Ammonite taxonomy and biostratigraphy for the upper Aptian-lower Albian (Lower Cretaceous) of Cerro Chino, Chihuahua State, northeast Mexico

In this paper we study the ammonoid taxonomy and biostratigraphy from the upper Aptian to the lower Albian of the Cerro Chino area, with an emphasis on an accurate taxonomic characterization of the American endemic forms Kazanskyella, Quitmanites, Immunitoceras and Huastecoceras. These genera are important because they are characteristic of the unique ammonite fauna of the Central Atlantic province. In a critical taxonomic study of these endemic forms, we review numerous holotypes and other specimens that are currently housed in several collections in the United States and Mexico. Based on our analysis, we propose a local zonation from the upper Aptian to the lower Albian, with three ammonoid zones (Kazanskyella minima, Hypacanthoplites sp. and Douvilleiceras sp.), based on the Cerro Chino sections. This newly proposed zonation constitutes a step forward in the development of the standard Central Atlantic province ammonoid zonation, particularly because biostratigraphic data for this province during this time span are very scarce. In general, the uppermost Aptian ammonoid record worldwide is scarce and/or condensed, and so the fauna preserved at this location is significant, making the contribution here even more important. In this work, we are not able to pin down the position of the Aptian/Albian boundary based solely on the ammonoids from these sections.