Basin Partitioning Along the Laramide Deformation Front in the Southern Rocky Mountains: Paleogene Provenance Record of the Raton and Galisteo-El Rito Basins

Abstract

Large-scale partitioning of the Cretaceous Cordilleran (Sevier) foreland basin into isolated Laramide basins is addressed through analysis of the provenance record in the Paleocene-Eocene Raton and Galisteo-El Rito basins of southern Colorado and northern New Mexico. These broken foreland basins flanked by basement-cored uplifts record the retreat of the Cretaceous Western Interior Seaway and Paleogene progradation of fluvial and alluvial-fan systems. We conducted detrital zircon U-Pb geochronology on Upper Cretaceous through Eocene sandstones from the Raton and Galisteo-El Rito basins in order to constrain source rocks and patterns of regional exhumation related to changing deformation patterns. Major grain populations derive from: (a) Mazatzal-Yavapai transitional basement (1800–1600 Ma) of the Sangre de Cristo range, (b) 1400 Ma granitic intrusions, (c) 1200–900 Ma Grenville crystalline rocks, (d) Paleozoic rocks of the Appalachian orogeny (500–300 Ma), (e) recycled grains from Mesozoic strata and (f) Mesozoic igneous rocks from the Cordilleran magmatic arc (<250 Ma). These basins record the partitioning of the Cretaceous foreland basin by Laramide basement uplifts, recognizable in both the provenance signal and depositional styles. In the Raton basin, an unconformity (angular in places) between the Upper Cretaceous Vermejo and Raton formations is coincident with this change in source composition, corresponding to the eastward propagation of the Laramide deformation front, and resultant advance of flexural depocenters in the interior of the North American plate. Cordilleran, Appalachian, and Grenville peaks are only found in the Cretaceous Dakota and Vermejo formations associated with the Western Interior Seaway of the Sevier foreland. Cordilleran peaks are absent from Paleogene samples, consistent with significant, continental drainage reorganization during early Laramide deformation. These new data bear upon reconstructions of North American paleodrainage and have important implications for potential linkages between major fluvial systems of the southern Rocky Mountains and Paleogene deepwater reservoir units in the Gulf of Mexico basin.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015