CHRONOSTRATIGRAPHY OF EARLY PALEOGENE TERRESTRIAL SEDIMENTARY SECTION IN THE TERRY BADLANDS, EASTERN MONTANA

The Cretaceous-Paleogene (KPg) mass extinction is one of the five major Phanerozoic mass extinction events and it offers a unique opportunity to study the mechanisms of global ecosystem collapse and subsequent recovery. Despite numerous studies on the extinction event and the immediate aftermath, relatively few studies have focused on ecosystem recovery on a several million-year timescale after the extinction event, particularly in terrestrial environments, which may respond differently to environmental changes than marine ecosystems. To do this, a thorough long-term record of terrestrial biotic and climatic changes throughout the post-KPg recovery is needed.

This study aims to improve our knowledge of post-KPg recovery in terrestrial environments. In particular, we seek to elucidate the rate and duration of the recovery of mammalian fauna and the relationship between the recovery timeline and potential drivers such as climate change. To do this, we are developing a high-precision chronostratigraphic framework for post-KPg terrestrial sections in the Terry Badlands, eastern Montana. These sections include early Paleogene fluvial and parafluvial sediments from the upper part of the Tullock through the Tongue River members of the Fort Union Formation, extending the stratigraphic record from the well-documented KPg boundary in the Hell Creek area to ~2 Myr post-recovery.

Our approach constrains the ages and durations of magnetic chrons C29n-C25n using high-precision ⁴⁰Ar/³⁹Ar geochronology and magnetostratigraphy. Paleontological and paleoclimate data will be incorporated to establish a comprehensive chronostratigraphic framework for terrestrial post-KPg ecosystem recovery. Our high-precision framework will enable the correlation of our local sections to other early Paleogene sites globally. Here we present our chronostratigraphic framework for the Terry Badlands section of eastern central Montana.