Origin of Petroleum 



291 



and faster loss of C'^ than of C^- has oc- 

 curred during diagenesis. However, data on 

 parts of the sequence, especially on extracts 

 from phytoplankton and sediments, are still 

 too scanty for the process to be considered 

 certain as yet. 



Craig (1954) suggested that variations in 

 OVC^^ be used to correct ages based on 

 Qii/Qi2 measurements. However, such cor- 

 rections were not applied to the ages of the 

 sediment from the basins (Table 19) because 

 the original C^VC^- ratio may be independ- 

 ent of C^VC^-, owing to the nature of the 

 water media of growth (Rafter, 1955fl) and 

 because the C^VC- ratio in the sediments 

 may be a function of selective oxidation 

 rather than of fractionation. 



Origin of Petroleum 



Petroleum and asphalt, because of their 

 uses as fuel, building material, and medicine, 

 have been known to man from ancient times, 

 being mentioned in the Bible and in other 

 ancient Uterature. The origin of petroleum 

 was considered a great mystery, although by 

 the middle of the nineteenth century Lyell 

 (1850, p. 252) could write the half-truth that 

 petroleum seems to be formed by the action 

 of subterranean fires on vegetable substances 

 buried in the sedimentary strata. A few 

 years later in 1866 M. Berthelot produced an 

 inorganic theory of origin of petroleum by 

 reaction of carbon dioxide with free alkaline 

 metals in the earth's interior, and in 1877 

 D. Mendeleef developed his famous theory 

 of reaction between water and carbides in 

 the earth's interior (Clarke, 1920). Since 

 then theories of organic origin have gener- 

 ally prevailed over inorganic ones. How- 

 ever, during the past few years the possibility 

 of inorganic origin of petroleum has received 

 renewed attention. As discussed by Link 

 (1957), Fred Hoyle and Immanuel Velikov- 

 sky recently have published opinions that 

 petroleum was brought to Earth by meteor- 

 ites, a reiteration of an 1890 theory by N. V. 

 Sokoloff. Even more recently, Kropotkin 

 (1957) strongly favored the inorganic origin 

 of petroleum on the basis of its presence in 



stony meteorites and in fractured igneous 

 and metamorphic rocks and its rarity in 

 some areas of abundant coal. Because of 

 the strong stands taken by proponents of the 

 inorganic versus the organic theories of pe- 

 troleum genesis in the U.S.S.R., a large sym- 

 posium on the question was convened there 

 during late 1958 (Committee on Origin of 

 Oil, 1958). 



Evidence most frequently cited in favor of 

 the organic origin of petroleum is its nitro- 

 gen content, the presence of porphyrins, and 

 its optical rotation, all being otherwise typi- 

 cal of organic substances. In addition to 

 these chemical and physical properties is the 

 general restriction of petroleum to strata rich 

 in fossils, usually only of marine types. For 

 most oil fields, particularly those of southern 

 California, there is little disagreement to the 

 statements that the temperature of the sedi- 

 mentary source rocks has always been low 

 (probably less than 150°C) and that the pres- 

 sure has been low (probably less than 500 

 kg/sq cm). Evidence for the first point is 

 the presence of porphyrins in petroleum — 

 desoxophylloerythrin would be destroyed by 

 prolonged heating to even 150° C. Evidence 

 for the second point is the presence of pe- 

 troleum in strata of Los Angeles Basin that 

 have never been buried deeper than they are 

 now and have not been subjected to great 

 lateral pressures of folding. There is much 

 more disagreement on the question of dis- 

 tance of migration of petroleum, owing to 

 both geological and chemical uncertainties 

 in identifying the source rock for any par- 

 ticular petroleum accumulation. 



If petroleum is accepted as having an or- 

 ganic origin, the important question of how 

 it is derived remains. Two diff'erent gen- 

 eral methods are worthy of consideration: 

 whether it is a survival or a product of dia- 

 genesis or both. Favoring survival is the 

 fact that hydrocarbon-like lipids are present 

 in phytoplankton and their C'VC^- ratios 

 are like those of the hydrocarbon fractions 

 of organic matter in sediments and of petro- 

 leum. Also favoring survival is the general 

 decrease with depth of paraffin-naphthenes 

 in the basin cores (although increases have 

 been noted in some cores from the Gulf of 



