Abyssal Deposits

deepwater deposits occupying about 90 percent of the floor of the world’s oceans. Abyssal deposits are found predominantly at depths of more than 3 km. They form under conditions of oxidation, chiefly by the settling to the bottom of skeletal parts of plankton organisms (foraminifers, coccoliths, pteropods, diatomaceous algae, radiolarians, and certain others), as well as minute mineral particles formed by the decomposition of land rock and carried into the open areas of the ocean by marine currents and winds. In addition, particles of volcanic origin (the ejecta of land and underwater volcanoes), the products of underwater weathering or deepwater chemical precipitation (concretions), and cosmic dust play a role in the formation of abyssal deposits.

Abyssal deposits are divided into organogenic and polygenic deposits, depending upon the predominance of particles of one origin or another. Organogenic deposits include lime muds (the most widely found are foraminifer or globigerine) and silica muds (diatomaceous or radiolarian). The content of skeletal particles in them ordinarily exceeds 20 percent and can reach 90–98 percent (in the globigerine muds).

Polygenic abyssal deposits are a deepwater red clay characterized by the finest particulate structure (up to 90 percent clay particles) and by an insignificant content (several percent) of organogenic remains. Typical components of the red clay include iron manganese nodules and other concretions, teeth of predatory fishes, and ear bones (otoliths). The other lime components, aside from the indicated ones, do not settle in the area of the red clay (depths greater than 5 km) but rather are dissolved in the water as a consequence of the low temperatures and enormous pressure.