The surface geometry of the Last Glacial Maximum ice sheet in the Andøya  Ska ˚nland region, northern Norway, constrained by surface exposure dating and clay mineralogy ATLE NESJE, SVEIN OLAF DAHL, HENRIETTE LINGE, COLIN K. BALLANTYNE, DANNY MCCARROLL, EDWARD J. BROOK, GRANT M. RAISBECK AND FRANCOISE YIOU BOREAS Nesje, A., Dahl, S. O., Linge, H., Ballantyne, C. K., McCarroll, D., Brook, E. J., Raisbeck,G. M. & Yiou, F. 2007 (July): The surface geometry of the Last Glacial Maximum ice sheet in the Andøya  Ska ˚nland region, northern Norway, constrained by surface exposure dating and clay mineralogy. Boreas, Vol. 36, pp. 227  239. Oslo. ISSN 0300-9483. Blockfields, weathering boundaries and marginal moraines havebeen mapped along a longitudinal transect from northern Andøya to Ska ˚nland in northern Norway. The degree of rock-surface weathering above and below glacial trimlines, clay  mineral assemblages and surface exposure dating based on in situ cosmogenic 10 Be have been used to reconstruct the vertical dimensions and timing of the Last Glacial Maximum (LGM) of the Scandinavian Ice Sheet in this region. The cosmogenic exposure dates suggest that the lower blockfield boundary/ trimline along the Andøya  Ska ˚nland transect represents the upper limit of the Late Weichselian ice sheet, with an average surface gradient of c. 9.5 m/km. The surface exposure dates from Andøya pre-date the LGM, suggesting that the LGM ice sheet did not reach mountain plateaux at northwest Andøya. The results thus support evidence from lake sediment records that the northern tip of Andøyawas not covered by the Scandinavian Ice Sheet during the LGM. Atle Nesje (e-mail: atle.nesje@geo.uib.no), Department of Earth Science, University of Bergen, Alle ´gaten 41, NO-5007 Bergen, Norway, and Bjerknes Centre for Climate Research, University of Bergen, Alle ´gaten 55, NO-5007 Bergen, Norway; Svein Olaf Dahl (e-mail: svein.dahl@geog.uib.no), Department of Geography, University of Bergen, Fosswinckelsgate 6, NO-5020 Bergen, Norway, and Bjerknes Centre for Climate Research, University of Bergen, Alle ´gaten 55, NO-5007 Bergen, Norway; Henriette Linge (e-mail: henriette.linge@geo.uib.no), Bjerknes Centre for Climate Research, Alle ´gaten 55, NO-5007 Bergen, Norway, and Department of Earth Science, University of Bergen, Alle ´gaten 41, NO-5007 Bergen, Norway; Colin K. Ballantyne (e-mail: ckb@st-and.ac.uk), School of Geography and Geosciences, Universityof St Andrews, St Andrews, Fife KY16 9AL, UK; Danny McCarroll (e-mail: d.mccarroll@swansea.ac.uk), Department of Geography, University of Wales, Swansea, Singleton Park, Swansea SA2 8PP, UK; Edward J. Brook (e-mail: brooke@geo.oregonstate.edu), Department of Geosciences, 104 Wilkinson Hall, Oregon State University, Corvallis, OR 97331  5506, USA; Grant M. Raisbeck (e-mail: raisbeck@ csnsm.in2p3.fr); Francoise Yiou, Centre de Spectrome ´trie Nucle ´aire et de Spectrome ´trie de Masse, F-91405 Campus Orsay, France; received 10th April 2006, accepted 8th September 2006. Previously published models of the thickness of the Late Weichselian Scandinavian Ice Sheet have sug- gested an entirely covered landmass in Norway (Vorren 1977; Andersen 1981; Boulton et al. 1985; Siegert et al. 1999, 2001). Consideration of the geographical dis- tribution of certain plant species has generated con- siderable debate concerning the possible existence of ice-free areas (refugia) in the western Scandinavian mountains during the Last Glacial Maximum (LGM) (e.g. Birks 1993; Brochmann et al. 2003). The main geological argument for ice-free areas in western Scandinavia during the LGM has been the consistent geographical and altitudinal distribution of trimlines marking the lower boundary of frost-shattered bedrock and continuous mantles of autochthonous blockfields with sharp lower limits (e.g. Nesje et al. 1987, 1988). Blockfields commonly consist of in situ angular boulders and stones up to several metres thick and formed through mechanical and chemical weathering of the local bedrock. Various investigations have demonstrated that the blockfields in summit regions of Scandinavia and Svalbard are of pre-Late Weichse- lian age (Nesje et al. 1987, 1988; Kleman & Borgstro ¨m 1990; Rea et al. 1996; Landvik et al. 2003). Occurrences of clay  mineral assemblages in blockfield material in western Norway have been interpreted as the result of preglacial weathering (Roaldset et al. 1982). The areas of the most extensively and deeply weathered block- fields in southern Norway occur on the preglacial land surface (Nesje et al. 1988). Extrapolation of the pale ´ic surface in southern Norway into the North Sea by following seismic reflectors (Jensen & Schmidt 1992) suggests that this surface (and thus the most well- developed blockfields) may be of Mesozoic to Tertiary age. In places, blockfield debris extends below the surface of the inferred trimline, but this reflects subsequent down-slope mass movement (allochtho- nous blockfields) (Nesje et al. 1988). In parts of western Scandinavia, pinnacled alpine summits characterize areas above certain altitudes, DOI 10.1080/03009480601024804 # 2007 Taylor & Francis