Biogenuos sediments

Image source

• They are hard remains of once-living organisms. The two major types include:

• macroscopic:
  Visible to the naked eyes.
  (like shells, bones, teeth)

• Microscopic:
  Tiny shells of tests
  (e.g biogenic ooze)
  mainly algae and protozoans.

Biogenic sediment composition

Two main common chemical compounds.
• Calcium carbonate (Caco³)
• Silica (Sio2) or Sio2 n H2o)

Calcium carbonate in biogenic sediment.

Cocci lithospheres (also called) nanoplankton.

• Photosynthetic algae.
• Coccoliths individual plates from dead organism.
• Rock chalk.
• Lithified coccolith rich ooze.
• Foraminefera.
• Protozoans.
• Use external food.
• Calcerous oozes.

Silica in biogenous sediments

• Diatoms

• photosynthetic algae
• diatomaceous earth

• Radiolarians

• Protozoans
• use external food

Distribution of biogenic sediment

• Productivity
• Destruction
• Dilution

Neritic deposits

Neritic deposits are deposited by Lithogenous sediments, and contain biogenous sediments.
Marine Sediments

Carbonate deposits;

• Carbonate minerals containing Co3
• Marine carbonates primarily limestone- CaCo3.
• Most limestone contain fossil shells
  suggests biogenic origin.
  Ancient marine carbonates constitute 25% of all sedimentary rocks on earth.

Carbonate deposits

• Stromatolites

• Fine layers of carbonate
• Warm, shallow-ocean, high salinity
• Cyanobacteria

Calcareous ooze and the CCD

• CCD: Calcite compensation depth.
  Depth where CaCo3 readily dissolves.
  Rate of supply= rate at which the shell dissolve.

• Warm, shallow ocean saturated with calcium carbonate.

• they are majorly found in a cool, deep ocean undersaturated with calcium carbonate present.

• Lysocline: found at a depth at which a significant amount of CaCo3 begins to dissolve rapidly.

• Scarce calcareous ooze below 5000meters (16,400feet) in modern ocean.
• Most ancient calcareous oozes are at greater depths, moved by sea floor spreading actions

Hydrogenous marine sediments

• Minerals precipitate directly from seawater:
  • Phosphates
  • Manganese nodules
  • Metal sulphides

• Small proportion of marine sediments

• Distributed in diverse environments

Manganese nodules

• they are first sized lumps of manganese, iron and other metals.
• Very slow accumulations rates.
• Mainly commercial uses.
• Unsure why they are not buried by seafloor sediments.

Phosphates and carbonates

• Phosphates
  
  Image source
  File:Copper(II) phosphate

• phosphorus-bearing
Occur beneath areas in surface ocean of very high biological productivity.
• Economically useful as fertilizer.

Carbonates

• Aragonite and calcite
• Oolites

Metal sulfides

• Metal sulfides contains:
• Iron
• Nickel
• Copper
• Zinc
• Silver
• Other metals associated with hydrothermal vents.

Evaporites

Image source
File:Halite Teepee structure Dead Sea 031712.JPG - Wikimedia

Evaporites are minerals that are formed when seawater evaporates.

• Restricted open ocean circulation
• High evaporation rates
• Halite (common table salt) and gypsum.

Cosmogenous Marine sediments

• Macroscopic meteor debris
• Microscopic iron-nickel and silicate spherules (small globular masses)

Image source

File:Tektites, Indochinite - Center for Meteorite Studies - Arizona State University - Tempe, AZ

Tektites, space dust
Overall, insignificant proportion of marine sediments.

References

• Link

• Oxford geology dictionary

• link

• link