MULTIPLE S-ISOTOPIC EVIDENCE FOR EPISODIC SHOALING OF ANOXIC WATER DURING THE LATEST PERMIAN MASS EXTINCTION

Global fossil data indicate that profound biodiversity loss preceded the final catastrophe that killed nearly 90% marine species on a global scale. Extraterrestrial impact, the eruption of Siberian basalts, oceanic anoxia, or perhaps some combination of these has been proposed to explain the end-Permian extinction. To better understand the extinction processes, we measure all four sulfur isotope (³²S, ³³S, ³⁴S, ³⁶S) for pyrites in sedimentary rocks from the Meishan section in South China. The Meishan section arguably provides the most detailed records of the Latest Permian biotic crisis. Fossil records suggest that the onset of biodiversity loss began during deposition of Bed 22 with an extinction rate of <33%, and continued until the end-Permian extinction event which is preserved in Beds 25-26. The end-Permian extinction preserved by Beds 25-26 is estimated to have marked a loss of 94% of marine species within a short geological time.

We observe a unique sulfur isotope signal (-d34S-D33S) that suggests episodes when porewater sulfate was converted nearly quantitatively to sulfide. This may have resulted from limitation of sulfate supply by a near shutdown of bioturbation during shoaling of anoxic water. The episodic nature of this record (Beds 22-24) leading up to the Permian-Triassic boundary suggests a prolonged deterioration of oceanic environments during the Late Permian mass extinction.