The ammonite fauna of the La Manga Formation (Late Callovian-Early Oxfordian) of Vega de la Veranada, Neuquen Basin, Argentina

摘要

A well exposed section of the La Manga Formation in the locality Vega de la Veranada (north of the Neuquen Province, Argentina), sampled bed-by-bed, has provided a diverse ammonite fauna. This fauna indicates an age range comprising the Lamberti to Cordatum zones, older than concluded in previous studies by different authors. There have been identified 20 species belonging to 14 genera (Hecticoceras, Choffatia, Collotia, Rehmannia, Araucanites, Euaspidoceras, "Perisphinctes", Vinalesphinctes, Peltoceratoides, Neoprionoceras, Lissoceratoides, Veranadaites n. gen., Subvinalesphinctes, and Cubasphinctes). It is introduced Veranadaites n. gen. (Type species: Veranadaites palmicostatus n. gen. et n. sp.) for small Early Oxfordian sphaeroceratids closely related to the Late Callovian-Early Oxfordian Araucanites. Choffatia schilleri n. sp. (Upper Callovian), as part of the guide assemblage, is taken as the index of the schilleri Horizon (new). Peltoceratoides pressulus LEANZA (Lower Oxfordian), as part of the guide assemblage, is taken as the index species of the pressulus Horizon (new). A chronostratigraphic zonation for the Callovian-Oxfordian interval in the Andean Neuquen and Tarapaca basins is proposed based on the two existing quasi-independent scales. After revision of the age of the guide ammonites, the Primus, Dimorphosus, and Eugenii zones are inserted between the Patagoniensis and Pressulus zones. The Pressulus Zone is standardized by designation of the pressulus Horizon as its base.