Organic Geochemical Evidence for Pine Tar Production in Middle Eastern Sweden During the Roman Iron Age

Several funnel-shaped features of unknown function were discovered at excavations related to a new stretch of the highway E4 in middle Sweden during 2002–2003. These features could be sub classed into two categories: large funnel-shaped pits dated to 600–1100 AD (Vendel period – Viking Age) and small funnel-shaped pits dated to 240–540 AD (late Roman Iron Age – Migration period) respectively. Soil samples were analysed for diterpenoids derived from abietic acid (mainly retene, abietic acid, dehydroabietic acid and methyl dehydroabietate) by Gas Chromatography-Mass Spectrometry (GC-MS) in order to test the hypothesis that the features might be connected to pine tar manufacture. For comparison, samples from historically known pine tar and charcoal production features were analysed. The resinous fraction in the larger funnel-shaped features were very similar to those of the historical pine tar and charcoal production features, while the composition in the small funnel-shaped pits was dominated by retene and methyl dehydroabietate. The biomarker, methyl dehydroabietate, could be identified in several of the soil samples from the funnel-shaped pits. We suggest that both of these features have been used for pine tar production, which makes the smaller funnel-shaped features the oldest known tar production features in Europe.