Global mercury cycle during the end-Permian mass extinction and subsequent Early Triassic recovery

Abstract

The end-Permian mass extinction (EPME) at ∼252 Ma was the most severe extinction in the Phanerozoic. Marine ecosystems devastated by the EPME had a highly prolonged recovery, and did not substantially recover until after the Smithian–Spathian substage boundary (SSB) of the Lower Triassic (5 to 9 Ma after the EPME). While the Siberian Traps large igneous province (STLIP) has been invoked as the driver of the mass extinction, there remains controversy as to the cause of the protracted Early Triassic recovery; although renewed STLIP volcanism has been suggested. These previous studies though have drawn conclusions based on geochemical records of sediments deposited in northern latitude settings. To investigate the relationship between STLIP and extinction/recovery processes on a global base, we examined mercury chemostratigraphy, including mercury concentrations and isotopes, from high southern latitude and equatorial sections that span the Late Permian Changhsingian to Early Triassic Spathian substage successions; the Guryul Ravine section, Kashmir in northern India, and the Chaohu section in southern China. Organic and inorganic carbon-isotope data define the EPME horizon in the Chaohu section and the SSB in the Guryul Ravine section, respectively. Hg/TOC values are dramatically elevated approaching the EPME horizon and maintain high values until the lower Isarcicella Isarcica conodont zone, the base of which is believed to be the end of the mass extinction. In the stratigraphically overlying beds, Hg/TOC generally displays lower values with slight fluctuations through the two sections. These fluctuations are likely related to the increased terrestrial Hg influx associated with strong chemical weathering in the Early Triassic, as shown by a positive correlation between the contents of Hg and Al, and by less positive Δ199Hg values in Early Triassic samples. Our data, presenting the first Southern Hemisphere Hg record from Guryul Ravine, in combination with previous results, indicates that anomalous high mercury deposition at the EPME occurred globally. The generally positive Δ199Hg values at this time reflects atmospheric-derived Hg, consistent with a volcanic Hg source which we suggest indicates global impact of STLIP eruption. In contrast, there is no evidence for a global Hg/TOC anomaly during the protracted Early Triassic biotic recovery, suggesting that potentially renewed STLIP volcanism had only a northern hemisphere influence on the global Hg cycle. This more limited impact, may still have played a role in the delayed Early Triassic recovery.