Stable carbon and oxygen isotope shifts in Permian seas of West Spitsbergen-Global change or diagenetic artifact?

Abstract

We performed petrographic, cathodoluminescence, electron-microprobe, and isotopic analyses of brachiopod shells from the Permian Kapp Starostin Formation in West Spitsbergen to reevaluate the >9‰ negative shift in δ13C and δ18O values reported in 1989 by M. Gruszczynski, S. Halas, A. Hoffman, and K. Malkowski. The δ13C and δ18O values within shells typically decrease with increasing luminescence, indicating diagenesis. Nonluminescent (NL) shell δ13C and δ18O values are 4.3‰ and 6.2‰ higher, respectively, than those of associated cements and matrix. For the same stratigraphic interval, δ13C and δ18O values of the NL shells are equal to, or substantially greater than, those reported by Gruszczynski et al. For the interval where those authors saw a 10‰ δ13C shift, our mostly NL Spiriferella polaris shells only yield a 1.5‰ shift. Gruszczynski et al. reported a 9‰ δ18O shift, whereas we observe almost none. Our results strongly suggest that the >9‰ isotopic shifts reported in Gruszczynski et al. are diagenetic artifacts. On the other hand, their Kazanian-Tatarian δ13C maximum of 7.5‰ is substantiated by our data. This Late Permian 13C maximum represents the highest spiriferid brachiopod δ13C values in the Phanerozoic and, within stratigraphic uncertainty, correlates with the whole-rock δ13C maximum in East Greenland and northwestern Europe. The δ13C shift may reflect changes in global storage of organic carbon indicated by coal-volume changes in the Late Permian.