INTEGRATING 3D STRUCTURAL GEOLOGY DATASETS ACROSS REGIONS WITH VARIABLE ELEVATION DATUMS

A new seamless statewide structural geology dataset has been created for Kentucky. These new data consist of a pair of raster surfaces: one depicting the dip angle of geological surfaces below horizontal, and one that displays the dip azimuth of those beds. By removing the dependence on elevation values, a continuous pseudo-surface is created where various analyses can be performed of the structure, regardless of area or scale.

USGS has published 707 7.5-minute Geologic Quadrangles (GQs) at 1:24,000 scale, covering the entire state of Kentucky. These maps were later vectorized by KGS into digital GIS formats in 2004. Because the geology of Kentucky contains parts of three sedimentary basins, the near-surface strata from which relative elevations could be calculated varies from place to place. The 707 GQs were therefore mapped across a total of 155 different structural datums. Although this use of a local datum is productive at smaller scales, creating regional or statewide 3D maps with the structural contour data results in a patchwork of discontinuous contour sets, separated in vertical space. In addition to the issue of variable datums, several of the original published 7.5-minute GQs did not include elevation contours depicting the near-surface geologic structure.

For areas where data was absent, new structural interpretations were produced using whatever KGS subsurface well data (oil, gas, and water) was available for local marker beds. These newly interpreted structural contours were then input into the geoprocessing scripts along with the structural contours from the published GQs to create a statewide coverage. To eliminate the vertical offsets that exist between differing stratigraphic datums for structural measurements, contour sets were separated by datum, and then individual 3D raster surfaces were calculated from the elevation contours in the GQs for each (continuous) datum area. Dip and azimuth raster files were then calculated from each of those 3D surfaces, thereby retaining the attitude of the structures in space without a dependence on a datum horizon. These individual dip/azimuth datasets were then merged to create a continuous theoretical surface representing the near-surface geologic structure of the local geology across the Commonwealth of Kentucky.