Planktic Foraminifera and Calcareous Nannoplankton Biostratigraphy of the Neogene of Mexico Part I- Middle Pliocene

Abstract

Calcareous nannofossils and planktic foraminifera that are diagnostic for precise geologic ages have been identified in some marine Tertiary formations in Mexico. The original age assignments of these formations have persisted in the literature and some revisions are necessary for the Mexican sections to conform with the chronostratigraphy that has been developed for the rest of the world. New planktic evidence now affords assignment of the Mexican beds to precise trans-oceanic Neogene zones. Part I of this report is concerned with the middle Pliocene (Zone N.20) to which the following formations at designated localities are referred: Agueguexquite, Filisola, Concepcion Inferior, Concepcion Superior, and several unnamed formations. Subsequent studies will deal with the successively older formations, including the Encanto, Deposito, La Laja, Tuxpan, Guajalote, Escolin, Anahuac, Coatzintla, Meson, Alazan, and Palma Real formations.