THE USE OF 3D PHOTOREALISTIC MODELS TO CORRELATE THE STRUCTURE AND STATIGRAPHY OF FIVE OUTCROPS OF THE AUSTIN CHALK/ EAGLEFORD SHALE CONTACT IN CEDAR HILL, TEXAS

The Cedar Hill outcrop located off Highway 1382 in Dallas County, Texas, is well known for its exposed contact between the Austin Chalk and the underlying Eagleford Shale formations. The correlation of the faults in the area between several locations over two intersecting roads has always been unclear. As a test as well as to save the sites digitally and therefore eventually provide access to it virtually over the internet, a project was organized to map these sites by undergraduate and graduate students from The University of Texas at Dallas. The five outcrops along Highway 1382 extend over a distance of 0.4 miles with exposures on both sides. These formations were scanned with a fast terrestrial laser scanner, the Riegl-LPM 800 from the University of Idaho, and they were photographed with a 10 mega-pixel digital camera. Control points were derived from RTK GPS to register the scans to each other and to globally reference the data to world coordinates. Undergraduates used the modeling program 3DPH by Alfarhan and White, which has an efficient workflow to create photorealistic 3D virtual models of the outcrops from the laser scanner point clouds and the photographs. The outcrops have been modeled in 3D as photorealistic virtual models and are displayed with the OpenSceneGraph® viewer. Alfarhan's modeling program 3DLT incorporates diagnostic tools, which allow for the determination of the strikes and dips of planar surfaces of the faults and the extension of stratigraphic contacts, bedding planes, and fault surfaces across the model in order to analyze their relationship to similar features at other outcrops. This was a test of the technique to model, detect, measure, and extrapolate subtle changes in geology across a regional area and has proven to be a successful tool. Ultimately, the models will be made available through the Internet.