CHRONOLOGY OF LAURENTIDE ICE SHEET FLUCTUATIONS SURROUNDING THE LAST GLACIAL MAXIMUM, CENTRAL INDIANA, USA

The chronology of Laurentide Ice Sheet (LIS) advance to and retreat from its maximum Oxygen Isotope Stage (OIS) 2 limit is important because it permits evaluation of the driving mechanisms of ice sheet growth and decay and provides a terrestrial chronology that can be compared to the marine record and other paleoclimate proxies. New radiocarbon and optically stimulated luminescence (OSL) dating from outcrop and core in central Indiana has refined the timing of Huron-Erie Lobe OIS 2 advance to and retreat from the maximum limit. Fourteen new radiocarbon ages within or below late Wisconsin (OIS 2) till from three sites within 5 km of the maximum limit indicate an age of 24.0 k cal yr BP for maximum ice sheet extent in central Indiana, in agreement with chronology from the Lake Michigan Lobe (Illinois) and other sections of the Huron-Erie Lobe (Ohio). The LIS subsequently retreated >50 km between 24.0 and 21.6 k cal yr BP, as recorded in the formation of glacial Lake Eminence and deposition of stratified sediments atop the deglaciated surface. Till deposition associated with a significant (>40 km) readvance ca. 21.6 k cal yr BP buried fossiliferous stratified sediments, including those of glacial Lake Eminence, and the advance came within 10 km of the maximum limit. An additional record of LIS advance is recorded in the timing of outwash aggradation and associated slackwater sedimentation in the West Fork White River valley and tributaries. Eight radiocarbon ages from a core 10 km beyond the OIS 2 limit indicate slackwater sedimentation began ca. 27 k cal yr BP and continued until ca. 20.5 k cal yr BP, representing the timing of ice sheet advance into and out of the paleo-White River drainage basin. Ice sheet advance and retreat rates average ca. 40 m/yr both before and after the global Last Glacial Maximum (ca. 26 to 21 k cal yr BP), when ice was within ca. 50 km of the OIS 2 maximum. Retreat rates increased slightly to ca. 50 m/yr after 21.6 k cal yr BP, as ice retreated ca. 110 km from central Indiana to the Union City Moraine (19.3 k cal yr BP) in northeastern Indiana.