Consider the following statements :
I. In general, the terrigenous deposits are derived from the land and are mainly deposited on the continental shelves.
II. From the shore onwards, there is a gradual increase in the coarseness of the terrigenous deposits.
III. The muds, the finest materials, are the terrigenous deposits.
IV. The colouring of the muds depends upon their chemical content.
Which of the above statements are correct ?
Ans: (3) I, III and IV (as per APPSC official final key)
Ocean deposits are of two kinds. Terrigenous deposits come from the land through rivers, wind and glaciers. Pelagic deposits (oozes, red clay) come from organic remains and volcanic dust in the deep sea. Terrigenous deposits settle mainly on the continental shelves and slopes (I is correct).
Coarse material settles first near the shore, so coarseness decreases seaward (II is wrong). The finest terrigenous deposits are muds (III is correct). Their colours (blue, red, green) depend on their chemical content, e.g. iron sulphide or glauconite (IV is correct).
Note:
- Calcareous ooze and siliceous ooze (diatom, radiolarian) are pelagic deposits.
- Red clay covers the largest area of the deep ocean floor, mainly in the Pacific.
- Ocean salinity averages 35‰. The Dead Sea has about 238‰.