A critical re‐analysis of constraints on the timing and rate of Laurentide Ice Sheet recession in the northeastern United States

Abstract

We review geochronological data relating to the timing and rate of Laurentide Ice Sheet recession in the northeastern United States and model ice margin movements in a Bayesian framework using compilations of previously published organic 14C (n = 133) and in situ cosmogenic 10Be (n = 95) ages. We compare the resulting method‐specific chronologies with glacial varve records that serve as independent constraints on the pace of ice recession to: (1) construct a synthesis of deglacial chronology throughout the region; and (2) assess the accuracy of each chronometer for constraining the timing of deglaciation. Near the Last Glacial Maximum terminal moraine zone, 10Be and organic 14C ages disagree by thousands of years and limit determination of the initial recession to a date range of 24–20 ka. We infer that 10Be inherited from pre‐glacial exposure adds 2–6 kyr to many exposure ages near the terminal moraines, whereas macrofossil 14C ages are typically 4–8 kyr too young due to a substantial lag between ice recession and sufficient organic material accumulation for dating in some basins. Age discrepancies between these chronometers decrease with distance from the terminal moraine, due to less 10Be inherited from prior exposure and a reduced lag between ice recession and organic material deposition. 14C and 10Be ages generally agree at locations more than 200 km distal from the terminal moraines and suggest a mostly continuous history of ice recession throughout the region from 18 to 13 ka with a variable pace best documented by varves.

New age constraints reveal moraine stabilization thousands of years after deposition during the last deglaciation of western New York, USA

“…Our findings support the observations and conclusions from numerous studies that radiocarbon dates can be extreme minimum age constraints on deglaciation (Curry et al, 2018;Fisher et al, 2020;Florin and Wright, 1969;Halsted et al, 2023;Yansa et al, 2020). In New England, minimum-limiting radiocarbon ages may be the reason for the discrepancy between the timing of moraine deposition as recorded by 10 Be exposure dating (e.g., Balco et al, 2002;Corbett et al, 2017) and radiocarbon ages of basal macrofossils in lakes and bogs (e.g., Peteet et al, 2012).…”

The Laurentide Ice Sheet in southern New England and New York during and at the end of the Last Glacial Maximum – A cosmogenic-nuclide chronology

“…Summing the Providence River sequence with several varve sequences in Connecticut and southern Massachusetts between the base of the NAVC and Providence (including the Quinnipiac/Haverstraw varves), the ice margin must have retreated past Barrington, Rhode Island by ~20.1 ka and north of Providence by ~19.5 ka (Figures 1 and 2; Oakley and Boothroyd, 2013). Three cosmogenic exposure ages ~30 km north of the Rocky Hill Dam average 18.3 ± 0.3 ka, corroborating the deglaciation timing in northern Connecticut (Drebber et al, 2023). The NAVC reveals that the LIS margin was north of New England by 13.6 ka (Ridge et al, 2012), following relatively minor advances or stillstands at least in the White Mountains and in Maine (e.g., Borns et al, 2004;Bromley et al, 2015;Davis et al, 2015;Dorion et al, 2001, Hall et al, 2017Kaplan, 2007;Koester et al, 2017;Thompson et al, 2017).…”