Early Late Permian coupled carbon and strontium isotope chemostratigraphy from South China: Extended Emeishan volcanism?

Abstract

Carbon isotope compositions of carbonates (δ13Ccarb) document a new 3.5‰ CIE toward lower values concomitant with an Emeishan Large Igneous Province (ELIP)-related drowning event (Mapojiao Event, southern Guizhou) during the early Wuchiapingian. Organic carbon isotope data (δ13Corg) have a 2‰ shift toward higher values across the drowning event, showing decoupling with the δ13Ccarb evolution. Rock-Eval and palynofacies analyses suggest an elevated flux of terrestrial organic matter (OM) during the drowning episode. Therefore, the decoupling between δ13Ccarb and δ13Corg is best explained by the mixing of different organic carbon pools in the δ13Corg curve. Strontium isotope data (87Sr/86Sr) also show a transient shift from 0.70715 to 0.70694 associated with this early Wuchiapingian carbon isotope excursion (CIE), which is superimposed on the late Permian prolonged global rising trend. This short-lived 87Sr/86Sr excursion is best interpreted as an enhanced hydrothermal flux related to a short pulse of ELIP-related volcanism.Comparison of the Mapojiao Event with other C isotope records from South China and other parts of Tethys reveals substantial discrepancies. Moreover, older Capitanian CIEs concomitant with ELIP-related drownings are also not laterally reproducible in time. The local distribution of CIEs across Guadalupian-Lopingian (G-L) interval indicates the influence of local factors such as bathymetry and increased burial rate of terrestrial OM, rather than perturbations in the global carbon cycle to due volcanism. This prevents the C isotope record to be used as a global correlation tool during Capitanian and Wuchiapingian times. Comparison of palaeobiodiversity changes with perturbations in C isotope compositions across the G-L interval shows that only the oldest CIE was associated with a modest extinction event as documented in South China. Hence, this study undermines any systematic coupling and causal relation between extinctions and iterative perturbations of the C isotope record during the G-L interval.