Oosterella (Ammonoidea) from the Taraises Formation (upper Valanginian), Durango, northeast Mexico

Abstract

This paper contributes to the knowledge of the upper Valanginian ammonite faunas of the Taraises Formation in northeast Mexico. The fossils were collected on a bed-by-bed basis from a predominately marly section in the state of Durango. The stratigraphic interval studied contains distinctive horizons defined by rich ammonite assemblages that include species of the family Oosterellidae. Index species such as Oosterella begastrensis, O. gaudryi, O. cultrata, and O. cultrataeformis have not been recorded from Mexico hitherto. Unlike other areas with Tethyan affinity such as Spain, France and Hungary, in Mexico these species co-occur in the same stratigraphic levels. The presence of the species of Oosterella, along with associated faunal elements such as Ceratotuberculus linguituberculatus, Rodighieroites belimelensis, Olcostephanus ( Olcostephanus) balestrai, O. ( Jeannoticeras) colorinensis, Karakaschiceras sp. and Bochianites spp., enable the assignment of the Mexican sediments to the upper Valanginian Peregrinus Zone of the standard biozonal scheme for the Mediterranean Faunal Province.