Schmidt-hammer R-values from glacially-scoured bedrock surfaces across glacier-foreland boundaries: Insights into Holocene weathering rates with implications for exposure-age dating

Matthews, John A.; Mourne, Richard W.; Wilson, Peter; Hill, Jennifer L.; Robbins, Celia; Winkler, Stefan

Abstract

Schmidt-hammer R-values were measured on glacially-scoured bedrock outcrops located inside and outside of 11 ‘Little Ice Age’ glacier-foreland boundaries in the Jotunheimen and Jostedalsbreen regions of southern Norway. Analysing paired samples differing in exposure age by ~10,000 years constitutes a field experiment on chemical weathering rates within and between regions. Mean R-values (± 95 % confidence intervals) from inside sites were 65.9 ± 0.6 and 66.9 ± 0.6 for rock surfaces composed of pyroxene-granulite gneiss in Jotunheimen at altitudes of 990–1360 m above sea level and granite and granitic gneiss in the Jostedalsbreen region at 270–620 m a.s.l. The corresponding values from outside sites of 39.9 ± 0.9 and 39.0 ± 0.9 were significantly lower, indicating a higher degree of chemical weathering. In contrast, regional differences in mean R-values were insignificant. A similar pattern is reflected in indices of rock weathering (39.0 % for Jotunheimen and 41.6 % for Jostedalsbreen), and weathering rate (2.8 R-value units and 3.0 units per 1000 years, respectively). These results imply an estimated minimum age resolution of Schmidt-hammer exposure-age dating of ~265–315 years and a maximum age range of ~20,000 years. They suggest potential application of the Schmidt hammer to both studies of weathering rates and exposure-age dating at the regional scale, despite lithological variation associated with different rock types and climatic variation associated with altitudinal differences of up to 1000 m between the sites.

• Journal Article Type: Article
• Acceptance Date: Mar 7, 2024
• Online Publication Date: Mar 26, 2024
• Publication Date: Jun 1, 2024
• Deposit Date: Aug 15, 2024
• Publicly Available Date: Mar 27, 2026
• Journal: Geomorphology
• Print ISSN: 0169-555X
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 454
• Article Number: 109139
• DOI: https://doi.org/10.1016/j.geomorph.2024.109139
• Public URL: https://uwe-repository.worktribe.com/output/12789668