Geomorphic evidence for recurrent cold-based ice conditions in Nordic uplands during the Quaternary glaciations (Aurivaara Plateau, North Sweden)

The Aurivaara Plateau in northern Sweden (68°N) displays apparently contrasting geomorphic patterns: on the one hand, wide-spread glacial deposits suggesting the complete overriding of the area by the Scandinavian ice sheet; on the other, well-preserved fragile tors and related spalling rounded corestones similar to those found in non-glaciated areas like Dartmoor. The association of preglacial weathering residuals and allochthonous deposits belonging to several Quaternary glaciations are attributed to a dominantly cold-based glacial regime. Field investigations and laboratory analyses of morainic material associated with 15 tor-like features scattered on the plateau suggest that till material and erratic blocks were repeatedly dropped during deglaciation stages deep into the tor joints and within associated blockfields without the glacial periods having had any significant erosional impact. The overall conservative glacial system of this upland area strongly contrasts with the high geomorphic impact of glacial erosion in the nearby lowland area, where Quaternary glaciations resulted in the 190 m overdeepening of the Torneträsk basin. The Aurivaara case study therefore supports both the glacial palimpsest theory developed in Scandinavia and the selective erosion model established in Scotland and North America.