Carbon isotopic compositions and origin of Paleozoic crude oil in the platform region of Tarim Basin, NW China

Abstract

Based on the carbon isotopic compositions of Cambrian-Ordovician source rocks Kerogen Samples and Paleozoic crude oil in the platform region of Tarim Basin, the origin and source of Paleozoic crude oil were investigated. There are at least two sets of source rocks with different carbon isotope compositions in the Cambrian, the Lower Cambrian source rock with lighter carbon isotope composition and Middle-Upper Cambrian source rock with heavier carbon isotope composition, while the Ordovician source rock is somewhere in between. The δ13C values of Paleozoic crude oil samples are wide in distribution range, from −35.2‰ to −28.1‰. The crude oil with lighter carbon isotopic compositions (δ13C−29.0‰) was mainly derived from the Middle-Upper Cambrian source rocks, and the crude oil with δ13C value in between may be derived from Cambrian source rocks. It is concluded through analysis that the Cambrian source rock could become the major source rock in the Tarim Basin and the platform region has huge potential oil and gas resources in the deep formations. Key words: Tarim Basin, Cambrian, Ordovician, marine hydrocarbon, oil source, carbon isotope composition