Late Quaternary Landscape Evolution and Tectonic Geomorphology of the Lower Ohio River Valley, USA

The lower Ohio River valley is a terraced fluvial landscape that has been significantly influenced by the advance and retreat of glaciers in its upper drainage basin and by changes in the Holocene climate. The lower Ohio Valley is also susceptible to crustal deformation and seismic shaking produced by the Wabash Valley (WVSZ) and New Madrid (NMSZ) seismic zones. Geomorphic mapping, sediment coring, geophysics, and optically stimulated luminescence (OSL) dating were used to develop a chronostratigraphic framework of sediments and landforms in the valley and to evaluate fluvial responses to glaciation, Holocene climate change, and neotectonic deformation.;Sediments deposited during marine oxygen isotope stage (MIS) 6 or earlier were only found in the subsurface. The elevation of the last interglacial (MIS 5) Sangamon paleosol preserved on the valleys edges indicates that MIS 6 alluvium filled the valley to within 7 m of the modern floodplain. The river incised ∼22 m into MIS 6 outwash before the end of MIS 5e, and was aggrading by 114 +/- 11 ka (MIS 5d). OSL ages indicate the river aggraded 8-14 m by the middle of MIS 3, and had incised ∼10 m and started aggrading again by 29.9 +/- 2.7 ka before MIS 3 ended. Aggradation continued into MIS 2, and maximum aggradation occurred by 21.4 +/- 1.0 ka, which is synchronous with the last glacial maximum in Ohio. The Ohio River incised the MIS 2 outwash and formed a suite of fill-cut terraces that decrease in age as elevation decreases, recording the river's adjustment to fluxes in sediment load and meltwater discharge during deglaciation. From 13.5 +/- 2.1ka to 11.7 +/- 2.7 ka the Ohio river incised up to 3 m, possibly in response to the Bolling Allerod interstadial, and began meandering at ∼11.7 +/- 2.7 ka which at the beginning of the Holocene. From 5.4 +/- 0.7 ka to ∼4ka, roughly the timing of the Holocene atlithermal, the river incised ∼5 m, and since ∼4ka the river has aggraded at least 4 m, which corresponds to the Neoglacial. The OSL and radiocarbon ages of terraces and alluvium indicate the lower Ohio River is highly sensitive to changes in climate.;Seismic features within the lower Ohio valley provide insight into the longer term seismic history and indicate there was significant, episodic shaking in the past. Geomorphic mapping, trenching, and seismic reflection profiles identified a previously unknown fault in the Ohio River floodplain. The fault (herein named the Uniontown fault) is approximately 10 km long and connects two larger mapped faults that are part of the Hovey Lake Fault System. OSL and radiocarbon dating indicate the most recent offset on the Uniontown Fault occurred between 5.5 and 0.9 ka. This coincides with the establishment of the modern course of the Ohio River around the fault, indicating faulting diverted the course of the Ohio River. This is similar to how the Mississippi River was diverted around the Reelfoot Fault during the 1811-1812 New Madrid earthquakes.