SECT. 2] 



ABYSSAIy PLAINS 



346 



of the interplain channel, which is 50 mi long. The northern interplain channel 

 has no feeding channels and appears to be an older feature, the approaches to 

 which have since been silted up. 



The pattern of these channels can only be explained by the horizontal flow 

 of turbidity currents rejuvenated at the southwest corner of the Biscay Plain 

 by an increase of gradient. Before the plains were so connected, one can imagine 

 the Biscay Plain to have been filling with both pelagic and turbidity-current 

 sediment faster than the northern part of the Iberia Plain where turbidity- 

 current sediment was scarcer. When the level of the Biscay Plain reached the 

 level of the sill, which is covered with pelagic sediment only, subsequent 



2650 I 



E 

 2700 I 



2 I 3 



■I I i 



2650-1 i 



[Southern Chonnel _^ 



STOO-T 



20 noullcol miles 



Fig. 26. Profiles of southwestern portion of the Biscay Abyssal Plain, showing feeding 

 channels. Depth in fathoms (uncorrected). Vertical exaggeration, 100 : 1. (After 

 Laughton, 1960.) 



turbidity flows from the north Avould pour into the Iberia Plain and start to 

 cut a channel back toward the north. The stage reached at present is that the 

 cutting back has left the region of the gap itself and is in the Biscay Plain. 

 Dredging, coring and photography of the head of this erosion have shown semi- 

 consolidated pelagic sediments, vertical cliffs and exposed rocks. 



A similar abyssal gap, the Vema Gap,i has been found between the Hatteras 

 Abyssal Plain and the Nares Abyssal Plain. This is 20 mi wide, 70 mi long and 

 the change of depth of the interplain channel is 170 fm. Associated with the 



1 For a new chart of Veina Gap and associated interplain channels see Chapter 12, 

 Fig. 14, p. 247. 



