ACHIEVING A COMMON STRATIGRAPHIC FRAMEWORK FOR SEAMLESS REGIONAL GEOLOGIC MAPPING IN THE NORTH-CENTRAL APPALACHIAN VALLEY AND RIDGE PROVINCE OF VIRGINIA, WEST VIRGINIA, MARYLAND, AND PENNSYLVANIA

The U.S. Geological Survey (USGS) has a goal of achieving a seamless geologic map of the nation by the year 2030. In the Appalachian Valley and Ridge Province, numerous stratigraphic nomenclatural inconsistencies exist between adjacent states that require reconciliation. To meet this goal, a regional workshop organized in August 2022 by the USGS Appalachian Basin Geologic Mapping Project brought together representatives from the geologic surveys of Virginia, West Virginia, Maryland, and Pennsylvania to achieve consensus on a common stratigraphic framework for seamless mapping across the north-central Appalachians. A pre-workshop survey given to all invited participants helped identify the key stratigraphic issues to be addressed. The workshop opened with presentations by regional experts on each of the six primary Paleozoic systems, as well as on surficial mapping. A field trip on the second day allowed on-the-outcrop discussions, followed by two days of round-table discussions framed around a straw-man stratigraphic chart summarizing existing nomenclature and the geographic use of names taken from the U.S. Geologic Names Lexicon ("Geolex"). For each unit having problematic mismatches between geologic maps, the focus was on addressing three questions: (1) what is the nature of the issue?; (2) can the issue be resolved through discussion in the room?; (3) does the issue require additional research to be resolved?

The result of this workshop was a revised stratigraphic chart for Paleozoic strata ranging from the Cambrian to the Pennsylvanian system with mutually agreed-upon stratigraphic names and map units to facilitate 1:100,000 scale compilations across these four state boundaries. Pragmatic solutions to facilitate seamless mapping primarily included consensus on contact placement and grouping of units within Silurian, lower and middle Devonian, and Mississippian carbonate and clastic strata. The new framework and its divisions will be formally published through the USGS to serve as a tool for future consistent geologic mapping.