CARBONATE ASSOCIATED SULFATE, EUXINIA, THE SIBERIAN TRAPS AND THE END PERMIAN MASS EXTINCTION

The End Permian mass extinction is associated with extreme sulfur isotopic fluctuations in carbonate associated sulfate (CAS). The isotopic anomalies have been attributed to bolide impact (Kaiho et al., 2001), overturn of a stratified ocean (Newton et al., 2004; Kaiho et al., 2006), Siberian Trap volcanism (Maruoka et al., 2003), chemocline upward excursions (CUE) during prolonged euxinia (Kump et al., 2005; Riccardi et al., 2006), or a combination of the last two (Marenco et al., in prep.).

A comparison of published CAS results from P-T boundary sections in Italy (Newton et al., 2004), China (Kaiho et al., 2006; Riccardi et al., 2006), Iran (Korte et al., 2004), and Turkey (Marenco et al., in prep.) shows much dissimilarity between localities within the Tethys Ocean. The highest isotopic values are recorded in Turkey, where the majority of samples exhibit values higher than +20 ‰. Italy and Iran exhibit values between +10 and +20 ‰. Sections in China reveal the lowest isotopic values, with a large fraction of samples exhibiting values lower than 0 ‰, and as low as -30 ‰. The wide range of CAS isotopic values might reflect localized variations within the Tethys Ocean. CUE might produce lower isotopic values in zones of upwelling, while isotopic values might decrease with proximity to the Siberian Traps.

Another explanation is that CAS extraction is not as faithful to true seawater sulfate as once thought. It has been shown that pyrite oxidizes during the extraction of CAS, causing an increase in [CAS] and a decrease in sulfur isotopic composition (Marenco et al., in revision). Anaerobic extraction of CAS (e.g., Newton et al., 2004) might not be sufficient to prevent the oxidation of pyrite. The effect of pyrite on CAS analyses is a function of abundance, isotopic composition and grain size. Because pyrite is a common constituent of sedimentary rocks, it is important for CAS researchers to quantify pyrite abundance and isotopic composition in their CAS samples (e.g., Riccardi et al., 2006; Marenco et al., in prep.); with this data, it may be possible to quantify the effect of pyrite oxidation. Before we can begin to understand the effects of CUE and Siberian Trap volcanism on P-T seawater sulfate and the End Permian mass extinction, we need to be assured that our CAS results are indicative of primary seawater sulfate values.