Paleoenvironmental interpretation using fossil record: San Juan Raya Formation, Zapotitlán basin, Puebla, Mexico

Abstract

The San Juan Raya Formation is world-wide recognized because of the high diversity and abundance of fossils. In this study nine biofacies, three ichnofacies and ten lithofacies were recognized and interpreted on the basis of the influence of several environmental factors such as water depth change, sedimentation rate, water salinity and substrate consistency. Among these factors, salinity variations were apparently crucial for developing and replacement of the different biofacies. Most of biofacies and ichnofacies inhabited in subtidal, shoreface and inner shelf zones. The aim of this investigation is to provide a comprehensive reconstruction of the different faunal benthonic assemblages and paleoenvironments in a sector of the San Juan Raya Formation during Early Cretaceous time. The results indicate that the paleoenvironmental model for the study area corresponds to a shallow marine, open-coast, storm-dominated clastic system, characterized by several variations in subenvironments, from foreshore to offshore. Along a measured composite column of about 765.5 m in length, nine cycles of transgression-regression were identified, with the shallowest stage at the 200 and 500 m levels and the deepest conditions at 300, 400 and 765.5 m in the column.