chapter 5: marine sediments fig. 5-23. sediments reveal earth history sediments lithified mineral...
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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 Cosmogenous
Lithogenous sediments
Rock fragments from land Transported to oceans by
Rivers Wind Ice Gravity flows
Rivers transport much sediment
Fig. 5-5
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
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
Biogenous sediments Hard parts of once-living
organisms Shells, teeth, bones
Fig. 5-10
Calcareous ooze (CaCO3) Microscopic protozoans, foraminifer Microscopic algae, coccolithophores
Siliceous ooze (SiO2) Microscopic protozoans, Radiolaria Microscopic algae, diatoms
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
Shells and silt-clay fall through seawater column to seafloor
Neritic biogenic sediments Modern carbonates shallow, warm ocean
Coral reefs Ooid shoals Beach sands
Stromatolites hypersaline
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
Hydrogenous sediments
Dissolved ions precipitate from seawater Manganese nodules Inorganic carbonates Metallic sulfides Evaporites
Manganese nodules
Very low rate of accumulation
Larger nodules grow larger faster
Origin is unknown
Fig. 5-18
Cosmogenous sediments
Extraterrestrial fragments Glassy tektites Fe-Ni micrometeorites Found in deep ocean where other sediments accumulate very slowly
Mixtures of sediment types
Most marine sediments are mixtures of the four types of sediment Usually one sediment type is dominant
Mixed marine sediments
Examples: Neritic seds mainly lithogenous although shell fragments are common
Coarse calcareous rubble in shallow tropical oceans mixed with quartz
Calcareous ooze most common in deep sea floor (water depth < 4500m)
Abyssal clay most common in deeper ocean
Distribution of marine seds
Fig. 5-23
Fig. 5E