PREGLACIAL SURFACE REMNANTS AND QUATERNARY GLACIAL REGIMES IN NORTHWESTERN SWEDEN

We present a detailed map of the distribution of preglacial surface re mnants in the Kebnekaise region of northwestern Sweden. In this mounta in area we discern four important large-scale geomorphological units, each representing a specific set of erosional agents and formative con ditions. These are: (i) intact preglacial surface remnants, characteri zed by gentle slopes, round summits, wide shallow valleys, and an abse nce of rock basins; (ii) preglacial surface remnants showing signs of minor glacial erosion and deposition; (iii) glacially scoured surfaces , including glacial troughs; (iv) deep fluvial valleys cut into the pr eglacial surface. The pattern of glacial erosion is explained as the r esult of three specific modes of glaciation known to have existed duri ng the last 120,000 years, and inferred to have repeatedly prevailed d uring the last 2.75 million years: cirque glaciation, mountain ice she ets, and Fennoscandian ice sheets. A deep-ocean oxygen-isotope record of foraminifera from the North Atlantic (DSDP 607) was used to infer t he temporal extent of these modes of glaciation during the last 2.75 m illion years. We interpret the preglacial landscape preservation and t he pattern of glacial erosion in terms of the configuration, the basal thermal regime, and the duration of such glaciation events. The avera ge subglacial thermal regime of both ice sheet types was frozen on the uplands and melting in the main valleys, where outlet glaciers and ic e-streams formed. The pre-glacial landscape is best preserved at inter mediate elevations, low enough not to have been covered by cirque glac iers, and apparently high enough not to have experienced melted-bed co nditions and subglacial erosion during ice sheet overriding events. In a narrow high-relief zone along the elevation axis, interglacial fluv ial erosion was morphologically important. The absence of glacial eros ion on uplands in this zone allowed fluvial erosion to commence on the same locations during each ice-free interval. In contrast, no persist ent fluvial valley pattern could develop in zones subjected to repeate d glacial scouring and hence, derangement of fluvial patterns.