Carbonate clumped isotope constraints on burial, uplift and exhumation histories of the Colorado Plateau

Abstract

The timing, extent and driving mechanisms of burial, uplift and exhumation of the Colorado Plateau, and the carving of the Grand Canyon have been at the center of a long-standing controversy. Here, we develop a new approach to constrain burial and exhumation histories of sedimentary basins from the distributions of 'clumped' isotope compositions in carbonate minerals. We apply this approach to constrain peak-burial temperatures and infer the extent of peak sediment overburden and total exhumation of the Colorado Plateau at several sites extending from the Plateau's southwestern margin to its interior. Our constraints are broadly consistent with independent reconstructions of thermal history from low-temperature thermochronometry and oil-maturation indices. Together these data suggest that ∼3 km of rocks have been removed by erosion across the Plateau. This inferred prior extent of sediment overburden is consistent with the presence of a ∼1 km deep canyon at the Upper Gorge of the Grand Canyon during the Early Eocene, and therefore with topography at that time similar to today. Combined with the published record of partial exhumation—based on apatite-thermochronometry and stratigraphic constraints—we find that 63-83% of the total exhumation of the southwestern Plateau occurred prior to the Neogene. This is consistent with Sevier-Laramide contractional tectonism and/or pre-Neogene modification of the Colorado Plateau lithosphere driving uplift there. In contrast, apatite thermochronometry suggests that in the interior plateau, ∼50% of the total exhumation has occurred after the integration of the Colorado River – indicating a much younger source for uplift and the exhumation there. Considering recent suggestions that efficient exhumation of the Plateau by escarpment-retreat is associated with the incision of the drainage system, early exhumation of the Lower Gorge and Grand Wash segments of the Grand Canyon is consistent with the pre-Neogene carving of these segments, followed by relative stability of the base level.

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