Biogenous Deposits

Biogenic deposits are fine-grained red, brown or light-colored skeletal remains of planktonic organisms that have been deposited on the ocean floor.  Biogenic deposits are referred to as oozes. There are two different groups of biogenic oozes; calcareous oozes and siliceous oozes. Biogenic deposits of biogenic oozes cover almost three quarters of the ocean floor. The remainder is covered by terrigenous material. While a vast number of marine species contribute to the deposition of material in the ocean floor, only a small group of marine organisms contribute to the deposition of calcareous and siliceous oozes in the deep ocean floor.

Biogenic oozes

Biogenic sediment is a fine-grained type of deposit that derives from drifting organisms in the water column. These fine-grained particles sink slowly down the water column until they´re deposited in the ocean floor. These particles are composed primarily of the calcareous and siliceous remains of microscopic phytoplankton and zooplankton. Biogenic oozes may be classified into two different groups; those producing calcareous ooze include coccolithophores, foraminifera and other benthic organisms, such as pteropods. Those secreting siliceous ooze comprise microscopic diatoms, which are found drifting in the euphotic zone, and radiolarians, covering large portions of the ocean floor as radiolarian ooze.

Kinds of biogenic sediments

Biogenic sediments are those that contain 30% of either calcareous or siliceous organic matter known as oozes. Calcareous oozes contain nearly 30% of the skeletal material of a number of planktonic organisms. Calcareous oozes may be divided based on the type of organism present in the sedimentary deposition. Globigerina ooze is characteristic of tests of foraminifera. Pteropod ooze contains shells of pelagic mollusks. Coccolith ooze contains a vast number of coccoliths and rhabdoliths, forming the protective structure of coccolithophores. Siliceous oozes comprise two forms, including diatom ooze and radiolarian ooze.

The distribution and abundance of marine organisms that generate biogenic deposits in the ocean floor depend on environmental factors, such as nutrient content and ocean temperature. The dissolution rates depend on the chemistry of the deep ocean waters and the chemistry, in turn, is influenced by the rate in which marine snow sinks to the bottom waters. The chemistry also depends on the deep ocean water circulation and the rate at which CO2 has been accumulating in the ocean floor. A vast number of marine organisms contribute to the organic material accumulating in the deep ocean as marine sediment, but only a limited group of organisms, either calcareous or siliceous, contributes to the deposition of biogenic pelagic sediments.

Distribution of biogenic ooze

The distribution of biogenic oozes varies considerably and depends on factors, including temperature, abundance of nutrients, ocean currents and the ocean’s depth. Globigerina are the predominant types of deposits. Diatoms are restricted to a band across the North Atlantic Ocean and to a continuous belt in Antarctica. Radiolarian oozes are limited to an equatorial region on the Pacific Ocean. Pteropod oozes are found in great quantities in the Atlantic Ocean. The Pacific Ocean, perhaps because of its size, contains a great percentage of most types of biogenic deposits. Calcareous deposits abound in the Indian and Atlantic Oceans.

The principal contributors to the biogenic deposits in the deep ocean floor are not only the calcareous and siliceous organisms living in the surface waters, but also other marine organisms whose decomposing corpses fall from the surface water down to the ocean floor as marine detritus (marine snow). The organic matter may provide carbon, hydrogen, nitrogen and many other elements. Many benthic organisms, on the ocean floor, depend on this material for survival and may decompose it, eventually, returning the elements as solution in the ocean water. The colors of biogenic oozes may vary. Calcareous oozes are typically white or whitish in color. The siliceous tests of diatoms and radiolarians are glassy, although, they may appear white.