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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)

Abstract


Journal of Sedimentary Petrology
Vol. 62 (1992)No. 6. (November), Pages 1098-1111

Halite Pseudomorphs After Gypsum in Bedded Previous HitAnhydriteNext Hit--Clue to Gypsum-Previous HitAnhydriteNext Hit Relationships

Susan D. Hovorka

ABSTRACT

Halite pseudomorphs after gypsum crystals preserve depositional textures and record the early diagenetic history of Previous HitanhydriteNext Hit beds in cyclic Permian evaporites of the Texas Panhandle. The well-documented sedimentologic setting and good preservation of fabrics permit identification of a sequence of diagenetic processes in gypsum. Gypsum (rather than Previous HitanhydriteNext Hit) was the dominant sulfate precipitated, even at salinities near halite saturation. Large gypsum crystals grew vertically on floors of brine pools, surrounded by a matrix of autochthonous transported gypsum sand and silt. All gypsum has been diagenetically altered to Previous HitanhydriteNext Hit ± halite, but the diagenetic fabrics vary depending on position within regressive evaporite cycles. Because the composition and texture of the primary sediment were similar throughout the Previous HitanhydriteNext Hit bed, these different diagenetic fabrics are interpreted as the result of changes in the processes of replacement of gypsum by Previous HitanhydriteNext Hit and halite as the shallow burial environment became increasingly saline. In the lower parts of Previous HitanhydriteNext Hit beds, diagenesis in low-salinity brines favored obliteration of primary sedimentary structures by formation of nodules. In the middle parts of beds, introduction of high-salinity brine into the shallow burial environment favored alteration of gypsum to Previous HitanhydriteNext Hit and preservation of pseudomorphs after large gypsum crystals. At the top of Previous HitanhydriteNext Hit beds, introduction of halite-saturated brines into gypsum sediments on the floor of the brine pool resulted in pervasive replacement of gypsum by halite. Petrogr phic relationships indicate that most or all of the primary gypsum was altered to Previous HitanhydriteTop in the very shallow (< 2 m) burial environment under the influence of saline diagenetic brines.


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