First report of Oxfordian planktic foraminifera and ammonites from the Cerro Pelon ´ area, Veracruz State, Mexico. Microfacies, paleoenvironmental interpretation and biostratigraphy

Abstract

A bed-by-bed sampling of Oxfordian macro- and microfossil assemblages was conducted in the Ignacio López Rayón area (the ILR section), Veracruz, Mexico for the first time, and the information obtained was interpreted considering earlier interpretations of data from studies of land outcrops in nearby areas and offshore in southeastern Mexico. Lithology, sedimentary structures, and the analysis of the fossil record obtained allow to interpret eco-sedimentary conditions compatible with restricted middle to outer inner-shelf environments showing occasional connections to open-sea waters. Dysoxic, organic-rich sea bottoms were subjected to deposition of fine calcisiltites with a variable content in carbonates and bioclasts, and interbedded with shaly-silty horizons, while subtle currents resulted in common lamination. In such a context, the discontinuous co-occurrence of planktic forams and the persistent record of the ammonite genus Gregoryceras is reported and illustrated for the first time from southeastern Mexico.