ABSTRACT

Dolomitic quartzarenites and quartzwackes of the Keefer Sandstone, as observed in four cores, underwent a complex diagenetic history, beginning somewhat soon after deposition as a marine-shelf sand and continuing through progressively deeper burial. Accompanying burial was a corresponding rise in temperature, to a maximum of about 100° C. The diagenetic processes include cementation by quartz, calcite, anhydrite, and gypsum followed by extensive dolomitization.

During early diagenesis, secondary quartz formed as syntaxial overgrowths on detrital grains. An initial stage of overgrowth development appears to be as a "meniscus" cement around tangential grain contacts. As burial increased, a second generation of cement precipitated. In Roane County, West Virginia, this was anhydrite and gypsum, precipitating from hypersaline waters. Formation waters were slightly less saline in Wayne County where poikilotopic calcite cement developed. Dolomitization was the last major diagenetic event. Dolomite mostly replaced earlier cements, but often it extended beyond these and replaced quartz grains (corrosion along margins), fossils, and clay minerals.

Final porosity is low, ranging from 1 to 6 percent. Most primary pore space has been occluded by the two generations of cement and dolomite. Minor secondary porosity is due to the partial dissolution of calcite grains and cement.