Ammonoids of the Genus Yakutosirenites from the Carnian Stage of Northeast Asia

详细

Ammonoids of the genus Yakutosirenites (Sirenitidae) from the Carnian deposits of Northeast Asia have been revised. On the basis of the study of morphogenesis of the most important shell structures, the genus Yakutosirenites is subdivided into two subgenera: Yakutosirenites with the type species Sirenites pentastichus Vozin, 1964 and Vozinites with the type species Sirenites armiger Vozin, 1965. A description of the genus and its subgenera and species is given. The significance of the species of these subgenera for biostratigraphic subdivision and correlation of the lower/upper Carnian boundary interval is substantiated. The Boreal–Tethyan correlation of the Yakutosirenites pentastichus Zone has been clarified. For the first time, taking into account the Yakutosirenites revision data, the upper part of this zone is compared only to the Arctosirenites canadensis beds of Arctic Canada and to the lower subzone of the Tropites welleri Zone of British Columbia, which are equivalent to the lower part of the Tropites subbullatus Zone of the Alpine standard.