GEOPHYSICAL DATABASES AND GEOLOGIC MAPPING IN MINNESOTA: A WORK IN PROGRESS

Geologic mapping, a primary responsibility of the Minnesota Geological Survey (MGS), is commonly supported by geophysical data. Acquisition of geophysical data leads to a mixture of files that are not easily maintained or accessible to the map-makers. Advances in computer technology and web-based delivery of maps and data are, however, enabling the MGS to provide a more unified system of data management and use that facilitates geologic mapping. Because bedrock outcrops in Minnesota are scarce, gravity and magnetic data are crucial to mapping Precambrian terranes. The geophysical data, acquired over the last 40 years have been recast into GIS compatible formats and made available to MGS geologic mappers. More than 560,000 line kilometers of high-resolution aeromagnetic data, as well as a recently upgraded gravity data-base of nearly 58,000 stations, have been compiled into geo-referenced grids of both original and derivative-enhanced data. A rock properties data-base, consisting of all readily available determinations of density, magnetic susceptibility, and natural remanent magnetization, is now available as a 4,100-line dbf (UTM coordinates) file and posted with other geologic data on the MGS web site. Using any GIS system, these grid and point data can be easily queried, extracted and combined with other data to help produce a geological map. Other digital developments at the MGS also benefit geologic mapping. Foremost among these is the water well database, which consists of over 300,000 wells with verified locations and geologic data. These geo-referenced data are used for a variety of applications, including ground water analysis, geologic cross-sections, and mapping of surface and subsurface geology. Another data management project is a geologic mapping system (GEMS) that that allows consistent entry of field measured structural and geologic data into the ArcView GIS application. Currently our geologic mapping efforts are a hybrid of old and new methods. We are working towards an integrated system of digital data and GIS tools that assist MGS geologists with creating geologic maps and making at least some of the information available to professionals outside of the MGS.