Abstract
Wetland environments, with their excellent conservation conditions, provide geoarchaeological archives of past human activities. However, the subsurface soil is difficult to access due to high groundwater tables, unstable sediments, and the high cost of excavation. In this study, we present a ground-based non- and minimal-invasive prospection concept adapted to the conditions 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 geophysically surveyed intensive linear magnetic anomaly parallel to the Carolingian canal, we aimed to prove potential off-site traces of Carolingian construction activities. In this context, we built up a high-resolution cross-section using highly depth-accurate direct push sensing and ground-truthing. Our results showed the exact geometry of the canal and the former banks. Thus, the magnetic mass anomaly could be clearly located between the buried organic-rich topsoil and the Carolingian banks. The thermoluminescence dating showed that the position of the magnetic mass anomaly reflected Carolingian activities during the construction phases, specifically due to heat exposure. Moreover, we found hints of the groundwater supply to the 5-metre wide navigable fairway.
Highlights
IntroductionThere is a demand for remote, non-invasive, and minimal-invasive exploration approaches for cross-scale, multi-method, and systematic surveys in wetland geoarchaeology in order to investigate, and to monitor, vulnerable archaeological features, e.g., pile dwellings
We modelled the depth of the anomaly at six positions by performing approximately 30 depth calculations out of the superconducting quantum interference device (SQUID) data set (Figure 6)
We focus on the significance of the results of the SQUID magnetic survey and the high-resolution direct push sensing (Figure 9)
Summary
There is a demand for remote, non-invasive, and minimal-invasive exploration approaches for cross-scale, multi-method, and systematic surveys in wetland geoarchaeology in order to investigate, and to monitor, vulnerable archaeological features, e.g., pile dwellings. Non-invasive geophysical surveys can be conducted from large to small spatial scales [9] in a cost-saving way in a wide range of combinations. They offer different sensitivities depending on physical material characteristics, e.g., suspicious values of the magnetic field strength of fire-affected sediments or striking values of electrical conductivity of saturated ditch fillings, e.g., [12,13]. For effective conduction and credible results of non- and minimal-invasive exploration methods, a well thought-out field strategy with the on-site decision [18] as well as a combination of carefully selected parameters with suitable sensitivities for the targeted features are necessary [14,19,20]
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