Coastal Evaporite and Tidal-Flat Sediments of the Upper Clear Fork and Glorieta Formations, Texas Panhandle

Red beds, evaporites, and carbonates of the upper Clear Fork and Glorieta Formations (Permian) of the Texas Panhandle form an association of facies deposited in nearshore and supratidal environments along an arid coastline. Carbonates were deposited in inner-shelf depositional environments and exhibit upward-shoaling, sabkha-like successions of dolomitic mudstones containing nodular anhydrite. Landward of the shoaling carbonates was a vast salt plain, or sabkha, in which evaporites were deposited in supratidal brine pans and salt flats. Brine pan environments on the seaward parts of the salt plain were intermittently flooded by periodic tides or ground-water seepage. Deposits of gypsum and relatively pure halite formed in the shallow ponded waters. Salt-flat environments landward of brine pans were exposed for long periods of time. Evaporites in salt-flat environments were deposited in surficial salt crusts and interstitially in previously deposited carbonate, evaporite, or clastic host sediments. A common salt-flat facies is red siliciclastic mud in which displacive growth of halite crystals created chaotic mixtures of mud and salt.The development of broad mud-rich tidal flats that extended across most of the study area periodically terminated evaporite sedimentation. The upper Clear Fork and Glorieta Formations are considered a single lithogenetic unit. Together these units define a broadly regressive cycle of deposition characterized by an increase in supply of clastic sediments through time. During the time of upper Clear Fork deposition, evaporite and carbonate depositional systems were predominant in the Texas Panhandle. In Glorieta time, clastic environments migrated basinward, and mudflat and salt-flat facies were deposited across much of the Texas Panhandle. In addition to the broad cycle of regression that characterizes the upper Clear Fork-Glorieta lithogenetic unit, there were multiple cycles of inner-shelf, brine pan, and salt-flat facies, which are a record of shorter term fluctuations in the pattern of sedimentation. These cyclic facies patterns were controlled by a delicate dynamic balance among competing processes of basin subsidence, eustatic sea-level variation, clastic sediment supply, and aggradation/progradation of intertidal and supratidal sediments.