Schmidt-hammer exposure ages from periglacial patterned ground (sorted circles) in Jotunheimen, Norway, and their interpretative problems

Winkler, Stefan; Matthews, John A.; Mourne, Richard W.; Wilson, Peter

Abstract

© 2016 Swedish Society for Anthropology and Geography Periglacial patterned ground (sorted circles and polygons) along an altitudinal profile at Juvflya in central Jotunheimen, southern Norway, is investigated using Schmidt-hammer exposure-age dating (SHD). The patterned ground surfaces exhibit R-value distributions with platycurtic modes, broad plateaus, narrow tails, and a negative skew. Sample sites located between 1500 and 1925 m a.s.l. indicate a distinct altitudinal gradient of increasing mean R-values towards higher altitudes interpreted as a chronological function. An established regional SHD calibration curve for Jotunheimen yielded mean boulder exposure ages in the range 6910 ± 510 to 8240 ± 495 years ago. These SHD ages are indicative of the timing of patterned ground formation, representing minimum ages for active boulder upfreezing and maximum ages for the stabilization of boulders in the encircling gutters. Despite uncertainties associated with the calibration curve and the age distribution of the boulders, the early-Holocene age of the patterned ground surfaces, the apparent cessation of major activity during the Holocene Thermal Maximum (HTM) and continuing lack of late-Holocene activity clarify existing understanding of the process dynamics and palaeoclimatic significance of large-scale sorted patterned ground as an indicator of a permafrost environment. The interpretation of SHD ages from patterned ground surfaces remains challenging, however, owing to their diachronous nature, the potential for a complex history of formation, and the influence of local, non-climatic factors.

• Journal Article Type: Article
• Acceptance Date: May 18, 2016
• Online Publication Date: Nov 29, 2016
• Publication Date: Nov 29, 2016
• Deposit Date: Nov 29, 2016
• Publicly Available Date: Jul 20, 2018
• Journal: Geografiska Annaler, Series A: Physical Geography
• Print ISSN: 0435-3676
• Electronic ISSN: 1468-0459
• Publisher: Taylor & Francis
• Peer Reviewed: Peer Reviewed
• Volume: 98
• Issue: 3
• Pages: 265-285
• DOI: https://doi.org/10.1111/geoa.12134
• Keywords: sorted circles, periglacial patterned ground, alpine permafrost, Schmidt-hammer exposure-age dating (SHD), mechanical Schmidt hammer, RockSchmidt, alpine permafrost, Holocene climatic variations, Jotunheimen, Norway
• Public URL: https://uwe-repository.worktribe.com/output/908714
• Publisher URL: http://dx.doi.org/10.1111/geoa.12134
• Additional Information: Additional Information : This is the peer reviewed version of the following article: Winkler, S., Matthews, J., Mourne, R. and Wilson, P. (2016) Schmidt-hammer exposure ages from periglacial patterned ground (sorted circles) in Jotunheimen, Norway, and their interpretative problems. Geografiska Annaler: Series A, Physical Geography, 98 (3). pp. 265-285, which has been published in final form at http://dx.doi.org/10.1111/geoa.12134. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
• Contract Date: Nov 29, 2016