Comparing floral and isotopic paleoelevation estimates: Examples from the western United States

Describing paleoelevations is crucial to understanding tectonic processes and deconvolving the effects of uplift and climate on environmental change in the past. Decades of work has gone into estimating past elevation from various proxy archives, particularly using modern relationships between elevation and temperature, floral assemblage compositions, or oxygen isotope values. While these methods have been used widely and refined through time, they are rarely applied in tandem; here we provide two examples from the western United States using new multiproxy methods: 1) combining clumped isotopes and macrofloral assemblages to estimate paleoelevations along the Colorado Plateau, and 2) combining oxygen isotopes and phytolith methods to estimate paleoelevations within the greater Yellowstone region. Clumped isotope measurements and refined floral coexistence methods from sites on the northern Colorado Plateau like Florissant and Creede (CO) consistently estimate low (< 2km) elevations through the Eocene/Oligocene, suggesting slower uplift and a south-north propagation of the plateau. Oxygen isotope measurements and C4 phytolith estimates from sites surrounding the Yellowstone hotspot consistently estimate moderate uplift (0.2-0.7km) propagating along the hotspot track, suggesting migrating dynamic topography associated with the region. These examples provide support for the emerging practice of using multiproxy methods to estimate paleoelevations for important time periods, and can help integrate environmental and tectonic records of the past.