Continental slope depth zone, otherwise termed as bathyal depth zone is a part of the continental margin that lies between the continental shelf and the ocean-ward continental rise.
The oceanic depth zone from 200 metres to 4,000 metres (4 km) into the open ocean constitutes this zone of continental slope. The marine waters of this zone are mostly dark except the upper thinnest layer which is penetrated by the sunlight. The following are the principal characteristics of this depth zone.
(a) It is dimly to very dimly lighted upto about 1000 m (1 km).
(b) Beyond above mentioned distance, this depth zone is dark, quiet and cold.
(c) The temperature of this zone is as low as 10° C and the hydrostatic pressure is high.
(d) Width of this zone varies from 16 km to more than 160 km.
(e) The average slope of this zone is in between 3° – 6°.
(f) The depth of this zone ranges from 200 to more than 3000 m.
(g) This zone is devoid of wave actions and sea currents. However, it is frequently witnessed by density (turbidity) currents.
(h) The floor of this zone is frequently witnessed by turbidity (density) currents.
(i) The sloping floor is somewhat irregular by deeply cut channels forming submarine canyons.
(j) The nature of slope of the bottom surface may be straight or concave.
(k) The sediments of the slope zone are texturally fine grained in general. However, compositionally the slope sediments are heterogeneous comprising of variously coloured clastic muds, silts, fine sands, greywacke, volcanic muds, coralline and foraminifera silts and a variety of organic oozes (shells of micro-organisms).
(1) Economic importance:
(i) Deepwater oil and gas fields
(ii) Phosphorite deposits
(iii) Varieties of sea food and source of dissolved salts.