­­­­­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 the thermal history 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, tectonic uplift 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 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 Tertiary, and therefore with topography at that time similar to today. We further suggest that in the southwestern quarter of the Plateau the exhumation has taken place over an uplifted surface dissected by canyons. This suggestion is inconsistent with previous interpretations that view the plateau and canyon landscape as reflecting planation at base level followed by surface uplift and canyon incision. Instead, we suggest that lithologically controlled retreat of escarpments has played a key role in the removal of kilometers of rock from above the plateau surface, while maintaining an overall planar landscape.