EUXINIA AS THE CAUSE OF THE END-PERMIAN MASS EXTINCTION: EVIDENCE FROM SULFUR ISOTOPE CHEMOSTRATIGRAPHY

High-resolution δ³⁴S data from carbonate associated sulfate reveal extreme and rapid sulfur isotopic fluctuations (up to 10‰) in association with the end Permian mass extinction in Turkey, followed by smaller but significant rhythmic fluctuations in the Early Triassic. During the latest Permian, a large reservoir of anoxic and sulfidic deep water and a much smaller oxygenated surface ocean, susceptible to rapid isotopic adjustment because of its small volume, likely existed. The euxinic deep water expanded into the photic zone (as demonstrated by recent biomarker studies) where the flux of ³⁴S-depleted sulfide drove the rapid isotopic changes within the surface water mass. The rhythmic isotopic fluctuations (~5‰) following the Permo-Triassic boundary may represent the shrinking influence of the euxinic water mass and argue against some extrinsic catastrophic mechanism for the extinctions (e.g., bolide impact). The release of toxic H₂S into the surface ocean and perhaps the atmosphere had drastic consequences for marine and terrestrial life and likely led to the largest mass extinction in Earth's history.