Deglaciation of the highest mountains in Scandinavia at the Younger Dryas-Holocene transition: evidence from surface exposure-age dating of ice-marginal moraines.

John A. Matthews, Henriette Linge, Atle Nesje, Peter Wilson, Richard W. Mourne, Stefan Winkler, Geraint Owen, Jennifer L. Hill, Stefan Haselberger, Jesper Olsen

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    Abstract

    Surface exposure–age dating was applied to rock surfaces associated with ice-marginal moraines at elevations of ~1520–1780 m a.s.l. on the slopes of Galdhøpiggen and Glittertinden, the two highest mountains in Scandinavia located in the Jotunheimen mountains of central southern Norway. This is important for understanding the pattern and timing of wastage of the Scandinavian Ice Sheet at the Younger Dryas–Holocene transition. Cosmogenic exposure dating (here 10Be dating) of boulders from the moraine ridges yielded overall mean ages (corrected for glacio-isostatic uplift, surface erosion and snow shielding) of ~11.6 ka from Galdhøpiggen and ~11.2 ka from Glittertinden. Similar 10Be ages were also obtained from additionally collected proximal and distal erratic boulders and bedrock samples. These enabled age calibration of Schmidt-hammer R-values and independent Schmidt-hammer exposure-age dating (SHD) of the moraine ridges, which yielded comparable mean SHD ages of ~10.8 and ~10.6 ka from the Galdhøpiggen and Glittertinden sites, respectively. Taking account of the age resolution and other limitations of both dating techniques, the results suggest that the two sets of moraines have approximately the same age but that neither technique can distinguish unambiguously between moraine formation in the late Younger Dryas or Early Holocene. Together with features of moraine-ridge morphology and estimates of equilibrium-line altitude depression of ~360–575 m (corrected for land uplift), the results imply moraine formation during short-lived re-advances of active glaciers, at least the lower reaches of which were warm-based. It is concluded that the local glaciers remained active and advanced during deglaciation either very late in the Younger Dryas or very early in the Holocene, possibly in response to the Preboreal Oscillation at ~11.4 ka. The study supports the concept of a thin Younger Dryas ice sheet and places time constraints on the timing of final deglaciation in southern Norway.

    Original languageEnglish
    Pages (from-to)139-163
    Number of pages25
    JournalBoreas
    Volume53
    Issue number2
    Early online date27 Dec 2023
    DOIs
    Publication statusPublished (in print/issue) - 1 Apr 2024

    Bibliographical note

    Publisher Copyright:
    © 2023 The Authors. Boreas published by John Wiley & Sons Ltd on behalf of The Boreas Collegium.

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