The sources of isotopically light carbon released during the end-Triassic mass extinction remain in debate. This study uses mercury (Hg) concentrations and isotopes from a pelagic Triassic-Jurassic boundary section (Katsuyama, Japan) to track changes in Hg cycling. Hg enrichments at Katsuyama, far from terrigenous runoff, record atmospheric Hg deposition and exhibit negative mass independent fractionation (MIF) of odd Hg isotopes, indicating derivation from terrestrial organic-rich sediments rather than deep-Earth volcanic gases. The data suggest combustion of sedimentary organic matter by igneous intrusions and/or wildfires played a significant role in the environmental perturbations, analogous to modern anthropogenic fossil fuel combustion.

Jun Shen, Runsheng Yin, Thomas J. Algeo, Henrik H. Svensen, Shane D. Schoepfer