부산대학교 도서관

This article presents data on lithology, biostratigraphy, and molluscan paleontological characteristics of the Lower Volgian–Upper Ryazanian interval of the Yanov Stan Formation obtained from the core of the Novoyakimovskaya-1 parametric well. The formation consists of mudstone-siltstone intercalation with rare sandstone beds and numerous levels with carbonate concretions. For the first time, abundant glendonites are reported from the Yanov Stan Formation, including stratigraphic intervals from which they have not been previously known. An almost complete 290-m core of the Yanov Stan Formation with abundant ammonites and bivalves was obtained. This enabled us to develop a detailed biostratigraphic zonation of the section based on ammonites and bivalves. The following succession of ammonite zones, known in Western Siberia and, mainly, in Eastern Siberia (from bottom to top), was established: Paravirgatites lideri, Pavlovia iatriensis, Dorsoplanites ilovaiskii, D. maximus, Epivirgatites variabilis, Praechetates exoticus, Craspedites okensis, Praetollia maynci, Hectoroceras kochi, and Surites subanalogus. The bivalve succession, distinguished based on the members of the genus Buchia, includes the following Buchiazones: Buchia mosquensis, B. unschensis, B. okensis, ?B. jasikovi, and B. volgensis. The molluscan assemblages of the studied core, starting at least from the upper Middle Volgian, are similar to the coeval assemblages from the eastern part of the Yenisei–Khatanga depression and the Laptev Sea coast but differ from those from Western Siberia. This suggests the existence of some environmental factors that prevented the free distribution of mollusks from the western part of the Yenisei–Khatanga depression into the West Siberian basin.