Geologic mapping in the Phil Pico Mountain quadrangle and analysis of the Carter Oil Company Carson Peak Unit 1 well have provided additional constraints on the erosional and uplift history of this section of the north flank of the Uinta Mountains. Phil Pico Mountain is largely composed of the conglomeratic facies of the early Eocene Wasatch and middle to late Eocene Bridger Formations. These formations are separated by the Henrys Fork fault which has thrust Wasatch Formation next to Bridger Formation. The Wasatch Formation is clearly synorogenic and contains an unroofing succession from the adjacent Uinta Mountains. On Phil Pico Mountain, the Wasatch Formation contains clasts eroded sequentially from the Permian Park City Formation, Permian Pennsylvanian Weber Sandstone, Pennsylvanian Morgan Formation, and the Pennsylvanian Round Valley and Mississippian Madison Limestones. Renewed uplift in the middle and late Eocene led to the erosion of Wasatch Formation and its redeposition as Bridger Formation on the down-thrown footwall of the Henrys Fork fault. Field observations and analysis of the cuttings and lithology log from Carson Peak Unit 1 well suggest that initial uplift along the Henrys Fork Fault occurred in the late early or early middle Eocene with the most active periods of uplift in the middle and late Eocene (Figure 8, Figure 24, Appendix 1). The approximate post-Paleocene throw of the Henrys Fork fault at Phil Pico Mountain is 2070 m (6800 ft). The Carson Peak Unit 1 well also reveals that just north of the Henrys Fork fault at Phil Pico Mountain the Bridger Formation (middle to late Eocene) is 520 m (1710 ft) thick; an additional 460 m (1500 ft) of Bridger Formation lies above the well on Phil Pico Mountain. Beneath the Bridger Formation are 400 m (1180 ft) of Green River Formation (early to middle Eocene), 1520 m (5010 ft) of Wasatch Formation (early Eocene), and 850 m (2800 ft) of the Fort Union Formation (Paleocene). Stratigraphic data from three sections located east to west across the Phil Pico Mountain quadrangle show that the Protero-zoic Red Pine Shale has substantially more sandstone and less shale in the eastern section of the quadrangle. Field observations suggest that the Red Pine Shale undergoes a facies change across the quadrangle. However, due to the lack of continuous stratigraphic exposures, the cause of this change is not known.



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Physical and Mathematical Sciences; Geological Sciences



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Eocene, Red Pine Shale, Uinta Mountains, Bridger Formation, Wasatch Formation, Henrys Fork Fault, Uplift, uplift history, anticline, syncline, Laramide, Green River Formation, Bishop Conglomerate, inverted cobble stratigraphy, unroofing, unroofing sequence, conglomerate, Phil Pico Mountain, Flaming Gorge, Utah, Wyoming, Paleocene, clast, erosional history, north flank, facies change, strike-slip fault, Madison Limestone, Weber Sandstone, Vr, VrTwo, VrOne, geologic mapping, geology, glacial deposits, Smiths Fork, Uinta thrust, cuttings, lithology log, erosion, Carson Peak well, geologic map, cross-section, stratigaphy, stratigraphic column, unit descriptions, tectonic history, Tertiary, depositional, deposition, Proterozoic, Precambrian



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