Abstract
Mid-Continent evaporite sequences exhibit a common association with red beds and carbonate rocks. These lithologic elements can be interrelated in a model of coastal evaporite sedimentation, based on modern analogs of evaporites in association with mud-rich tidal flats, coastal sabkhas, and hypersaline brine pans.
As an example of these relations, upper Clear Fork-Glorieta strata (Permian, Leonardian) in the Texas Panhandle contain red beds, evaporites, and carbonate rocks, and are characterized by a gradual basinward (southerly) shift in facies through time. Upper Clear Fork rocks in the study area record dominance of coastal evaporite and carbonate environments early in the development of the study interval. Evaporites and associated carbonates, which were deposited in hypersaline, tide-fed brine pans, landward of open-marine shelf environments, include (1) algal-laminated carbonate rocks, commonly with swallowtail-crystal pseudomorphs after gypsum, (2) laminated anhydrite, and (3) mud-banded salt. Chaotic mudstone-salt is present and was deposited in landward salt-mud flats. Glorieta rocks record late-stage dominance of siUciclastic sedimentation. Laterally-persistent Glorieta siliciclastic units consist of mudstone-siltstone fades, deposited in intertidal mud flats, and grade basinward into sandstone and dolomite deposited in clastic shelf environments. Periods of silidclastic deposition alternated with periods of evaporite deposition. During sedimentation of each sihdclastic sequence, mud flats prograded seaward into the shelf terrane. Subsequent deposition of evaporites was on the expanded mud flats surface.
This example exhibits many similarities with evaporite sequences in other parts of the Permian basin, parts of the Salina basin, and selected salt occurrences in the Rocky Mountains. Understanding of facies interrelations is important in predicting resource potential of evaporite beds, and the occurrence of hydrocarbons in evaporite-associated strata.
