GIS AS AN IMPORTANT AID TO VISUALIZING AND MAPPING GEOLOGY AND ROCK PROPERTIES IN REGIONS OF SUBTLE TOPOGRAPHY: AN EXAMPLE FROM NORTH-CENTRAL OKALHOMA

The purpose of this study is to assess the feasibility and practicality of using Geographic Information Systems (GIS) to visualize, quantify, and evaluate relationships between bedrock geology and topography. The study site is located in north-central Oklahoma where poorly consolidated Permian and Pennsylvanian-age sedimentary rocks of differing types and properties have been dissected by the regional drainage system. The erosion of these rock types has produced a subtle but well-defined topographic expression. Data for the analysis was obtained using 30m digital elevation models (DEMs) available from the USGS National Elevation Dataset (NED). Using the DEMs, a slope was calculated for each pixel in the study area and a slope map was created with ESRI Spatial Analyst in ArcMap. Visual inspection of the slope map reveals that areas with common slope are frequently in close proximity and correspond closely, but not exclusively, with the properties of the underlying bedrock formations. This finding is significant for areas with subtle topographic expression because this variation in topography and the relationship with the underlying bedrock would normally not be recognized in most conventional multi-use mapping programs (soil, water, ecology, land use, or geology). Therefore, this GIS-based technique, when used in conjunction with conventional techniques, can quickly enhance the efficiency, accuracy, and applicability of multi-use mapping programs. An on-going field program is attempting to document and quantify the reasons for the observed correspondence between the bedrock formations and their characteristic topographic expressions. Field samples of bedrock at a select number of sites are being used to establish reasons why some formations or parts of formations are more (or less) susceptible to erosion than others. A major but unexpected finding of work to date is that the entire region appears to be riddled by two sets of closely-spaced, through-going, surface fractures (one set trending NE – SW, the other, NW – SE). It is possible that this system of fractures has previously eluded researchers due to the poorly consolidated nature of the regional bedrock and their concealment due to the development of gullies and other drainage systems (as determined by the fractures).