COMPARATIVE ANALYSIS OF SEDIMENTARY MERCURY GEOCHEMICAL RECORDS ACROSS THE CRETACEOUS-PALEOGENE BOUNDARY FROM THE NORTH AMERICAN INTERIOR

The North American Interior contains a spectacular paleosol record of terrestrial environments across the Late Cretaceous to early Paleogene, including the Cretaceous-Paleogene (K/Pg) boundary. From New Mexico to North Dakota, these basins have been paramount to our understanding environmental and biological change associated with the end-Cretaceous mass extinction (ECME). High pedogenesis rates have allowed for environmental reconstructions at centennial timescales or finer, resulting in chemostratigraphic records that can resolve some of the nuances and details regarding environmental change surrounding the K/Pg at a scale that marine records cannot resolve. Sedimentary mercury (Hg) geochemical records from these basins have the potential to track the eruptive phases of the Deccan Traps as well as the environmental effects associated with the bolide impact, both of which are considered responsible for the ECME.

We generated sedimentary Hg concentration data from a latitudinal transect of U-Pb and biostratigraphically constrained terrestrial paleosols from the North American interior that span the Upper Cretaceous to lower Paleogene. There are significant variations in the Hg chemostratigraphic morphologies between sites with clear indications that some of the Hg enrichments are directly associated with the bolide at the K/Pg. Our comparative datasets also suggest a strong control on Hg accumulation and preservation in North American Interior paleosols based on the local depositional environment, with some locations exhibiting trends that are likely related post-depositional alteration of primary geochemical signatures. We also find significant differences in Hg geochemical reconstructions from low-energy environments compared to high-energy environments as revealed by sedimentological structures. These records show that many different basins should be studied to reveal any systematic trend in atmospheric Hg deposition in paleosols before ascribing any interpretations to larger-scale geologic phenomena.