WATERSHED-SCALE PROVENANCE HETEROGENEITY WITHIN NONMARINE BASIN FILL: SOUTHERN GREATER GREEN RIVER BASIN, WESTERN US

Weathering, erosion, and transport processes of modern landscapes and fluvial systems are commonly investigated at the watershed or sub-watershed scales. These investigations are facilitated by the known parameters of modern river networks: watershed size, elevation, relief, bedrock lithology, climate, and other key attributes. Studies of ancient fluvial deposits typically lack this synoptic perspective and have traditionally relied on paleocurrent analysis and sandstone framework-grain composition. Detrital zircon age analysis can greatly refine such interpretations but is often limited in geographic or stratigraphic sampling density. The present study examines the importance of sampling density, based on n=4905 detrital zircon analyses from N=18 samples collected from an area of Green River basin ~90 km in radius (~25,000 km²). Two approaches to identifying sample similarity are utilized—multi-dimensional scaling and DZmix modeling—each of which delineates seven distinct chronofacies. Four of these reflect long-distance sediment transport. Chronofacies CO-1 and CO-2 indicate a primary sediment source in central Colorado, corroborating previously proposed long-distance sediment transport via the Aspen paleoriver. Chronofacies ID-1 and ID-2 were delivered to the basin from central Idaho by the Idaho paleoriver. In contrast, chronofacies UT-1 and UT-2 are interpreted to reflect local drainage from the Uinta uplift south of the basin, and chronofacies WY-1 appears to have been sourced from the Rawlins, Granite, and Sierra Madre uplifts to the north and east. These results reveal the influence of at least four discrete watersheds on sedimentation in the southern and eastern Greater Green River Basin and record these lateral changes in provenance at the kilometer scale. Data from this study show the dominance of the Aspen paleoriver as a sediment source to the southeastern Greater Green River Basin as it pins Uinta-derived clastics to the basin edge. The results of this study highlight the need for caution in the interpretation of paleoaltimetry or detrital thermochronology studies based on low-density regional sampling of sandstone deposits.