72 



Med j an Diameters of Sediments on the Slopes and Canyons 



On the offshore slope below the shelf, basin slope,, there 

 is a fairly regular decrease of median diameters with depth. 

 Isopleth lines of median diameters usually show the same general 

 pattern as topographic contoiurs. However, this pattern is 

 interrupted at places by small patches of sediment which are 

 coarser or finer than the surrounding sediment, which are the 

 result of slumping on these slopes, Emery and Terry (1956) 

 have shown that the topography of the basin slope of the Palos 

 Verdes Hills is made up of innumerable small landslide scars, 

 and that the sediments themselves on the slope and at the 

 base of the slope show evidence of slumping. The same pro- 

 cesses are undoubtedly active on the basin slopes and the 

 slopes of the submarine canyon in Santa Monica Bay. 



The sand fraction of the sediment on the slope off the 

 outer portion of the central shelf is a phosphorite-glauconite- 

 shell sand, the same as the sand portions on the shelf above. 

 Thus, it evidently has been derived by slumping of material 

 or is winnowed from the outer edge of the shelf. The same 

 sand fraction is present in the patch of coarse sediment in 

 the bottom at the mouth of Redondo Canyon, It is also similar 

 to the material occurring on the shelf above. Isolated 

 patches of fine material on the slopes may be areas where fine 

 sediment is building up under conditions of normal deposition. 

 The submarine canyons generally contain a tongue of fine- 

 grained sediment along the axes of the canyons. This is 

 particularly true in Redondo Canyon where fine-grained sedi- 

 ment lies close to shore in the upper end of the canyon. The 



