Ammonite biostratigraphy of the Sierra del Patrón section (Durango State, Mexico) and its bearing on the lower/upper Aptian boundary of the Central Atlantic Province

The present contribution documents the ammonite record of the La Peña Formation from the la Sierra del Patrón (Durango State, Mexico). Twenty one taxa have been recognized among the 354 specimens collected bed-by-bed. Our biostratigraphic analysis of the ammonite distribution allow us to improve the zonation for the transition of the lower/upper Aptian boundary of northeast Mexico, composed of the upper lower Aptian Dufrenoyia justinae interval Zone (including the Dufrenoyia scotti/Burckhardtites nazasensis concurrent range Subzone at its top) and the lower upper Aptian Caseyella aguilerae interval Zone (including the Gargasiceras? adkinsi total range Subzone at its base). The lower/upper Aptian boundary is herein well characterized by means of endemic or quasi-endemic taxa and a strong ammonite faunal turnover marked by a renewal at the generic and family levels comparable with those of the Mediterranean-Caucasian regions (end of Deshayesitidae balanced by the renewal in the douvilleiceratid, desmoceratid and acanthohoplitid stocks). The proposed zonation of the Sierra del Patrón section is an important step forward in the development of the Aptian zonation for the Central Atlantic Province and its correlation with the Standard Mediterranean ammonite zonation.