A possible link between the Carnian Pluvial Event, global carbon-cycle perturbation, and volcanism: New data from the Qinghai-Tibet Plateau

摘要

The Carnian Pluvial Event (CPE) is recorded widely across the Tethys region. Here we present high-resolution carbonate (delta C-13(carb)) and organic (delta C-13(org)) carbon-isotope records and mineral data from the Boli La to lower Bagong formations in the Quemo Co area of the Qiangtang Basin, Qinghai-Tibet Plateau. In this studied section, a calcareous fine-grained sandstone bed that yields a detrital zircon maximum depositional age of 232.5 +/- 3.3 Ma, together with ammonoid species and bivalves, allows identification of the Carnian Stage. An intensification of siliciclastic supply and a large drop in calcite and illite is recorded in the Carnian section, suggesting a palaeoclimatic shift from arid to warm and humid during the CPE. A negative carbon-isotope excursion (CIE) in both delta C-13(org) and delta C-13(carb) is also reported, which could be explained by a global perturbation of the carbon cycle and the release of CO2 enriched in C-12. The magnitude of the negative CIE in the Quemo Co area displays a significant shift towards lighter values compared to other reported carbonate carbon-isotope values across the onset of the CPE. A combination of both volcanic emissions from the synchronous Wrangellia large igneous province and release of methane clathrate hydrate is the most likely explanation for the significant negative excursion in delta C-13.