9405684 Ward We propose to investigate the biostratigraphy, magnetostratigraphy, and strontium isotope stratigraphy of the Upper Cretaceous Rosario Formation of southern California and Baja California. It has long been known that macrofossils are extremely abundant from various horizons of the Rosario Formation. Nevertheless, there has been relatively little study to date investigating the biostratigraphy of these sections, especially outcrops exposed in Baja California. We have identified three target sections located in Baja California that hold the promise of greatly increasing our understanding of Upper Cretaceous chronostratigraphy of the Pacific Coast. We have recently discovered that molluscan fossils from these sections are composed of a mixed assemblage of Pacific Coast endemics and Gulf Coast and European species. Of greatest importance are European zonal index ammonites, recognized here for the first time form the Pacific Coast region. Our target sections have already been partially sampled for magnetostratigraphy. By integrating a more complete magnetostratigraphic sampling with a revised biostratigraphy, we will produce, for the first time, a first order correlation between Pacific Coast Upper Cretaceous strata and the stratotype sections in Europe, and with Tethyan sections of the Gulf Coast, Western Interior and Atlantic Coast Plain.
