Glaciation of the English Lake District during the Late-glacial: a new analysis using 10Be and Schmidt hammer exposure dating

Recalibration of published ¹⁰Be ages from the classic cirque moraines at Keskadale, Lake District, in combination with calibrated relative ages provided by Schmidt hammer exposure dating (SHED) in the nearby Ling Comb cirque, provide new insights into the extent and retreat history of glaciers during the Late-glacial interval (14.7 - 11.7 ka). Based on a globally-calibrated production rate, glacial surfaces at Keskadale return exposure ages of 12.3 ± 1.1 ka (lower moraine) and 12.5 ± 1.0 ka (upper cirque threshold). A new ¹⁰Be age of 8.6 ± 0.9 ka is reported from a boulder from the lower moraine crest which may reflect post-depositional exhumation, erosion or instability. Alternative locally-calibrated production rates from Scotland produce ¹⁰Be ages that are 5 - 10% older and push the oldest exposure ages to the Allerød-Younger Dryas boundary. At Ling Comb, ~4 km from Keskadale, granitic moraine boulders return calibrated relative ages which span the last glacial-interglacial transition, but these vary by ~6% depending on the choice of production rate. As post-depositional erosion of moraines can profoundly influence the distribution of boulder exposure ages, these data are interpreted as minimum limiting ages, with moraine deposition constrained conservatively to 11.6 ± 1.3 ka to 12.3 ± 1.4 ka. While lithological and geomorphological processes, in combination with production rate uncertainty, complicate interpretation of these datasets, these data appear consistent with Younger Dryas glaciation of Lake District cirques.