GLOBAL CLIMATIC AND ECOLOGICAL CORRELATIONS DURING THE EARLY PERMIAN (CISURALIAN)

The early Permian was a time when cool, glaciated conditions, similar to those of the present-day, shifted to warm, non-glaciated conditions.  As a result, climatological and ecological information about this time period is pertinent in studying the causes and effects of modern global warming.  This study presents new oxygen and carbon stable isotopic data (d¹⁸O and d¹³C, VPDB) from carefully screened, early Permian brachiopod shells from the Ural Mountains.  Using cathodoluminescence (CL) microscopy, 24 specimens were determined to be well-preserved and were used for 95 stable isotopic analyses.  Inter-specimen variability within each time horizon was lower than 0.5‰ and intra-specimen variability was lower than 0.2‰.

The d¹⁸O values of the specimens analyzed average between -2.2‰ and -2.7‰ through the Asselian, Sakmarian, and early Artinskian (297-283 Ma).  Values then rapidly increase by 3‰ in the late Artinskian and early Kungurian (~275 Ma).  The low values before the Kungurian do not suggest glacial conditions and thus disagree with the geological evidence for a glacial maximum during the Asselian.  These data also disagree with the early Permian maximum and subsequent decline in d¹⁸O suggested from brachiopod shell fragments from the Usolka section in the Urals (Korte et al., 2005. Palaeogeog., Palaeoclim., Palaeoecol. 224, 333-351). However, our data are similar to those obtained from North American brachiopods (Grossman et al., 2008. Palaeogeog., Palaeoclim., Palaeoecol. 268, 222-233).  The cause of this discrepancy is unknown, but could be a result of differences in regional oceanographic factors or in source material (i.e. wholly preserved brachiopods versus brachiopod shell fragments).  The Artinskian-Kungurian increase in d¹⁸O from this study is further evidence for the aridification of the epicontinental seas of Laurussia and possibly a return to cooler conditions.

The d¹³C data from the specimens discussed in this study show a gradual decrease of about 1.5‰ from the late Asselian to the Artinskian, followed by a sharp increase of about 1.5‰ in the late Artinskian.  This d¹³C increase  is not seen in previously published data from Russia or North America.  Further work is required before any strong conclusions can be made on global d¹³C variability during the early Permian.