187 GIS and GPS Utility in the Geologic Mapping of Complex Geologic Terrane on the Mascot, Tennessee 7.5’ Quadrangle By Barry W. Miller and Robert C. Price III
Tennessee Department of Environment and Conservation Division of Geology 3711 Middlebrook Pike Knoxville, TN 37921 Telephone: (865) 594-6200 Fax: (865) 594-6105 e-mail: [email protected], [email protected]
INTRODUCTION specifically, the ability to input data directly into the GPS unit would affect the geologic mapping process. The bedrock geology of the Mascot, Tennessee 7.5’ Quadrangle was mapped in 2003 under a STATEMAP METHODOLOGY AND RESULTS cooperative agreement between the U.S. Geological Sur- vey and the Tennessee Division of Geology. The Mascot Quadrangle is located in the Valley and Ridge Province of Utilizing the Trimble GeoExplorer 3 GPS east Tennessee; the bedrock consists of folded and faulted and Data Dictionary for Geologic Field Data Cambrian and Ordovician strata (Figure 1). The Tennes- Collection see Division of Geology purchased two Trimble GeoEx- plorer 3 Global Positioning Systems (GPS), which were A GPS data dictionary contains a catalog of the used in conjunction with ESR ArcView 3.2 Geographic features and attributes pertinent to an endeavor or project. nformation System (GS) software to record the geologic It is used in the field to control the data collection of a field data and present the results of the geologic mapping. feature (e.g., an object, geologic station, rock outcrop, The decision to utilize GPS technology for this map- etc.) and its attributes (e.g., object information, soil type, ping project was initially based on the geologic complex- rock lithology, etc.). Using the Trimble GPS data diction- ity of the Mascot Quadrangle and the need to improve the ary, a geologic data spreadsheet was created to record the accuracy of geologic station location. The Division of Ge- important geologic aspects and their values relevant to the ology had previously used GPS units to locate oil and gas mapping of the Mascot Quadrangle (Figure 2). Recording wells in a well inventory study, but the majority of well geologic observations involved scrolling through attribute data was input into a field book or datasheet. The Mascot windows (e.g., lithology) and choosing their values (e.g., project would help determine how the utility of GPS and, shale, limestone, sandstone) from a predefined drop-down
Figure 1. Location of the Mascot 7.5’ Quadrangle. 187 188 DGTAL MAPPNG TECHNQUES ‘06
Figure 2. The GPS data dictionary (top) for the Mascot 7.5’ Quadrangle with expanded menu selections for the geologic attributes (bottom).
menu. Attribute menu nomenclature was abbreviated to fit using a menu keypad. The data dictionary and accom- the constraints of the drop-down menu screen on the GPS panying spreadsheet were updated as needed when new unit. Numerical fields for strike and dip of planar features useful mapping criteria were observed. such as bedding, joints, and cleavage required direct user The geologic data generally were input via the data input. Strikes were measured in azimuth degrees (using dictionary, while the GPS unit collected the satellite- the right hand rule) to facilitate the proper rotation of geo- based coordinate information. The latitude and longitude logic symbols when compiling the data in ArcView. Two coordinates were collected by the GPS unit in a decimal general geologic attribute fields containing drop-down degree format so that, later, field station locations could menus of additional pertinent geologic information ac- be plotted in ArcView (Figure 3). After returning to the quired during mapping include soil character, chert type, office, the data files were downloaded to a computer, and karst features, and mining activities. A final comment field the coordinates were differentially corrected to a local allows the mapper to input directly any other observations base station over the Internet to improve accuracy. GS AND GPS UTLTY N THE GEOLOGC MAPPNG OF COMPLEX GEOLOGC TERRANE 189
Figure 3. Example of part of the fieldwork database for the Mascot 7.5’ Quadrangle.
