MERCURY ANOMALIES AND THE TERRESTRIAL PERMIAN-TRIASSIC MASS EXTINCTION IN SOUTHWESTERN CHINA

The Permian-Triassic transition saw global environmental changes and the greatest Phanerozoic mass extinction likely caused by the eruption of the Siberian Traps. However, the precise temporal link between marine and terrestrial crisis and volcanism remains unclear. Here, we report anomalously high mercury (Hg) concentrations in terrestrial strata from southwestern China, which were synchronous with Hg anomalies at the marine latest Permian extinction horizon recorded worldwide. The same sediments record increased abundance of fossil charcoal coincident with the onset of a negative carbon isotope excursion (CIE) and the extinction of tropical rainforest vegetation, both of which occurred immediately before the peak of Hg enrichment. These data demonstrate that ecological deterioration occurred in tropical peatlands prior to the main marine mass extinction. Interestingly, in our study the peak in Hg concentrations and Hg/TOC ratios also occurred after the onset of the negative CIE, suggesting a decoupling between the C and the Hg that could depend on the source of these two elements, be it volcanic, thermogenic, or from different reservoirs. Such decoupling deserves more future attention as it suggests different mechanisms of C and Hg release to and/or processing in the end-Permian environment. Additionally, high occurrences of abnormal spores (unseparated tetrads) within the Hg anomalies interval indicated severe environmental stress, that were probably caused by atmospheric pollution and toxic heavy metal enrichment linked to Siberian Traps emissions.