Abyssal fans, also known as deep-sea fans, underwater deltas, and submarine fans, are underwater geological structures associated with large-scale

sediment deposition Deposition is the geological process in which sediments, soil and rocks are added to a landform or landmass. Wind, ice, water, and gravity transport previously weathered surface material, which, at the loss of enough kinetic energy in the fluid, ...

and formed by turbidity currents. They can be thought of as an underwater version of alluvial fans and can vary dramatically in size, with widths from several kilometres to several thousands of kilometres The largest is the Bengal Fan, followed by the

Indus Fan The Indus Fan is one of the most significant depositional feature of the offshore Indus basin. It is the second largest fan system in the world after the Bengal Fan between India, Bangladesh and the Andaman and Nicobar Islands, Andaman Islands. The ...

, but major fans are also found at the outlet of the Amazon,

Congo Congo or The Congo may refer to either of two countries that border the Congo River in central Africa: * Democratic Republic of the Congo, the larger country to the southeast, capital Kinshasa, formerly known as Zaire, sometimes referred to a ...

, Mississippi and elsewhere.

Formation

Abyssal (or submarine) fans are formed from turbidity currents. These currents begin when a geologic activity pushes sediments over the edge of a

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

and down the continental slope, creating an underwater landslide. A dense slurry of muds and sands speeds towards the foot of the slope, until the current slows. The decreasing current, having a reduced ability to transport sediments, deposits the grains it carries, thus creating a submarine fan. The slurry continues to slow as it is moved towards the continental rise until it reaches the ocean bed. Thus results a series of graded sediments of sand, silt and mud, which are known as turbidites, as described by the Bouma sequence.

References

Sources

* * * Allen, Philip & Allen, John, 2005. Basin Analysis: Principles and Applications. 2nd ed. Blackwell. {{physical oceanography, expanded=other Abyssal fan Coastal and oceanic landforms

Formation

See also

References

Sources