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The AAPG/Datapages Combined Publications Database

Journal of Sedimentary Research (SEPM)


Journal of Sedimentary Research, Section A: Sedimentary Petrology and Processes
Vol. 64A (1994)No. 2. (April), Pages 339-348

Petrographic and Geochemical Constraints on the Formation and Diagenesis of Previous HitAnhydriteNext Hit Cements, Smackover Sandstones, Gulf of Mexico

S. I. Dworkin (1), L. S. Land (2)


Previous HitAnhydriteNext Hit cement is common in sedimentary rocks, yet its origin is poorly understood. The high concentration of sulfate in sea water and the lack of appreciable sulfate in most other natural waters suggests that Previous HitanhydriteNext Hit cement may have a marine origin, but the relatively late timing of most anhydride cement tends to preclude sea water as the source of sulfate.

Previous HitAnhydriteNext Hit cement is present in Upper Jurassic sandstones in the Gulf of Mexico as poikilotopic masses in which detrital grains are replaced and as smaller patches that have replaced single detrital grains. Previous HitAnhydriteNext Hit is a relatively late cement and postdates all other volumetrically significant authigenic phases, including K-feldspar, dolomite, quartz, and most calcite cements.

The expected isotopic composition and trace-element concentration of marine-derived Late Jurassic Previous HitanhydriteNext Hit cement is predicted based on analyses of bedded Previous HitanhydriteNext Hit and on analyses found in the literature. The expected chemical signature is: ^dgr34S (^pmil CDT) = +16, ^dgr18O (^pmil SMOW) = +14, 87Sr/86Sr = 0.7069, Sr = 1500-2500 ppm, Ba < 20 ppm, and Mg > 200 ppm. When geochemical analyses of Smackover Previous HitanhydriteNext Hit cements are compared to the predicted composition, it is apparent that most of the cement is not of marine origin.

Two generations of Previous HitanhydriteNext Hit cement have been identified in the East Texas basin on the basis of their strontium isotopic compositions and their strontium concentrations. An early cement may have been derived from slightly modified Late Jurassic sea water, whereas a second group of cements may have precipitated later in the burial history or may represent recrystallization of the first cement. The chemistry of Louisiana and Mississippi basin Previous HitanhydriteNext Hit cements indicates that the sulfate was derived from dissolved bedded Previous HitanhydriteNext Hit and was reprecipitated in the sandstones from fluids that had undergone extensive water-rock interaction after considerable burial. This study suggests that late Previous HitanhydriteTop cements in sedimentary rocks are most likely derived from remobilized calcium sulfate de osits.

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