84 



in relic sands and gravels, and in sediments containing 

 authigenic minerals and shell fragments. There is a tendency 

 for the sediment to become better sorted at 300 feet which is 

 approximately at the shelf break. This may be due to turbu- 

 lence at the edge of the shelf which would tend to create a 

 better-sorted sediment. The curve is fairly uniform to a 

 depth of 1,000 feet and then has another peak due to the 

 relationship of poor emd moderate sorting to fine grained 

 deposits on the outer slopes. 



Calcium Carbonate 



Origin of Calcium Carbonate 



It is believed that all, or practically all, of the cal- 

 civim and magnesium carbonates in sediments are due to the 

 accumulation of shells. The examination of sand fractions of 

 the sediments from Santa Monica Bay indicates that the most 

 abundant organic remains are the tests of Foraminifera. How- 

 ever, in some areas, notably on the central shelf projection 

 and the shelf south of Redondo Canyon, fragments of larger 

 shelled animals constitute a considerable proportion of the 

 sediment. 

 Distribution of Calcitim Carbonate 



Percentages of calcium carbonate in the sediments are 

 shown in Figure 26. The percentage increases in an offshore 

 direction, being low over most of the shelf and slightly 

 higher on the offshore slopes. The exceptions to this distri- 

 bution are the extremely high percentages found in the patches 



