chapter 5: marine sediments fig. 5-23. sediments reveal earth history sediments lithified mineral...

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