NEW REFERENCE SECTIONS IN VIRGINIA AND WEST VIRGINIA OF THE UPPER DEVONIAN FOREKNOBS FORMATION NEEDED FOR SEAMLESS MAPPING ACROSS STATE AND QUADRANGLE BOUNDARIES IN THE CENTRAL APPALACHIAN BASIN

A challenge for the U.S. GeoFramework initiative (USGI) is to reconcile stratigraphic inconsistencies across geologic map boundaries. Many such inconsistencies exist within the Upper Devonian siliciclastic strata of the Appalachian Basin. These strata have been fundamental in linking the stratigraphic rock record to the Paleozoic tectonic evolution of North America, understanding Devonian basin paleogeography, and investigating geofluid reservoirs. The current divisions in the central Appalachian Valley and Ridge province (West Virginia, Virginia, Maryland, and Pennsylvania) are the Brallier Formation and the overlying Greenland Gap Group, which contains the Scherr and the Foreknobs Formations. The latter is subdivided into five named members (Mallow, Briery Gap, Blizzard, Pound, and Red Lick). During the last few decades, these stratigraphic conventions have resulted in inconsistent mapping at 1:24,000 scale across quadrangle and state boundaries. A proposed revision is to abandon the Scherr Formation and include that interval within the Brallier Formation along with the Mallow Member, placing the lower boundary of the Foreknobs Formation at the base of the base of the lowest pebble conglomerate associated with a ridge-forming sandstone (currently mapped as the base of the Briery Gap Member). This revision would leave the Foreknobs as the only unit in the Greenland Gap Group, and thus obviating the group name.

The utility of these stratigraphic revisions has been demonstrated within the Winchester 30 x 60-degree sheet through targeted mapping on lidar-derived base imagery. Additionally, this work will highlight new reference sections for this interval at relatively recently exposed roadcuts on US Rt 50 in VA/WV and Rt 48 in WV along with an effort now underway to record these sections as high-resolution 3D digital outcrop models. The results of this work will digitally preserve several well-exposed sections that can be used as standards in definition and revisions to these units and will help to resolve current stratigraphic inconsistencies across map boundaries.