INFLUENCE OF THE ASPEN PALEO-RIVER ON THE SEDIMENTOLOGY AND MINERALOGY OF THE EOCENE GREEN RIVER FORMATION, WY

Lacustrine deposits provide some of the most detailed and complete records of Earth history. In addition to cataloging perturbations in climate, tectonics, magmatism, and weathering, lake deposits can also provide a unique record of regional drainage evolution. Detailed investigation of fluvial facies within and adjacent to the Wilkins Peak Member of the Green River Formation reveals a surprisingly complex history of both local and regional drainage to Eocene Lake Gosiute between ~51.5-50.0 Ma. Based on U-Pb detrital zircon ages (N=15, n=3348), sandstone petrographic compositions (N=40) and paleocurrent indicators (N=7, n=375), we have distinguished three primary chronofacies (A, B and C) within the southern Green River basin. Chronofacies A includes significant Paleocene, mid-Mesoproterozoic and late-Paleoproterozoic grain populations, interpreted to derive from the Colorado Mineral Belt (CMB) and its host rocks ~300 km southeast. Its arkosic composition supports first-cycle derivation primarily from crystalline basement, and paleocurrents indicate generally northwest transport, via the Aspen paleo-River. This result supports the hypothesis that magmatic CO₂ emanating from the CMB played a key role in the deposition of lacustrine Na-carbonate evaporite (trona) in Wyoming. Chronofacies B, in contrast, has detrital ages indicative of local derivation from the Uinta uplift. Northward paleocurrent indicators, subarkose and sublithic compositions, and Grenville-aged detrital zircons all suggest recycling of Uinta Mountain Group quartzite. Chronofacies C represents a unique detrital signature not clearly associated with either the CMB or the Uinta uplift, suggesting additional sources of detritus to the west (thrust belt) or to the north of Lake Gosiute. Ongoing work aims to document these sources and to build a more robust understanding of the relationship of Lake Gosiute to its contemporary watershed.