A TREE-RING STUDY OF WOOD OF POSSIBLE YOUNGER DRYAS AGE FROM CENTRAL ILLINOIS

A deposit of logs preserved in alluvial sands was discovered at a limestone quarry in central Illinois in the 1990s. Two preliminary radiocarbon dates at that time gave ages of 10,160 and 10,430 ¹⁴C years BP, which fall into the age range of the Younger Dryas event at 10,000 to 10,500 ¹⁴C y BP (ca. 11,500 to 12,800 Calendar y BP). There is abundant evidence for deterioration of climate to glacial-like conditions in the N. Atlantic associated with this event, largely based on European paleoclimate records. If these ¹⁴C dates are representative of the wood in this deposit, the logs would be extremely valuable in providing insight into Younger Dryas environmental conditions in central N. America. We collected about 30 samples from this deposit in August 2001 for species and dendrochronological analysis, with the hope of eventually applying more specialized methods such as stable isotope analysis. Unlike many of the slightly older wood deposits found in the Upper Midwest that are conifers and dominantly spruce, our samples were all hardwoods. Preservation condition of the collected timber varies widely. A few samples are unusually well preserved. They contain pith and even fragments of bark. Only one log showed flattening to an elliptical cross-section, presumably from some extreme force (probably by weight of sediment overburden), but all of the other samples appear normal in this regard. The logs and wood fragments in our collection had 35 to nearly 200 rings. Measured tree-ring width series are cross-datable. Correlation between the series varies from 0.35 to 0.6 at p<0.05. Standard deviation and mean sensitivity of averaged tree-ring series are 0.35 and 0.21, respectively. There is a good potential to develop a tree-ring width chronology for the studied site. We are obtaining additional radiocarbon dates on some of the samples to help us further develop the chronology of samples.