A relict landscape in the centre of Fennoscandian glaciation: Geomorphological evidence of minimal Quaternary glacial erosion

Abstract

The Parkajoki area in northeastern Sweden is situated near the central area of Fennoscandian glaciation. Despite its location, the area is dominated by landforms induced by subaerial weathering and erosion processes, such as well-developed tors and associated saprolites, boulder fields, and boulder depressions. The glacial geomorphology is dominated by lateral and proglacial meltwater channels. Subglacial imprints indicative of thawed-bed conditions and reshaping by glacier sliding (e.g., fluting, drumlins, striae) are lacking. Hence, most of the landscape still exhibits a preglacial appearance. Because of its location, near the central area of glaciation, we attribute preservation to frozen-bed conditions of overriding ice sheets. The widespread distribution of well-developed tors and boulder fields, and the degree of chemical weathering of the bedrock, indicate that the area has been protected from glacial erosion during all glacial cycles since ice sheet initiation in the late Cenozoic. Unlike most other areas with tors in glaciated regions, the Parkajoki area is uniquely situated in the lowlands at 150–400 m.a.s.l. Moreover, this relict landscape is surrounded by glacial landscapes (including drumlins, ribbed moraine, and eskers) of varying age and at similar elevation. Hence, topographical reasons for this area being persistently cold-based cannot be invoked. By inference, we conclude that strain heat release never managed to cancel the initial subglacial permafrost conditions. We attribute this to divergent ice flow towards the convex outline of the ice sheet margin during deglaciations and to the relative roughness of the area compared to its surroundings. The implication is that to explain preservation throughout the Quaternary, all large-scale glaciations must have had a similar evolution concerning ice sheet configuration and internal dynamics as the last glaciation for which good constraints on evolution and outline are available.