The Permian–Triassic boundary (PTB, ~252 Ma) crisis was the most severe mass extinction episode in Earth history. It is now widely accepted that the ultimate trigger of this crisis was eruptions of the Siberian Traps Large Igneous Province (STLIP), based on temporal correspondence demonstrated by high-resolution zircon U-Pb dating. However, direct links between the STLIP and the end-Permian mass extinction are virtually lacking. Hg concentration and isotopic data have been generated for numerous PTB successions in recent years, but nearly all of these sites were located in the paleo-Northern Hemisphere and Equatorial regions. There is a lack of Hg records for more distal regions (e.g., in the paleo-Southern Hemisphere) that will be needed to test the global scope of STLIP influence.
In a recently published study in Nature Communications (https://www.nature.com/articles/s41467-022-35272-8), the coauthors (from China, South Africa, the United States, and the United Kingdom) analyzed Hg concentrations and isotopes in Permian–Triassic boundary successions of the Karoo Basin in South Africa and the Sydney Basin in Australia, both of which were located in the paleo-Southern Hemisphere. A sharp rise in Hg concentrations at the stratigraphic level of the PTB extinction event in all four study sites documents intense fluxes of volcanogenic material in association with the biocrisis. Positive Δ199Hg values indicate that the Hg inputs were atmospherically sourced and had likely travelled a long distance prior to deposition. These findings are consistent with the STLIP being the source of volcanogenic Hg in the study successions, demonstrating the global distribution of ejecta from that large igneous province and, thus, its global influence.
Until now, the stratigraphic position of the extinction horizon in the Karoo Basin has been uncertain owing to the immense thickness of fluvial sandstones comprising the boundary interval and their sparse fossil content. Because volcanogenic Hg is deposited rapidly, concentration spikes provide a high-resolution geochemical fingerprint of the timing of the STLIP eruptions in PTB sections globally. The Hg spikes identified in the Nature Communications study demonstrate that the eruptions began in the middle of the Palingkloof Member of the Balfour Formation, between previous placements of the extinction horizon at both lower and higher stratigraphic levels. These findings validate the use of Hg as a volcanic proxy in ancient sediments and demonstrate that Hg concentration peaks can serve as a geochemical event marker for global stratigraphic correlations.
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