SECT. 2] 



ABYSSAL PLAINS 



321 



abyssal hills abutting the chain of large seamounts comprising Atlantis, Plato, 

 Cruiser and Great Meteor. The sediment supply has been sufficient to pond the 

 sediments and create an abyssal plain in the area of maximum depth. 



South of a line joining the Canary Islands and Greater Meteor Seamount, 

 the abyssal hills west of the plain do not form a solid boundary but merely 

 dissipate the energy of turbidity currents, which are then unable to reach the 

 axis of maximum dej)th further west (Fig. 7). 



Sea level 



1000- 



E 

 o 



o 



c 2000 



^ 3000 



Continental shelf edge- 



Abyssal Ploin 



1000 800 600 400 200 



Distonce from the coast in nautical miles 



Fig. 7. Profile of Cape Verde Abyssal Plain. Vertical exaggeration, 100 : 1. There has been 

 insufficient material transported westward by turbidity currents to cover the irregular 

 topography 1000 mi from the coast. (After Laughton, 1959.) 



h. Sierra Leone and Gambia Abyssal Plains 



A 50,000-mi2 abyssal plain lies between the continental rise off Sierra Leone 

 and the Romanche Trench portion of the mid-oceanic ridge. This plain is 

 separated from the Gambia Abyssal Plain to the north by the Sierra Leone 

 Rise and appears to be separated from the Guinea Abyssal Plain to the east by 

 an area of abyssal hills. The Gambia Abyssal Plain lies north of the Sierra 

 Leone Rise and is separated from the Cape Verde Plain by abyssal hills. 



C. South Atlantic 



Abyssal plains are not as well developed in the South Atlantic as they are in 

 the North Atlantic. An extensive abyssal plain of 80,000 mi^, the Pernambuco 

 Abyssal Plain, extends eastward of Pernambuco Province, Brazil ; but the 

 abyssal plains of the southern part of the Brazil Basin and the Argentine Basin 

 are surprisingly small and intermittent. Whereas on either side of the North 

 Atlantic, abyssal jalains are found in all but a very few areas, in the South 

 Atlantic there are many places where the continental rise merges with the 

 abyssal hills without an intervening abyssal plain. The Argentine Abyssal 

 Plain, which follows the base of the continental rise east of Argentina, is 30 to 

 150 mi in width and covers an area of 100,000 mi 2. It resembles in relative 

 location the Hatteras and Nares Abyssal Plains of the North Atlantic but is 



