Late Devonian fossils and position of the Frasnian-Famennian boundary in the Foreknobs Formation of Virginia and West Virginia

Abstract

ABSTRACT The Upper Devonian Foreknobs Formation is a series of sandstones and siltstones that outcrops in the central Appalachian Basin from Pennsylvania south into Virginia and West Virginia. The Foreknobs Formation is generally regarded as the delta slope portion of the Catskill clastic wedge (= Catskill delta) occurring between the dark marine lithologies of the underlying Brallier and Scherr Formations and the younger fluvial red beds and conglomerates of the overlying Hampshire Formation. Progradational and retrogradational pulses of the clastic wedge are recorded in the alternating siltstones and sandstones before grading into nonmarine lithologies at its top. Well-preserved fossils are very abundant within the Foreknobs Formation. They have aided in locating the Frasnian-Famennian Stage boundary and have provided important information regarding its namesake extinction event. The progradation of the clastic wedge during Foreknobs Formation deposition allowed for both shallow- and deep-water environments to exist up to and across the Frasnian-Famennian boundary, which may have contributed to some uncertainty in correlating the lithostratigraphic position of the boundary with the biostratigraphic signature of the extinction event.