Biostratigraphy of Guadalupian (Mid­dle Permian) am­mo­noids from the Olinalá For­ma­tion, southern Mex­i­co

Abstract

An am­mo­noid biostratigraphic analysis was conducted for the Permian Olinalá For­ma­tion, Guer­rero state, southern Mex­i­co. Bed-by-bed sampling yielded 113 am­mo­noids belonging to 14 dif­fer­ent taxa. The biostratigraphic analysis allowed us to identify two am­mo­noid Zones: Paraceltites ele­gans and Coahuiloceras sp., and one subzone: Pseudagathiceras spinosum. According to the GSSP-de­fined boundaries, these biostratigraphic zones extend from the Roadian-Wordian to the lower Cap­i­ta­ni­an interval. To support the biostratigraphic analysis, several key taxa were reviewed from a taxonomic per­spective. This taxonomic assessment validated the genus Coahuiloceras. A quantitative analysis based on morphometric ratios of the species of the genera Timorites and Coahuiloceras reveals a clear di­ver­gence between both groups. In addition, the biostratigraphic framework of the Olinalá succession is compared with previously published biostratigraphic data from Sonora, Coahuila and Texas, high­light­ing similarities and differences among these areas. The identified fauna in the Olinalá For­ma­tion is main­ly associated with the Amer­i­can Realm.