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Pakistan Earthquake – 7.6 M agnitude

Pakistan Earthquake – 7.6 M agnitude. October 8, 2005 (8:50 p.m. local time). Ocean Sediments. Origin and Distribution. Marine Sediments. Most ocean floor covered by marine sediments. Sediment thickness is thinnest at mid-ocean ridge and thickest at continental margins.

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Pakistan Earthquake – 7.6 M agnitude

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  1. Pakistan Earthquake – 7.6 Magnitude October 8, 2005 (8:50 p.m. local time)

  2. Ocean Sediments Origin and Distribution

  3. Marine Sediments • Most ocean floor covered by marine sediments • Sediment thickness is thinnest at mid-ocean ridge and thickest at continental margins

  4. Types of Ocean Sediments • Terrigenous – “rock-derived” • Biogenous – “life-derived” • Hydrogenous – “water-derived” • Cosmogenous – “cosmic-derived”

  5. Sediment Distribution - Lithogenous

  6. LithogenousSediments • Composed mostly of quartz sand and clay • Derived from the weathering of rocks – continents or volcanic islands • Transported by rivers, glaciers or wind • Most deposited on continental margins • Covers about 45% of ocean floor

  7. Lithogenous Sediment - Examples Mississippi River Sahara Desert Mt. Pinatubo • Red Clays • Terrigenous from rivers, dust, and volcanic ash • Transported to deep ocean by winds and surface currents • Common in deep oceans • Accumulates 2 mm (1/8”) every 1,000 years

  8. Sediment Distribution - Biogenous • Calcareous and Siliceous Oozes

  9. Biogenous Sediment • Biogenic ooze – greater than 30% biogenous sediment • Composed mostly of hard skeletal parts of once-living organisms • Two main compositions of hard parts: • Calcium Carbonate (CaCO3) • Coccolithophore (phytoplankton) • Foraminifera (zooplankton) 2. Silica (SiO2) a) Diatoms (phytoplankton) b) Radiolarian (zooplankton)

  10. Biogenous – Calcareous Examples • Composed of CaCO3 Foraminifera Foraminifera • Widespread in relatively shallow areas Coccolithophore

  11. Biogenous – Siliceous Examples Radiolarians • Composed of SiO2 • Base of food chain Diatoms

  12. Sediment Distribution – Calcareous/Siliceous

  13. Biogenous – Calcareous oozes • Cold bottom waters undersaturated with respect to CaCO3 • slightly acidic ( CO2) • readily dissolves CaCO3 • Cover greater than 50% of ocean floor • Distribution controlled by dissolution processes • Calcium Carbonate Compensation Depth (CCD) – the depth at which the rate of accumulation of calcareous sediments equals the rate of dissolution • Pacific Ocean – 500-1,500 m CaCO3 is found • Atlantic Ocean – 4,000 m

  14. Biogenous – Siliceous Ooze • Covers 15% of ocean floor • Distribution - areas of high productivity (zones of upwelling) • Dissolve more slowly than calcareous particles • Diatoms common at higher latitudes • Radiolarians common at equatorial regions

  15. Siliceous Oozes

  16. Sediment Distribution - Hydrogenous

  17. Hydrogenous Sediments • Produced by chemical processes in seawater • Sediment precipitates from water • Some Examples: • Oolites – occur in surface waters supersaturated in CaCO3 • Manganese Nodules – manganese, iron deposits accumulate in areas of low sedimentation • Evaporites – “salt precipitates” form in areas of high evaporation

  18. Hydrogenous - Examples Sea salt Manganese Nodules Oolitic sand

  19. Cosmogenous – microtektites Tektites – result from collisions with micrometeors Fragments of Earth’s crust melt and spray outward from impact crater Crustal material re-melts as it falls back and forms glassy tektites Microtektites • Sediments derived from extraterrestrial material (micrometeorites) • Widespread but not abundant

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