The climate transition at the end of the Last Glacial Maximum (LGM, 25,000 – 13,000 ¹⁴C years BP) is not well understood for the North American Midwest, due to a scarcity of data for this time period. A number of relict basins in the interlobate complex of western Ohio contain geoarchives that span the late LGM transition, thus providing ideal sites for further examining climate change.

Site 0201 of the Mechanicsburg township holds the oldest archive, with a basal date of 16,197 ±97 ¹⁴C years BP (Lab #AA45079). Within the sedimentary archive, a sharp transition from older, mottled clays to banded silt 4.5 m above the core base dates to 13,370 ±280 ¹⁴C years BP (Lab #Beta – 158295). High resolution loss-on-ignition (LOI) analysis shows consistently low organic productivity before this later date, then a dramatic increase in organic productivity above this transition. Chlorophyll content analysis, which yields a measure of phytoplanktonic biomass within the basin through time, corresponds with the LOI data.

Climate conditions within the 0201 site thus remained relatively stable during the time period from 16,197 ±97 to 13,370 ±280 ¹⁴C years BP. On a more regional scale, site 0201 is one of a cluster of basins with basal radiocarbon dates that range from 15,350 ±100 to 16,197 ±97 ¹⁴C years BP. These dates suggest that the ice margin had receded north of the region as early as 16,197 ±97 ¹⁴C years BP in order to allow this suite of kettles to form in a periglacial environment.