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Abstract: Sabkha Facies Nodular Previous HitAnhydriteNext Hit and Paleotemperature Determination

David J. J. Kinsman

The coastal sabkha is the normal successor environment following offlap of shelf and lagoonal facies sediments in climatic regions of net evaporation. Evaporation of interstitial pore waters typically leads to precipitation within the sediments of gypsum and sometimes of Previous HitanhydriteNext Hit. Sabkha-facies gypsum crystals are typically discoidal in shape. Previous HitAnhydriteNext Hit, in part a replacement of gypsum by a dissolution-reprecipitation reaction, and in part a primary precipitate is developed as nodular and enterolithic structures with a felted-lath crystal fabric.

Field data from the Persian Gulf, Baja California, and other areas demonstrate that the occurrence of gypsum or Previous HitanhydriteNext Hit commonly does not follow a simple equilibrium distribution related to temperature and H2O (brine salinity). Field data indicate that Previous HitanhydriteNext Hit formation proceeds in brines close to halite saturation. Initial nucleation of Previous HitanhydriteNext Hit also requires a seasonal high temperature in excess of 35°C; only areas of high continentality achieve these temperatures today. Once formed, the long-term preservation of Previous HitanhydriteNext Hit depends on the mean annual temperature; values in excess of 20°C are required for preservation of Previous HitanhydriteNext Hit in halite-free sabkhas.

Ancient sabkhas have been widely recorded in the geologic column and nodular Previous HitanhydriteTop of distinctive sabkha structures and fabric is fairly common. These occurrences now can be used to give minimum seasonal high and minimum mean-annual temperatures. For those intervals where paleolatitude reconstructions can be made with reasonable certainty these temperature data can be used as one component of a world climatic synthesis.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA