/ 



I 



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596 KAPLAN AND RITTENBERG [CHAP. 23 



of asphaltic material than of the other hydrocarbons in some argillaceous sedi- 

 ments from Britain, but the difference was not as great as in the southern 

 California basin sediments. Petroleum per se has not been recognized in recent 

 marine sediments. Perhaps one reason for failure to isolate light-weight hydro- 

 carbons is because of inadequate techniques. Removal of the low-boiling-point 

 solvents used for extractions may also remove low-molecular-weight products, 

 including gaseous hydrocarbons, which are known to be present (Emery and 

 Hoggan, 1958). 



The work with southern California basin sediments (Orr and Emery, 1956) 

 reveals that the highest concentrations of hydrocarbons occur in the most 

 reducing sediments. This suggests that aerobic degradation may be the only or 

 certainly the major form of removal of these substances from the sediment. 

 Except for the upper 5 to 10 cm, there appears to be little correlation in con- 

 centration with the depth of burial to about 500 cm; there is some indication, 

 however, that the paraffin-naphthene fraction does decrease. 



c. Lipids 



These compounds are vital and major constituents of all living matter. Under 

 certain circumstances they become the dominant substance in the organism, 

 particularly in algae (Spoehr et al., 1949). The most important type of lipid is the 

 neutral fat or ester of fatty acids and glycerol. Such fats have apparently not 

 been isolated in sediments, although Shabarova (1954) isolated salts of oleic 

 acid from a Black Sea ooze, and Plunkett (1957) identified seven short chain 

 mono-, di- and tricarboxylic acids from the Cariaco Trench. These fatty acids 

 have been considered as source material for petroleum (Brooks, 1952). Little 

 information is available on the lipid content of marine sediments, although 

 complex lipids, including waxes, have been isolated from peat (Abelson, 

 1959). A wide range of fatty acids is present in petroleum. 



d. Porphyrins 



In recent years the porphyrins have assumed special importance in supporting 

 the theories postulating the biological origin of petroleum. The vast majority, 

 if not all, organisms contain porphyrins as components of blood, respiratory 

 enzymes or chlorophylls. In the marine environment, it is generally accepted 

 that the chlorophylls contributed by phvtoplankton are the chief source of 

 the porphyrins in the sediment. Chlorophyll, a tetrapyrrole with a central 

 magnesium atom, has never been isolated in the sediments of marine basins 

 (Orr, Emery and Grady, 1958) or lakes (Vallentyne, 1957). Instead, its first 

 breakdown products, pheophytin (which is chlorophyll minus the magnesium), 

 chlorophyllin (loss of phytol group) and pheophorbide (loss of magnesium as 

 well as phytol group) are present. The diagenetic process leading to the chloro- 

 phyll transformation is not known, nor is it known whether this occurs in the 

 water column soon after the death of the organism and before settling or after 

 deposition has occurred. The conversion of chlorophyll-type jjorphyrin to the 

 nickel or vanadyl type found in petroleum (Treibs, 1936) is still a mystery. 



