Holocene loess in Illinois revealed by OSL dating: Implications for stratigraphy and geoarchaeology of the Midwest United States

Most uplands in Illinois are blanketed by late-Wisconsinan Peoria Loess, and the conventional wisdom is that little or no dust accumulation occurred during the Holocene (11.7 ka to present). In a recent effort to investigate if Illinois Holocene loess was deposited and preserved, we applied optically stimulated luminescence (OSL) dating to seven locations where loess is thick. These include four sites along the Mississippi River in westernmost Illinois, and three loess bluffs south of the Illinois River in central Illinois. Our results suggest that Holocene-aged loess is preserved along the Mississippi River in the state of Illinois; in contrast, no Holocene loess was found south of the Illinois River in the central portion of the state. In addition to its spatially limited distribution, Holocene loess thicknesses range only up to 1 m. Nevertheless, loess stratigraphy and OSL dating results provide the first Holocene loess reported east of the Missouri River. Our new finding also resolves the long-time archeological puzzle that a number of artifacts of several thousand years old were buried by upland loess along the Mississippi River.