Bivalves from the Delendzhian–Dulgalakhian Boundary Beds of the Middle Permian of the Lower Reaches of the Lena River (Northern Verkhoyansk Region, Northern Siberia)

Abstract

Based on new extensive collections and revision of the previously known bivalve Inoceramus-like mollusks, the faunal characteristics of the Delendzhian–Dulgalakhian (Wordian–Capitanian) boundary beds of the Middle Permian of lower reaches of the Lena River (northern Verkhoyansk Region, northern Siberia) are amended. The upper part of the Delendzhian beds is characterized by abundant and diverse representatives of Inoceramus-like bivalves of the genera Kolymia, Evenia, and Okhotodesma. All of them became extinct at the Delendzhian–Dulgalakhian boundary. In the lower part of the Dulgalakhian Horizon, individual Maitaia bella Biakov occur; somewhat upward in the section, there is Atomodesma sp. From the upper part of the Delendzhian Horizon, a new species, Kolymia peregoedovi sp. nov., is described. Permian kolymiids are figured.