QUATERNARY–NEOGENE(?) EVOLUTION OF THE LICKING RIVER IN NORTHERN KENTUCKY

The Licking River has been a major drainage for central and northern Kentucky, a tributary of the Ohio River, and former tributary of the Teays River throughout the Quaternary and into the Neogene. Although previous work has addressed fluvial evolution, active surficial mapping in northern Kentucky by the Kentucky Geological Survey provides an opportunity to apply new techniques to test long-standing hypotheses of the Licking River.

The De Mossville and Butler quadrangles show evidence of fluvial aggradation and planation, and more than 250 ft of incision. Digital elevation models and slope maps derived from airborne LiDAR (1 m resolution) show the trace of a channel at ~700 ft elevation with meander lengths of ~10,000–14,000 ft and a belt width of ~3,400–6,400 ft. The paleochannel is composed of sand, silt, and gravels, including quartz and chert from Carboniferous bedrock upriver in central Kentucky. Gray silty clay overlies the alluvium and is interpreted as lacustrine deposits resulting from glacial damming at the mouth of the Licking.

The Licking River Valley dissects the upland paleochannel or is within close proximity. LiDAR and field mapping reveal four regional terraces at ~570 ft (Qat4), ~530 ft (Qat3), ~510 (Qat2) ft, and ~500 ft (Qat1). Quartz and chert gravels have been observed at multiple sites between the paleochannel and Qat4, although they are not associated with geomorphic features. Qat4 is composed of yellowish brown silt, sand, and minor quartz gravels, and appears to represent the thickest package of material. Qat3 is composed of brown silt loam with minor soil-horizon development, and is the most expansive terrace. Qat2 and Qat1 are increasingly narrow and composed of brown silt loam with no soil horizons. The river channel is at ~490 to 460 ft elevation in the study area, with meander lengths of ~8,500–12,500 ft, a belt width of ~6,500–7,500 ft, and a very limited floodplain.

Much of the timing and history of the Licking has been based on qualitative observations, including degrees of weathering and corresponding elevations. However, we now have the tools to test these assumptions. This study is ongoing and will include the first quantitative constraints on burial ages of the paleochannel alluvium using 10Be-26Al cosmogenic radionuclides, and of the lower terraces using optically stimulated luminescence.