Soil chemistry, vegetation history and human impact at the Late Holocene iron production site of Åskagsberg, western Sweden

Abstract

A Viking Age/Early Medieval slagheap and remains of clay from furnace walls have been found in the close vicinity of a mire at Åskagsberg, western Sweden (60°17’30’’N, 5°31’42’’E). About 100 m south of the mire, groundwater movements have favoured precipitation of iron oxides to form red soil. Despite the low concentrations of iron in the primary minerals, the red soil contains c. 60% Fe2O3. These concentrations allow direct iron production. The silica content (2–7% SiO2) is probably too low for slag formation, however. To compensate for this deficiency, it is likely that till that was rich in silica was collected at the margin of the mire for mixing with the red soil. A maximum of 10 m3 of red soil is estimated to have been mined, containing c. 104 kg iron. Charcoal incorporated in a piece of slag collected from the bottom of the heap was radiocarbon dated to 990–1160 cal AD. A marked decrease in tree pollen concentration, contemporary with an increase in charcoal particles, indicates that wood cut from the surrounding forest was used for charcoal production between 1000 cal AD and 1350 cal AD. Small-scale cultivation and forest grazing were dated to AD 1600, corresponding to the initiation of the Finnish colonisation.