The Upper Part Of The Upper Triassic Chinle Formation And Related Rocks Southeastern Utah And Adjacent Areas

Five uranium exploration cores from Lisbon Valley in the Paradox Basin of southeastern Utah provide examples of sedimentary structures and lithofacies from the Lower Permian Cutler Formation and the overlying Moss Back Member of the Upper Triassic Chinle Formation. The Cutler Formation consists of reddish-brown to purple, arkosic sandstone, siltstone, and mudstone of fluvial and floodplain origin interbedded with reddish-orange sandstone and mud-stone deposited in sabkha, eolian dune, and sand-sheet settings. The colors are indicative of the respective depositional settings. An erosional nconformity separates the top of the Cutler from the overlying Moss Back Member of the Chinle Formation. The Moss Back consists of greenish- to bluish-gray limestone-nodule conglomerate, siliciclastic sandstone, and siltstone deposited in high-energy fluvial channels and crevasse splays and on adjacent levees and floodplains. The drab colors of the Moss Back reflect the high organic-carbon content of strata deposited and preserved below the water table. These five cores record eolian and fluvial sedimentary structures and lithofacies sequences not well preserved in outcrops, they provide the basis for interpretation and comparison of depositional environments from lithofacies analysis in core and outcrop studies, and they establish the sedimentologic background for future petrographic and geochemical research on cores and outcrops from the Lisbon Valley area.