Submarine Canyons 



47 



at Dume, Redondo (Fig. 47), Carlsbad, and 

 Coronado Canyons. They are probably 

 also present at Newport, La JoUa, and Cata- 

 lina Canyons, but their form is less regular. 

 For the above five best-known canyons or 

 groups, the fans have volumes several times 

 greater than those of the eroded canyons 

 above them (Table 4). As will be discussed 

 later, the basins contain large additional 

 quantities of sediments derived from shallow 

 water probably through the canyons. The 

 excess of volume of deposition over the vol- 

 ume of erosion of areas that are submarine 

 at present can be equated only with the 

 erosion of presently subaerial areas, by lit- 

 toral drift of sand intercepted by the canyon 

 heads, or by shelf sand slumped down the 

 sides of the canyons. Perhaps the presence 

 of an especially large fan at the mouth of 

 the small Carlsbad Canyon means that this 

 canyon formerly extended to nearer the 

 shoreline where it could intercept much of 

 the littoral drift of sand south of Newport 

 Beach. Filling up of its head may have al- 

 lowed this drift to continue southward to 

 Scripps and La Jolla Canyons. 



The second, or erosional, form of the can- 

 yon extension beyond the slope is a long 

 narrow channel which may cross the fans, 

 as discussed briefly for Coronado Canyon by 

 Emery, Butcher, Gould, and Shepard (1952). 

 Detailed deep-water soundings revealed the 

 presence of a "deep-sea channel" extending 

 beyond the mouth of the main part of La 

 Jolla Canyon and across at least part of the 

 San Diego Trough (Menard and Ludwick, 

 1951; Shepard, 1951a; Buffington, 1952). 

 Other such channels, mostly only 50 to 300 



feet deep, 0.2 to 2 miles wide, and bordered 

 by levees, have been described off" Monterey 

 Canyon by Dill, Dietz, and Stewart (1954), 

 in the Atlantic Ocean by Ewing, Heezen, 

 Ericson, Northrop, and Dorman (1953), and 

 in the Indian Ocean by Dietz (1953). De- 

 tailed surveys would probably show that 

 many such channels cross the floors of basins 

 on which the submarine canyons of Chart I 

 end. To date they have been found only at 

 Coronado, Redondo (Fig. 47), Mugu, Hue- 

 neme, and possibly off" San Pedro and New- 

 port Canyons. 



The age of the submarine canyons may be 

 determined partly from the age of the strata 

 which they cut (Emery and Shepard, 1945). 

 La Jolla Canyon is cut partly through Cre- 

 taceous shales and sandstones (Fig. 48). La 

 Jolla and Scripps Canyons are cut partly 

 through Eocene conglomerates, sandstones, 

 and shales. Coronado, La Jolla, San Pedro, 

 Redondo, Santa Monica, Dume, Mugu, Tan- 

 ner, and probably Santa Cruz and Newport 

 Canyons are cut through Miocene shales, 

 limestones, or basalt. San Pedro Sea Val- 

 ley and Coronado Canyon are cut partly 

 through Pliocene shales. According to Po- 

 land and his colleagues (Crowell, 1952), the 

 heads of Newport, Redondo, and Hueneme 

 Canyons are cut partly through Pleistocene 

 clays, silts, sands, and gravels. Data of the 

 same workers show that Hueneme, Santa 

 Monica, San Pedro, Newport, and probably 

 Mugu and San Gabriel Canyons have land 

 extensions that have become filled with Re- 

 cent gravels, sands, and silts of both marine 

 and nonmarine origin. These stratigraphic 

 relationships show generally older rocks oc- 

 curring at progressively greater distance from 

 shore and depth of water. In summary, 

 where any data are available, the canyons 

 are known to be cut through the strata of 

 their particular area, and some are cut 

 through strata as young as Pleistocene; thus, 

 at least some of the canyons were cut at least 

 in part in Late Pleistocene time. 



Origin 



The discovery of submarine canyons was 

 reported somewhat earlier on the Atlantic 



