HIGH-RESOLUTION SEDIMENTARY [HG] RECORDS ACROSS THE PETM FROM A TERRESTRIAL LATITUDINAL TRANSECT IN NORTH AMERICA

The Paleocene-Eocene Thermal Maximum (PETM) occurred ~56 Ma and is associated with global warming due to elevated carbon emissions and is demarcated by a negative carbon isotope excursion (N-CIE). It is considered by many researchers to be the best analog to modern climate change. Several hypotheses have been put forth to explain the N-CIE that defines the PETM interval, including destabilization of marine methane clathrate, enhanced volcanism, a bolide impact, and/or global-scale conflagration (e.g., biomass burning). A new approach to determining the possible cause(s) of the PETM is the use of sedimentary mercury (Hg) concentrations. Each of these aforementioned processes has the potential to perturb both the local and global cycling of mercury but resolving the temporal controls on local Hg dynamics may rule out some of them.Here, we assess the temporal evolution of Hg chemostratigraphic trends from a latitudinal transect from terrestrial sites in North America. These new data represent the first high-resolution study of terrestrial Hg cycling during the PETM.

We will present new sedimentary [Hg] data from the Bighorn, Hanna, and Piceance Creek basins. In the north-central Wyoming Bighorn Basin, the PETM is recorded in vertically stacked mudstone paleosols of the Willwood Formation. Rapid deposition in this fluvial setting provides an expanded stratigraphic record of changing Hg concentrations, much of which may have been deposited directly from the atmosphere. In the south-central Wyoming Hanna Basin, the PETM is recorded in poorly-drained floodplain deposits and associated fluvial sandbodies. In Colorado, the PETM occurs at the transition between the mudrock-dominated Atwell Gulch member and sandstone-dominated Molina member of the Wasatch Formation. Here, overbank strata vary from poorly drained to well-drained paleosol endmembers, with the major difference between PETM and non-PETM strata being the preponderance of crevasse splay deposits within the PETM overbank. We hypothesize that PETM sedimentary [Hg] fluctuations were controlled by variations in the regional hydrological cycle rather than volcanogenic outgassing of mercury. These new data will help to determine what controlled the Hg cycle across the PETM in terrestrial environments and may help to constrain the ultimate driver of the PETM.