The distribution characteristic and its significance of compound specific isotopic composition of aromatic hydrocarbon from marine source rock and oil in the Tarim Basin, western China

Aromatic hydrocarbons are generally main distillation of crude oil and organic extract of source rocks. Bicyclic and tricyclic aromatic hydrocarbons can be purified by two-step method of chromatography on alumina. Carbon isotopic composition of individual aromatic hydrocarbons is affected not only by thermal maturity, but also by organic matter input, depositional environment, and hydrocarbon generation process based on the GC-IRMS analysis of Upper Ordovician, Lower Ordovician, and Cambrian source rocks in different areas in the Tarim Basin, western China. The subgroups of aromatic hydrocarbons as well as individual aromatic compound, such as 1-MP, 9-MP, and 2,6-DMP from Cambrian-Lower Ordovician section show more depleted C-13 distribution. The delta C-13 value difference between Cambrian-Lower Ordovician section and Upper Ordovician source rocks is up to 16.1aEuro degrees for subgroups and 14aEuro degrees for individual compounds. It can provide strong evidence for oil sourc correlation by combing the delta C-13 value and biomarker distribution of different oil and source rocks from different strata in the Tarim Basin. Most oils from Tazhong area have geochemical characteristics such as more negative delta C-13(9-MP) value, poor gammacerane, and abundant homohopanes, which indicate that Upper Ordovician source rock is the main source rock. In contrast, oils from Tadong area and some oils from Tazhong area have geochemical characteristics such as high delta C-13(9-MP) value, abundant gammacerane, and poor homohopanes, which suggest that the major contributor is Cambrian-Lower Ordovician source rock.