NEW INTERPRETATIONS OF QUATERNARY DEPOSITS IN THE OHIO RIVER VALLEY IN WESTERN KENTUCKY

Recent geologic mapping along the Ohio River valley near Owensboro and Henderson Kentucky has produced new geologic interpretations of nonlithified geologic materials in the area. These new interpretations have significant implications as lithologic prediction models for various applications, including seismic hazard assessment, land-use planning, and groundwater modeling.

Landform mapping and subsurface data have identified a previously unreported paleochannel of the Green River trending northeastward from the modern Green River into downtown Owensboro. Lithologies associated with the paleochannel are consistent with sediment in the modern Green River, and are less diverse and generally finer grained than Ohio River deposits. The paleochannel is incised into the highest Ohio River outwash terrace and the associated Pleistocene lake terrace, and is thus younger than both. The Beds at Hubert Court identified by Ray (1965) are an extension of this paleochannel northeast of downtown Owensboro.

The previous depositional model predicts complex sand and gravel bodies in outwash deposits filling the Ohio River valley, and fine-grained, slackwater lithologies in adjacent tributaries. Throughout the region, thin beds of silt and fine sand are interbedded with lacustrine units adjacent to the Ohio River valley and are interpreted as splay deposits of the aggrading Ohio River. However, current mapping has identified numerous localities with significant bodies of sand and minor gravel below a veneer of slackwater sediment. In the area south and northeast of Owensboro, KY, as far as 8 km beyond the Ohio River valley margin, 9 to 15 m of lacustrine silt and clay are underlain by 11 to 20 m of fluvial sand and associated gravel. The Green River paleochannel is mapped roughly 8 km north of this area, but whether the sand is from the Green River, the Ohio River, or both is currently unknown. Smaller buried sand bodies may represent point-bar deposits of minor tributaries that flowed across lake plains between periods of major impoundment.

A pulmonate gastropod collected from a lacustrine deposit near Owensboro was dated at 22,060 ± 80 radiocarbon years, supporting a Late Wisconsinan age for the lacustrine units.