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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 organic14C (n= 133) andin situcosmogenic10Be (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 organic14C ages disagree by thousands of years and limit determination of the initial recession to a date range of 24–20 ka. We infer that10Be inherited from pre‐glacial exposure adds 2–6 kyr to many exposure ages near the terminal moraines, whereas macrofossil14C 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 less10Be inherited from prior exposure and a reduced lag between ice recession and organic material deposition.14C and10Be 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.
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This content will become publicly available on December 6, 2025
Cosmogenic 21 Ne exposure ages on late Pleistocene moraines in Lassen Volcanic National Park, California, USA
Abstract. We report new cosmogenic 21Ne in quartz exposure ages from 18 samples on three distinct moraines deposited in the Lost Creek drainage, approximately 3–7 km down-valley from Lassen Peak in Lassen Volcanic National Park. Although measuring 21Ne in quartz is generally straightforward, accurate 21Ne exposure dating of deposits of late Pleistocene is rarely possible due to the significant quantities of non-cosmogenic 21Ne present in most lithologies. Young quartz-bearing volcanic rocks have been observed to be an exception. We take advantage of moraine boulders sourced from the ∼ 28 ka dacite of Lassen Peak to generate a chronology of alpine deglaciation in Lassen Volcanic National Park. Ages from three distinct moraines are in stratigraphic order at 22.1 ± 3.8, 20.2 ± 2.4, and 15.3 ± 3.8 ka and generally agree with other terminal and some recessional moraine ages across the Cascade Range and Sierra Nevada of the western United States. To date, these are among the youngest surfaces ever dated using cosmogenic 21Ne and provide a cost-effective proof-of-concept approach to dating moraines where applicable.
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- Award ID(s):
- 1948416
- PAR ID:
- 10593439
- Publisher / Repository:
- Copernicus Publications
- Date Published:
- Journal Name:
- Geochronology
- Volume:
- 6
- Issue:
- 4
- ISSN:
- 2628-3719
- Page Range / eLocation ID:
- 639 to 652
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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