Between 70 and 55 million years ago (latest Cretaceous & Paleocene), the earth had a greenhouse climate and underwent massive changes that included a drop in sea level, massive eruptions of flood basalt (Deccan Traps), the extinction of the dinosaurs (K-T boundary), the Laramide orogeny, the explosive radiation of mammals, and a major episode of rapid global warming known as the Paleocene-Eocene Thermal Maximum (PETM). The paleoclimatic record of this time provides an invaluable context for understanding the mechanisms for establishing, maintaining, and escape from greenhouse climates, the relationships between marine and terrestrial environments, and aspects of current and future climate change. The goal of this research is to develop a high-resolution temporal framework for this critical 15-million-year interval based on a series of terrestrial rock sequences from several basins in the Rocky Mountain Region. Cretaceous and Paleocene rocks of the Rocky Mountain region contain a rich record of climatic fluctuations, the best and most sampled terrestrial biotic record in the world (especially fossil plants and mammals), and extensive exposures suitable for magnetostratigraphy and geochronology. Our approach will integrate biostratigraphy (documenting the stratigraphic succession of fossil organisms), magnetostratigraphy (measuring reversals in the earth's magnetic field), and geochronology (dating interlayered volcanic ash beds using the radioactive decay of uranium to lead in zircon crystals). In several cases, we will directly date the boundaries of magnetic polarity reversals. Together, these techniques will allow us to evaluate whether sedimentary cycles preserved in marine and lacustrine sedimentary rocks are controlled by earth's orbital dynamics and interactions with the other planets in the solar system. Though much discussed, this test has never been performed for rocks of this age. The project will result in very high-resolution enhancement of the geologic time scale that will refine temporal correlation worldwide. For example, recent deep-sea core studies dated by magnetostratigraphy and biostratigraphy have documented high-resolution biotic, ocean temperature and climate records from far-flung ocean basins. By linking these records with high-resolution geochronology of the terrestrial rocks in our study area, we hope to provide a framework for better understanding of greenhouse climate dynamics and related terrestrial events.
