Weathering processes and Quaternary origin of an alpine blockfield in Arctic Sweden

The weathering and origin of an autochthonous blockfield in the northern Swedish mountains were investigated through an examination of fine matrix and clasts from two pits excavated across ridge-top sorted circles; one on a summit, the other in a saddle. At the summit, fine matrix chemical weathering is limited to the production of poorly crystallized Al- and Fe-oxyhydroxides, whereas some additional vermiculitization and gibbsite crystallization occurs in the saddle. In both locations, volumes of clay-sized matrix are low, mass balance calculations indicate only minor elemental losses and no chemically etched grains are visible under a scanning electron microscope (SEM). In addition, soil horizons are absent and chemical weathering intensity is uniformly low across both excavated sorted circles. Minor clast chemical weathering consists of Fe oxidation, which dominates in the matrix-rich circle centres, and some rind development, which increases in frequency in the clast-rich rings. The dominance of physical weathering processes and the presence of only minor chemical weathering, in both fine matrix and clasts, indicate that the blockfield is not a Neogene weathering remnant. Rather, the blockfield has a Quaternary origin, developing during interglacials, interstadials and the Holocene, primarily through subsurface weathering processes.