The carbon isotope study of biomarkers in the Maoming and the Jianghan tertiary oil shale

In terms of the individual carbon isotope data of biomarkers present in the typical freshwater lake sediment (Maoming oil share) and saline lake sedim ent lake (Jianghan oil shale) of China, this paper discusses their precurso rs and depositional environments of biomarkers in both sediment samples. Ou r studies showed that phytane and pristane of the Maoming oil shale were de rived from the phytol side chain of chlorophyll a. By comparing the isotopi c composition of 4-methyl sterane with that of sterane and hopane, it is su ggested that 4-methyl sterane which has a higher abundance in the Maoming o il shale come from bacteria. The isotopic composition of biomarkers from th e Jianghan rock sample (saline lake sediment) is significantly different fr om that of the Maoming oil shale (freshwater lake sediment). Gammacerane wa s derived from haloprotozoan, with delta(13)C being about -25.8 parts per t housand, just in consistency with the value reported in previous studies. T he isotopic composition of phytane and pristane in the Jianghan rock is sim ilar to that of sterane and 4-methyl sterane derived from phytoplanktons, i llustrating their common precursors were algae. This paper reported for the first time the carbon isotope data of porphyrin obtained by GC-IRMS techni ques. The approximate delta(13)C Of C32DPEP and C31DPEP porphyrin from the Jianghan Basin indicated that the porphyrin was derived from chlorophyll. I n the Maoming oil shale C32DPEP was enriched in C-13 relative to C(32)etio and C31DPEP, implying that C32DPEP came from chlorophyll, and C(32)etio and C31DPEP are of other origins.