SECT. 2] 



ABYSSAL PLAINS 



333 



the Bering Sea (Udiiitsev et al., 1959), in which the abyssal plain probably 

 exceeds 100,000 mi^ in area. The abyssal plain in the Okhotsk Sea probably 

 does not exceed 30,000 mi2 (Udintsev, 1957). 



e. Southern California basins 



Lying off the coast of Southern California is a series of thirteen isolated 

 basins which lie in the continental margin, their long axes oriented parallel to 

 the coastline (Fig. 15). The floor of each of these basins is occupied by a plain. 

 The largest of these plains lie in the basins nearest the coastline (Fig. 16). 

 Emery (1960) divides the basin floors into basin aprons and basin plains. The 



1I8°40' 



34°00 



doodo 



33°40' 



Fig. 16. Floor of the yanta Monica Basin. (After Emery, 1960.) 



basin aprons have gradients between 1 : 70 and 1 : 30 in their upper portions 

 but, in the lower parts, the gradients range from 1 : 800 to 1 : 100. 



The basin plains fulfill the definition of abyssal plains in having gradients 

 less than 1 : 1000 and in some cases the gradients are as low as 1 : 6000. The 

 basin aprons and basin plains slope away from the obvious sources of sediments 

 and are apparently fed by sediment distributed through the deep-sea channels 

 associated with the many continental-slope submarine canyons. The distribu- 

 tion of sediments in this manner has been well demonstrated by the work of 

 Gorsline and Emery (1959) in their study of the San Diego Basin. 



3. Trench Abyssal Plains 



A trench abyssal plain is an abyssal plain lying in the bottom of a deep-sea 

 trench. Since the initial discovery of the Puerto Rico Trench Abyssal Plain in 



