--> GIS Compilation and Analysis of Near-Surface Structure Data from 707 Geologic Quadrangle Maps in Kentucky

47th Annual AAPG-SPE Eastern Section Joint Meeting

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GIS Compilation and Analysis of Near-Surface Structure Data from 707 Geologic Quadrangle Maps in Kentucky


Between the years 1960 and 1978, the United States Geological Survey, in cooperation with the Kentucky Geological Survey (KGS), 196 professional geologists mapped the surface geology of the entire state of Kentucky at a scale of 1:24,000, and published 707 7.5-minute quadrangle maps. The geologic information from these maps were later digitized into vector- based GIS files by KGS staff between 1998 and 2005, making Kentucky the first US state to be entirely digitally mapped at a 1:24,000 scale. For the majority of these Geologic Quadrangles, structural elevation contours based upon a local subsurface stratigraphic datum were included along with the stratigraphic contacts, fault locations, and other geologic information gathered during the original mapping effort. In an effort to create a seamless, statewide dataset, structural contours were interpreted for the remaining 36 quadrangles using currently available state records from oil, gas, and water wells, along with LiDAR high-resolution elevation data. Although using a local datum for structural elevation data on individual quadrangles is necessary for detailed precision and ease of mapping, it presents a challenge when trying to merge the map data across a whole state. Because Kentucky straddles three separate continental basins (Appalachian, Illinois, and the Mississippi Embayment), 153 distinct datums were used for geologic quadrangle structural elevation data. Trying to create a statewide 3D display from this data produces 153 locally continuous surfaces, interrupted by vertical offsets at each datum boundary. In order to merge this dataset while retaining the relevant structural information, KGS researchers created dip and azimuth maps of the raster surfaces generated from the structure contours for each individual structural datum domain. Because displays convey only slope information (and not specific elevations), adjacent domains with different datums could then be merged into a seamless, statewide coverage. These new GIS products can now be used for the analysis of numerous geologic attributes. For example, locations of buried, previously unmapped faults can be interpreted from linear abrupt changes in dip (sediment drape across fault tip). Or, by comparing the structural dip with that of the LiDAR digital elevation model, estimations of relative erosional rates for various formations can be compared. This GIS layer will soon be available to the public for display or download from the KGS website.