TECTONOMORPHIC INFLUENCE ON SEDIMENT SOURCES AND PATHWAYS THROUGH WEST TEXAS: DETRITAL ZIRCON GEOCHRONOLOGY OF THE LATE CRETACEOUS-PALEOGENE TORNILLO BASIN, BIG BEND NATIONAL PARK

Spatiotemporal variations in tectonic style are expressed by evolving topography, and exert a primary control on how sediment is generated by erosion and transported from source-to-sink. During Late Cretaceous-Paleogene time, New Mexico and south and west Texas were situated in a transitional tectonomorphic landscape between nascent Laramide topography and the Mexican Cordillera. There is considerable uncertainty surrounding the nature of the Cretaceous-Paleogene sediment routing systems that dissected this region, including the course of paleo-rivers, their catchment extent, and their debouchment locations along the Gulf of Mexico. A better characterization of the drainage system is vital to estimating sediment delivery to the Gulf of Mexico, and, broadly, understanding source-to-sink sediment transfer in systems defined by distinct, evolving tectonomorphic provinces. Detrital zircon (DZ) U-Pb geochronology is used to determine sediment source terranes, evaluate sedimentary recycling, quantify catchment sizes, and estimate sediment fluxes. DZ U-Pb provenance results from Cretaceous-Paleogene fluvial sediments of the Tornillo Basin in west Texas consist of dominantly Late Cretaceous age modes with subordinate Paleocene, Jurassic, Permian and minor Silurian-Ordovician, 1.1, 1.4, and 1.7 Ga modes. The DZ age spectra also contain an Early Cretaceous “arc gap” consistent with western U.S. sources and inconsistent with sources in the western Mexican Cordillera. Rim/core age relationships show four rim/core clusters: late Cretaceous/Jurassic, Late Cretaceous/1.1-1.5 Ga, Permian/1.5-1.6 Ga and Ordovician/1.1 Ga. These DZ results suggest a more extensive paleo-catchment system for the Tornillo Basin than previously inferred, potentially sourced from well within the western U.S. Cordillera, and/or recycled from Jurassic and Cretaceous sediments in the Mexican Laramide belt (e.g., Sabinas uplift). The interplay of possible arc/basement and recycled sedimentary sources show that sediment input to the Tornillo Basin was controlled by evolving Laramide topography in the U.S. and Mexico. This provides valuable insight into source-to-sink systems situated in transitional tectonomorphic landscapes, and the complexity of establishing sediment sources in such highly variable terranes.