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The Origin of Marine Sediments
  • Lithogenous particles are derived from preexisting rocks by weathering (disruption of rocks by wind, temperature, water), deposited by wind or rivers
  • Volcanogenic particles are derived from vulcanic eruptions, range from boulders to dust
  • Glacially derived particles are ground from rock beds by moving glaciers
  • Biogenic particles: shells or skeletons of organisms that sink to the sea floor after the organisms death; made of silicate or carbonate

  • Diatom sediments

    Sediments of foraminifera (left) and radiolaria (right)

    Distribution of different biogenic sediment types. Note the predominance of radiolarian sediments near the equator, and diatom ooze around Antarctica; pteropod calcareous ooze is mainly deposited in the Atlantic Ocean

  • Stromatolites: cyanobacteria produce these deposits by trapping fine sediments into mucous mats; cyanobacteria live on the surface of such aggregates, the inner part becomes cemented by carbonate, which precipitates chemically upon raise of pH by cyanobacterial photosynthesis

    Stromatolites, Australia

  • Hydrogenous deposits from as a result of chemical reactions within seawater or between seawater and sediments; most known example are manganese nodules, with „growth rates“ of 5-10 mm/million yr (0.2-0.4‘/million yr).

  •   Manganese nodules
  • Cosmogenous particles originate from space, mostly Ni-Fe, and Si particles
  • Classification scheme of sediments according to the ratio of silt, clay, and sand (Shepard, 1954)

  • Vertical gradients within soft sediments: major zonation in oxic and anoxic depths; note highest nitrite (NO2) concentrations at the oxic-anoxic interface; only reduced substrates (NH4, CH4, H2S) are found in anoxic depths

  • Biological processes show a similar vertical zonation in soft sediments; heterotrophic respiratory metabolism prevails in oxic surface layers; chemoautotrophic bacteria reside at the oxic-anoxic interface; anoxic layers contain anaerobic heterotrophic bacteria that use reduced substrates (H2S, NH4+, SO42-) for energy and organic carbon