Stratigraphy of the Middle Jurassic Deposits of the Bureya Trough according to New Paleontological Data from the Soloni Section (Russian Far East)

Some taxa of belemnites, bivalves, gastropods, and brachiopods, previously unknown in the Russian Far East (except for Eastern Siberia and Northeast Russia), of both Tethyan and Boreal Arctic origin, have been recorded in the Middle Jurassic of the Soloni River (Bureya River basin). In particular, bivalve assemblages were found to increase in abundance throughout most of the Bajocian section at the Soloni River, similar to what is observed in Siberian sections. However, the first appearance of some species of the genus Grammatodon and trigoniids was recorded in this area much earlier than in Siberia. This, combined with a revision of the taxonomic composition of previously recorded fossils, has made it possible to refine the biostratigraphic subdivisions of not only the studied section, but also the uppermost Lower–Middle Jurassic marine deposits of the Bureya Trough as a whole. The age ranges of the local lithostratigraphic units have been refined to a greater degree. It has been established that the Sinkal’tu Formation corresponds to the Upper Toarcian–lowermost Lower Bajocian, the Epikan Formation to the uppermost Lower Bajocian, the El’ga Formation to the Upper Bajocian, and the Chagany Formation to the Bathonian–Callovian. Data on the palynological assemblages identified in these formations are provided. The recent studies of cephalopods and bivalves from Siberia, the Russian Far East, and southern Alaska have led to the development of a refined interregional correlation scheme for Bajocian deposits in these regions.