CORING GEOPHYSICAL ANOMALIES: TOWARDS NEOTECTONIC CONSTRAINT ALONG THE HOVEY LAKE FAULT, LOWER WABASH VALLEY FAULT SYSTEM

VANCE, D.M, and WOOLERY, E.W., Dept. of Geological Sciences, University of Kentucky, Lexington, KY 40506; and VANARSDALE, R.B., Dept. of Earth Sciences, University of Memphis, Memphis, TN 38152, woolery@uky.edu.

Previous high-resolution seismic (shear-wave) reflection profiles collected over the Hovey Lake fault revealed high-angle displacement and folding extending above the Paleozoic bedrock, and into the Quaternary sediment. Time displacement calculations from those data showed approximately 10.5 m of normal offset on the top-of-bedrock horizon, and 2 m of reactivated reverse displacement along the earliest-arriving Quaternary soil reflector at a depth of 5 m. Preliminary coring adjacent to the primary deformation zone found organic material in a soil horizon located 7.7 m below ground surface. Subsequent carbon-14 tests dated this material at approximately 37,000 YBP.

During the latest work at this site we drilled 11 continuously cored holes across the 300-m-wide deformation zone that was defined by the seismic images. The holes were drilled to depths ranging between 5 and 6 meters (i.e., just below the shallowest resolvable depths seen on the seismic profiles). The resultant cross-section correlates very well with the geophysical interpretation (e.g., fault locations and apparent northwest-dipping fabric). More importantly, the deformation appears to reach the surface. Two organic samples were recovered from the deformed horizons at 1.2 and 4.5 meters depth. The carbon-14 tests indicated that their ages were approximately 1,100 and 31,000 YBP, respectively. The latter is similar in age to the previously dated material; unfortunately the former is not well enough constrained to eliminate the possibility of post-deformation emplacement. A defensible answer will require higher-resolution analysis (i.e., paleoseismology trenching) of the structure.