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The Upper Silurian Henryhouse Formation, of the Hunton Group (Upper Ordovician-Lower Devonian), is a major hydrocarbon reservoir in the Anadarko basin. Detailed examination of Henryhouse cores were conducted at many localities in the basin, west of T10 W. Sedimentary structures, lithology, fossil content, and fabric relationships were used as criteria to recognize various depositional facies. Subtidal, intertidal, and supratidal facies can be distinguished readily, and their spatial relationships consistently indicate a shallowing-upward sequence. Previously unreported nodular anhydrite (replaced and unreplaced) occurs at the top of the sequence, suggesting that hypersaline conditions developed in supratidal environments.
Three stages of dolomitization were documented in the Henryhouse Formation. Petrographic, cathodoluminescent, and isotopic techniques were used to investigate the genesis and textural relationships of various dolomite types. The following paragenetic sequence was discerned: (1) penecontemporaneous hypersaline dolomite occurring as brownish, hypidiotopic, 60-80 µm rhombs concentrated in the supratidal and intertidal facies; (2) marine water-fresh water mixing dolomite occurring as white rims around preexisting hypersaline dolomite and as anhedral, white rhombs in vugs and molds; (3) deep burial vug, mold, and fracture-filling baroque dolomite.
Cathodoluminescence reveals that typical Henryhouse dolomite exhibits dully luminescing cores with outer bright rims corresponding to the dark core and light rim seen in plane light. This zonation represents two stages of dolomitization.
Oxygen isotope ratios range from -2.2 to -9.9 (mean -4.6) ^pmil vs. PDB, whereas the carbon isotope ratios range from 0 to + 3.3 (mean + 1.4) ^pmil vs. PDB. The considerably light ^dgr180 reflects a fresh water influence. Values of ^dgr13C may represent initial composition because of their resistance to alteration.
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