Early cambrian carbon isotope stratigraphy in the tarim basin and a correlation with the yangtze platform

Abstract

Carbon isotope chemostratigraphy has been used worldwide for stratigraphic correlation. In this study, δ13Ccarb values are estimated for the Early Cambrian Sugaitebulake section in the Tarim Basin, Xinjiang Autonomous Region, China. As a result, one positive and two negative carbon isotope excursions in the studied section were identified. The δ13Ccarb values reached the maximum negative excursion (N1: −12.39‰) at the basal of the Yuertusi Formation, and then increased to P1. After P1, δ13Ccarb values sharply decreased to about −7.06‰ (N2) in the studied section. The pattern of δ13Ccarb in the Early Cambrian is comparable to the synchronous records of other sections, such as the Laolin section, the Xiaotan section and the Anjiahe section of the Yangtze Platform. It is concluded that the Early Cambrian Yuertusi Formation from the Tarim Basin is within the Nemakit-Daldynian stage, and the lower strata of the Yuertusi Formation may belong to the Zhujiaqing Formation (Meishucun Formation) of the Yangtze Platform. The Ediacaran/Cambrian boundary of the Tarim Block should be located in cherts and phosphorites successions at the basal of the Yuertusi Formation. The δ13Ccarb negative excursion N1 is just across the PC/C boundary, and may be related to certain biomass extinction due to anoxic sedimentary environment, transgression and/or the oceanic overturn. The second δ13Ccarb negative excursion N2 may account for the sea-level falling in the Early Cambrian.