C isotopic variations in the lower-middle Frasnian (lower Upper Devonian) of the Rudny Altai

We conducted isotope–geochemical studies of the Upper Devonian of the Rudny Altai. Whole-rock carbon isotope analyses of the studied section represented by carbonate fore-reef facies reveal a negative excursion at the base of punctata Zone. When compared to conodont biofacies turnovers and the Upper Devonian events chart, the new data have demonstrated a synchronism between the negative excursion and the coeval decline in conodont biodiversity corresponding to the Middlesex anoxic event of the Frasnian Stage of the Upper Devonian.