Preliminary Study on the Reversed Distribution of Stable Carbon Isotopes in Sedimentary Organic Matter

In the present paper, the distribution of carbon isotopes of sedimentary organic matter are studied in the aspects of soluable portion (i.e., abstracts) and insoluble component (i.e., kerogen) as well as in the groups of EOM (i. e. , saturated hydrocarbon, aromatic hydrocarbon, non- hydrocarbon and asphaltene), results show that the distribation of δ~(13)C value are as follows: it is higher in kerogen than in abstracts, and for the abstracts, it decreases in the proper order of asphaltene, non-hydrocarbon, aromatic hydrocarbon and saturated hydrocarbon. The study revealed that different sedimentary environment that fed by different biologic group may resulted in the abnormal distribution of carbon isotopic composition, for instance, it may be havier in non-hydrocarbon than in asphaltene, and aromatic hydrocarbon havier than non-hydrocarbon, the authors defined these phenominon as partially reversed carbon isotopic distribution of sedimentary organic matter; and if the carbon isotop is havier in soluble sedimentary organic matter than in kerogen, it would be called as totally reversed distribution. Normal carbon istopic composition are usually found in higher plant input limnetic facies and interfluval lacustrine, Partially reversed distribution is usually found in the facies that input mainly by higher plant but suffered intensivly bacterial action and input also by lipid of lower biomass. Totally reversed carbon isotopic distribution is often found in marine sedimentaty rocks that with a very high evolution degree of organic matter.