TECTONIC ISOLATION AND DRAINAGE REORGANIZATION IN THE WESTERN ANCESTRAL ROCKY MOUNTAINS (Invited Presentation)

Exhumation of Ancestral Rocky Mountain (ARM) basement-cored uplifts and attendant drainage reorganization in the late Paleozoic are recorded in adjacent ARM basins. Before ARM deformation, this province of the Laurentian Western Interior was occupied by a shallow sea and low relief topography. Regionally, late Paleozoic sediment sourcing has been linked to transcontinental sediment transport from the Appalachian Mountains. However, in the ARM corridor of CO, UT, AZ, and NM sediment sources change along with initiation of a series of flexurally-subsiding, tectonically isolated basins, and bounding uplifts. Detrital zircon data, paleocurrent analyses, sandstone petrography, facies stacking, and stratigraphic architecture document the nature of this transition and the subsequent spatial variability of sediment dispersal in the Paradox Basin. Immediately prior to ARM deformation, detrital zircon populations in the Paradox Basin match those across western Laurentia and feature a multi-modal population consistent with a broad, transcontinental drainage network. With the onset of ARM deformation, detrital zircon populations in the Paradox Basin change from the multi-modal pattern, which continues to dominate much of western Laurentia, to simple populations of only 1–3 age modes. This change occurs across a maximum flooding surface, which we interpret to be driven by rapid flexural subsidence in response to crustal thickening during exhumation of the basin-bounding Uncompahgre Uplift. Following ARM deformation in the Triassic, transcontinental drainage is reestablished through the ARM corridor, introducing a multimodal population of detrital zircon ages that match sources in the Ouachita-Marathon Mountains to the southeast. Detrital zircon mixing model results, facies distributions, and isochore maps aid in creating a series of sediment sourcing maps that illustrate the degree of tectonically-induced basin isolation pre-, syn-, and post-ARM tectonics.

We observe similar changes ~150 km to the east, in the Central Colorado Trough, which is bounded on both east and west by ARM uplifts. This similarity between flexural response and sediment source isolation suggests that tectonic isolation is a common element during drainage network reorganization in areas affected by intraplate deformation.