Marine sediments are the deposits of insoluble materials in the form of fine as well as large sediments of rocks, soil particles, and decomposed particles of living organisms. These sediments are transported from land by means of rivers, streams, ice, and wind, while some of the particles, which are organic in nature, are those which were formed as a result of the decomposition of living animals and plants living within the aquatic ecosystem. Some of the minerals and salt are dissolved in the seawater, while the insoluble materials get accumulated on the sea floor. On the basis of their origin, the seafloor sediments may be classified into three groups: (i) terrigenous sediment, (ii) biogenous sediment, and (iii) hydrogenous sediment.
(i). Terrigenous Sediment:
The most common sediment that covers the deep ocean floor, and grey and brownish mud. This mud mainly consists of mineral grains derived from the erosion of land. These sediments had been transported by rivers flow, glacial movement, and winds for thousands of years. Some of the transported minerals and salts were dissolved in the seawater, while the insoluble particles settled down on the floor, thus adding the composition of the seafloor sediments.
(ii). Biogenous Sediment:
This sediment is derived mainly from the shells and skeletons of marine animals and plants. ”Calcareous Ooze” is the most common biogenous sediment. This sediment is produced by organisms that live in the surface waters of the sea. Other biogenous sediments include ”siliceous ooze” and phosphate-rich materials. Oozes of silica are derived from the silica shells of diatoms (single-celled algae), and radiolaria (single-celled animals). The phosphate-rich sediment is formed due to the accumulation of bones, teeth, and scales of fishes and other animals.
(iii). Hydrogenous Sediment:
This sediment contains minerals that crystallize directly from seawater through various chemical processes. For example, some limestone is formed in this way. From the economic point of view, ”manganese nodules” are the most important hydrogenous sediment. These rounded, blackish, potato-sized nodules contain a complex mixture of minerals, which include Mn, Fe, Cu, Ni, and Co.