Cave sediments constrain the latest Pleistocene advance of the Laurentide Ice Sheet in the Champlain Valley, Vermont, USA

Abstract

ABSTRACTOptically stimulated luminescence (OSL) and infrared stimulated luminescence (IRSL) dating were applied to cave sediments that were protected from the Marine Isotope Stage 2 (MIS‐2) advance of the Laurentide Ice Sheet (LIS) in the Champlain Valley of western Vermont. Evidence indicates that these sediments were derived from a subaerial landscape, requiring that the ice margin was north of the Champlain Valley when they were deposited. A basal sandy gravel was deposited during MIS‐4 (∼68 ka), sand near the middle of the composite stratigraphy was deposited during MIS‐3 (∼55 ka), and a layer of coarse sand in the stratigraphically highest position was deposited at the onset of MIS‐2 (∼35 ka). The youngest age constrains advance of the LIS south of the international border early in MIS‐2, and is combined with other available evidence to constrain ice advance rates over the 12 000 years leading up to the Last Glacial Maximum. Rates estimated from limiting ages were relatively slow (25 ma−1) as the ice ascended the adverse slope out of the St. Lawrence Lowland, increased as the margin advanced through the Champlain Valley, perhaps aided by subglacial bed deformation or ice streaming, and were fastest (∼100 ma−1) as the margin approached the terminal moraine position.