TWO AND THREE-DIMENSIONAL MAPPING OF EVAPORITE KARST IN WESTERN OKLAHOMA

As part of the STATEMAP component of the USGS's National Cooperative Geologic Mapping Program, the Oklahoma Geological Survey has been undertaking a 2-part mapping program consisting of: 1) a series of 1:100,000-scale reconnaissance geologic maps of the entire State that will become the foundation for a new 1:500,000-scale geologic map of Oklahoma; and 2) detailed 1:24,000-scale geologic maps of metropolitan areas, which helps identify potential engineering and environmental hazards in rapidly growing urban areas. The 1:100,000-scale mapping performed in Western Oklahoma has helped delineate the extent of gypsum karst with in the Blaine and Cloud Chief formations. The Nescatunga system, located within the Blaine Formation, in particular has a history of highway collapse hazards. Recent expansion of Highway 412 through Western Oklahoma has led to the detailed three-dimensional mapping of karst intersecting the highway Cavern morphology and distribution in Western Oklahoma evaporite karst systems were mapped using laser/global positioning systems. Digital mapping of cavern voids makes use of a reflectorless laser rangefinder with internal inclinometer linked to a digital compass and referenced to global positioning systems receivers positioned outside the cavern entrances. This is a standard surveying technique for use under bridges and beneath heavy tree canopies. A series of control stations are laser-located along a cavern traverse at approximately 20 meter intervals and marked by mounted reflectors. Fifty or so additional laser positions of cavern floors and walls are taken as offsets from each station. Positioning data is downloaded onto a laptop computer and visualized with GIS and CAD software, enabling a real-time geo-referenced image of cavern shape to be developed. Sub-decimeter scale accuracy is achieved and verified by reoccupation of stations and by positioning from two or more GPS locations at different entrances. The resulting digital 3-D map of a portion of each cavern system investigated is used in interpretation of the surface geophysical results, both in order to provide “ground truth” for the geophysical surveys and to refine the methods for use in cavern detection in surface-inaccessible sites. This system can be used to monitor the expansion to the karst systems by reoccupying the survey stations every year or two.