Upper Aptian ammonite biostratigraphy of the Agua Salada and Mural formations, Sonora State, northwest Mexico

Abstract In this work we study the ammonoid biostratigraphy of five stratigraphic sections of the upper Aptian in the Lampazos area, and one in the Tuape area, based on 147 specimens systematically collected bed by bed. Most of the fauna is endemic to the Central Atlantic province. A new genus and species was erected: Sonoraceras tepachensis gen. nov. sp. nov. Taxonomic and systematic analyses were carried out in order to frame this new taxon. Another taxonomic contribution presented in this work is the comparison between the endemic genus Kazanskyella and its European counterpart, the genus Parahoplites. These taxonomic contributions were complemented with fourteen 3-D models of some key specimens. We also propose a local zonation for the upper Aptian, which consists of two ammonite interval zones, Kazanskyella minima and Immunitoceras immunitum, and one horizon Sonoraceras tepachensis. Since the ammonite biostratigraphy for the upper Aptian is poorly elaborated in the Central Atlantic, this newly proposed zonation constitutes a step forward in the development of a standard Central Atlantic province ammonite zonation and its correlation to the standard Mediterranean zonal scheme.