Contributions in the Callovian biostratigraphy of the Cachíos Formation in its type Section, Yura, Arequipa (16 ° S)

Abstract

This study presents a taxonomic analysis and a proposal for biostratigraphic organization based on ammonites that were collected at the top of the Cachíos Formation (Yura Group), precisely in the unit stratotype of the Yura Group, in the Province of Arequipa, southern Peru (16° S). These horizons are included in successions of black shales with notorious non-sedimentary deformations (i.e. faults, slumps and olistolites), which are commonly found interspersed with quartz sandstones and gravelstones, which are also usually sedimentary lenses. The paleontological horizons reported in this study are relevant in Callovian biostratigraphy of southern Peru because they consist of rich levels of ammonoids attributed to the genera Reineckeia sp., Cadoceras sp. and Macrocephalites sp. Due to the fact that these specimens appear in more than one stratigraphic level, it allows us to propose the extension of the biostratigraphic zone of Reineckeia sp. due to the significant occurrence of this species marking the age of Callovian, as well as to affirm that the sedimentary contribution in this locality has been very fast and can be linked to very active tectonic processes related to shallow environments.