SECT, 2] ABYSSAL, PLAINS 337 



shown ill his figures is smooth and thus analogous to abyssal plains, and what 

 jiercentage is irregular. 



5. Abyssal Gaps, Interplain Channels, Mid-Ocean Canyons and Deep-Sea 



Channels 



In many areas of the flat deep-sea floor, especially on and associated with 

 abyssal plains and the deep-sea fans found at the base of submarine canyons, 

 are small depressions a few miles across and some tens of fathoms deep and 

 varying in length from 10 mi to 1500 mi. They were first noted by Shepard and 

 Emery (1941) leading from the base of submarine canyons off Southern 

 California and have been found subsequently in most oceans of the \vorld. 

 Channels or canyons in the deep-sea floor have at least three modes of occur- 

 rence: (1) The extensions of submarine canyons which lead from the continental 

 slope on across the continental rise to the abyssal plains. These are sometimes 

 called "deep-sea channels". However, other investigators simply refer to them 

 as submarine canyons. (2) Mid-ocean canyons, which are found in abyssal 

 plains and have great length. They are usually unbranched and have not been 

 traced to continental slope canyons. (3) Interplain channels. These are small 

 channels or canyons which are associated with abyssal gaps. They begin in one 

 abyssal plain and end in another and have no direct connection with submarine 

 canyons of the continental slope. 



A. Deep-Sea Channels Associated with Submarine Canyons and Deej)-Sea Fans 



Whatever the mechanism by which submarine canyons may have been cut 

 into the edge of the continental shelf, it is well established that periodic turbidity 

 currents flush sediment through them and build up depositional fans where the 

 canyon reaches the lower gradients of the ocean basin. These deep-sea fans 

 have been found at the bases of nearly all submarine canyons, notably the 

 Hudson Canyon (Ericson, Ewing and Heezen, 1951), La Jolla Canyon (Menard 

 and Ludwick, 1951), the Monterey Canyon (Dill, Dietz and Stewart, 1954), and 

 many others off the California coast (Menard, 1955; Gorsline and Emery, 

 1959). A comparison of the volume of the deep-sea fans off central California 

 with the available erosion products from the adjacent land areas has led 

 Menard (1960) to date the fans as pre-Pleistocene. Recent surveys of the sea- 

 ward extensions of other submarine canyons throughout the world has also 

 revealed the existence of deep-sea fans or families of deep-sea fans, which are 

 collectively referred to as abyssal cones (Heezen, Ewing, Menzies and Granelli, 

 1957). 



Crossing these fans and abyssal cones are channels diverging from the mouth 

 of the submarine canyon and gradually losing their identity once they have 

 reached the abyssal plain. They are often characterized by leveed banks (Fig. 

 19) (Bufhngton, 1952 ; Dietz, 1958) and off the California coast there is a strong 

 tendency for them to hook left, i.e. to the south, contrary to what one would 



