GIS AND GPS UTILITY IN THE GEOLOGIC MAPPING OF COMPLEX GEOLOGIC TERRANE ON THE MASCOT, TENNESSEE 7.5' QUADRANGLE

The Trimble GeoExplorer® 3 Global Positioning System (GPS) and the ESRI ArcView® 3.2 Geographic Information System (GIS) software were used to compile geologic field information and present the results of geologic mapping in the Mascot, Tennessee 7.5' Quadrangle. Using the Trimble GPS data dictionary feature, a geologic data spreadsheet was set up which contained attribute fields such as lithology, rock color, bedding thickness, formation contacts, etc. This GPS spreadsheet was designed for rapid data input by predefining many of the geologic attributes (e.g., fine-grained limestone, coarsely crystalline dolomite, dark gray, light gray, etc.) in dropdown menus. Numerical fields were included in the database for azimuth degree attitudes of bedding, joints, cleavage, fold axes, etc. Additional pertinent geologic information on soil, chert, karst, mining, etc. could also be input in the database by menu or text fields. These geologic attributes were usually input while the GPS unit collected the satellite-based coordinate information. After returning to the office, the coordinates were differentially corrected to a local base station to improve accuracy. The geologic information was exported as a dBase file and used in ArcView® to produce a preliminary geologic compilation map. This compilation map included separate point themes for lithology, bedding attitudes, formation contact points and other pertinent geologic features recorded in the database. This compiled information was used to draw in contacts and faults as line themes to produce the “final” version of the Mascot Geologic Quadrangle map in ArcView®.

The GPS unit facilitated accurate location of station points in complex geologic areas where formation units were repeated within short distances due to imbricate faulting as well as location in areas with few useful landmarks. Hardcopies of the topographic map were still needed for navigation and station point location and field books were needed for lengthy geologic descriptions, sketches, etc. The ESRI GIS software enabled accurate plotting of the GPS coordinate information and manipulation and display of the database attribute information. Despite minor GPS and GIS problems in the field and office, the two systems worked well in unison to complete the task of geologic mapping in the Mascot Quadrangle.