Utilizing ESRI ArcView 3.2 GIS Software line themes on the geologic compilation map (Figure 7). and the GPS Database to Produce the Mascot To produce the “final” version of the geologic map Quadrangle Geologic Map in ArcView, stratigraphic contacts and fault lines were di- vided into solid (exactlocation), dashed (approximateloca- tion), and dotted (coveredlocation) line segments based on The differentially corrected GPS data file (.cor) was contact location certainty. These contact line themes were exported in dBase format and transferred into a compilation converted to formation polygon themes. The formation database that was used in ArcView to compile a prelimi- polygons were colored and displayed beneath a partially nary geologic map. Additional fields in the compilation transparent raster topographic base map. The color pallet database are included to plot the symbol orientation for of the raster map was adjusted such that the underlying planar features (SYMROT) and print selected geologic polygons could be displayed while important features symbols (PRNT_STK) and dip numbers (PRNT_DP#) in such as roads, streams, and contour lines also were vis- ArcView (Figure 4). The SYMROT field was used to rotate ible. Formation labels then were added to the geologic the geologic symbols by using the formula “270° minus map. To avoid clutter, the lithologic and geologic feature the azimuth strike.” The compilation map included point point themes were not displayed in the final version of the themes for lithology, bedding attitudes, formation contact geologic map (Figure 8). A geologic cross-section loca- points, and other geologic features recorded in the database, tion line was placed on the map. n the ArcView layout all of which are shown as unique points or symbols on the view, titles, labels, and a geologic symbol explanation map (Figure 5 and 6). Dip value labels were added to the were added as well as a written scale, bar scales, and a bedding attitude symbols. These point themes were used to north arrow (Figure 9). The geologic cross-section, strati- interpret the location of stratigraphic contacts and the sur- graphic column, and geologic descriptions were drafted face trace of axial planes and faults, which are each separate separately using Adobe llustrator 8.0 software. 190 DGTAL MAPPNG TECHNQUES ‘06
Figure 4. Example of part of the compilation database for the Mascot 7.5’ Quadrangle. Note SYMROT, PRNT_ STK, and PRNT_DIP columns near the right side of figure.
ADVANTAGES AND DISADVANTAGES where the geologic traverse needed to proceed. Areas that ENCOUNTERED contained observable geologic characteristics, but were deemed inaccessible, were also plotted on the paper map. Advantages of using GIS and GPS technology during Field books were used for lengthy geologic descriptions, the geologic mapping process included the drastic reduc- sketches, or other information. GPS satellite acquisition tion of office time to input field data into a spreadsheet was occasionally hampered under heavy forest canopy or format that can be used in ArcView. Prior to using GPS, when satellites were not in proper array. On these occa- office time was required to determine field point coordi- sions, station locations were plotted directly on the paper nates and enter field book data into a spreadsheet. Also, the map, and the correct coordinates were added later to the GPS data dictionary facilitated the compilation of data from compilation database. There were no independent checks two mappers in that it listed basic attributes to record and and balances in place designed to detect GPS user input constrained how the attributes were described. The GPS errors. The ArcView compilation map was also printed dictionary also provided a framework by which to set up on a periodic basis to guide future traverses and provide a a consistent GIS compilation database between separate map for the geologists to use in the field. mappers, and share data between mappers on a daily basis. This methodology may not be suitable when geologic Disadvantages included the need for a paper copy of mapping involves long stays in the wilderness away from the topographic map in the field for navigation, station the office and electricity. In this study, data files needed to be point location, and plotting contact lines. The paper map downloaded every day or two because of GPS memory limi- was also needed to plot the data in the field to determine tations and the GPS batteries had to be recharged every day. GS AND GPS UTLTY N THE GEOLOGC MAPPNG OF COMPLEX GEOLOGC TERRANE 191
Figure 5. Part of the Mascot 7.5’ Quadrangle compilation map with lithologies, geologic contacts, and other geo- logic features shown as discrete points or symbols.
CONCLUSIONS VENDOR CONTACT INFORMATION
Despite minor problems in the field and office, the Adobe Illustrator—Adobe Systems, Inc., 345 Park Ave., San Trimble GeoExplorer 3 Global Positioning System and Jose, CA 95110-2704 USA, (800) 833-6687,
Figure 6. Part of the Mascot 7.5’ Quadrangle compilation map with bedding strike and dip symbols for the point features shown in Figure 5. GS AND GPS UTLTY N THE GEOLOGC MAPPNG OF COMPLEX GEOLOGC TERRANE 193
Figure 7. Part of the Mascot 7.5’ Quadrangle compilation map with geologic contact lines (black), fault lines (red), and formation abbreviations. In the printed version, the fault lines appear as thick black lines. Map includes geo- logic point features (see Figure 5) and bedding attitude symbology (see Figure 6). 194 DGTAL MAPPNG TECHNQUES ‘06
Figure 8. Part of the Mascot 7.5’ Quadrangle compilation map with polygons filled with appropri- ate geologic formation colors. Geologic point features are not shown. Bedding attitude symbology shown. GS AND GPS UTLTY N THE GEOLOGC MAPPNG OF COMPLEX GEOLOGC TERRANE 195
Figure 9. Open file version of the Mascot Geologic Quadrangle Map.