Stable isotope (δ13Cker, δ13Ccarb, δ18Ocarb) distribution along a Cambrian outcrop section in the eastern Tarim Basin, NW China and its geochemical significance

Abstract

This study investigated the geochemical features of the lower Paleozoic strata of Yaerdang Mountain outcrop along with the core samples from well TD2∈ in the eastern Tarim Basin, NW China. The total organic carbon abundance, hydrocarbon-generating precursor biospecies, and stable isotope ratios of organics and carbonate (δ13Cker, δ13Ccarb and δ18Ocarb) were comprehensively studied for their possible correlative constraints during sedimentary evolution. The results revealed that the δ13Cker (VPDB) of Cambrian kerogens along the outcrop section varied from −34.6‰ to −28.4‰, indicating an increasing tendency from the lower Cambrian to the upper Cambrian. This was on the whole accompanied by the variation in the δ13Ccarb and δ18Ocarb along the profile, which might be associated with the changes in the sea level and also in the compositional variation of benthic and planktonic biomass. The large variation in the stable carbon isotope ratios up to 6‰ along the outcrop section reflected the heterogeneity of the Cambrian source rocks from the eastern Tarim Basin. Hence, the 13C-enriched crude oils from well TD2∈ might have been derived from a localized stratum of Cambrian source rocks. The results from this study showed the possibility of multiple source kitchens in the Cambrian–lower Ordovician portion of Tarim Basin.

Keywords

• Kerogen
• Heterogeneity
• Tarim Basin
• Stable isotope geochemistry