TERRESTRIAL MERCURY CONCENTRATION RECORDS ACROSS THE CRETACEOUS-PALEOGENE INTERVAL IN NORTH AMERICA

The trigger of the end-Cretaceous mass extinction (ECME) at the Cretaceous/Paleogene (K/Pg) boundary is heavily debated. The leading hypotheses support either an extraterrestrial impact event, the eruption of the Deccan Traps, or some combination of both as the ultimate cause of environmental destabilization across the ECME. Although geochemical, sedimentological, and biostratigraphic data have been used to support a dominant role for each scenario, the ultimate mechanism behind the ECME remains ambiguous. Recently, sedimentary mercury (Hg) concentrations have been used as a proxy to track atmospheric deposition of Hg during the ECME, but natural factors leading to enhanced Hg accumulation, especially in marine environments, paired with the fragmentary sedimentary archive, have made these records difficult to interpret. The North American paleosol record during this interval of Earth’s history is exceptional, and we take this unique opportunity to track atmospheric Hg deposition with unprecedented resolution.

To test these aforementioned hypotheses, 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. Since the putative drivers of the ECME may deliver large quantities of Hg to Earth’s surface, the morphology of the Hg concentration records from these sites will yield important information regarding the respective sources of Hg, thus enabling us to evaluate whether Hg accumulation was controlled by an impact, enhanced volcanic activity, or a combination of both, and subsequent biogeochemical feedbacks associated with each. For example, abrupt and transient sedimentary Hg anomalies at the K/Pg boundary will support the impact scenario, whereas broader sedimentary Hg enrichments in the Upper Cretaceous and early Paleogene sediments will support a volcanic role if they occur contemporaneously with the main eruptive phases of the Deccan Traps. These records will also give insight into the fidelity of paleosols as archives of atmospheric Hg deposition.