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 (SiO 2 ) 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 (CaCO 3 ) Microscopic protozoans, foraminifer Microscopic algae, coccolithophores Siliceous ooze (SiO 2 ) 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 CaCO 3 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