LARAMIDE-DRIVEN EROSION, INTERMONTANE BASIN FILL, AND DRAINAGE REORGANIZATION IN NORTH-CENTRAL NEW MEXICO

Paleogene basin development and sedimentation associated with Laramide-style structures are recorded in fluvial deposits of north-central New Mexico. Specifically, the geographically separate El Rito, and Galisteo and Diamond Tail formations are archives of drainage network reorganization driven by exhumation of local uplifts. However, the lack of age control for El Rito Formation deposition means that correlation to the Galisteo Formation is tenuous, which carries with it implications for basin evolution, sediment sourcing, and tectonic activity. We use geologic mapping, measured stratigraphy, and sediment provenance data from detrital zircon U-Pb geochronology, conglomerate clast counts, and paleocurrent analysis to elucidate the fluvial evolution and relationship among these formations. Provenance interpretation is aided by a detrital zircon mixing model, which allows quantitative comparison of source-sink zircon samples to determine the degree of individual source contributions. Maximum depositional ages based on detrital zircon U-Pb geochronology suggest that the El Rito and Galisteo formations are not coeval. Furthermore, these formations also differ in their mechanism of accommodation. Specifically, tectonic subsidence preserved the Galisteo Formation. On the other hand, the El Rito Formation provides a unique window into cut-and-fill processes rarely preserved in the proximal reaches of intermontane fluvial systems. Field-based stratigraphic relationships suggest that El Rito Formation accommodation was predominantly driven by ‘bathtub-style” infilling of erosional relief. Moreover, these data support the presence of east-flowing tributaries feeding a south-flowing El Rito trunk stream. Systematic up-section changes in detrital zircon U-Pb age distributions of the El Rito Formation contrast with clast count data; specifically, clast counts ubiquitously exhibit quartzite-clast-dominant compositions, whereas detrital zircon age distributions clearly distinguish bedrock source populations between eastern and western hinterlands. Previous work and new data presented herein are integrated into a 3-stage synthesis of Galisteo and El Rito basin evolution that explores their connectivity to North American-scale river networks that drained into the Gulf of Mexico.