SEDIMENT ROUTING TO THE EOCENE GREATER GREEN RIVER BASIN USING PAIRED GEOCHRONOLOGY-GEOCHEMISTRY OF DETRITAL ZIRCON

The Eocene greater Green River Basin (gGRB) in southwest Wyoming is one of the most studied lacustrine basins due to its excellent exposure, fossil preservation, and hydrocarbon resources. However, sediment routing of volcaniclastic detritus is debated. Previous research has suggested a single Eocene volcaniclastic sediment source, including the Absaroka volcanic province to the north, the Challis volcanic province to the northwest via the paleo Idaho River, and the Colorado Mineral Belt to the southeast via the paleo Aspen River. Research has not conclusively determined an Eocene sediment source or whether there are multiple sources because the age of potential sources is non-unique. We implement a mix of standard basin analysis tools as well as detrital zircon U-Pb geochronology paired with trace element and Lu-Hf geochemistry to characterize gGRB volcaniclastic detritus placed in the context of newly characterized stratigraphic sections. Potential sediment sources are characterized using modern rivers tapping each volcanic province. Basin samples show an east-west compositional variability reflected in Eu anomalies; log10 Eu/Eu* values range from -1.3 to -0.4 in the west and -2.7 to -0.5 in the east. Lu-Hf geochemistry of basin samples also shows a mix of radiogenic and nonradiogenic melt sources; ɛHfT values range between -36 and -4 for ages 52-47 Ma. Source samples range from -30 to -4 for ages 50-45 Ma. Radiogenic grains in the basin samples are likely sourced from the southern Challis volcanic province, whereas nonradiogenic grains may be sourced from the Absaroka volcanic province. These results suggest the gGRB volcaniclastic detritus were sourced from more than just a single source. This indicates a more complex sediment routing history to the gGRB, modifying our current understanding of the paleogeography and evolution of drainage patterns in the Eocene intermountain west.