Digital geologic mapping of the Ferron Sandstone, Muddy Creek, Utah with GPS and lasers

The traditional approach to geologic mapping consists of sketching, taking orientation and thickness measurements with compass and tape, and noting positions of features on topographic maps or photos. These methods are time consuming, often difficult to realize in rough terrain, and poorly constrain lateral variations in sedimentary facies in relatively flat lying strata. We describe a case study that captures the three-dimensional architecture of sandstone bodies and key geological surfaces such as stratigraphic boundaries and faults using digital capture techniques. The Ferron sandstone in Utah is a superbly exposed ancient delta deposit that provides an important outcrop analog to fluvio-deltaic subsurface reservoirs. It has been the focus of many traditional outcrop studies, but here we use a methodology ("cybermapping") based on GPS with offsets from a continuous ranging mode reflectorless laser rangefinder ("laser sketch") for collection and analysis of basic stratigraphic and structural data in a relatively remote area. We also show how this data can be analyzed and visualized in three dimensions. The study area was mapped in two days, which included hiking several kilometers into the area. On-the-fly and rapaid static post processing of GPS surveying was used for positioning the reflectorless laser rangefinders; 60,000 points were acquired mapping sedimentological and strucutral features, terrain, and control points. The resultant quantitative 3D model of the geology and terrain allowed robust geometric visualization and analyses.