Gannett Group of Western Wyoming and Southeastern Idaho

摘要: The Jurassic and Cretaceous Gannett Group in the thrust belt of western Wyoming southeastern Idaho, primarily freshwater deposition, consists five units (in ascending order): Ephraim Conglomerate, Peterson Limestone, Bechler Formation, Draney an upper mudstone unit here raised to formation status designated Smoot Formation. All formations are thickest type area, along Idaho-Wyoming line, where total thickness exceeds 5,000 ft. is underlain, with apparent conformity, by marine glauconitic sandstone Stump Sandstone overlain conformably lower Tygee Member Bear River Conglomerate Formation consist conglomerate, sandstone, red containing beds abundant calcareous nodules. Grain size coarsest area becomes finer eastward, both disappear abruptly westward. Charophytes ostracods present parts these formations. part contains a molluscan fauna. Limestones limestone interbedded gray shale charophytes ostracods. newly designed mudstone, siltstone, calcareous, nodular which also contain Except for Ephraim, all fluvial lacustrine biota. Nine species 11 were found Gannett. One charophyte three new. Cypridea A Theriosynoecum angularis Clypeator corrugatus known only from Peterson. anomala, C. nitidula, wyomingensis, brevicornis, compta, persulcatum, Cypris purbeckensis Amblyochara latifasciata Bechler, throughout Draney, middle Smoot. Mesochara diminuta, Metacypris A, Eucandona Flabellochara harrisi, Atopochara trivolvis, Stellatochara mundula, Mesochar voluta, Charaxis striatus, Obtusochara cylindrica nonmarine Group. Lower mollusks age. Early Neocomian cannot be distinguished fossil evidence, but may represented coarse clastic rocks Ephraim. Aptian age; however, biota more like that overlying Albian latifasciata, angularis, very sparse. first two River. Three restricted absent Four eight Therefore, seems transition interpreted partly