New age constraints reveal moraine stabilization thousands of years after deposition during the last deglaciation of western New York, USA
Abstract. The timing of the last deglaciation of the Laurentide Ice Sheet in western New York is poorly constrained. The lack of direct chronology in the region has led to a provocative hypothesis that the Laurentide Ice Sheet re-advanced to near its Last Glacial Maximum terminal position in western New York at ~13 ka, which challenges long-standing datasets. To address this hypothesis, we obtained new chronology from the Kent (terminal) and Lake Escarpment (first major recessional) moraines using radiocarbon ages in basal sediments from moraine kettles supplemented with two optically stimulated luminescence ages. The two optically stimulated luminescence ages date the Kent (terminal) position to 19.8 ± 2.6 and 20.6 ± 2.9 ka. Within the sediment cores from both moraines, the lowest reliable radiocarbon ages range from 15,000–15,400 to 13,600–14,000 cal yr BP. Below these dated levels is sedimentologic evidence of an unstable landscape during basin formation; radiocarbon ages from these lowest sediments are not in stratigraphic order and date from 19,350–19,600 to 14,050–14,850 cal yr BP. The oldest radiocarbon age of 19,350–19,600 cal yr BP – from a rip-up clast – suggests ice-free conditions at that time. We interpret that the 5 kyr lag between the optically stimulated luminescence ages and the lowest reliable radiocarbon ages is the result of persistent buried ice in ice-cored moraines until ~15 to 14 ka. The cold conditions associated with Heinrich Stadial 1 may have enabled the survival of ice-cored moraines in permafrost until after 15 ka, and in turn, climate amelioration during the Bølling Period (14.7– 14.1 ka) may have initiated landscape stabilization. This model potentially reconciles the sedimentological and chronological evidence underpinning the provocative re-advance hypothesis, which instead could be the result of moraine instability during the Bølling-Allerød periods (14.7–13 ka). Age control for future work should focus on features that are not dependent on local climate.
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