Organic Constituents 



281 



Figure 226. Rate of deposition 

 of pheophytin and hydrocar- 

 bons in surface sediments of 

 basins expressed in mg/cmV 

 yr. Compare with Figure 207 

 for rates of deposition of other 

 constituents of sediments. 



117121 120 119 118 117 



phytin is lost much faster, indicating its 

 greater susceptibility to oxidation. The 

 nearshore basins where the least oxidation 

 should occur, owing to their shallow water 

 depth, low oxygen content, rapid rate of de- 

 position of detrital sediments, and low or 

 negative Eh of interstitial water, are the 

 ones in which pheophytin is buried most 

 rapidly in terms of weight per unit area per 

 unit time (Fig. 226). The greater preserva- 

 tion more than makes up for the greater 

 dilution by detrital sediments in these basins, 

 so that pheophytin also reaches its highest 

 concentration there in terms of percentage 

 weight of total sediment (compare Figures 

 203 and 208). In summary, the pheophytin 

 content of the sediments must be influenced 

 by diff'erences in its production by phy- 

 toplankton, dilution with inorganic sedi- 

 ments, and oxidation in the water and sedi- 

 ment. Production in the area varies by a 

 factor of about 1000 (Fig. 86), about four 

 times the range of pheophytin concentration 

 in the basin sediments, and it is probably 

 responsible for high values, especially in 

 Tanner Basin. The rate of deposition of 

 total sediment varies by a factor of 15 in 

 the basins (Table 20), but dilution does not 

 lower the pheophytin content in the near- 

 shore basins, aside from the eff^ects of 

 turbidity current deposits (Fig. 224). Oxi- 

 dation appears to be the main factor that 

 controls pheophytin, permitting the highest 

 concentrations in sediments where oxidation 

 is reduced by low Eh and rapid burial. 



Another group of pigments, the carot- 

 inoids, or yellow pigments, were noted in 

 the extracts for pheophytin. More com- 



plete studies were made by Fox, Updegraff", 

 and Novelli (1944), whose data indicate that 

 the carotinoids are more easily oxidized 

 than even pheophytin. Of the carotinoids 

 investigated, carotenes (hydrocarbon form) 

 and xanthophylls (oxidized form), the latter 

 appears to be the more easily oxidized. In 

 plants and animals xanthophyll is com- 

 monly several times more abundant than 

 carotene, but the reverse is true in sediments 

 owing to the more rapid rate of oxidation 

 of xanthophyll. Values in various materials 

 (Table 25) indicate the relative importance 

 of the two pigments, but measurements are 

 few in number and distribution and thus are 

 of uncertain relationship to environment. 

 When more study has been made of these 

 pigments, they may prove to be excellent 

 supplements to chlorophyll derivatives in 

 serving as measures of environment. Al- 

 though carotinoids do not occur in petrol- 

 eum as pigments, the carotenes may con- 

 tribute directly to the hydrocarbon content 

 of petroleum. 



Hydrocarbons 



In 1952 Smith reported the presence of 

 hydrocarbons in Recent sediments of the 

 Gulf of Mexico. Samples of a core from 

 Santa Cruz Basin were sent to him, and the 

 results of his study of these were also pub- 

 hshed (Smith, 1954). The abundance of 

 hydrocarbons showed a clear dependence on 

 environment with especially high concentra- 

 tions in the sediments of the southern Cali- 

 fornia basins, so Smith's work was followed 

 up at the University of Southern California 



