AN NEW AND UNUSUAL EXPOSURE OF THE SUB-MIDDLE DEVONIAN UNCONFORMITY AT THE FALLS OF THE OHIO, KENTUCKY AND INDIANA

The famous fossil beds of the Falls of the Ohio are mostly in the Middle Devonian (Eifelian) Jeffersonville Limestone. At low water, the basal unconformity of the Jeffersonville with the mid- Silurian (Wenlock, Homerian) Louisville Limestone is exposed along Little Slough, on a small arch, between the main fossil beds and Wave Rock on Goose Island. A few years ago, a new exposure of the Louisville Limestone was found in a creek bed draining Goose Island. The new exposure formed during annual high-water erosion from the Ohio River. The exposed bed is only 6 m² but is interesting because (1) it is bordered on all sides by the Jeffersonville Limestone; (2) it is stratigraphically higher than the Louisville Limestone along Little Slough; (3) it is separated from, but near the general trend of the mapped arch; (4) it contains halysitid corals and bedding rotated nearly perpendicular to horizontal; and (5) bedding on one margin is soft-sediment deformed and folded. Exposure of Silurian strata above the position along Little Slough indicates more irregular local relief on the Devonian/Silurian unconformity than previously thought. The bed appears to represent a rotated block of Silurian strata poking up into and draped by the Devonian Jeffersonville Limestone at a paleotopographically higher position than the undisturbed beds exposed on Little Slough only a short distance away. How the beds became rotated is difficult to infer because of limited exposure. Perhaps, future river erosion will provide more clues.