IN SEARCH OF HOLOCENE LOESS, RESULTS FROM THE HAVANA LOWLAND, CENTRAL ILLINOIS

The majority of Illinois is blanketed by late Wisconsin Peoria Loess, and it is still a question whether there is identifiable Holocene dust deposit. If Holocene loess were present, it would provide an important archive on the region’s paleoclimate and valuable information on the evolution of local landscapes over the last 10,000 years. One of the best potential locations for preservation of Holocene dust deposition is downwind (southeast) of the Havana Lowland along the Sangamon River in central Illinois. This assessment is based on the model of Mason et al. (1999) that emphasizes the effects of saltating sand and topographic barriers on the deposition of loess in sparsely vegetated landscape. The model has successfully explained thick loess deposits in various locations in the Upper Midwest and Great Plains, including a location in southwestern Nebraska where 6 m of Holocene loess is found on a bluff downwind of a geomorphic obstacle. Under a very similar topographic setting and with saltating sand upwind, we identified two thick loess sections (>12m) on the bluff south of the Sangamon River where Holocene loess may be present. However, optical dating on samples of the uppermost of the 2 sections (depths from 0.4-1.3 m from the ground surface) yields 5 ages ranging from 16 to 23 ka. This indicates minimal dust accumulation in central Illinois in the Holocene, and confirms the conventional wisdom that the retreat of Laurentide ice sheet had stopped providing silt-sized particles as a regional loess source.