286 



Sediments 



cores from both Santa Barbara and Tanner 

 Basins had negative EKs to the sediment- 

 water interface, whereas the depth of nega- 

 tive Eh in cores from Santa Catahna and 

 Santa Cruz Basins was at about 270 cm. 

 The aromatic fraction is irregular at depth 

 in all four basins, with perhaps the nearest 

 approach to a decrease in Santa Barbara 

 Basin. Irregularity of depth trends in hydro- 

 carbons are also present in five cores, 2 to 3 

 meters long, from the Gulf of Mexico as de- 

 scribed by Stevens, Bray, and Evans (1956) 

 where, however, concentrations are much 

 lower than in the California basin cores, 

 averaging about 3-ppm paraffin-naphthenes 

 and 7-ppm aromatics. Irregular concentra- 

 tions with a tendency toward higher values 

 at depth were also present in some longer 

 drill cores described by Smith (1954) from 

 the Gulf of Mexico. 



The areal distribution of hydrocarbons 

 based on analyses of eight basins (Tables 14 

 and 27) reveals the highest concentrations in 

 Santa Barbara Basin, which has the most re- 

 ducing conditions, and the lowest concentra- 

 tions in San Clemente and Long Basins, 

 which are among the most oxidizing of the 

 basin sediments. When compared with the 

 better-known distribution of green porphyrin 

 pigments (Fig. 229), a general parallelism 

 can be noted. The parallelism also extends 

 to marsh sediments where Smith (1954) 

 found hydrocarbons present in amounts 

 more than twice as great as in any basin 

 sediment (Table 27) and where pheophytin, 

 with a concentration of 476 ppm (Orr, 

 Emery, and Grady, 1958), is more than four 

 times as abundant as in any basin. 



Evidently the same factors of production, 

 dilution, and oxidation affect hydrocarbons 

 as affect pheophytin. Oxidation appears to 

 be the most important factor controlling the 

 concentration of hydrocarbons in sediments, 

 as it is for pheophytin. This conclusion is 

 supported by the similarity of the areal pat- 

 terns of rates of deposition for the two or- 

 ganic materials in basin sediments (Fig. 226 

 and Table 20). As shown by Table 2 1 , about 

 880 tons of hydrocarbon accumulate in the 

 sediments each year, with 80 per cent of it 

 in the basins that comprise only 17 per cent 



HYDROCARBONS (PPM"^ 



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 SAN CLEMENTE 



PIGMENTS (P?^ PHEOPHYTIN) 



Figure 229. Comparison of concentrations of hydrocar- 

 bons and pheophytin in sediments of eight basins. Note 

 the use of different scales for the two materials. 



of the sea floor area of Chart I. Lipids in 

 phytoplankton that can be extracted with 

 the same methods used for hydrocarbons in 

 sediments amount to about 3200 ppm by dry 

 weight (Smith, 1954, 2000 ppm; Stevens, 

 Bray, and Evans, 1956, 4000 ppm; Orr, 3200 

 and 3500 ppm). These materials are almost 

 exclusively paraffin-naphthenes with virtu- 

 ally no aromatics. Since the annual produc- 

 tion of phytoplankton in the region is about 

 42 milhon tons (Fig. 153), about 135,000 tons 

 of hydrocarbon-like materials are produced 

 annually in the area of Chart L About 0.65 

 per cent of this annual production is buried 

 in the bottom, mostly in basins, representing 

 a percentage loss almost exactly the same as 

 that for total organic matter and 250 times 

 less than that for pheophytin. 



In the basin sediments hydrocarbons vary 

 between 0.05 and 0.60 per cent of total or- 

 ganic matter and average 0.30 per cent. 

 Additional hydrocarbons can be produced 

 from the sediment by pyrolysis. Assays at 

 500° C by the Petroleum and Oil-Shale Ex- 

 periment Station, U. S. Bureau of Mines, 

 Laramie, on samples from Santa Barbara, 



