Tescheniceras gen. nov. (Ammonoidea) and the definition of the Valanginian/Hauterivian boundary in Butkov Quarry (Central Western Carpathians, Slovakia)

Abstract

Jurassic and Lower Cretaceous successions of the Manin Unit of the Central Western Carpathians are exposed in Butkov Quarry in the Middle Vah Region, Slovakia. A significant part of the macrofauna belonging to neocomitid ammonites, formerly classified under the genus Teschenites Thieuloy, 1971, occurs in deposits spanning the Valanginian/Hauterivian boundary. The original definition of Teschenites was accompanied by uncertainties in the taxonomic and stratigraphic position of its original type species, i.e., Hoplites neocomiensiformis Uhlig, 1902. The present contribution focuses on and provides a possible taxonomic solution by establishing the new genus Tescheniceras . In Butkov Quarry, the new genus includes five species. Tescheniceras flucticulum (Thieuloy, 1977), the type species, is the most abundant. Tescheniceras callidiscum (Thieuloy, 1971), the subzonal species for the uppermost Valanginian (Thieuloy 1971b), occurs only sporadically. Because Acanthodiscus radiatus (Bruguiere, 1789), the index species for the basal Hauterivian ( radiatus Zone) in the international ammonite zonation, does not occur in the locality, the basal Hauterivian is indicated by the first appearance of the genus Spitidiscus Kilian, 1910.