SPATIAL VARIABILITY IN PALEOSOL-BASED PALEOCLIMATE PROXIES AND EOCENE PALEOCLIMATE IN WYOMING

Constraining changes in continental interior climates is critical for connecting paleoclimate, tectonics, and landscape evolution. Paleosols (fossil soils) are a key record of these settings because they form at Earth’s surface in the “critical zone” of interaction between the biosphere, geosphere, and atmosphere. Proxies based on paleosol chemistry can be used to reconstruct paleoclimate (e.g., precipitation, temperature), atmospheric composition, and (more tenuously) altitude. However, statistical uncertainty associated with such proxies is typically limited to calibration and dataset variability. Many paleosol studies rely on one or a handful of paleosol profiles, but extrapolate interpretations to landscape and basin scales without considering the uncertainty associated with spatial geochemical variability. To constrain statistical error associated with using single vs. multiple paleosol profiles for paleoclimate reconstructions, we sampled a 3-km transect of a laterally-continuous paleosol in the Eocene Wasatch Fm. of the Green River Basin (GRB), at the Oregon Buttes locality. Despite apparent redox variability (i.e., both oxidizing and reducing conditions), paleosol geochemistry was largely homogenous across the transect, supporting previous findings (Hyland et al., 2016). We resampled a subset (n=1 thru 10) of the profiles and used those subset geochemical data to recalculate paleoclimate proxy values, then compared that to the value determined by the full transect. Based on these results, we can adjust proxy error to include uncertainty from only using a single or a limited number of profiles. Additionally, we compared paleoclimate results to those from a penecontemporaneous paleosol in the Wind River Basin (WRB; Hyland et al., 2013), northeast of the GRB, and found that GRB had higher precipitation and temperature than WRB. Together, these results point to the importance of using multiple paleosol profiles when possible, incorporating “representativeness” uncertainty, and limiting interpretations to a landscape/basin as opposed to a broader region.