REVISITING THE CLASSICS: INTERMEDIATE-SCALE COMPILATION MAPPING IN THE VALLEY AND RIDGE OF CENTRAL PENNSYLVANIA – METHODS, PRELIMINARY RESULTS, AND PITFALLS

The Pennsylvania Geological Survey (PaGS) is currently conducting intermediate scale (1:48k) compilation mapping in the Valley and Ridge Province in central Pennsylvania for a block of nine 7.5-minute quadrangles. Large scale (1:24k) bedrock geologic maps for eight of these quadrangles (McAlveys Fort, Barrville, Allensville, Belleville, Lewistown, Newton Hamilton, McVeytown, and McCoysville) covering portions of Centre, Huntingdon, Mifflin, Juniata, and Perry Counties were completed in the 2000s and the early 2010s by two teams of authors. The Burnham 7.5-minute quadrangle, the northeastern-most in the study area, is currently in draft status and will be completed as part of this effort. The PaGS will produce a seamless, intermediate scale bedrock geologic map, establish a stratigraphic framework for future mapping efforts in this area, and outline methods for future compilation mapping projects as part of this study. Discontinuities at quadrangle boundaries (colloquially referred to as border busts or border faults) are present and will be rectified via targeted field mapping and review of imagery derived from QL2 lidar data. Similarly, legacy map contact placement will be evaluated for conformation with topography, as the legacy maps were produced before the widespread availability of lidar and were drawn on topographic base. When available, the original field notes will be referenced in order to understand the rationale for contact placement and structural interpretations. The level of detail within the legacy field notes is sometimes discordant. This has highlighted the need to establish standardized requirements for field notes used in future mapping projects. Similarly, variations in GIS data organization between the legacy publications has underscored the need to utilize best practices for archiving digital data. To this end, the PaGS is leveraging ESRI ArcGIS Online (AGOL) and FieldMaps to standardize data collection between different authors. Consistent schemes for mapping at scales smaller than 1:24k will be established following other small-scale mapping efforts along strike to the southwest. Compilation of large-scale maps within a regional context will aid in identifying local variability and may help to resolve stratigraphic issues at the basin scale.