232 



Sediments 



Nevertheless, the relative heights of the 

 peaks for quartz, plagioclase, and orthoclase 

 were found to be approximately proportional 

 to the percentage of the three minerals pres- 

 ent in several natural sand samples that had 

 been examined by staining and optical meth- 

 ods. Thus the ratios of peak heights on the 

 diffraction record were assumed to serve as 

 measures of the weight ratios in samples of 

 basin muds. A total of sixteen samples were 

 studied from San Pedro Basin, seven from 

 Santa Monica Basin, and one each from 

 nearly all the other basins, the continental 

 slope, and the deep-sea floor. The results of 

 all analyses, averaged by basins, yield a 

 quartz-to-feldspar ratio of 2.2: 1, similar to 

 the average ratio obtained optically for many 

 samples of sands from the beaches and main- 

 land shelves. There appears to be no syste- 

 matic regional variation, and individual sam- 

 ples varied from the average by no more 

 than a factor of 2. By the same method the 

 average plagioclase-to-orthoclase ratio was 

 found to be 4.5:1, again within the range 

 characteristic of the sands from the mainland 

 beaches and shelves. Particularly in near- 

 shore basins biotite is common, locally in 

 excess of 10 per cent. Its flat shape permits 

 easy transportation in suspension from 

 beaches and other areas of winnowing. 



G. Chemical composition. Spectrochemi- 

 cal analyses were made of 58 samples from 

 6 cores by California Research Corporation 



in 1953. Since the only preanalysis treat- 

 ment was drying to 140° C, these bulk analy- 

 ses include mineral solids, sorbed solids, and 

 dissolved solids of the pore water. The per- 

 centage of silicon was determined gravimet- 

 rically and of carbonate ion gasometrically. 

 The results (Fig. 197) show only a slight 

 dependence on grain size for the range of 

 grain sizes of these particular cores. Had 

 the size range included both sands and clays, 

 there would have been a clearer relationship 

 to grain size. 



The most abundant cation is silicon, ex- 

 cept in the core from the continental slope 

 (Table 17) in which calcium is greater. Both 

 sihcon and calcium lie in the region of values 

 found by Murray and Renard (1891) for 

 green mud and are somewhat difl'erent from 

 their value for blue mud. Reference to Fig- 

 ure 1 97 shows a clear relationship of calcium 

 to carbonate ion; however, an over-all aver- 

 age of 0.44 per cent more calcium (in terms 

 of total sample weight) was found by spec- 

 trochemistry than is needed to satisfy the 

 carbonate ion as calcium carbonate. This 

 excess is probably the calcium present in clay 

 minerals, as indicated by the average of 0.63 

 per cent calcium in analyses of clay minerals 

 of the off'shore region after removal of cal- 

 cium carbonate by acid digestion (Grim, 

 Dietz, and Bradley, 1949). Aluminum is the 

 second or third most abundant cation, yield- 

 ing an average silicon-to-aluminum ratio of 



PARTS PER MILLION 



10,000 1000 



MICRONS 



Figure 197. Chemical compo- 

 sition of cores from basin 

 floors. Most are spectrochem- 

 ical analyses by California 

 Research Corporation after dry- 

 ing to 140°C; gasometric car- 

 bonate ion and grain size were 

 previously reported by Emery 

 and Rittenberg (1952) on the 

 same cores (Santa Barbara 

 Basin, AHF 1856; Santa Cata- 

 lina Basin, AHF 1633); sihcon 

 was measured gravimetrically 

 by Griffin-Hasson Laboratories 

 on later cores (AHF 2622E and 

 AHF 2187-8), 0.1 mile and 13 

 miles distant, respectively. 



