Organic Constituents 



289 



higher than in petroleum, for which 8 hes 

 mostly between —22.2 and — 29.4%o ac- 

 cording to Wickman (1956) and Silverman 

 and Epstein (1958) (Fig. 231). The latter is 

 nearly the same as for terrestrial plants, 

 -21.1 to -26.7%o. Values in the 24 basin 

 and other southern California marine sedi- 

 ments that were analyzed range between 



— 19.9 and — 24.8%o for total organic mat- 

 ter. These values are closer to those for 

 petroleum in general and to two southern 

 Cahfornia petroleum samples reported by 

 Silverman and Epstein (1958), —23.0 and 



— 23.1%o in particular. The values in the 

 sediments are similar to others reported for 

 organic matter in deep-sea sediments by 

 Landegren (1954) and to two samples of 

 shale from the Los Angeles Basin. This cor- 

 respondence indicates either that fractiona- 

 tion with relative loss of C^^ has occurred 

 between the synthesis of tissue by phyto- 

 plankton and deposition of the debris in the 

 sediment, or that the organic matter in sedi- 

 ments is dominated by a part of the organic 

 matter that is both resistant to oxidation and 

 has a lower C^VC^- ratio than the bulk of 



the original tissue. Some data suggest that 

 the latter is more likely because a hydrocar- 

 bon chromatographic fraction prepared from 

 phytoplankton was found by Silverman to 

 have a 5 of — 30.4%o. Organic matter ex- 

 ractable by solvents from three depths in 

 Santa Barbara Basin sediments and hydro- 

 carbon fractions from the same basin also 

 have shghtly lower 8 values ( — 23.3%o) than 

 does total organic matter in the sediments, 

 falling more nearly in the range of petroleum 

 than even the organic matter. For compari- 

 son, 8 values for carbonate in the sediments 

 are far higher, +0.9 to -1.9%o. This dif- 

 ference between 8 values for carbonate and 

 organic matter is well known from studies by 

 Craig and others. 



At depth in the basin sediments 8 values 

 based on organic matter present a consistent 

 decrease (carbon becoming lighter) in each 

 of five cores for which values at several 

 depths are available (Table 28). Differences 

 between top and bottom core samples range 

 up to 2.3%o, well beyond the error of 

 analysis. 



Craig (1953) and Parks (1957) reported 



Figure 231. Distribution of C'VC" S values in %ofor different materials: 1, Marine and terrestrial plants and marine 

 invertebrates (Craig, 1953). 2, Paraffin fraction from phytoplankton consisting of 97% dinoflagellates. 3, Extract from 

 Pliocene shale, Los Angeles Basin. 4, Total organic matter in Miocene shale, Los Angeles Basin. 5, PHocene-Miocene 

 petroleum, Los Angeles Basin. 6, Oligocene petroleum, Ventura Basin. 7, Various petroleums. Tertiary on left and 

 Paleozoic on right. 8, Natural gas. Triangles and range bar for petroleums indicate analyses reported by Silverman 

 and Epstein (1958) or by Silverman (personal communication), circles indicate analyses reported by Landegren (1954), 

 and dots indicate analyses on California basin sediments made by T. A. Rafter financed by grant from National 

 Science Foundation. 



