PRELIMINARY PRECAMBRIAN GEOLOGIC MAP OF THE CENTRAL UNITED STATES

The United States Geological Survey’s (USGS) National Geologic Synthesis (NGS) project is compiling published maps into an integrated database and producing four new derivative maps of the conterminous United States depicting Quaternary, Earth’s Surface, Bedrock, and Precambrian geology. These four layers accommodate the significant differences in geologic mapping styles throughout the country, including the separation of subsurface Precambrian rocks as its own layer in the central United States. Derivative maps are faithful to, and retain information from, their original sources. They are composited together to form a consistent map, to which is applied a set of synthesis units based on standard, searchable attributes (e.g., age, geologic material), resulting in a harmonized representation. This facilitates rapid assembly of derivative products while preserving information from their published sources (e.g., unit descriptions).

Here we present a preliminary synthesized Precambrian geologic map of the central United States, merged from 11 sources in the National Cooperative Geologic Mapping Program’s (NCGMP) Geologic Map Schema (GeMS) format at a target scale of 1:1,000,000. Faults and contacts are consistently symbolized according to the Federal Geographic Data Committee (FGDC), and about 500 unique units were joined by age and lithology into approximately two dozen compilation units, reflecting a strategy employed in earlier national- and continental-scale geologic maps. Source maps include outcrop information in the Rocky Mountains and Great Lakes where present, but primarily represent compilations of borehole and geophysical data. Prominent structures include the Midcontinent Rift, Medicine Hat block, Wyoming and Superior cratons, Great Falls tectonic zone, and Trans-Hudson and Central Plains orogens. Gaps in western Nebraska highlight the need for new subsurface mapping in the midcontinent. This work supports mineral exploration and resource assessments, as well as scientific research related to paleotectonic models and basin analysis.