Marine vs. Terrestrial Organic Matter

Hayes et al. (1999) systematically evaluated the carbon isotope fractionation between carbonates and coeval organic matter for the past 800 Ma. They concluded that earlier assumptions of a constant fractionation between carbonate and organic matter is untenable and that fractionations may vary by about 10%o depending on the dominant biogeochemical pathway as well on environmental conditions. 

Questions concerning the origins of coal and petroleum center on three topics the nature and composition of the parent organisms, the mode of accumulation of the organic material, and the reactions whereby this material was transformed into the end products. 

Petroleum or crude oil is a naturally occurring complex mixture, composed mainly of hydrocarbons. Although there are, without any doubt, numerous compounds that have been formed directly from biologically produced molecules, the majority of petroleum components are of secondary origin, either decomposition products or products of condensation and polymerization reactions. 

Combined stable isotope analysis ( C, D, N, has been used successfully in petroleum exploration (Stahl 1977 Schoell 1984 Sofer 1984). The isotopic composition of crude oil is mainly determined by the isotopic composition of its source material, more specifically, the type of kerogen and the sedimentary environment in which it has been formed and by its degree of thermal alteration (Tang et al. 2005). Other secondary effects like biodegradation, water washing, and migration distances appear to have only minor effects on its isotopic composition. 

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