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benthic currents in seas and oceans that are characterized by increased density.
Turbidity currents arise as a result of an earthquake or other factors on a slope of the sea bottom when the equilibrium of large masses of loose clastic deposits is disrupted and submarine landslides are formed; the sliding material is stirred up and, in the form of a mud (turbid) flow, descends along the slope at high speed over a distance as great as hundreds of kilometers; in the process the turbidity currents not only carry sediments but also erode the ocean floor. This may promote the formation of submarine canyons. Particles of various sizes (ranging from clay to coarse grainy material) are interspersed in turbidity currents. Saturation with suspended matter gives turbidity currents great density. Therefore, larger fragments are transported in suspension matter within a finer-grained “mud.” Discharge takes place on the bottom of sea and ocean basins, in submarine canyons, and in glacial troughs.
When the velocity and density of a turbidity current decrease, large and heavy particles, and then smaller and smaller particles, down to the size of mud, drop out of the suspended matter. The next turbidity current brings a new portion of sediment; a second layer is formed, with gradual internal sorting that is separated by a sharp boundary from the inferior layer. The layers can be traced over large distances. The thickness of each layer is usually modest, but the thicknesses of various layers range from a few centimeters to a few meters. Repeated deposition of layers forms a sedimentary layer with repeating stratification. Such a formation of deposits has been verified experimentally. The deposits of turbidity currents (“turbidites”) are widespread in recent seas and in many mineral deposits of varying geological age.
REFERENCESBotvinkina, L. N. Sloistost’ osadochnykh porod. Moscow, 1962.
Shepard, F. P. Morskaia geologiia. Leningrad, 1969. (Translated from English.)
Bouma, A. H., and A. Brower [eds.]. Turbidites. Amsterdam-New York, 1964. (Developments in Sedimentology, vol. 3).
L. N. BOTVINKINA