LUMINESCENCE DATING OF PALEOLIQUEFACTION FEATURES IN THE WABASH RIVER VALLEY AREA OF INDIANA

In the winter of 1811-1812, the central Mississippi Valley was sparsely populated and contained few man-made structures, and as a result, the great New Madrid earthquakes (M 7.5–8) caused minimal damage. These earthquakes stimulated seismic hazard studies throughout the central U.S., which eventually led to the discovery of large sand blows caused by liquefaction that occurred during prehistoric earthquakes in the lower Wabash River Valley of southern Indiana and Illinois (Obermeier and others, 1991). As part of continuing efforts to characterize the seismic hazard in the central U.S., the U.S. Geological Survey (USGS) is working to better understand the causes and the chronology of paleoearthquakes throughout the region, including the Wabash River Valley.

Sand blows are lenticular sand bodies that were erupted onto paleo-ground surfaces and were fed by sand-filled dikes that were sourced from subjacent liquefied sand beds. Previous studies in the Wabash River Valley area have bracketed the ages of the sand blows using radiocarbon samples collected from exposures of Holocene alluvium in river banks. We collected samples at two sites on the Wabash River; Peankishaw Bend, and the Black River site. Sand blows and sand dikes in the cut-bank exposures at these sites have been dated using radiocarbon (Munson and Munson, 1996). We are using optically stimulated luminescence (OSL) dating from these ‘calibration sites' to test the possibility of using OSL to date sand blows where either conflicting radiocarbon data exist or where there is no datable organic material in the exposed section. We analyzed fine sand-sized quartz grains using blue-light OSL dating by single aliquot regeneration features (SAR) (Murray and Wintle, 2000). Dose recovery and plateau tests ensured that the sediments were responsive to optical techniques. Ages obtained via OSL on the Black River Member and the Conger Creek Member allows us to compare the resulting OSL ages with the radiocarbon evidence.