Date of Graduation

1991

Document Type

Dissertation/Thesis

Abstract

The Oriskany Sandstone in West Virginia is a hybrid sandstone and exhibits a high degree of variability in the amount of quartz and carbonate framework constituents. Fluctuating energy conditions and sedimentation rates, distance from the source area, and changes in the depositional environment are responsible for the lithologic variation. Four facies have been identified in the Oriskany. Facies 1 is a very fine-grained, bioturbated calcareous sandstone to sandy limestone, and contains a diverse marine fauna. It was deposited in a quiet water environment, near wave base, and represents the beginning of clastic influx into the shallow Oriskany sea. Facies 2 is a medium-grained, well-sorted, crossbedded quartz arenite that was deposited as a submarine sand ridge by storm or tidal currents. Facies 3 is a medium- to fine-grained, bioturbated and laminated fossiliferous sandstone with interbeds of sandy limestone. It records fair-weather deposition in an environment characterized by variable wave and current energy. Facies 4 is coarse-grained to pebbly, fossiliferous sandstone overlain by medium- to fine-grained laminated sandstone. The facies typically exhibits an erosional base and infiltration fabrics, and represents storm events that periodically interrupted normal shelf sedimentation. The Oriskany shows an overall regressive pattern of sedimentation. Best illustrated in Greenbrier 6, quartz grain size coarsens upward as does the amount of quartz. Lateral changes are also recorded in fair-weather and storm deposits. The Oriskany in eastern cores is more quartzose and storm deposits are thicker, reflecting close proximity to the eastern source area. The sandstone in the east-central cores is thinner and more calcareous. In the western cores storm deposits thin to several millimeters in western cores suggesting deposition in more distal regions of the basin. Lithology and the diagenetic processes of cementation and dissolution have exerted the greatest influence on porosity. In eastern cores all interstitial porosity has been occluded by secondary quartz and late stage Fe-calcite cement. In western cores there is a significant increase in interstitial porosity. Pore types have been identified as (1) primary intergranular pores, (2) solution pores, (3) recrystallization/silicification pores, (4) intercrystalline pores, and (5) combination pores. Marion 321 and Pocahontas 23 showed less than 3% porosity formed by incomplete cementation (intergranular) with minor amounts of other pore types. Samples from Kanawha County, with an average of 12% porosity, showed a predominance of primary intergranular porosity. In Wood 1266, with an average of 7% porosity, secondary pores account for most of the porosity, except near the top where primary intergranular porosity dominates. Porosity in the sandy dolomitic Oriskany in Johnson 31305, averages 12%, and is dominated by intercrystalline pores occurring between replacement and cement crystals of calcite and dolomite.

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