Resolving Paleo-floral Temperatures using the Clumped Isotope (Δ47) Thermometer: Implications for Florissant and Colorado Plateau Uplift

Abstract:

Reconstructing paleo-temperatures is important for understanding past climatic and tectonic conditions. Some of the most widely used methods for reconstructing terrestrial temperatures are derived from floral characteristics, but these methods often disagree when applied to the same floral assemblages. Because floral assemblages are often preserved in carbonate-bearing lacustrine sediments, new methods like clumped isotope (Δ₄₇) thermometry can provide an independent comparison for resolving discrepancies in paleotemperature estimates while using the same sampled materials. Here we sampled carbonates for clumped isotope (Δ₄₇) analysis in 15 extensively studied Cenozoic paleo-floral assemblages from across the western United States, and used the results in combination with floral estimates to help resolve mean annual temperatures (MAT) for these sites in the past. Applying this paired method allows for the revision of MAT estimates from important floras such as the Florissant (~18°C) and Creede (~9°C) assemblages of the northern Colorado Plateau (Colorado, USA). These revised temperatures, in addition to new traditional stable isotope data (δ¹⁸O), suggest a more gradual uplift history for the region, which may have important implications for the overall development of the plateau and for the dynamics of the paleo-Colorado River drainage.