Schmidt hammer exposure dating (SHD) the Last Glacial-Interglacial Transition in Wester Ross, Scotland

Abstract

Understanding the extent, retreat dynamics and climate-glacier coupling of the Scottish Ice Sheet during the Last Glacial-Interglacial Transition (LGIT) is hampered by a highly fragmentary geomorphological record, and is dependent on a precise and accurate dating framework to constrain deglaciation. On land, readvance of the retreating ice margin is recorded in part of NW Scotland by moraines of the Wester Ross Readvance at ~15.4-15.8 ka, preceding the Lateglacial Interstade and the Loch Lomond Stade ~12.9-11.7 ka. While the number of dated landforms has increased in recent years, the LGIT chronology in NW Scotland is primarily based on a limited number of samples per site, using Terrestrial Cosmogenic Nuclide Dating (TCND) methods that can yield conflicting or uncertain results. This highlights the value of developing complementary dating methods. Previous studies have questioned the reliability of the Schmidt hammer exposure dating (SHD) technique on lithologies other than granite. This research (i) evaluates the use of SHD on sandstone in the NW Scottish Highlands; (ii) develops a local, lithology-specific calibration curve; (iii) applies this to estimate the age of undated surfaces and tests existing interpretations of landscape change during the LGIT. Field results from a 1,500 km2 area of NW Scotland conclude that SHD can detect significant differences (p <0.001) between Torridonian sandstone surfaces of Wester Ross Readvance and Loch Lomond Stadial age. Based on 31 existing, re-calibrated 10Beages, a calibration curve was generated (R2 = 0.58, p <0.001) for the period ~18-11 ka BP, and applied to 17 undated Torridonian sandstone surfaces. Our findings support the view that on selected lithologies and with rigorous adherence to careful field procedures, SHD can represent a valuable, cost-effective and reliable tool for obtaining large numerical dating samples for landforms in formerly glaciated terrain.