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The Viola Limestone in the Arbuckle Mountains was deposited on a carbonate ramp within the southern Oklahoma aulacogen. Depositional environments within the Viola ranged from anaerobic deep-ramp, through dysaerobic mid-ramp, to fully oxygenated shallow-ramp conditions. Corresponding microfacies in the southeastern Arbuckles include, respectively, nonbioturbated, spiculitic pelletal packstones; thoroughly
bioturbated fossilferous wackestones and packstones; and pelmatozoan packstones and grainstones.
A complex diagenetic history has occluded virtually all primary porosity within the Viola. Petrographic evidence suggests that the following approximate sequence of diagenetic events has occurred; (1) microboring and subsequent micritization of bioclasts to form micrite envelopes; (2) very early submarine cementation that bound the loosely sorted allochems and partly occluded porosity, characterized by drusy overgrowths on trilobite and brachiopod fragments, bladed, void-filling cement, and turbid, inclusion-rich syntaxial overgrowths on pelmatozoan fragments; (3) initial compaction evidenced by local fracturing of elongate bioclasts; (4) neomorphism, including the inversion of aragonitic allochems to calcite and the recrystallization of micrite to microspar and pseudospar in the pres nce of low-salinity pore fluids; (5) freshwater cementation dominated by clear syntxial overgrowths on pelmatozoan fragments and pore-filling mosaic calcite that filled virtually all remaining pore space; (6) selective dolomitization; (7) silicification, including the formation of chert nodules and the replacement of bioclasts and calcite cements by microgranular quartz and/or lutecite; (8) compaction and pressure solution, probably due to deep burial, characterized by nonsutured seam stylolites, sutured seam stylolites oriented subparallel to bedding, and sutured grain boundaries; and (9) tectonically imposed pressure solution indicated by sutured seam stylolites oriented at high angles to bedding that developed during the late Paleozoic deformation of the Arbuckle Mountain.
The Viola Limestone is known as a reservoir rock and possible source unit for hydrocarbons throughout much of south-central Oklahoma. Thorough understanding of the nature and timing of diagenetic events is important for the further economic development of the Viola Limestone and other similar carbonate ramp deposits.
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