Sulfur isotopic evidence for chemocline upward excursions during the end-Permian mass extinction

The latest Permian was a time of major change in ocean chemistry, accompanying the greatest mass extinction of the Phanerozoic. To examine the nature of these changes, samples from two well-studied marine sections that span the Permian-Triassic boundary have been analyzed: the Meishan and Shangsi sections located in Southern China. Isotopic analysis of the carbonate-associated sulfate in these samples provides a detailed record of several isotopic shifts in delta S-34(CAS) approaching and across the PTB, ranging from +30 to -15 parts per thousand (VCDT), with repeated asynchronous fluctuations at the two locations. We interpret the patterns of isotopic shifts, in conjunction with other data, to indicate a shallow unstable chemocline overlying euxinic deep-water which periodically upwelled into the photic zone. These chemocline upward excursion events introduced sulfide to the photic zone stimulating a bloom of phototrophic sulfur oxidizing bacteria. We hypothesize that elemental sulfur globules produced by these organisms and 34 S-depleted pyrite produced in the euxinic water column were deposited in the sediment; later oxidation led to incorporation as CAS. This created the large changes to the delta S-34(CAS) observed in the latest Permian at these locations. (c) 2006 Elsevier Inc. All rights reserved.