Chapter 5: Marine Sediments

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Chapter 5 Marine Sediments
Fig. 5-23
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Sediments reveal Earth history

• Sediments lithified
• Mineral composition
• Sedimentary texture
• Past climate
• Plate motions
• Age of seafloor
• Fossil evolution and extinction

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Sediments classified by origin

• Lithogenous
• Biogenous
• Hydrogenous
• Cosmogenous

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Lithogenous sediments

• Rock fragments from land
• Transported to oceans by
• Rivers
• Wind
• Ice
• Gravity flows

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Rivers transport much sediment
Fig. 5-5
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• 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

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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

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Biogenous sediments

• Hard parts of once-living organisms
• Shells, teeth, bones

Fig. 5-10
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• Calcareous ooze (CaCO3)
• Microscopic protozoans, foraminifer
• Microscopic algae, coccolithophores
• Siliceous ooze (SiO2)
• Microscopic protozoans, Radiolaria
• Microscopic algae, diatoms

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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

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Shells and silt-clay fall through seawater column
to seafloor
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• Neritic biogenic sediments
• Modern carbonates shallow, warm ocean
• Coral reefs
• Ooid shoals
• Beach sands
• Stromatolites hypersaline

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• 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

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Hydrogenous sediments

• Dissolved ions precipitate from seawater
• Manganese nodules
• Inorganic carbonates
• Metallic sulfides
• Evaporites

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Manganese nodules

• Very low rate of accumulation
• Larger nodules grow larger faster
• Origin is unknown

Fig. 5-18
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Cosmogenous sediments

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

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Mixtures of sediment types

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

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Mixed marine sediments

• Examples
• Neritic seds mainly lithogenous although shell
  fragments are common
• Coarse calcareous rubble in shallow tropical
  oceans mixed with quartz

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

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Distribution of marine seds
Fig. 5-23
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Fig. 5E