Basins and Troughs 



221 



Figure 188. Relationship of 

 median diameter and calcium 

 carbonate of basin and conti- 

 nental slope sediments. Cal- 

 cium carbonate was computed 

 from determinations of carbo- 

 nate ion, assuming all is com- 

 bined with calcium. Note that 

 calcium carbonate increases 

 directly with distance from 

 shore, whereas grain size de- 

 creases at first and then 

 increases. 



4: 



%. 



%. 



\. 



% 



% 



%W///.A^^ 



'''''///^////' 



CONTINENTAL SLOPE 

 OFFSHORE BASINS 

 NEARSHORE BASINS 

 LOS ANGELES BASIN 



//////////////////////^^^^^ , •• 



^ 



MEDIAN DIAMETER IN MICRONS 



years have elapsed since deposition of sedi- 

 ment now at depth. In fact, the percentage 

 of calcium carbonate finer than 4 microns 

 in most cores decreases with depth of burial 

 (Table 15). Total calcium carbonate also 

 decreases with depth in most of the cores, 

 but comparison of the percentages of total 

 calcium carbonate and calcium carbonate 

 finer than 4 microns indicates that the de- 

 creases are not quite parallel. There is a 

 slight concentration of calcium carbonate in 

 the finer sizes of the nearshore basins and in 

 the coarser sizes of the offshore basins, as 

 though dilution by reworked calcium car- 

 bonate is most important in nearshore basins 

 and dilution by foraminiferal tests is most 

 important in off"shore basins. Thus, the 

 summary of Table 15 agrees with and ampli- 

 fies the results shown in Figure 189. 



B. Sorting of sediment. Median diame- 

 ters and Trask sorting coefficients are avail- 

 able for several thousand sediment samples 

 from the sea floor off southern California. 

 When the two parameters are plotted against 

 each other (Fig. 190), they present a pattern 

 having a wide degree of scatter; nevertheless, 

 the pattern shows a trend of finer sizes with 

 poor sorting and coarser sizes with good 

 sorting. In general, the former points denote 



MICRONS 



62 16 4 



MICRONS 

 62 16 4 



SAN PEDRO 

 BASIN 

 4688 



VZZA 



YZZZ^ 



SANTA CATALINA 

 BASIN 

 77771 4704 



-TZZZZZZZl 



^ 



TZZl 



-m 



SAN NICOLAS 

 BASIN 



'///A 317-330 



WEST CORTES 

 BASIN 



4674 



^ 



^ZZZ 



CONTINENTAL 

 SLOPE 



4697 



V77^/, 



-m 



VTTA 



Figure 1 89. Histograms comparing grain-size distribution 

 of whole sample with that of detrital fraction and calcium 

 carbonate in each grade size that was separated by suc- 

 cessive decantation steps. Note the general seaward 

 decrease in grain size, the concentration of calcium car- 

 bonate in coarse grain sizes at and near the continental 

 slope, and its similarity of grain size to detrital fractions 

 in nearshore basins. 



