Origin of Petroleum 



293 



Figure 232. The chemical com- 

 position of various organic 

 materials. Averages for coal 

 are from Clarke (1920, p. 763). 

 Those for phytoplankton. or- 

 ganic chemical groups, petro- 

 leum, and natural gas are from 

 various tables in this work. 

 Corners of triangle indicate 

 100% carbon, hydrogen, and 

 combined oxygen, nitrogen, 

 and sulfur, respectively. Dia- 

 gram adapted partly from 

 Kropotkin (1957). Note the 

 differences in evolutionary trend 

 of coal and petroleum. 



ATOMIC RATIO H/C 

 1 2 3 4 



-PETROLEUM 

 -NATURAL GAS 



(Fig. 195). The shales, which make up about 

 half the section, have an average median 

 diameter of about 14 microns (Table 12), de- 

 creasing irregularly with depth (Fig. 233). 

 Calcium carbonate in the shales averages 

 about 4.9 per cent and total organic matter 

 about 2.6 per cent (Tables 12 and 14). These 

 values of median diameter, calcium carbon- 

 ate, and organic matter form reasonable 

 continuations of the trends from offshore to 

 nearshore basins (Figs. 188, 196, 201, 203, 

 and 204), as do their rates of deposition 

 (Figs. 207 and 208). It is evident from the 

 foregoing that the sediments of Los Angeles 

 Basin are so closely related to those now 

 being deposited in the present nearshore 

 basins that many of the small differences 

 which do exist can serve as measures of the 

 changes taking place at depths (or times) 

 beyond the reach of cores of basin sediments, 

 provided of course that the environment of 

 deposition during the Pliocene Epoch was 

 not very different from that existing at 

 present. 



The sediments of Los Angeles Basin, hav- 

 ing a 2.6 per cent content of organic matter 



WELL CORES 



COMPOSITE FROM FIVE 

 WELLS OF DOMINGUEZ 

 HILLS & SIGNAL HILL 

 OF LOS ANGELES BASIN 



Figure 233. Sediment data for composite section near 

 middle of Los Angeles Basin. From Emery and Ritten- 

 berg (1952, Fig. 30). 



