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A sulfur and strontium isotopic investigation of Lower Permian anhydrite, Palo Duro Basin, Texas, U.S.A.

Applied Geochemistry
Publication Date
DOI: 10.1016/0883-2927(89)90015-2
  • Earth Science


Abstract Lower Permian Wolfcamp and Wichita carbonates and anhydrites, Palo Duro Basin, Texas Panhandle, record a change from a normal marine to marine evaporite depositional environment. Isotopic compositions of S and Sr in anhydrite were determined to investigate the age of Wolfcamp and Wichita strata and the paragenesis of eight anhydrite forms. Bedded nodular mosaic (Wichita) and replacive nodular (Wolfcamp) anhydrites have S and Sr isotopic compositions that record precipitation from Early Permian (Wolfcampian) to Leonardian) seawater. Silicified nodular, coarsely crystalline nodular, fossil- filling, and vein-filling anhydrites have enriched S isotopic compositions relative to Permian seawater, whereas euhedral and anhedral replacive anhydrites have depleted S. The Sr isotopic composition of most anhydrite forms indicates an Early Permian marine origin, however, Sr in anhydrite veins is slightly radiogenic compared to Permian seawater. The Sr isotopic compoition of bedded nodular mosaic anhydrite indicates as Leonardian seawater source of material. The γ 34S values are slightly enriched. relative to values predicted from the S age curve, suggesting an excursion of the S isotopic evolution trend of Early Permian seawater. Replacive nodular anhydrite 87Sr/ 86Sr ratios are slightly higher than those of bedded nodular mosaic anhydrite reflecting incorporation of Sr from older marine pore waters or replaced sediments or from dissolution of detrital siliciclastic minerals. Anhydrite paragenesis is interpreted from stratigraphic, mineralogic, petrographic, and isotopic data. Bedded nodular mosaic and replacive nodular anhydrite precipitated as marine evaporite strata prograded across underlying normal marine carbonate sediments. Siliified and coarsely crystalline nodules and anhydrite fossil-filling precipitated at essentially the same time as bedded and replacive nodular anhydrite but in environments where sulfate reduction was more extensive. Euhedral anhedral replacive anhydrite formed in shallower environments where S redox cycling occurred prior to CaSO 4 precipitation. Anhydrite vein-fills formed last and incorporated radiogenic Sr released during alteration of detrital siliciclastic grains.

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