Detailed biostratigraphy of the Middle Callovian – lowest Oxfordian in the Mikhaylov reference section (Ryazan region, European part of Russia) by ammonites

Study of the sections near the Mikhaylov (Ryazan region) has made it possible to improve the infrazonal subdivision of the Middle Callovian – Lower Oxfordian of the European Russia by ammonites. The Athleta Zone is the most complete in the studied sections. A sequence of kosmoceratid biohorizons (phaeinum, proniae, rowlstonense and kuklikum) is established here, as well as infrazonal units based on a phylogenetic sequence of species of the genus Funiferites. A study of the paleobiodiversity and frequency of occurrence of ammonites at different intervals of the section showed that the ammonite assemblages of the Athleta Zone are Sub-Boreal or Sub-Tethyan, while in the Lamberti Zone they are Boreal, and in the Lower Oxfordian they are Arctic. It is also shown that the change in ammonite composition in the sections coincides with the cycles of transgressions and regressions of Boreal basins. New species and subspecies of the ammonites Funiferites allae compressum, Cadoceras (Eichwaldiceras) intermedium, Brightia (B.) lominadzei, B. (B.) progzhellensis, B. (B.) eccentrtica, B. (Glyptia) canaliculata stankevitchae, Zieteniceras rarecostatum are described.