226 



Sediments 



The most complete information on sand 

 and silt layers is from San Pedro and Santa 

 Monica Basins where a detailed study was 

 made in 1956-1957 (Gorsline, 1958; Gorsline 

 and Emery, 1959) with financial aid from 

 California Research Corporation, La Habra. 

 This study was initiated after five or six cor- 

 ing attempts during one day of 1955 at the 

 west end of San Pedro Basin failed to pro- 

 duce more than bent core barrels having a 

 few grains of sand sticking to them. The 86 

 piston cores that were collected, together 

 with 30 earlier simple gravity cores and 

 about 170 surface samples, provide a reason- 

 ably dense grid of samples for both San 

 Pedro and Santa Monica Basins. The results 



reveal the presence of sand and locally of 

 fine gravel layers at the mouths of Hueneme, 

 Mugu, Dume, and Redondo Submarine 

 Canyons (Fig. 193). Farther basinward the 

 layers become thinner, are separated by 

 thicker interbeds of normal green muds, and 

 are irregularly finer-grained (Fig. 187, mid- 

 dle and bottom). The sands are most abun- 

 dant on the subsea fans and the areas 

 traversed by deep-sea channels which extend 

 basinward from the mouths of at least Hue- 

 neme, Mugu, and Redondo Submarine Can- 

 yons. Cores from the basin slopes contain 

 no sand layers and consist of sediment that 

 is coarser than the muds and finer than the 

 sands of the basin floors. At the foot of the 



4663 



150- 160 CM 



4489 



135-150 CM 



4663 



122 -I 28 CM 



4648 



150 - 163 CM 



4486 



ei-76 CM 



4489 



30-^33 CM 



\ ^ qo 



Figure 193. Photographs of typical sedimentary features in cores of basin sediments. From Gorsline and Emery (1959, 

 PI. 1). Core 4663 (150-160 cm and 122-128 cm), laminated silty sand layers with flow structures in their upper portions, 

 from basin floor. Core 4489 (135-150 cm), thick graded medium-to-coarse sand layer, from a subsea fan. Core 4648 

 (150-163 cm), gray silt layers (downswept ends are resuU of coring operation), from basin floor near base of steep 

 side slope. Cores 4486 (61-76 cm) and 4683 (109-137 cm), massive sandy silt with gravel and shallow-water mollusks, 

 from upper parts of subsea fan. Core 4489 (30-33 cm), graded coarse-sand layer with sharply defined top, from upper 

 part of a subsea fan. 



