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.