Epeirogenic Controls on Canadian River Incision and Landscape Evolution, Great Plains of Northeastern New Mexico

Abstract

The Canadian River has carved a deep bedrock canyon into the Great Plains of northeastern New Mexico in response to a complex interaction of post‐Laramide, epeirogenic rock‐uplift processes along the Jemez lineament and downstream baselevel fall caused by late Tertiary and Quaternary evaporite dissolution. Broad, slow‐bulging along the Jemez lineament, a lithospheric‐scale structure with prolific late Cenozoic volcanism along its trend, helps drive incision in the canyon. Canadian River canyon fluvial terraces, mapped and correlated according to soils, elevation, and rock‐type criteria, reveal longitudinal profiles that appear broadly warped across the Jemez lineament and converge to the modern channel profile both upstream and downstream of the canyon. Similarly, the modern channel long profile is distinctly and broadly convex through its Great Plains reach, a unique feature among major rivers draining the eastern flank of the southern Rocky Mountain front. Radiocarbon‐dated charcoal from terrace alluvium and an 40Ar/39Ar‐dated basalt flow within the canyon constrain long‐term average rates of bedrock incision to ∼0.06–0.07 mm/yr. River incision along the Jemez lineament has produced youthful canyons and escarpments and eroded Tertiary rocks relative to other regions along the southern Rocky Mountain front. Whereas rock‐uplift processes prevail in the canyon reach, baselevel changes driven by a well‐documented process of salt‐dissolution subsidence have controlled the evolution of reaches downstream of the canyon. Removal of bedrock along the northern flank of the Jemez lineament bulge fosters opposing dips in the valley flanks, resulting in the Canadian escarpment (northern flank) that stands up to 200 m higher than the Caprock (southern flank). These findings suggest that post‐Laramide, thermally driven epeirogeny is in part responsible for the high‐standing topography evident on the western Great Plains of northeastern New Mexico.