Lower Valanginian ammonite biostratigraphy of the Cañón de la Vaca section, Taraises Formation, Coahuila state, northern Mexico

Abstract

The present work carries out a biostratigraphic analysis of the Valanginian ammonite record from the Cañón de la Vaca section in the Sierra de Parras, Coahuila, Mexico. The collection of ammonites exhibits an abundance of specimens, representing a biodiverse range of taxa, and numerous occurrences throughout the biostratigraphic section. This record in the Taraises Formation allowed a solid identification and diagnosis of the ‘Thurmanniceras’ pertransiens, Neocomites neocomiensiformis and Karakaschiceras inostranzewi zones, along with the Neocomites premolicus, Neocomites neocomiensiformis, Busnardoites campylotoxus, Karakaschiceras inostranzewi and Neocomites platycostatus subzones. These biostratigraphic units corresponds to the lower Valanginian of the Standard Mediterranean Ammonite Zonation. Among the collected ammonites, numerous specimens of significant biostratigraphic importance remain scarcely known or lack a proper taxonomic identification. This situation has been already observed in other sections, such as Peña del Águila, Zacatecas, Mexico, and in the Betic Cordillera, southeast Spain. Fortunately, these unknown taxa can be compared with other sections in Mexico and with lower Valanginian ammonites from Spain, facilitating a more comprehensive biostratigraphic analysis. The present biostratigraphic analysis is expected to contribute to an increased understanding of lower Valanginian strata, thereby enabling future taxonomic and biostratigraphic research on the lower Valanginian in Mexico and globally.