Spår i marken : Grundämnes- och lipidanalys av jordprover för studier av rumslig organisation och postdepositionella processer i undersökningsområde 1 (UO1), Bårby borg under folkvandringstid

Sammanfattning

Archaeological soils and sediments contain chemical and biomolecular traces of past human activities, providing valuable insights into site formation processes, spatial organisation, and patterns of use. This study aims to investigate variations in elemental composition and lipid profiles in soil samples from an excavation area at Bårby ringfort, Öland, Sweden, dated to the Migration Period. The aim was to examine how organic and inorganic signatures vary between different stratigraphic contexts and to assess their relationship to use, deposition, and post-depositional processes within the excavated structures. Soil samples from occupation layers, floor-related cultural deposits, and a burnt destruction layer were analysed using X-ray fluorescence spectroscopy and gas chromatography-mass spectrometry. Statistical analyses revealed significant differences in elemental composition between context types. Occupation layers displayed consistently elevated concentrations of phosphorus (P), zinc (Zn), and iron (Fe), together with rich assemblages of bone, ceramics, and macrobotanical remains. These patterns are interpreted as the result of repeated deposition and long-term accumulation of organic material associated with everyday activities. In contrast, the burnt layer exhibited substantial internal variability, reflecting a complex mixture of charred building materials, redeposited sediments, and organic residues. Floor-related deposits showed comparatively lower concentrations of anthropogenically associated elements and occupied an intermediate position within the dataset. Lipid analyses produced relatively homogeneous profiles dominated by common plant-derived fatty acids. No resin-related biomarkers were identified, suggesting either variation in organic building materials between structures or the degradation of more sensitive compounds through burning and post-depositional alteration. The results demonstrate that chemical differences between depositional environments can be identified despite extensive burning, disturbance, and long-term post-depositional processes. Rather than representing strictly separated activity areas, the analysed contexts appear to form part of a shared depositional landscape shaped by recurring human activities, destruction events, and subsequent chemical transformation.