CREATING GEOLOGIC MAPS IN A GIS ENVIRONMENT

West Virginia has a wealth of geologic and mineral resources information. Petroleum resources extraction began in 1859, and development of a digital oil and gas database at the West Virginia Geological and Economic Survey (WVGES) began in the late1960s. Large-scale coal mining in West Virginia, which began immediately after the Civil War, has generated vast amounts of coal resource and mining information. In 1995, the WVGES Coal Bed Mapping Program (CBMP) began developing a GIS-based mineral inventory. This inventory includes several GIS layers including structure grids, thickness grids, mining, and outcrops for each economically mineable coal bed. We have developed a system to produce geologic maps utilizing structure grids and other information produced by CBMP, shallow oil and gas information, and GIS analysis in combination with traditional fieldwork.

In northern West Virginia, Pennsylvanian unit boundaries are frequently associated with coals. Our mapping methodology involves several steps to produce a map of unit contacts and other horizons of interest. CBMP grid data is first evaluated to find geographic and stratigraphic gaps in coverage. Fieldwork and log data is then used to fill these gaps. Subtracting grid values from the digital elevation model values and contouring the zero line create an outcrop line of each critical horizon. These lines are subsequently smoothed, attributed, and plotted on topographic bases for field verification. If errors are found, the grid and outcrops are corrected and verified in the field. The final step is to use these lines as outcrop polygon boundaries and complete the geologic map. Lines are attributed based on certainty of the outcrops. Cross sections are constructed by sampling the gridded models of the critical horizons along section lines and plotting the results. Detailed models can be developed for areas of interest where adequate exposures and core data are available.