PRELIMINARY BEDROCK GEOLOGIC MAP OF THE CENTRAL AND NORTHEASTERN UNITED STATES

The USGS National Cooperative Geologic Mapping Program’s (NCGMP) National Geologic Synthesis project is creating new national geologic maps by synthesizing published maps into an integrated database and producing four derivative map layers; Quaternary, Earth’s Surface, Bedrock, and Precambrian. These four layers accommodate the significant differences in geologic mapping “style” across the country, most notably the difference between separate Quaternary and bedrock maps in the glaciated regions, and single-layer earth surface maps elsewhere. Derivative map layers are faithful to, and retain information from, the original source maps. They are composited together to form a consistent map, to which is applied a set of synthesis map units on top of the original map units, presenting a harmonized representation. These synthesis map units are procedurally applied to the original data based on standard, searchable attributes that are assigned to each original map unit (e.g., age and geologic material). This facilitates rapid assembly of derivative map products while preserving information from the source maps (e.g., original unit descriptions). Here we present a preliminary synthesized bedrock geologic map of the northeastern and central United States. This map is composited from 22 source maps in NCGMP’s Geologic Map Schema (GeMS) format at a target scale of 1:500,000 (source map scales vary from 1:670,000 to 1:100,000 scale depending on the region). Faults and contacts between units are consistently attributed using a standard symbology but otherwise have not been modified. About 3000 thousand source map units (with their original descriptions preserved) are synthesized by age and lithology into about a hundred compilation units, reflecting the strategy employed in earlier national and continental scale geologic maps. We further demonstrate the flexibility of this approach by presenting additional derivative maps produced by querying the geodatabase.