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 glaciallytransported
boulders e 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
31.4e48.8 ka (10Be) and 31.7e60.0 ka (26Al). This challenges the view that any glaciation this far south
must belong to Middle Pleistocene glaciations, such as the Anglian Stage (c. 480e420 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) 4e3) 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 (26e21 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.

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ORCID for A.G. Brown: orcid.org/0000-0002-1990-4654

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