Cosmogenic nuclide exposure ages along a vertical transect in western Norway: Implications for the height of the Fennoscandian ice sheet

¹⁰Be and ²⁶Al exposure ages for bedrock samples from a vertical transect at Skåla, in western Norway, provide new constraints on the history of the Fennoscandian ice sheet. The weathered bedrock surface (autochthonous block field) mantling the summit of Skåla has an exposure age of >55 ka, suggesting that this surface formed before the last glacial maximum (∼ 18 ¹⁴C ka or ∼ 21 calendar ka). The block field is truncated by a glacial “trimline” at 1660 m above sea level. Glaciated bedrock below the trimline has an exposure age of 26–21 ka; the range depends on assumptions about erosion rate. Ice therefore receded from this altitude at about the time of the last glacial maximum. The ¹⁰Be age for bedrock immediately below a second, lower, trimline at Skåla suggests a glacial advance or stillstand at 18–13 ka, consistent with previously documented readvances or stillstands at the western and southern margins of the ice sheet.