Petrology, Diagenesis and Depositional Environment of the Tonkawa Sandstone in Southwestern Dewey County, Oklahoma

Abstract

The Pennsylvanian Tonkawa Sandstone of the Douglas Group of the Virgilian Series was studied in southwestern Dewey County, Oklahoma. Techniques employed included stratigraphic cross-section preparation, structural and isopachous mapping, analysis of core, and thin-section microscopy coupled with X-Ray diffraction. The Tonkawa Sandstones are present primarily as elongate and coalescing lobes which are thought to record deposition in deltaic environments during overall regression. Important Tonkawa Sandstone reservoir facies are interpreted to be distributary mouth bars and distributary channel fill sandstones. The Tonkawa Sandstones are very fine and fine grained, and moderately to well sorted. They classify as sublitharenites. Monocrystalline and polycrystalline quartz, metamorphic rock fragments, feldspars, and muscovite are the main constituents. Diagenesis has led to four major cementing minerals including silica, dolomite, calcite, and siderite. These cements are present in highly variable amounts. Chlorite is the most abundant authigenic clay mineral in the Tonkawa Sandstone. Kaolinite is locally abundant. Authigenic illite is a minor constituent. Porosity in the Tonkawa is mostly secondary. The development of secondary porosity is largely due to the dissolution of feldspars, fossil fragments, and carbonate cements.