ASSESSING TERRESTRIAL PALEOENVIRONMENTAL CHANGE ACROSS THE CRETACEOUS-PALEOGENE BOUNDARY IN EASTERN MONTANA THROUGH LIPID BIOMARKERS

The terrestrial paleoclimate record preceding and following the Cretaceous-Paleogene (KPG) mass extinction is underdeveloped in comparison to marine sections, despite the existence of high-resolution chronostratigraphies existing at many key terrestrial fossil localities. This discrepancy is due to the paucity of available terrestrial paleoclimate proxies that hampers the development of such records on land. Lipid biomarkers in the form of plant leaf-wax n-alkanes and bacterial membrane lipids (brGDGTs) present a unique opportunity to refine our understanding of the climate dynamics underway on land across the KPG mass extinction and into the subsequent recovery interval in the early Paleocene. The Hell Creek region of eastern Montana has the most well-developed chronostratigraphy of any terrestrial Late Cretaceous through Paleocene locality paired with perhaps the most well-documented vertebrate fossil record spanning this interval. Organic rich facies, such as lignites and carbonaceous shales, are abundant throughout the stratigraphy in the Hell Creek region and are amenable to developing a time calibrated lipid biomarker record as many of these lignite beds have intercalated volcanic ashes dated via ⁴⁰Ar/³⁹Ar on sanidine. Here, we present a preliminary n-alkane stable isotope and brGDGT-estimated paleotemperature dataset collected from lignite beds spanning the latest Cretaceous into the early Paleocene. Data spanning the same stratigraphic interval corresponding to the earliest Paleocene from two adjacent sections replicate the same fluctuations in n-alkane δ¹³C and δ²H as well as variation in brGDGT-inferred paleotemperature over this interval. These results to support variation in the regional climate over this interval but additional data under development will further elucidate these apparent fluctuations.