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

Abstract

A revision of ammonoids of the genus Yakutosirenites (Sirenitidae) from the Carnian deposits of Northeast Asia have been carried out. Based on the study of the morphogenesis of the most important structures of the shell, a division of the genus Yakutosirenites into two subgenus is proposed: 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 the biostratigraphic subdivision and correlation of the Lower/Upper Carnian boundary interval is substantiated. The boreal-thethyan correlation of the Yakutosirenites pentastichus zone have been refined. For the first time, taking into account the data of the revision of the genus Yakutosirenites, the upper part of the pentastichus Zone is compared only to the Arctosirenites canadensis Beds of the Arctic Canada and to the lower Subzone of the Tropites welleri Zone of British Columbia, wich are an equivalent to the lower part of the Tropites subbullatus Zone of the Alpine standard.