NEW TECHNIQUES FOR DIGITAL MAPPING OF OUTCROP STRUCTURES AT PEMAQUID POINT, MAINE

Using RTK GPS and total stations tied to a single 2-hour static datum post-processed through NOAA's website www.ngs.noaa.gov/OPUS, our digital mapping team focused on the structural geology of Pemaquid Point to study shearing deformation by mapping syntectonic granite intrusions and quartz veins at all observable scales. The team employed some technologies used during last year's field season: SpectraPrecision Total Stations, Trimble 5700 Dual Frequency GPS Receivers, and ArcView, one of ESRI's Geographic Information System (GIS) software packages. This year two new technologies were used in our mapping efforts: handheld WAAS-enabled Trimble GeoXT GPS and ArcGIS, ESRI's newest GIS software. Trimble GeoXT handheld GPS units were used to map selected outcrop features such as larger intrusions, soil lines, and tide lines and to collect additional geological structural data. The GeoXT is equipped with the Wide Area Augmentation System (WAAS) for real time correction, and has a precision of ~1m. The GeoXT, as a data logger with editable data dictionaries, was used to record the location and structural orientation of features throughout the project area. The map and structural data files were downloaded into Trimble's Pathfinder Office software and exported directly as shapefiles to ArcMap. Structural data files were also extracted for stereonet analysis and to plot structural orientation symbols. ESRI's ArcMap GIS software was used to process, display, and analyze the collected geologic survey data incorporating georeferenced geologic maps, topo and orthoquads, outcrop photos and stereonet plots. In the field, data was edited using shoulder harnessed laptop computers running ArcMap. In the GIS computer lab, ArcView and ArcMap were used to measure the angles of reorientation for deformed intrusions and calculate shear strain, measure the areas of granite boudins to calculate elongation, and plot oriented structural data. ArcMap was also used to generate topographic contours of outcrop surfaces, and to georeference field photos and scanned maps to survey data. Georeferenced handheld outcrop photos were used to enhance the detail in digitally mapped outcrop features.