Stratigraphy of Bedded Halite in the Permian San Andres Formation, Units 4 and 5, Palo Duro Basin, Texas

Seven cored wells through the bedded halite of the San Andres Formation have allowed an unusual, detailed analysis of the fabrics in halite. A descriptive classification system identified eight textural types of halite. These are: chevron halite rock, color-banded/vertically oriented halite rock, chaotic mudstone-halite rock, equant muddy halite rock, equant anhydritic halite rock, displacive halite in other sediments, cavity-filling halite cement, and fibrous fracture-filling halite cement. Genetic interpretation of the depositional environment in which halite textures formed resulted from analysis of the relationships between textures and comparison to ancient, modern, and experimental halite analogs. Chevron and color-banded/vertically oriented halite are recognized as textures formed subaqueously as halite precipitated on the floor of brine pools. Chaotic mudstone-halite rock, equant muddy halite rock, equant anhydritic halite rock are recognized as diagenetic alteration products formed by karstification and diagenetic recrystallization occurring at least partly in the subaerial environment. Displacive halite in other sediments, cavity-filling halite cement, and fibrous fracture-filling halite cement are products of precipitation of halite within the sediment during early diagenesis.

Very detailed logging of the halite fabrics and anhydrite and mudstone interbeds and partings in the seven cored wells allowed correlation on a meter scale between cores. A basin-wide pattern of alternation between zones of anhydritic halite with preserved brine pool fabrics and zones of halite with mudstone interbeds and altered textures was identified. These alternating zones can be traced as much as 100 km between the wells, providing evidence that the entire study area was one broad low relief evaporitic shelf. Net mud maps of the muddy intervals suggest that the geometry of mudstone beds might be broad, poorly-defined lobes. Isopachs of the anhydrite interbeds show variation in the facies pattern in each genetic cycle. Some anhydrite beds thicken toward southern Swisher County, while others are thickest to the west, in Deaf Smith County.