BARREMIAN AMMONITE BIOSTRATIGRAPHY FROM THE SAN LUCAS FORMATION IN THE HUETAMO REGION, MICHOACÁN, MEXICO

An analysis of the stratigraphic distribution of ammonite fauna collected from sections of the San Lucas Formation, in the Huetamo area (southwest Mexico) has enabled the establishment of a detailed succession of assemblages for the Barremian.The analysis of the stratigraphic distribution of ammonites species, has permitted recognize the transition between the lower Barremian identifying the Psilotissotia colombiana, and Pulchellia galeata Interval Zones and in the lowest part of the upper Barremian Toxancyloceras vandenheckii and Heinzia (Gerhardtia) veleziensis Interval Zones. Each zone is characterized by a set of diagnostic ammonites, which allows an accurate identification of zones. Some Mediterranean standard zones have been identified as the Nicklesia pulchella and Toxancyloceras vandenheckii Interval Zones, it indicates a Tethysian affinities of the Mexican ammonite association.