Turbidity Currents


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Turbidity Currents

 

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.

REFERENCES

Botvinkina, 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

References in periodicals archive ?
1986), respectively, and indicate long-distance transport by debris flows and/or high-concentration turbidity currents and finally rapid collective deposition of a pebble-sand mixture.
1986) respectively and indicate deposition by mixed low-concentration turbidity currents and hemipelagic sedimentation
2009, How of turbidity currents as evidenced by failure of submarine telecommunication cables, in Chiocci, F.
Most slides are complex, and may include a rotational component resulting in uplift in one area and down-drop in another; failure typically progresses from a slide to a debris flow and eventually a turbidity current (Locat and Lee 2002).
It means that decreasing the channel width causes the velocity and height of the current to increase simultaneously and this condition seems to delay the settling of particles in turbidity currents.
These factors again provide the conditions for minimizing the sediment deposition; thus, it seems that sedimentation rates can be greatly reduced by confining the turbidity currents.
Turbidity currents are powerful landslides of underwater debris.
Rare, very large turbidity currents periodically deposit thick sequences of sediment on oceanic abyssal plains, but their return periods span many thousands of years.
Standard HPC (hydraulic piston core) coring techniques normally used to recover the upper, softer sediment cannot penetrate the thick sand layers left by large turbidity currents.
SLIP 'N' SLIDE Scientists haven't often caught turbidity currents on the move.
1950, Turbidity currents as a cause of graded bedding: Journal of Geology, v.
But as more surveys are conducted with sonar systems along coastlines where strong turbidity currents might have flowed, it's likely that more gravel dunes will turn up.