Paleokarst Within the Knox Group of Alabama, East Side of the Black Warrior Basin
James Lee Wilson, Patrick Medlock, Roger Sels, 1993. "Paleokarst Within the Knox Group of Alabama, East Side of the Black Warrior Basin", Paleokarst Related Hydrocarbon Reservoirs, Richard D. Fritz, James L. Wilson, Donald A. Yurewicz
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Rocks of the Cambro-Ordovician systems are exposed in the Appalachian fold belt in the states of Tennessee, Virginia, Georgia, and Alabama, and extend westward from the southern Appalachians under the Black Warrior Basin of Alabama-Mississippi. These strata are practically all carbonate and were deposited on the eastern and southern passive margins of the North American craton. The great thickness of strata (up to 7000 ft. for the Lower Ordovician to Middle Cambrian) constitutes what R.N. Ginsburg has termed the Great American Bank, a vast Early Paleozoic carbonate platform extending from Newfoundland down the Appalachians, completely across the southern part of North America, and part way up the western part of North America, thus encircling more than half of the craton. The typical bank facies extends far up on the eastern craton, its characteristic strata being present as far north as the Canadian border. Throughout this extensive area the Cambro-Ordovician facies are very similar (Figs. 1 and 2). The Middle and Upper Cambrian develop sandy "pinch out" edges along the Transcontinental Arch and are onlapped by the Lower Ordovician. Practically all of the Lower Ordovician carbonate facies consist of shallow, restricted marine, dolomitized, upward shoaling, subtidal to tidal flat cycles. These occur over a broad area of more than 1000 miles (e.g., from the Oneota-Shackopee dolomites of Wisconsin to the Knox Group of the Warrior Basin in Alabama (Fig. 3 and 4).
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This volume is a compilation of papers relative to paleokarst and associated reservoirs. The examples illustrate many of the rock types, and stratigraphic, structural, and paleotopographic features of carbonate strata which result chiefly from solution and collapse due to ingress of meteoric waters at and below unconformities. Examples presented here range from settings with considerable dissolution and collapse to those with significant unconformities but little evidence of meteoric alteration. It is estimated that 20–30% of recoverable hydrocarbons are in some way related to unconformities. Paleokarst reservoirs may also be important future reservoirs for application of horizontal drilling technology.