Provenance record of Paleogene exhumation and Laramide basin evolution along the southern Rocky Mountain front

The Sangre de Cristo and Nacimiento uplifts of the southern Rocky Mountains formed key parts of a major Paleogene topographic boundary separating the Cordilleran orogenic system from the North American plate interior. This barrier largely isolated interior Laramide basins from a broad Laramide foreland with fluvial systems draining to the Gulf of Mexico, and thereby played a critical role in the evolution of continental-scale paleodrainage patterns. New detrital zircon U-Pb geochronology and heavy mineral provenance analyses of Cretaceous-Paleogene siliciclastic strata in the Raton, Galisteo-El Rito, and San Juan basins record the partitioning of the broad Cordilleran (Sevier) foreland basin by Laramide basement uplifts. These trends are recognized both in provenance signals and depositional styles corresponding to cratonward (eastward) propagation of the Laramide deformation front and resultant advance of flexural depocenters in the North American interior. Along the eastern flank of the deformation front, the Raton basin shows a mix of Cordilleran, Appalachian, and Grenville age zircons restricted to the Cretaceous Dakota and Vermejo formations, marine units of the Western Interior Seaway. Upsection, the Cordilleran age peaks are absent from Paleocene-Eocene units, consistent with significant Laramide drainage reorganization and isolation from Cordilleran sources to the west. In the Galisteo-El Rito basin system, a shift to dominantly Mazatzal-Yavapai basement ages is recognized in the Paleocene El Rito and Oligocene Ritito formations. The heavy mineral results show a corresponding shift to less mature, dominantly metamorphic source compositions. These new datasets bear upon Cretaceous-Cenozoic reconstructions of North American paleodrainage and have implications for potential linkages between major fluvial systems of the southern Rocky Mountains and Paleogene deepwater reservoir units in the Gulf of Mexico basin.