Insights into the Late Cretaceous through Early/Middle Eocene Evolution of the North American Cordillera from an Integrated Climate Modeling-Stable Isotope Study

Abstract:

The accessibility, complexity, and data-richness of the North American Cordillera have made this region an excellent, and often utilized, laboratory for broadening our understanding of the interactions between orogenesis, paleotopography, and paleoclimate. Regional studies have developed a broad range of topographical proxies that frequently support multiple theoretical and physical models of Cordilleran evolution. In an effort to address this complexity and more tightly constrain the parameter space of changing Cordilleran elevations, recent studies have combined paleoelevation proxy data with numerical simulation of climate. Here we connect climate simulation and stable isotopic elevation proxies to investigate the early/middle Eocene (~49Ma) relationship between the Sierran Arc and Sevier fold and thrust belt to the west and Laramide uplifts and foreland deformation to the east. Modeled δ¹⁸O_pt from a suite of simulations that systematically varies elevations west of the thrust front and elevation, width, and roughness east of the thrust front is in general agreement with δ¹⁸O_pt proxies from the Laramide region. This result suggests that as long as there are key similarities, multiple paleotopographic reconstructions could result in the observed proxy signatures. It may not, therefore, be possible to definitively describe the particular details of a given region. We should, however, be able to clearly define the broader orogenic and topographic context which that region occupies. In the case of the simulations we present here, the broader context appears to rest primarily upon hinterland elevations which, in spite of significant geographical and elevation differences in our implementation of Laramide topography, exert the primary control on δ¹⁸O_pt in the Laramide region. Furthermore, these simulations indicate that δ¹⁸O_pt in the Laramide region increases as hinterland elevations increase. This is counter to the trend over the high peaks/plateau proper and highlights the need for careful consideration of water source when assessing fluvially-derived δ¹⁸O_pt proxies in the foreland.