Clay mineralogy, chemical weathering and landscape evolution in Arctic–Alpine Sweden

Abstract

The purpose of this research was to: (1) characterize the clay mineralogy of soils in and adjacent to Kärkevagge, a recently deglaciated valley in Arctic Sweden, (2) document chemical weathering in a periglacial environment and (3) use the mineralogy to help explain landscape evolution. Soil samples were analyzed from 11 sites that differ in elevation, parent material, drainage, slope and vegetation. Parent materials include residuum, alluvium, colluvium and glaciofluvial material derived from garnet–mica–schist, plus, in one locality, a till of granitic origin. X-ray diffraction (XRD) was used to characterize the clay-size fraction (<2 μm). Muscovite, chlorite and mixed-layered (ML) minerals are the predominant soil minerals identified. ML minerals indicate chemical weathering and also act as tracers used to identify source areas of soil parent materials. High concentrations of ML minerals in the soils on the alpine ridges flanking Kärkevagge indicate in situ chemical weathering. At lower elevations within the valley, their distribution indicates that the ridges contributed sediments early on in the evolution of the landscape, but more recently the source has shifted towards ML-poor supply areas from lower elevations. Soil chemistry also supports this model; the alpine soils are base-poor while the valley soils are base-rich. The higher abundance of ML minerals in the alpine zone indicates either a long period of weathering or a greater period of development. The latter explanation supports the hypothesis that the ridge crests were covered by cold-based ice during the last glaciation; remnants of which still survive at the highest elevations. Cold-based ice preserved a pre-weathered landscape that was the primary source of the ML minerals in the soils in the valley.