Weathering regimes and pedogenic variability on large boulders, Karkevagge, northern Scandinavia

Soil and rock from mica-schist, and garnet-mica-schist boulders in Kärkevagge, a deglaciated valley in Northern Sweden, were used to characterize the weathering regime and determine the extent of pedogenic variability. The boulders approximated “closed-systems” as their tops were horizontal, and there was a minimal input of material.; The boulder-top soils were weakly developed, and exhibited the following characteristics: shallow depth; minimal horizonation; predominantly coarse sandy loam; well drained; acid pH; weak base saturation; and low CEC. They were classified as loamy, micaceous, acid, Lithic Cryorthents.; The following conclusions were established from field, laboratory, and statistical analyses: (1) Clay content was marginally greater in soils developed on garnet-mica-schist than mica-schist; (2) Silt and clay content did not reflect eolian sediment input; (3) Soils that have formed on boulder tops are characterized as residual soils; (4) Deeper soils had developed overlying vertical schistocity; (5) Muscovite, chlorite and mixed-layer (ML) minerals were the predominant clay minerals in the boulder soils, with the presence of the secondary clay minerals indicating that chemical weathering was occurring; (6) The soil-rock interface is presumed to be the location where most of the chemical activity concentrates, which when combined with the effects of schistocity indicates that microvariability and microenvironment are important to weathering and pedogenesis in Kärkevagge; (7) Despite characterization as weakly developed soils, embryonic spodic properties are evident in a number of the boulder-top soils; and (8) While Kärkevagge is a mild arctic environment, and boulder-top soil development was characterized as weak, there is substantial chemical weathering occurring in the form of oxidation. Based on these conclusions this study of the boulder-top microenvironment provided further support for chemical weathering as an active geomorphic process in Kärkevagge.