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Diagenesis and Porosity Development in Oriskany Sandstone of West Virginia

K. R. Bruner, M. T. Heald

Petrographic investigation of 12 Oriskany cores from West Virginia and surrounding states shows a complex relationship between diagenesis and porosity development. Deposited as a fossiliferous marine sandstone, the Oriskany is cemented by calcium carbonate and/or quartz, depending on the predominant clastic material (fossils or quartz). Porosity ranges from less than 2% to approximately 8%, and pore types vary across the state. Primary-intergranular and fracture are the major porosity types observed in all cores. Primary porosity is best developed in central and western areas where cementation is incomplete. Petroleumlike materials (paraffin in nature) commonly occur as pore linings or inclusions in secondary quartz. To the east, fracture porosity dominates in tightly cem nted sandstones, but vertical and horizontal fractures are observed in all cores. Many fractures, however, have been healed with quartz and calcite. Minor amounts of carbonate leaching supplements primary porosity. In Marion County, partial replacement of carbonate fossils by fringing microcrystalline quartz, along with recrystallization and subsequent leaching of the carbonate, has produced distinctive secondary pores. Porosity increases dramatically in western areas of the state. In addition to primary and secondary porosity, microcrystalline porosity within chert and phosphatic zones is present. Other minor and relatively insignificant porosity types in the Oriskany from all regions include intraskeletal, intragranular quartz and feldspar, and intercrystalline dolomite. Although overa l porosity is low, intergranular porosity and fracture porosity are best developed in quartz-rich zones.

AAPG Search and Discovery Article #91031©1988 AAPG Eastern Section, Charleston, West Virginia, 13-16 September 1988.