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Ninety Hunton cores have been studied, from which 37 Silurian samples from 21 wells were tested for porosity and permeability. Each sample was examined in thin section and was analyzed chemically for CaCO3, MgCO3, and HCl insolubles. The specimens range from limestones and calcareous mudstones having less than 1% MgCO3 to crystalline dolomites with more than 43% MgCO3. Porosity ranges up to 21%, and permeability to 305 md. Rocks with appreciable porosity and permeability have a circumscribed range in texture and composition: specimens with more than 5% porosity are confined to crystalline dolomites with more than 35% MgCO3 (65% dolomite), and those with more than 10% porosity to dolomites with more than 37% MgCO3 (80% d lomite). Much of the pore space is in the form of fossil molds and vacuities in the matrix surrounding oolites. The fossil molds were formed by leaching, and the porous oolites probably result from a primary porosity increased by dissolution. Not all dolomites have high porosity, and several specimens with more than 35% MgCO3 have less than 1% porosity; the latter condition appears to result from preservation of the fossils by calcspar and dolospar rather than as molds. Leaching of fossils and preservation by spar are confined to crystalline dolomite, thus indicating a genetic relation to dolomitization. A suggested sequence of events in the development of porosity is dolomitization and leaching, followed by some secondary cementation of pore space by spar.
Present information indicates a geographic concentration of these porous Silurian dolomites in the north-central and western parts of the Anadarko basin (data on the deeper parts of this basin are lacking).
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