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 ORCID: 0000-0002-0682-783X, Robbins, Celia and Winkler, Stefan (2024) Schmidt-hammer R-values from glacially-scoured bedrock surfaces across glacier-foreland boundaries: insights into Holocene weathering rates with implications for exposure-age dating. Geomorphology. (In Press)

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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 ~350–625 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.

Item Type:	Article
Article Type:	Article
Uncontrolled Keywords:	Schmidt hammer; R-values; rock-surface weathering; chemical weathering; exposure-age dating; glacier forelands; field experiment; South Norway
Subjects:	G Geography. Anthropology. Recreation > GB Physical geography G Geography. Anthropology. Recreation > GE Environmental Sciences
Divisions:	Professional Services > Academic Development Unit
Research Priority Areas:	Society and Learning
Depositing User:	Anne Pengelly
Date Deposited:	13 Mar 2024 12:33
Last Modified:	13 Mar 2024 12:33
URI:	https://eprints.glos.ac.uk/id/eprint/13822

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