older than Atlantic Deep Waters

  36. Global Thermohaline Circulation

  37. Carbonate Compensation Depth& Greenhouse Effect? • CO2 atmosphere, seawater & sediments are interrelated! • Will increase in atmospheric CO2 cause increase in dissolved seawater CO2? • Consequences of a shallow CCD? • Release into atmosphere of dissolved carbonate sediments?

  38. Hydrogenous Sediments • Lower concentrations than Lithogenous and Biogenous sediments • Ocean water usually is UNDERSATURATED, but.. • Hydrothermal Vent Minerals (metal rich sedim.) • Manganese Nodules (areas of low sedimentation) • Carbonate banks - CaCO3 precipitates at: • High Temperature • Low Pressure • High pH (low CO2) • Caused by high productivity - photosynthesis

  39. Bahamian Bank

  40. Carbonate Sediments

  41. Figure 3.23

  42. Chicxulub crater

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