SULFUR ISOTOPE ANOMALIES ACROSS PERMO-TRIASSIC BOUNDARY SECTIONS IN TURKEY

The biotic recovery from the end-Permian mass extinction was unique among mass extinction recoveries in that it was delayed for 4-8 million years (for comparison, the K-T rebound took less than 1 m.y. for most taxa). The causes of the mass extinction are still debated. Hypothesized extinction mechanisms can be grouped into ‘geologically instantaneous’ events and ‘long-lived’ events. Instantaneous extinction mechanisms in general do not account for the unusually long duration of the extinction aftermath.

A growing body of geochemical evidence would suggest that the extinction and the delayed recovery were linked by anomalous ocean/atmospheric chemistry (although it is possible that the causes of the mass extinction and the delayed recovery may be decoupled). Recent sulfur isotopic analyses of carbonate associated sulfate (CAS) across a Permo-Triassic boundary section in Italy show a positive isotopic excursion interpreted to have resulted from prolonged oceanic anoxia (Newton et al., 2004). Our high resolution CAS analysis of Permo-Triassic boundary sections in Turkey provides greater detail than previously available. In Turkey, as in Italy, Upper Permian strata exhibit extreme sulfur isotopic fluctuations over a short stratigraphic interval. Heavy sulfur isotopic values are found at the boundary and continue to rise through a series of nearly periodic 5 per mil fluctuations into the Lower Triassic. Model results indicate that the rapid fluctuations are consistent with a decreased oceanic sulfate reservoir.

Previously reported CAS and gypsum sulfur isotopic analyses from the western United States and elsewhere (e.g., Holser et al., 1986; Marenco et al., 2003) suggest that anomalous oceanic conditions were still present at the end of the Early Triassic (Spathian). Although the precise nature of oceanic sulfur dynamics through the entire Early Triassic is not yet understood, an ongoing CAS chemostratigraphic investigation in the western United States will better constrain the nature of this important geochemical system. The CAS data reported here supports a long-lived extinction mechanism the nature of which is yet to be resolved.