Systematics and biostratigraphy of ammonites across the Sinemurian/Pliensbachian boundary in the Ukrainian Carpathians (Pieniny Klippen Belt)

As the Sinemurian/Pliensbachian boundary (SPB) in GSSP is defined on the basis of the appearance of endemic ammonite species in the Cleveland Basin, documenting this transition in other regions and correlating the SPB at global scale is difficult. Ammonites described in our study occur in the Upper Sinemurian- Lower Pliensbachian deposits (Perechyn Formation) in the Priborzhavske section (Ukraine, Pieniny Klippen Belt, Eastern Carpathians) that was located on the transition between the NW European and Austroalpine domains in the western Tethys. They are preserved in a relatively continuous succession formed by marl- limestone alternation, shifting from well- bedded, spotted, shell - poor mudstones and wackestones (Raricostatum Zone) to wackestones and floatstones with common siliceous sponges (Jamesoni Zone). The boundary deposits are rich in well- preserved macrofossils (ammonites, belemnites, brachiopods, bivalves), microfossils (foraminifers, ostracods, calcareous nannoplankton) and ichnofossils. Ammonites belong to families Phylloceratidae (four species), Juraphyllitidae (2), Lytoceratidae (2), Schlotheimiidae (1), Oxynoticeratidae (3), Echioceratidae (3), Epideroceratidae (11), Eoderoceratidae (8), Coeloceratidae (1), Polymorphitidae (1), Liparoceratidae (3) and Eoderoceratoidea Incertae Sedis (2). The superfamily Eoderoceratoidea is diverse, it contains 26 species, among them seven new species and one new genus, including: Epideroceras inflatum nov. sp., E. kruglovi nov. sp., E. sykorai nov. sp., E. kalinichenkoi nov. sp., E. pliensbachien sis nov. sp., Bakonyceras transcarpathiensis nov. sp., and Transcarpathiceras ukrainiensis nov. gen. and nov. sp. New high- resolution biostratigraphic data show that the ammonite genus Villania appears for the first time in beds above the last appearance of the species Epideroceras gr. lorioli. The first appearance of this genus can accurately define the onset of Pliensbachian in the Euroboreal Domain. This locality, situated on the SE margin of the European shelf during the Early Jurassic, thus represents a useful auxiliary section for the SPB definition.