EMSIAN-EIFELIAN (LOWER–MIDDLE DEVONIAN) OF VIRGINIA–WEST VIRGINIA, AND A BASINWIDE SYNTHESIS AND SEQUENCE STRATIGRAPHY

Event and cyclic stratigraphic correlations permit incorporation of Emsian-Eifelian strata in VA and WV into a basinwide stratigraphic synthesis and sequence framework established in the central to northern part of the Appalachian Basin (NY, PA, NJ, MD, OH). Strata included in the synthesis are the Huntersville, Beaverdam/Needmore, Bobs Ridge, “Tioga”, and lower part of the Millboro/Marcellus formations. These comprise strata correlative with Emsian-Eifelian strata of the Esopus, Schoharie, Onondaga, Union Springs, and Oatka Creek formations of New York and equivalents across the basin. In the southern part of the VA-WV outcrop belt (Wytheville, VA; Frost WV) the Huntersville is correlative with the Esopus and Schoharie of New York; a glauconitic sandstone within the chert is correlative with the coarse cap of the Esopus. The succeeding glauconitic Bob’s Ridge SS is laterally equivalent to the Edgecliff Member (Onondaga Fm.); overlying shales are correlative with the Nedrow, Moorehouse, and Seneca members (Onondaga Fm.). Stratal patterns in northern VA-WV outcrops (Hedgesville, WV; Gainesboro, VA) are consistent with central Pennsylvania; a lower black shale overlain by calcareous shales, overlain by interbedded argillaceous limestones and shales, successively (=Esopus, Schoharie, and Onondaga). Across the region, a shallowing-deepening transition in the Purcell Member marks the Union Springs-Oatka Creek contact. Including the Oriskany SS below, six Pragian-Eifelian stratigraphic sequences are recognized. These comprise: bulk of Oriskany, where not underlain by a widespread lowstand unconformity; upper Oriskany and Beaverdam/lower Huntersville; Needmore/upper Huntersville; limestone–calcareous shale/Bobs Ridge and overlying shales up to below the Tioga A bentonite bed; Tioga A-G zone to upper Purcell; overlying black shales, including upper Purcell. The new correlations show that the “Tioga middle coarse zone” underlies the classic “Tioga A-G” bentonites of Pennsylvania and New York, and occurs in strata correlative with the Nedrow and or Moorehouse members (Onondaga Fm.). The Tioga "middle coarse zone" is reduced to absent from the northern Virginia-West Virginia outcrop belt into the central to northern portions of the basin.