It is the depth zone that forms an extensively I oceanic floor which is intervened by complex submarine topogra features and relief aspects of the ocean bottom.
These features are | oceanic foredeeps or trenches (b) mid-oceanic ridges (c) deep submarj fans (d) sea mounts (submerged conical submarine hillocks / peaks ii immersed under sea water) (e) sea guyots (rows of flat topped mounts). Other important features of this depth zone are as follows:
1. The average oceanic depths of this zone go down to more than 40 metres or 4 km. The foredeep or trench parts show more than lOktj depth below mean sea level.
2. The oceanic water of this zone is cold recording very temperature (<4° C).
3. This is an absolutely dark depth zone which is under very hydrostatic pressure.
4. The sediments of this depth zone are thin and condensed. It has very! slow rate of sedimentation.
5. The depth zone shows variably thick / thin covers of sediments.
6. The sediments of this depth zone comprise of very fine-grained and rather thin veneers of (a) red muds / clays (b) turbidites (c) Ferro- manganese (Ni, Co, Pb, Zn rich) nodules (d) varieties of deep sea pelagic muds comprising varieties of calcareous and siliceous oozes.
7. This zone is inhabited by very few marine organisms such as anaerobic bacterial organisms which thrive in reducing environment.