Numeric control on the late-glacial chronology of the southern Laurentide Ice Sheet derived from ice-proximal lacustrine deposits

We used a combination of radiocarbon and OSL dating in ice-proximal lacustrine silt and clay and outwash sand to estimate when ice of the Green Bay Lobe of the Laurentide Ice Sheet began retreating from its maximum position in south-central Wisconsin. The radiocarbon ages indicate that lakes had formed in the two tributary valleys by ~ 17.2 and 20.1 ka, respectively. The OSL ages indicate that the Green Bay Lobe was at its maximum position from about 26.4 ± 5.1 ka to 21.4 ± 3.3 ka. These data provide entirely new chronologic control on late Wisconsin (Marine Isotope Stage 2) glacial event in the upper Midwest, as well as the opportunity to directly compare radiocarbon and OSL ages in this setting.