New data on ammonites and stratigraphy of the Volgian stage in Spitzbergen

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Abstract
The stratigraphy of the Volgian in Spitzbergen is refined based on the new fossil collections. The lower Volgian is poorly characterized by ammonites being not subdivided into zones, and the only recognized stratigraphic unit within it are the Beds with Paravirgatites sp. in the upper part of the lower Volgian. The Pavlovia rugosa, Dorsoplanites ilovaiskii, Crendonites anguinus, and Praechetaites exoticus zones, the antiquus, erschovae, sachsi, sokolovi, laevigatus, and lambecki faunal horizons, and Beds with Laugeites cf. groenlandicus are recognized for the first time in the middle Volgian of Spitzbergen. Two successive levels are identified in the upper Volgian Craspedites okensis Zone characterized by differing morphotypes of Craspedites okensis. The Craspedites taimyrense Zone is proposed instead of the Craspedites nodiger Zone. No ammonites of the terminal Volgian Chetaites chetae Zone have so far been found in Spitzbergen. New species of Epivirgatites sokolovi sp. nov., E. laevigatus sp. nov., Praechetaites erschovae sp. nov., and P. confusus sp. nov. are described. The diagnosis of the genus Praechetaites is expanded.