EVALUATING MODELS FOR CRETACEOUS PALEODRAINAGE AND SEDIMENT ROUTING USING DETRITAL ZIRCON U-PB PROVENANCE AND GEOCHRONOLOGY IN THE COLORADO FRONT RANGE

Multiple models have been proposed for Early Cretaceous to the Paleogene North American paleodrainage and sediment routing, and for how continental-scale sediment dispersal patterns changed during this time period. One model shows the routing of sediment to the Western Canada Sedimentary Basin and Boreal Sea during the Early Cretaceous, representing a convergence of eastern- and western-derived river systems to form a continental-scale drainage system, which by the Paleocene evolved to drain to the Gulf of Mexico. Three different hypotheses are proposed to develop an alternative model for sediment routing to the Western Canada Sedimentary Basin: (a) sediments were sourced from the Appalachians to the east; (b) sediments were sourced from recycling older Mesozoic sediments of the southwestern US; or (c) sediments were recycled from the Canadian Shield but with no confluence of Appalachian- and western-sourced river systems to form a single continental-scale drainage. This study tests these models and hypotheses through examination of Jurassic-Lower Cretaceous Morrison, Lytle, and Dakota formations of the Colorado Front Range with the following objectives: (i) alluvial architecture outcrop studies to examine the style and scale of Cretaceous river systems and (ii) detrital zircon U-Pb geochronology and provenance analysis to test for their contribution to the interfered continental-scale drainage system. Preliminary dating of the detrital zircons sampled indicates convergence of eastern- and western-derived systems, with Colorado Front Range rivers sourcing both Appalachian and Western Cordillera grains. Additionally, outcrop studies found paleocurrent data with a N-NE-E trend on the Front Range and a W trend in Kansas, which is consistent with published research. Results of this study will verify or falsify ancient sediment routing and sediment dispersal patterns through determination of sediment provenance.