The Cambrian Drumian carbon isotope excursion (DICE) in the Keping area of the northwestern Tarim Basin, NW China

Abstract

The middle Cambrian is an important period for the decline of metazoans and the resurgence of microbialites. Based on the analysis of carbon and oxygen isotopes, detrital zircon UPb dating, and geochemical analysis, the middle Cambrian DICE (Drumian carbon isotope excursion) event was identified and its relationship with microbialites and sea-level changes was discussed in the Tarim Basin. The DICE event has a negative shift in δ13C from 0‰ to −3.2‰. About 15 m below the DICE, the youngest age of the detrital zircon was 504.5 Ma, which was consistent with the age of the DICE event. Stromatolites are abundant and agnostoid trilobite Ptychagnostus atavus is absent in the Keping area. The DICE event corresponds to the occurrence of hemispherical stromatolites in the shallow-water platform. Lithologic association and terrigenous clastic index show that the marine transgression and condensation layer occurred during the DICE event, which may be synchronized with organic matter oxidation when stratified water masses overturned during transgression.