Submarine volcanism ejects much of the pyroclastic material into the atmosphere by gas explosion and a large amount of these products accumulate in the vicinity of the volcanoes which leads to the formation of the volcanic oceanic islands.
The biogenic deposits which are more significant in the abyssal zone comprise calcareous and siliceous oozes. These oozes are rather different from those of the bathyal zone. These oozes are of three principal types-Globigerina ooze, Radiolarian ooze and Diatomaceous ooze.
This is the most wide-spread variety of oozes as foraminifera abound in the seas of both tropical and temperate regions. Globigerina is the most abundant genus of forminifera. The globigerina ooze is made up chiefly of the calcareous shells of that organism.
Globigerina ooze is most characteristically developed at depths ranging from 2700 to4500metres. In further deep zones calcareous sediments are not deposited, since at that depth the ocean cold waters are markedly under saturated with calcium carbonate and the calcareous shells of the forminifers are dissolved before deposition.
Globigerina ooze is white, slightly yellow or pinkish in colour.
It consists of accumulation of siliceoue shells of radiolaria, a minute organism of the phylum ‘Protozoa’. It occurs at depths from 4500 to 8000 metres.
It is confined to tropical seas and occurs chiefly in the tropical zones of the Pacific and Indian oceans. They are the deepest abyssal organic deposits. Rocks formed such deposits are called radiolarite.
Diatom oozes are produced by plankton plants which are microscopic algae with siliceous skeleton. Diatoms live in quite shallow water which is penetrated by sunlight.
Diatomaceous oozes are mainly accumulated in the cold, near-pole regions at depths between 1000 and 6000 metres. As we approach polar regions, the globigerina and radiolarian oozes gradually decline with more and more predominance of diatomaceous oozes.
As described above, the oceans and seas carry out erosion, transportation and deposition. Sometimes the coastal regions show a remarkable degree of erosion and barriers known as ‘groynes’ are constructed to check the coastal erosion.