Tansill, Salado, and Alibates Formations: Upper Permian Evaporite/Carbonate Strata of the Texas Panhandle

The Salado-Tansill and Alibates Formations are the youngest evaporite and carbonate facies within a thick Permian sequence of evaporites, carbonates, and red beds in the Texas Panhandle. They accumulated during the final stages of a regional regression that began in Early Permian time, and they record the last minor incursion and subsequent regression of Permian seas in the Texas Panhandle. Salado-Tansill salts and terrigenous red beds were deposited in the updip or proximal parts of a salt basin that existed northeast of the Delaware Basin. Terrigenous clastic facies were deposited on strike-oriented salt-mud flats; thicker salt units were deposited in shallow, supratidal brine pans and on the surface of supratidal salt-mud flats. Salado-Tansill salt originally extended throughout most of the Palo Duro Basin, but its distribution has subsequently been modified by dissolution. Alibates strata accumulated during a transgressive-regressive episode that may have begun as early as mid-Salado-Tansill time. Initial transgression is recorded in the Alibates Formation by an extensive basal dolomite throughout the Palo Duro and Dalhart Basins. Subsequent regression of the Alibates sea resulted in deposition of thick evaporites in the central and southern Palo Duro Basin. Alibates dolomite and evaporites were deposited in intertidal to supratidal, hypersaline environments that occupied a broad, low-relief evaporative plain. Algal mats bound aragonite mud and gypsum crystals to form laminated dolomite and interlaminated anhydrite and dolomite. Laminated gypsum was deposited on supratidal gypsum flats. Extensive shallow pending is indicated by the presence of "grass mat" gypsum. Geometries of the Salado-Tansill and Alibates basins were similar. Coincidence of paleoslope, correlatable extent, and depositional axes suggest a basinal geometry in which deeper basinal areas were located in the central and southern Palo Duro Basin.