Carbon Isotope Chemostratigraphy and Implications of Palaeoclimatic Changes During the Cisuralian (Early Permian) in the Southern Urals, Russia

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In order to meet the requirements for potential GSSPs in the Cisuralian Series (Early Permian), isotopic chemostratigraphy from the Carboniferous/Permian boundary to middle Artinskian using bulk carbonates was investigated under high-resolution biostratigraphical and new geochronologic constrains from three GSSP candidate sections at Usolka, Kondurovsky and Dal'ny Tulkas in the southern Urals, Russia. A gradually increasing trend in carbonate carbon isotope (δ13C) has been observed in the interval from the base of Asselian to early Sakmarian, which is generally consistent in timing with the increasing development of Glacial III or P1 from the latest Carboniferous to early Sakmarian (Early Permian) which prevailed in southern Gondwana. An excursion with double negative shifts in δ13C value is present around the Asselian/Sakmarian boundary in both the Usolka and Kondurovsky sections, which may have great potential to serve as chemostratigraphical marks for intercontinental correlation. The following highly positive excursion of δ13C in early Sakmarian indicates the maximium expansion of Glacial III or P1. The negative δ13C shift in the middle Sakmarian is possibly related to the quick collapse of Glacial III or P1 on the Gondwanaland. This negative shift is largely correlative with those documented in other areas of Russia, the North American Craton and South China, but further precise biostratigraphical and geochronologic constrains are neccessary to confirm this global signal. The late Sakmarian is characterized by a strong oscillation stage of δ13C, which probably indicates a complex climate transition marked by smaller alternating glacial–interglacial transitions during Glacial P2 superimposed on an overall warming trend. The sharp negative δ13C shift around the Sakmarian/Artinskian boundary at the Dal'ny Tulkus section is difficult to interpret. This is followed by long-term low values (<−10‰) during the most part of Artinskian Stage. We suggest that the deeply depleted δ13C values in the Artinskian at the Dal'ny Tulkas section might result regionally from the enhanced input of organic carbon after the melt-out of ice sheets and the subsequent degradation and isotopic refractionation of the microbial chemosynthetic processes on the buried organic matter.