MID-CRETACEOUS SEVIER HINTERLAND AT LOW SURFACE ELEVATION BASED ON CARBONATE CLUMPED ISOTOPES (Invited Presentation)

From the Late Jurassic to the Paleogene (~150-50 Ma), the western USA experienced contractional deformation due to subduction along the west coast, which constructed the North American Cordilleran orogenic belt. During orogenesis, it has been hypothesized that a high elevation plateau (“Nevadaplano”) was constructed in the hinterland region of the Sevier fold-thrust belt in Nevada, with attainment of elevations >2 km by the end of the Cretaceous. To understand the timing of the surface uplift of the Nevadaplano, we extended the paleoelevation record back by ~40 Myr using carbonate clumped isotope (∆₄₇) thermometry on well-preserved palustrine and pedogenic carbonates. We compare two mid-Cretaceous terrestrial carbonate ∆₄₇ datasets, one from the Cedar Mountain Formation (CMF) in the low-elevation Sevier foreland basin (Suarez et al., 2021) and one from the Newark Canyon Formation (NCF) in the Sevier hinterland (this study). Sample selection from both formations was based on facies analysis and screening for secondary alteration to ensure comparison of the most similar carbonate facies as possible. The NCF is ~6.5°C hotter (40.7ºC ± 1.4, 1s.e.) than the CMF (34.1ºC, ± 4.1, 1s.e.) during the early Albian and there is no significant difference in water oxygen isotope estimates (δ¹⁸O_water) between these two formations (NCF: –3.13‰ ± 1.4, 1s.e. and CMF: –3.51‰ ± 1.18, 1s.e.). Therefore, we interpret that the Sevier hinterland had not yet experienced significant surface uplift by early Albian (~112 Ma) in this region, although there was likely relief developing on the landscape. This result is consistent with evidence of regional faunal continuity across the Early Cretaceous Sevier hinterland and foreland that suggests a lack of a major topographic barrier between these two regions (Bonde et al., 2015). We interpret, therefore, surface uplift was decoupled from regional crustal thickening during the Early Cretaceous, and that the development of a high-elevation hinterland plateau was confined to the Late Cretaceous–early Paleogene (~100–55 Ma). This provides an important boundary condition for the tectonic development of the western USA during Cordilleran orogenesis and emphasizes the importance of carefully selecting the carbonate facies used in paleoaltimetry studies.