Database for the isopach map of the Brightseat Formation and Cretaceous–Paleogene boundary in Maryland and Virginia

The goal of the Atlantic Subsurface Stratigraphic Initiative (ASSI) is to create isopach and structural contour maps for all Coastal Plain formations within the Salisbury Embayment of Maryland and Virginia. Detailed information regarding thicknesses and extent of formations across state boundaries can then be utilized for more accurate documentation of the subaerial extent of aquifers across states. In support of this goal, lower Paleogene sediment elevation and thickness information from approximately 600+ data points from wells, cores, outcrops, and geologic maps were obtained from published and unpublished resources. Analyses started with production of a structure contour map of the unconformable contact of the Danian Brightseat Formation with underlying Cretaceous sediments, which represents the Cretaceous-Paleogene boundary in the Embayment. In addition, an isopach map of the Brightseat was produced using the Natural Neighbors interpolator in ArcGIS, creating a raster grid file that was symbolized every five feet. Results indicate a central depocenter with a thickness of 95 feet within Maryland with smaller thicknesses of the Brightseat surrounding. Although Danian sediments in southeastern Virginia were removed by the Chesapeake Bay impact event, up to 30 ft of possible Brightseat Formation has been identified from core and well data in southernmost Virginia.