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Thermal maturity of the Silurian and Lower Devonian rocks in Virginia west of New River decreases southwestward. Oil and gas shows are reported.
The total thickness of Lower Devonian plus Silurian strata ranges from 52 to 1,000 ft (16 to 305 m), with a maximum in Buchanan County. Sandstones were derived from sources southeast of the central Appalachian basin, some from lands southeast of the outcrop belt, and some formed by reworking of sandstones within the outcrop area. Sandstones change northwestward to shales in the Clinch and Rose Hill Formations. In the Middle Silurian and Helderberg Group, sandstones grade northwestward to limestones. Limestones in the Hancock Formation change westward to dolomite. The Onesquethaw Stage is represented by sandstone, chert, and limestone assigned to the Wildcat Valley and Huntersville Formations.
In the Middle Silurian (Keefer or "Big Six" sandstone) and Early Devonian (Wildcat Valley Sandstone), longshore currents carried sand across the southwest end of the basin toward Kentucky.
Several regional unconformities are present. These unconformities are mostly related to sea level changes, but some are probably tectonic in origin. Five unconformities are significant: (1) at base of Silurian, (2) at base of upper Helderberg over much of the area, (3) at base of Oriskany Sandstone, (4) at base of Huntersville Formation, and (5) at base of Upper Devonian black shales in extreme western Virginia, where Chattanooga Shale overlies Middle Devonian to Middle Silurian strata.
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