The first finding of Skeletognathus norrisi in association with higher plant spores and brachiopods in the Givetian-Frasnian boundary deposits drilled by borehole No. 8 Tsarichanskaya (East Orenburg uplift, Russian Platform)

   Research subject. Late Givetian-Early Frasnian brachiopods, conodonts and spores of higher plants from the Timan Horizon of borehole No. 8 Tsarichankaya.

   Material and methods. The biostratigraphical me thod was used to isolate fossils and to determine the taxonomic compositions of brachiopods, conodonts and higher plant spores from deposits drilled by borehole No. 8 Tsarichanskaya (interval 3637.00–3647.00 m), to substantiate their age and carry out a correlation. An improved technique of I. Kh. Shumilov and O. P. Telʼnova was used when proces sing spore samples.

   Results. The uppermost Givetian zonal species Skeletognathus norrisi (Uyeno) was identified. Brachiopods and higher plant spores in association with conodonts are typical for the Upper Timan Subhorizon. The results obtained clarify the paleontological characteristics of the Givetian–Frasnian boundary interval on the Russian platform. The findings indicate a wider range of the Skeletognathus norrisi stratigraphical distribution (the latest Givetian–Early Frasnian), including the Upper Timan Subhorizon.

   Conclusions. The marine and terrestrial fossils isolated from the same rock samples allowed the authors to provide a complex paleontological characteristic of the Upper Тiman Subhorizon, which is considered as being a variant of the D2-D3 boundary. It is significant for interregional correlations of different facies deposits.

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