Shelf Environment (Sublittoral) 



167 



yons, and basin floor. Superimposed on this 

 depth variation was found a secondary con- 

 trol exerted by type of bottom and presence 

 of local sewage discharge. An even finer 

 depth variation was discovered by McGlas- 

 son (1957) in a study of the foraminiferans 

 living on the shelf around Santa Catalina 

 Island; although the shelf edge is only about 

 1 10 meters deep, four depth assemblages 

 were noted. Depth facies also occur on off- 

 shore banks such as Coronado Bank off^ San 

 Diego (Butcher, 1951). The differences that 

 exist in the faunas of mainland shelves, is- 

 land shelves, and bank tops are great enough 

 that a critical comparison of the faunas from 



these environments should be profitable. A 

 study and comparison of the foraminiferal 

 faunas and their biozones in deeper water 

 are being carried on, as discussed in the sec- 

 tion on paleoceanography. 



Pleistocene representatives of the shelf en- 

 vironment have been described by Wood- 

 ring, Bramlette, and Kew (1946, pp. 86-103) 

 in the Palos Verdes Hills. Since most of the 

 Pleistocene mollusks are still living off south- 

 ern California, an attempt was made to work 

 out the depth relations of the strata by com- 

 parison with faunas collected from dredgings 

 of the present sea floors. The oldest strata, 

 the Lomita marl, contains calcareous algae 



II9"40 



II9°40' 



Figure 144. Comparison of biomasses of major animals living on the shelf near Santa Barbara. The holothurian is a 

 single species of Molpadia and the echiuroid is a single species of Listriolobus. Based on unpublished data of J. L. 

 Barnard. Compare with maps of the sediment character (Fig. 178). 



