The North American Newark Canyon Formation (~113–98 Ma) presents an opportunity to examine how various terrestrial carbonate facies reflect different aspects of paleoclimate during one of the hottest periods of Earth’s history. We combined carbonate facies analysis with δ13C, δ18O, and Δ47 datasets to assess which palustrine and lacustrine facies preserve stable isotope signals that are most representative of climatic conditions. Type section palustrine facies record the heterogeneity of the original palustrine environment in which they formed. Using the pelmicrite facies that formed in deeper wetlands, we interpret a lower temperature zone (35–40°C) to reflect warm season water temperatures. In contrast, the mottled micrite facies reflects hotter temperatures (36–68°C). These hotter temperatures preserve radiatively heated “bare-skin” temperatures that occurred in a shallow depositional setting. The lower lacustrine unit has been secondarily altered by hydrothermal fluids while the upper lacustrine unit likely preserves primary temperatures and δ18Owater of catchment-integrated precipitation. Based on this investigation, the palustrine pelmicrite and lacustrine micrite are the facies most likely to reflect ambient climate conditions, and therefore, are the best facies to use for paleoclimate interpretations. Average warm season water temperatures of 41.1±3.6°C and 37.8±2.5°C are preserved by the palustrine pelmicrite (~113–112 Ma) and lacustrine micrite (~112–103 Ma), respectively. These data support previous interpretations of the mid-Cretaceous as a hothouse climate. Our study demonstrates the importance of characterizing facies for identifying the data most representative of past climates.

The retroarc of the North American Cordilleran orogen in Nevada and Utah has been divided into the frontal Sevier fold-thrust belt in Utah, which accommodated shortening between ~145 and ~50 Ma, and a broad region of Nevada referred to as the ‘Sevier hinterland’. The hinterland is hypothesized to have developed into a high-elevation orogenic plateau (or ‘Nevadaplano’) at some point between the Late Jurassic and the Paleogene. Recent paleoaltimetry utilizing clumped isotope temperature estimates suggests that at least some basins on the Nevadaplano were at an elevation of 2.2-3.1 km by the latest Cretaceous. However, it remains uncertain precisely when the Nevadaplano attained these high elevations and if surface uplift developed steadily along with protracted shortening in the Sevier fold-thrust belt or occurred rapidly and was decoupled from the shortening record. In order to extend the surface elevation history of the Nevadaplano further back in time, we have investigated the type-exposure of the mid-Cretaceous (~113-98 Ma) Newark Canyon Formation (Knc) in central Nevada. The Knc records synorogenic sedimentation in the Sevier hinterland during the early to middle stages of shortening in the Sevier thrust belt. We will present terrestrial surface temperature estimates from clumped isotope analyses derived from palustrine, lacustrine, and pedogenic carbonate-bearing facies. Contextualized by structural evidence and corrected for secular climate change, these data suggest that the studied Knc basin had not developed substantial surface elevation by the mid-Cretaceous. However, there was likely some considerable surface relief in this region associated with active fold-thrust structures in the upper crust. Preliminary temperature estimates range between 22 and 70°C. These temperatures reflect a range of facies-specific differences in primary carbonate formation, as well as, diagenetic overprinting of some samples. Consistently warm temperatures throughout the stratigraphic section suggest that there was no significant cooling due to elevation gain between ~113 and ~98 Ma. We will discuss the implications of these results for the style and timing of deformation and surface uplift within the Nevadaplano.