A massive magmatic degassing event drove the Late Smithian Thermal Maximum and Smithian–Spathian boundary mass extinction

Abstract

The role of volcanism as a driver of climate change remains widely debated. Following the end-Permian mass extinction, the protracted Early Triassic recovery interval was characterized by extreme climatic and environmental perturbations (hyperwarming, intense subaerial weathering, and extensive marine euxinia) and large carbon- and sulfur-cycle perturbations. Although a magmatic trigger is widely accepted, details regarding the timing and magnitude of degassing and its relationship to contemporaneous climate changes remain poorly understood. In this study, we present new paired carbonate δ13C and carbonate-associated-sulfate δ34S data from deep-water settings in the Lower Triassic of South China to evaluate these issues. Our dataset reveals large positive shifts of both proxies across the Smithian/Spathian boundary (SSB), recording globally synchronous changes in the C and S cycles linked to co-burial of large quantities of organic matter and pyrite. Biogeochemical modeling of the C-S cycles shows that massive carbon release linked to increased magmatic degassing can account for observations of concurrent positive shifts of δ34S and δ13C, enhanced weathering, expanded marine euxinia, and the Late Smithian Thermal Maximum (LSTM). Measured increases in δ13C (+3.2 ± 1.6‰) and δ34S (+7.3 ± 2.3‰) across the SSB relative to their baseline values are consistent with a major magmatic degassing event during the Early to Middle Smithian, whose magnitude and rate we estimate at ~78,000 ± 13,000 Gt C and 0.26 Gt C yr−1, respectively. Our results provide evidence that Early–Middle Smithian degassing was the primary trigger of the LSTM and concurrent biotic crisis.