Volcanic temperature changes modulated volatile release and climate fluctuations at the end-Triassic mass extinction

Emplacement of the Central Atlantic Magmatic Province (CAMP) is thought to have triggered global environmental changes and the end-Triassic mass extinction (ETE). However, the mechanisms linking volcanism and environmental change are unclear. Here we provide new insight into these linkages by measuring the abundance of both sedimentary five- to six-ring polycyclic aromatic hydrocarbons (PAHs) and mercury from strata deposited in shallow marine environments across the ETE at the GSSP Kuhjoch section in Austria and St. Audrie's Bay section in the UK. To contextualize these data, we report results from laboratory experiments measuring the production of SO₂ and CO₂ during heating of limestone and mudstone. ETE sediments record parallel enrichments of mercury and five- to six-ring PAHs, which could have been produced by intrusive magma (mainly sills) and lava flows during the early stage of the CAMP emplacement; these data indicate a direct link between massive gas emission from sill contact metamorphism and the ETE. The fraction of coronene - a highly condensed six-ring PAH that requires greater energy to form compared to smaller PAHs - accumulated in the sediments during these initial volcanic events is low, and it coincides with the terrestrial plant turnover and initial marine extinction. Coronene increases to medium values coinciding with the final marine extinction level. Our heating experiments of typical carbonate and mudstone materials show that relatively low temperature heating (>350 °C) by sills releases massive amounts of SO₂ on a 100 yr time scale, whereas higher temperature heating (500-600 °C) forms more CO₂ on the same time scale. The combination of our end-Triassic geochemical data and laboratory results implies that low heating by sills caused SO₂-dominated gas emission to the stratosphere and low CO₂ emission, inducing global cooling that could have precipitated the mass extinction. The subsequent increase in coronene content indicates higher volcanic temperature that would have volatilized CO₂ rich gas; the consequence was a switch to greater CO₂ release and long-term (>10⁵ yr) global warming.