PLIO-PLEISTOCENE GEOLOGIC HISTORY OF THE KENTUCKY RIVER VALLEY IN CENTRAL KENTUCKY

Analysis of fluvial deposits and erosional features in the Kentucky River valley has produced a relative chronology of the Plio-Pleistocene drainage evolution of this major Ohio River tributary. This study utilized field observations, published geologic and topographic data, and extensive compilation and comparison of digital data, to examine the fluvial record preserved in the Kentucky River valley. Numerous fluvial features including abandoned paleovalleys, fluvial terraces and deposits, bedrock benches, and relict spillways between adjacent river valleys were identified during the course of the study.

The distribution and preservation of high-level fluvial deposits in the Kentucky River valley suggest a long period of gradual erosion, with no distinct straths preserved to suggest long term fluvial stability at any particular level. A major drainage reorganization related to a pre-Illinoisan glacial advance disrupted the northward flow of the Old Kentucky River toward the Teays River system and led to integration of the early Ohio River. Relict spillways between valleys adjacent to the Kentucky River are associated with this glaciation. The integration of the Ohio River greatly reduced the distance to base level, and led to abrupt incision and a change in erosional style for the Kentucky River. The abrupt incision caused abandonment of meander bends along the valley profile, resulting in the only preserved upland strath in the Kentucky River valley, which can be traced to the Parker Strath of the ancient Teays River system. No major terrace deposits or abandoned meanders are preserved along the valley walls between this strath and lower terraces related to Illinoisan(?) and Wisconsinan glacio-fluvial alluviation of the Ohio River valley.

Bedrock lithology and stratigraphy is the dominant control on valley morphology and on the distribution and preservation of modern and ancient fluvial deposits and features in the study area. Inheritance of valley morphology has resulted from the erosion of the river from one lithology down into another lithology with differing erosional susceptibility, thus superposing the meander patterns of the overlying valley style onto the underlying lithology.