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Paper No. 93-17
Presentation Time: 9:00 AM-1:00 PM
THE NEW DIGITAL SURFICIAL GEOLOGIC MAP OF VIRGINIA: A COMPLEMENT TO THE 2021 GEMS LEVEL-2 BEDROCK GEOLOGIC MAP OF VIRGINIA
In 2021, Virginia Energy (serving as Virginia’s Geological Survey) delivered to the USGS National Cooperative Geologic Mapping Program updated statewide digital geologic maps for the Commonwealth. Previously, statewide geologic maps were produced at 1:500,000-scale in 1916, 1928, 1963, and 1993. This 2021 “born-digital” map product was completed using the USGS Geologic Map Schema (GeMS) geodatabase format and compiled at a nominal scale of 1:250,000. In addition to bedrock contacts and map unit polygons, Virginia Energy also delivered derivative surficial map unit polygons. This is the first time that a comprehensive surficial geologic map was attempted at the statewide scale. Surficial units were identified using published geologic maps and interpreted using a compiled 10-meter resolution statewide LIDAR DEM assembled from 24 separate 1-to-5-meter LIDAR datasets generated between 2010 and 2019. Surficial units were digitized on-screen as part of the MapUnitOverlayPolys feature class at 1:24,000-scale. Over 7600 surficial features were digitized including alluvium, colluvium, fan deposits, river terraces, artificial fill, and Carolina Bays. Significant effort was made to update coastlines along the Chesapeake Bay and inland rivers. These boundaries served as contacts for both the surficial units and bedrock units, and contributed to database topology. In the Coastal Plain Province, east of the Fall Zone, some surficial deposits also serve as map units on the bedrock geologic map (e.g. Miocene/Pliocene-aged terrace deposits). Whenever possible, surficial Coastal Plain units were migrated from geologic map unit polygons to surficial map units, exposing older bedrock units underneath in the final iteration of the bedrock polygons. Along with the statewide geologic map, the surficial geologic map is currently in review. Virginia Energy will publish these finalized datasets as part of our digital web map services in 2023.