Abyssal Plains


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Abyssal Plains

 

deepwater plains of ocean basins and depressions of epicontinental seas. They are found within the bounds of the ocean floor and in the transitional zone and are divided into two morphological types—flat, or subhorizontal, and hilly. Flat abyssal plains are confined to the margins of ocean basins or to the centers of the basins of epicontinental seas. Hilly abyssal plains occupy a large part of the bottom of the ocean floor. The surface of the flat abyssal plain is characterized by exceptional evenness, with floor gradients of less than 0.001. Starkly contrasting solitary seamounts, evidently of volcanic origin, are also found. Flat abyssal plains are most widely found in the Atlantic (Hatteras, Biscay, Angola, and so forth). Their evenness is caused by the fact that they are unique traps that catch loose sediment (foraminiferal and diatomaceous silts and marine glacial deposits in polar waters).

The hilly abyssal plains show significant ruggedness. Relative variations of depth are from 500 to 1,000 m. The surface is a combination of hills and ridges separated by depressions; solitary seamounts are also frequently found. The floor is covered by deepwater deposits. Hilly plains are most widely found in the Pacific and Indian oceans and to a lesser degree in the Atlantic.

REFERENCE

Leont’ev, O. K. Kratkii kurs morskoi geologii. Moscow, 1963.
References in periodicals archive ?
Scientists know little about the benthic (deep-sea) species residing in the abyssal plains, but what they're learning shows them to be highly adapted to an extreme environment, where temperatures hover just above freezing and pressures become crushing.
Moreover, the addition of new sediments in abyssal plains depends on the gradual rain of particles from the sea surface.
Caption: Polymetallic nodules (left)--seen here with Psychropotes longicauda, a species of sea cucumber--dot the abyssal plains that cover nearly two-thirds of the earth's surface.
Sediment also might smother benthic organisms as it settles, particularly those living in abyssal plains, which never evolved to cope with such large amounts of sediment sinking from above.
when west Gondwana broke away and moved westward in the early Cretaceous, leaving the basalts of the Gascoyne and Cuvier abyssal plains behind, and
when a small part of Gondwana broke away to the north in the late Jurassic and the Argo abyssal plain formed from upwelling basalt behind the departing fragment,
Rare, very large turbidity currents periodically deposit thick sequences of sediment on oceanic abyssal plains, but their return periods span many thousands of years.
Examples of such sections include the Weddell Abyssal Plain (Leg 113) for the glacial history of West Antarctica, the Lau Basin (Leg 135) for volcanic history of adjacent islands, and the Argo Abyssal Plain (Leg 123) for the erosional history of the adjacent continents.
Located on the opposite side of an expansive abyssal plain from Wally's lair, the ridge hosts a hydrothermal hotbed of volcanic vents called black smokers.
Plunging into the ocean off the west coast of Vancouver Island, the more than 800 kilometers of fiber optic cables that connect the research stations stretch across the continental shelf, plummet down the slope and across an abyssal plain, and skirt hydrothermal vents near a mid-ocean ridge where the Earth gives birth to new ocean crust.
After 15 years of researching deep-ocean sedimentation, Orrin Pilkey realized that at cocktail parties people would listen more attentively when he talked about coastal erosion, hurricanes, and shoreline processes than about turbidity currents and abyssal plains.