Analysis of multiple cosmogenic nuclides constrains Laurentide Ice Sheet history and process on Mt. Mansfield, Vermont's highest peak

QUATERNARY SCIENCE REVIEWS

卷:205

Article

Corbett, Lee B.¹  Bierman, Paul R.¹  Wright, Stephen F.¹  Shakun, Jeremy D.²  Davis, P. Thompson³  Goehring, Brent M.⁴  Halsted, Christopher T.^1,2  Koester, Alexandria J.^2,6  Caffee, Marc W.^5,6  Zimmerman, Susan R.⁷ 

[1] Univ Vermont, Dept Geol, Burlington, VT 05401 USA

[2] Boston Coll, Dept Earth & Environm Sci, Boston, MA USA

[3] Bentley Univ, Dept Nat & Appl Sci, Waltham, MA USA

[4] Tulane Univ, Dept Earth & Environm Sci, New Orleans, LA 70118 USA

[5] Purdue Univ, Dept Phys & Astron, W Lafayette, IN 47907 USA

[6] Purdue Univ, Dept Earth Atmospher & Planetary Sci, W Lafayette, IN 47907 USA

[7] Lawrence Livermore Natl Lab, Ctr Accelerator Mass Spectrometry, Livermore, CA USA

关键词: Pleistocene;    Last glacial maximum;    Glaciation;    North America;    Geochronology;    Cosmogenic isotopes;    Erosion;   

DOI  :  10.1016/j.quascirev.2018.12.014

来源: Elsevier

【 摘 要 】

Constraining glacial history and process on Mt Mansfield, the highest peak in Vermont (1339 m a.s.l.), provides insight into how the Laurentide Ice Sheet shaped the underlying landscape, when latest Pleistocene ice retreated, and how upland and lowland glacial histories relate. Here, we quantify in situ cosmogenic Be-10 in 20 bedrock and boulder surfaces, as well as in situ cosmogenic C-14 in three of those surfaces, to assess subglacial erosion and exposure history. Isotopic concentrations indicate that Mt. Mansfield's lower elevations (similar to 400-1200 m a.s.l.) were deeply eroded by at least several meters during the last glaciation and then deglaciated rapidly; Be-10 ages across this elevation span are indistinguishable and average 13.9 +/- 0.6 ka (n = 15), suggesting that 800 m of ice thinning occurred within at most about a millennium. Conversely, the higher elevations (>1200 m a.s.l.) preserve a more complex geomorphic history. Mt. Mansfield's summit surfaces contain Be-10 from previous periods of exposure, indicating that the mountaintop landscapes were likely preserved beneath cold-based, weakly-erosive glacial ice. Exposure ages from the shorter-lived isotope, C-14, are younger (9.7 and 11.7 ka), suggesting that Mt. Mansfield's summit was covered until the early Holocene, perhaps by snowfields, ice carapaces, and/or till. Our findings, in context of previous work, suggest that thinning Laurentide ice flowed through the valleys for at most hundreds of years following deglaciation of the uplands, but that the summit remained shielded by ice or sediment for millennia after the valleys became ice-free. (C) 2018 Elsevier Ltd. All rights reserved.

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