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Chapter 5: Marine Sediments

Chapter 5: Marine Sediments. Fig. 5-23. Sediments reveal Earth history. Sediments lithified Mineral composition Sedimentary texture Past climate Plate motions Age of seafloor Fossil evolution and extinction. Sediments classified by origin. Lithogenous Biogenous Hydrogenous

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Chapter 5: Marine Sediments

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  1. Chapter 5: Marine Sediments Fig. 5-23

  2. Sediments reveal Earth history • Sediments lithified • Mineral composition • Sedimentary texture • Past climate • Plate motions • Age of seafloor • Fossil evolution and extinction

  3. Sediments classified by origin • Lithogenous • Biogenous • Hydrogenous • Cosmogenous

  4. Rock fragments from land Transported to oceans by Rivers Wind Ice Gravity flows Lithogenous sediments

  5. Rivers transport much sediment Fig. 5-5

  6. Most lithogenous sediments accumulate near continental margins • Wind-blown dust in deep ocean makes abyssal clay (red clay) • Mostly quartz (SiO2) • Chemically stable • Abrasion resistant

  7. Distribution of terrigenous sediments • Neritic mainly lithogenous • Coarser particles closer to shore • Beach sands, continental shelf deposits, turbidite deposits, glacial deposits • Pelagic • Finer particles farther from land • Wind blown or distal turbidite

  8. Hard parts of once-living organisms Shells, teeth, bones Biogenous sediments Fig. 5-10

  9. Calcareous ooze (CaCO3) • Microscopic protozoans, foraminifer • Microscopic algae, coccolithophores • Siliceous ooze (SiO2) • Microscopic protozoans, Radiolaria • Microscopic algae, diatoms

  10. Distribution of biogenic sediments • Ooze is 30% or more biogenic material (by weight) • Biologic productivity • Dissolution as shells settle through ocean • Dilution by non-biogenic material

  11. Shells and silt-clay fall through seawater column to seafloor

  12. Neritic biogenic sediments • Modern carbonates shallow, warm ocean • Coral reefs • Ooid shoals • Beach sands • Stromatolites hypersaline

  13. Pelagic biogenic sediments • Siliceous ooze beneath areas of surface ocean upwelling (high biologic productivity) • Calcareous ooze on seafloor less than about 4500 m • CaCO3 dissolves in cold seawater

  14. Hydrogenous sediments • Dissolved ions precipitate from seawater • Manganese nodules • Inorganic carbonates • Metallic sulfides • Evaporites

  15. Manganese nodules • Very low rate of accumulation • Larger nodules grow larger faster • Origin is unknown Fig. 5-18

  16. Cosmogenous sediments • Extraterrestrial fragments • Glassy tektites • Fe-Ni micrometeorites • Found in deep ocean where other sediments accumulate very slowly

  17. Mixtures of sediment types • Most marine sediments are mixtures of the four types of sediment • Usually one sediment type is dominant

  18. Mixed marine sediments • Examples: • Neritic seds mainly lithogenous although shell fragments are common • Coarse calcareous rubble in shallow tropical oceans mixed with quartz

  19. Calcareous ooze most common in deep sea floor (water depth < 4500m) • Abyssal clay most common in deeper ocean

  20. Distribution of marine seds Fig. 5-23

  21. Fig. 5E

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