Paired 26Al and 10Be exposure ages from Lundy: new evidence for the extent and timing of Devensian glaciation in the southern British Isles

Abstract

Lundy lies in a strategic geographical position for understanding the glacial history of the British Isles. The island bears evidence of glaciation, largely in the form of ice-moulded bedrock and glacially-transported boulders – an unusual occurrence this far south in the British Isles. Irish Sea ice penetrated the western Bristol Channel overriding Lundy from the northwest during the last phase of glaciation in this area. The results of paired terrestrial cosmogenic nuclide analyses (26Al/10Be) constrain the timing of this extensive glaciation and provide, for the first time, an age for the exposure of Lundy granite following deglaciation. The results from nine paired samples yield 26Al/10Be exposure ages of 31.4–48.8 ka (10Be) and 31.7–60.0 ka (26Al). This challenges the view that any glaciation this far south must belong to Middle Pleistocene glaciations, such as the Anglian Stage (c. 480–420 ka) and a Devensian age for the last glaciation is consistent with findings from the Isles of Scilly further south. However, the findings suggest early-mid Devensian (marine isotope stage (MIS) 4–3) glaciation of Lundy. It also implies that the island was exposed or covered for a short time by non-erosive cold-based ice at the global Last Glacial Maximum (LGM) during MIS 2 (26–21 ka). The potential exposure of the island throughout MIS 2 contrasts with the evidence from the Isles of Scilly and the Celtic Sea, which were glaciated at the LGM.