EXAMPLES OF ANALYSIS OF 3-D DIGITAL GEOLOGIC MODELS: MULTI-SPECTRAL ANALYSIS OF LITHOLOGY, FRACTURE ANALYSIS AND AN INTEGRATED 3-D GEOLOGIC INTERPRETATION OF THE JACKFORK SANDSTONE, BIG ROCK QUARRY, ARKANSAS

The outcrop at Big Rock in Arkansas was digitally captured using terrestrial laser scanners, RTK-GPS, conventional and thermal infrared photography. Sediments that crop out at this quarry are part of a submarine channel complex likely deposited at the base of slope.

A mid-range Riegl Z360i and long-range Riegl LPM-i800HA scanners have been used to sample the outcrop topography at high spatial resolution. The high-density 3-D point cloud from the laser scanners was used to create a digital model of the outcrop terrain. A photo real model of the outcrop was created by adding texture information to the 3-D model. This facilitated interpretation and reconstruction of the submarine channel complex architecture. An evaluation was made as to the additional interpretation possible with 3-D models rather than previous conventional techniques.

A surface classification algorithm has been developed to extract fracture orientation information directly from the point cloud. The method makes use of both spatial proximity and orientation of an initial coarse-grained modeling of the point cloud. Two different clustering methods (multileader and k-means) are applied in an unsupervised classification scheme. The result is the equivalent of making hundreds of conventional strike and dip measurements in even the most inaccessible parts of the outcrop.

Ground-based conventional (Canon EOS D60) and thermal infrared photography (PV320) was tested as a method to identify and differentiate sandstone and shale at the outcrop. Such multi-spectral images acquired from the ground, at close range, obliquely were co-registered and displayed in Red-Green-Blue colour space to create false colour images that are useful for highlighting lithologic variation.

Combining all these new techniques and using the information contained in the digital outcrop helped to better describe and interpret the outcrop geology.