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Depositional environments of marine‐dominated bedded halite, Permian San Andres Formation, Texas
Author(s) -
HOVORKA SUSAN
Publication year - 1987
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.1987.tb00591.x
Subject(s) - halite , geology , evaporite , sedimentary depositional environment , geochemistry , anhydrite , sedimentology , facies , ephemeral key , sedimentary rock , gypsum , paleontology , structural basin , algorithm , computer science
The interpretation of the depositional environments in which bedded halite is formed is a frontier of evaporite sedimentology. Facies studies, supplemented by geochemical data, define an evaporite shelf depositional environment for the halite of the San Andres Formation of the Palo Duro Basin, Texas Panhandle, that is significantly different from modern and previously described ancient halite‐precipitating environments such as playas, salinas, sabkhas, and barred basins. A coastal palaeoenvironmental setting for the San Andres halite is defined by its facies position between normal marine‐shelf carbonates and aeolian deposits. The San Andres brine pool extended over more than 10 000 km 2 but was very shallow. Perennial brine‐pool conditions (thick sequences of halite) alternated with ephemeral brine‐pool conditions (halite, haloturbated mudstone‐halite, mudstone interbeds, and microkarst). The depositional sequence in the perennial brine pool includes (1) flooding and minor dissolution of previously deposited halite, (2) precipitation of a thin lamina of gypsum, and (3) evaporation and precipitation of halite. Bottom‐growth forms of halite, including chevrons and vertically elongated crystals, are well preserved. Cumulates of foundered, floating crystals and rafts were probably abundant but have been almost completely recrystallized. Mudstone interbeds in halite and microkarst features cut into bedded halite record the episodic interruption of brine‐pool deposition and the establishment of subaerial conditions. Vertically elongated karst pits originate at the palaeosurfaces, cross‐cut primary brine‐pool fabrics, and are filled with geopetal sediment and coarse halite cement. Mudstone interbeds and mixtures of mudstone and halite have been haloturbated by the alternating growth and dissolution of halite reflecting conditions of fluctuating salinity. The geochemistry of halite from both ephemeral and perennial brine‐pool environments reflects the frequent influx of marine brine, indicating that communication with the marine environments to the south was ‘good’ considering that restriction was sufficient to precipitate halite.