Formation of kerogen

Several ideas have been presented in the literature on the formation process of humic substances in marine sediments. Abelson (1967) claimed that polymerization of unsaturated fatty acids in phytoplankters after their death accounts for the formation of kerogen in marine sediments. Abelson and Hare (1971), Hoering (1973), and Hedges (1976) studied reactions between carbohydrates and amino acids under laboratory conditions as a possible formation reaction of humic acid and humin in sediments. They prepared a number of artificial humic acids by reacting glucose with amino acids. The synthetic products resembled natural humic acid and humin. A comprehensive review was published by Abelson (1978). 

As we have just seen, the classical model for the formation of kerogen involves the condensation of the various products of microbial degradation that escape... 

Figure 1. Stages of kerogen transformation and hydrocarbon formation pathways in geological situations. Direct inheritange of low molecule weight compounds is indicated by block arrows (from Engel and Macko, 1993).

Formation of oil from kerogen is a disproportionation reaction related to a hydrogen-rich mobile phase and a hydrogen-depleted carbon residue. After crystalline... 

Two Type II-S kerogens (as defined by Orr (i)) from the onshore Santa Maria Basin Monterey formation were pyrolyzed in this study to determine (a) the distribution of sulfur and its isotopic composition among the various products formed during artificial maturation, and (b) maturation trends reflected in the sulfur isotopic and elemental S/C ratios of kerogens, and in the variation of C and H isotopes. In addition, S isotopes in pyrites, kerogens and bitumens from the two Monterey shale samples were examined to speculate on the mode of S incorporation into Santa Maria Basin sediments. 

Structure of Kerogen from Oil Shale of the Green River Formation, In Science and Technology of Oil Shale Ann Arbor Science Publishers, Inc. Ann Arbor, MI, 1976. 

Morgan W. A., Feigelson E. D., Wang H., and Frenklach M. (1991) A new mechanism for the formation of meteoritic kerogen-like material. Science 252, 109-112. 

Hydrous pyrolysis experiments of crude oils generated relatively large concentrations of mono-and dicarboxylic acid anions with relative abundances generally similar to those observed in sedimentary basin waters. But analysis of all of the pertinent data indicates that the major part of the organic acid anions in formation waters is probably generated by the thermal alteration of kerogen in source rocks (Kharaka et al., 1993b Lewan and Fisher, 1994). This conclusion is based on several observations ... 

Garcette-Lepecq A., Derenne S., Largeau C., Bouloubassi I., and Saliot A. (2000) Origin and formation pathways of kerogen-like organic matter in Recent sediments off the Danube Delta (northwestern Black Sea). Org. Geochem. 31, 1663-1683. 

Figure 1 Kerogen is a key intermediate in the formation of oil and gas. Numerous schemes have been proposed both for the formation and structure of kerogen. This diagram shows one of the schemes which favors the selective...

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