High-resolution direct push sensing in wetland geoarchaeology – first traces of off-site construction activities at the Fossa Carolina
in: Remote Sensing (2021)
Wetland environments provide geoarchaeological archives of past human activities with excellent conservation conditions. However, the underground is difficult to access due to high groundwater tables, unstable sediments, and high excavation costs. In this study, we provide a ground-based non- and minimal-invasive prospection concept adapted to the requirements of wetlands. We investigated the Fossa Carolina in South Germany, a canal that was intended in 792/793 AD by Charlemagne to bridge the Central European Watershed. Although the resulting Carolingian banks and the fairway with wooden revetments are very imposing, archaeological traces of off-site construction activities have not been identified hitherto. Based on a geophysical surveyed intensive and linear magnetic anomaly parallel to the Carolingian canal, we aim to prove potential off-site traces of Carolingian construction activities. In this context, we build up a high-resolution cross-section with highly depth-accurate direct push sensing and ground truth. Our results show the exact geometry of the canal and the former banks. Thus, the magnetic mass anomaly can be clearly located between the buried organic-rich topsoil and the Carolingian banks. According to the position of the magnetic mass anomaly and the TL dating, this reflects Carolingian activities during the construction phases, specifically due to heat exposure. Moreover, we found hints for groundwater supply to the 5 m wide navigable fairway.