Mercury evidence for combustion of organic-rich sediments during the end-Triassic crisis

The sources of isotopically light carbon released during the end-Triassic mass extinction remain debated. This study uses mercury (Hg) concentrations and isotopes from a pelagic Triassic–Jurassic boundary section (Katsuyama, Japan) to track changes in Hg cycling. Owing to the section’s location in central Panthalassa, far from terrigenous runoff, Hg enrichments at Katsuyama record atmospheric Hg deposition. These enrichments are characterized by negative mass-independent fractionation (MIF) of odd Hg isotopes, indicating derivation from terrestrial organic-rich sediments (Δ199Hg < 0‰) rather than deep-Earth volcanic gases (Δ199Hg ~ 0‰). The data support a significant role for combustion of sedimentary organic matter by igneous intrusions and/or wildfires in driving environmental perturbations during the event, analogous to modern anthropogenic combustion of fossil fuels.