Inherited landforms and glacial impact of different palaeosurfaces in southwest Sweden

Landforms are used as analytical tools to separate inherited features from the glacial impact on Precambrian basement rocks in southwest Sweden. The s tudy covers three different palaeosurfaces, the sub-Cambrian peneplain (rel ative relief (r.r.) 0-20 m) with the character of a pediplain, an uplifted and dissected part of the sub-Cambrian peneplain (r.r. 5-40 m) and an etch- surface (r.r. 20-135 m), presumably sub-Mesozoic. The surfaces were recentl y re-exposed, probably due to a Neogene upheaval with some pre-glacial resh aping. Strong structural control and no alignment with glacial erosional di rections other than those coinciding with structures,are arguments for etch processes as a most important agent for relief differentiation. This is st rengthened by the occurrence of saprolite residues and etchforms in protect ed positions. The glacial reshaping of the sub-Cambrian flat bedrock surfaces is negligib le. The glacial impact becomes more evident in the uplifted and dissected p arts of the peneplain and within the hilly sub-Mesozoic surface. The higher the initial relief the more effect of glacial erosion on individual hills, both on the abrading side, with formation of roches moutonnees, and on the plucking side. Detailed etchforms are preserved in protected positions in spite of erosion by a clearly wet-based ice. The magnitude of the Pleistoce ne glacial erosion is considerably less than the amplitude of the palaeorel ief in the entire area. Landscapes of areal glacial scouring have been described as comprising irre gular depressions with intervening bosses scraped by ice and labelled 'knoc k and lochan' topography, but we suggest that an etched bedrock surface is a prerequisite for this type of landscape to develop.