MESOZOIC-CENOZOIC BURIAL, UPLIFT, AND EROSION HISTORY OF THE WEST-CENTRAL COLORADO PLATEAU

Apatite fission-track data show that Permian strata forming the Colora do Plateau surface at the Grand Canyon underwent burial temperatures o f approximately 90-100-degrees-C in the Late Cretaceous, indicating th at approximately 2.7-4.5 km of Mesozoic strata covered the area at tha t time. This is similar to the approximately 2.5-3.5 km thickness of M esozoic section preserved to the north in southern Utah and confirms t hat those strata once extended south over a much broader area of the C olorado Plateau. Cooling from maximum burial temperatures began about 75 Ma, indicating that Laramide-age erosion removed approximately 1.3- 4.5 km of Mesozoic strata from the area. This erosion was probably cau sed by topographic relief created by Laramide reactivation of monoclin es and reverse faults. Permian strata in the Waterpocket monocline in southern Utah underwent burial temperatures of approximately 90-degree s-C in the Late Cretaceous, consistent with the idea that the Permian to Upper Cretaceous section exposed in the monocline formerly extended south over the Grand Canyon region.