Permian Bivalves of the Pronchishchev Ridge (North Siberia): New Data on Taxonomic Composition, Biostratigraphy, and Biogeographic Relationships

Abstract

Abstract—: Permian marine bivalves of the Pronchishchev Ridge (North Siberia) were systematically studied for the first time. The presence of the Middle and Upper Permian with five biostratigraphic levels was established based on fossil findings. In the Middle Permian, these are the bivalve Kolymia inoceramiformis–K. plicata (undivided) and Kolymia multiformis zones, and in the Upper Permian—the Maitaia bella Zone (Beds with Phestia ex gr. ovata), Maitaia belliformis Zone, and Intomodesma costatum Zone. The bivalve assemblages from the Middle and the lower Upper Permian (up to the Intomodesma costatum Zone) are similar in their taxonomic composition to those from the Western and Northern Verkhoyansk regions. The uppermost Permian fossil assemblages (Intomodesma costatum Zone) are different. They are represented almost exclusively by monotaxonic aggregations of the large pectinoid Streblopteria rotunda (Lutkevich et Lobanova) and rather rare representatives of the genus Intomodesma. The marine basin of the present-day Pronchishchev Ridge had stable links with the Verkhoyansk basin throughout almost the entire Permian. This basin was very shallow and may have experienced episodes of desalination. In the end of the Permian, the paleogeographic situation changed, and the connection between the Pronchishchev Ridge and the East Taimyr basins became more pronounced. Most characteristic bivalve species are illustrated, and a new species Kolymia rutskovi Biakov, sp. nov. is described.