Lower Cretaceous ammonoids from the Neuquén Basin, Argentina: The late Hauterivian Paraspiticeras and associated faunas

Abstract

The Paraspiticeras groeberi Zone (upper Hauterivian) is one of the five ammonoid biozones previously recognized in the Agua de la Mula Member of the Agrio Formation in the Neuquén Basin of west-central Argentina. However, the ammonoid faunas of this zone and the beds immediately below, corresponding to the upper levels of the current Crioceratites diamantensis Zone, remain poorly known. Extensive collections now allow us to recognize a diverse endemic ammonoid fauna. After an exhaustive taxonomic and stratigraphic review, the Paraemericiceras argentinense and Paraspiticeras bituberculatum Zones are proposed to replace the P. groeberi Zone and the original index species is now placed in Vutacuracrioceras gen. nov. Vutacuracrioceras groeberi first appears with the earliest Paraemericiceras argentinense gen. et sp. nov. and extends through both zones. It is joined in the Paraspiticeras bituberculatum Zone by the index species and Paraspiticeras sp. aff. P. precrassispinum, Australopseudothurmannia flexuosa gen. et sp. nov. and Hamulinites sp. Based on this new biostratigraphic scheme, the upper Hauterivian in the Neuquén Basin is represented now by six ammonoids zones that can be correlated provisionally with the European standard of the West Mediterranean Province of the Tethyan Realm.