VOLCANISM DRIVEN CARBON ISOTOPE FRACTIONATION ACROSS THE WUCHIAPINGIAN-CHANGHSINGIAN BOUNDARY INTERVAL: IMPLICATIONS FROM 187OS/188OS ISOTOPE STRATIGRAPHY

Geological and biological events in Earth history, e.g., meteorite impact events, hydrothermal pulses, ocean anoxic events, mass extinctions, and Snowball Earth glaciations are associated with perturbation of the global carbon cycle, documented by the stable carbon isotope record. For example, the Late Permian is characterized by three carbon isotope excursions (CIEs) spanning the Permian-Triassic Boundary, the Wuchiapingian-Changhsingian Boundary (WCB), and the Guadalupian-Lopingian Boundary. In contrast to the Permian-Triassic and the Guadalupian-Lopingian Boundary intervals, which are associated with mass extinctions and volcanism, the WCB records no recognizable biotic crisis and the mechanism driving C-isotope variation at this level remain poorly understood. The WCB at several sections in South China, Iran, and the Canadian Arctic is similarly characterized by significant CIE’s. Here we present high-resolution osmium isotope (¹⁸⁷Os/¹⁸⁸Os) stratigraphy for three WCB sections in South China (Lianyuan, Meishan and Shangsi) to investigate the potential cause(s) for WCB carbon isotope excursions. Our data show two unradiogenic Os isotope excursions that coincide with CIEs associated with the WCB. The unradiogenic Os isotope compositions are interpreted to reflect two pulses of mafic volcanism. Given the minor CIEs in the Canadian Arctic section coupled with the lack of evidence for any biotic crisis across the WCB, we conclude that the volcanism recorded in the South China WCB sections may be relatively localized, possibly related to Emeishan volcanism, that emitted insufficient volcanic CO₂ to cause a global biotic crisis. However, this volcanism may have contributed to increasing atmospheric pCO₂ leading up to the end-Permian mass extinction.