COMPUTER-GENERATED GEOLOGIC MAP OF THE BLOOMINGTON 7.5-MINUTE QUADRANGLE, INDIANA

The Indiana Geological Survey has completed a three-year geologic mapping project in Monroe County Indiana, with support from USGS STATEMAP. This project anticipated the need for geologic information to guide planning in and around Bloomington, a major population center along the proposed corridor for the Interstate 69 extension from Indianapolis to Evansville. The recently published geologic map of the Bloomington Quadrangle, located in the center of Monroe County, provides detailed mapping where Interstate 69 interchanges are planned and where urban growth is likely. The map will aid planners in assessing geologic hazards, such as karst features, and evaluating resources of dimension stone found in the Salem Limestone (Mississippian) and crushed stone resources of the Blue River Group (Mississippian).

The Bloomington Quadrangle component of the Monroe County project applied Indiana Geological Survey three-dimensional computer mapping techniques to large-scale (1:24,000) geologic mapping. The map was created by modeling rock unit boundary surfaces with computer gridding and contouring software using a variety of data sources. The rock unit models were tested to ensure that isolated exposures and subsurface occurrences of map units would fall between the appropriate upper and lower contacts. Outcrop and subcrop lines were generated by computing intersections between the contact-surface models and the bedrock-surface model. The resulting intersection lines were used to generate the bedrock-unit polygons shown on the geologic map. Unconsolidated deposits shown on the map were hand-drawn and then digitized, to ensure proper registration with topographic features.

The three-dimensional geologic modeling procedures used to create the Bloomington Quadrangle geologic map are designed to facilitate the production of derivative map products that will complement the geologic map and address specific planning needs. Map users will also be able to link to the project database for more detailed information and updates, as well as having access to geographic information system layers that are compliant with North American Geologic Map Data Model standards.