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

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.