Direct push applications in wetland (geo)archaeology

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In pre-historic and historic times floodplain edges and lake shorelines were preferential settlement areas. Buried archaeological features like pile-dwellings, weirs, hythes, or mills are fairly abundant in wetlands. These (geo)archaeological archives are highly valuable, since the high groundwater level ordinarily provides excellent preservation conditions for organic-rich proxy-parameters and artefacts. However, wetlands are characterised by difficult exploration conditions that require complicate and costly excavation techniques due to the impact of groundwater inflow and highly unstable trench edges. Alternatively used classical driving core techniques often suffer from high compaction rates of organic layers and thus show a bias in depth accuracies. Regarding these challenging issues we focus here on direct push sensing with special interest on two key sites in Bavaria: pile dwellings at Pestenacker (UNESCO-World Heritage Site) and Charlemagne's canal, the Fossa Carolina. Both locations represent prominent sites in wetlands which are characterised by complex archaeological strata but also by a high diversity of fluvial, palustrine and lacustrine facies types. Direct push sensing represents a set of tools for performing subsurface records by pushing small-diameter, hollow steel rods with different probes into the ground. This technique is mostly applicable in unconsolidated sediments that are typically less than 30 m below the surface. Thus, continuous in situ measurements provide high-resolution vertical data logs up to a depth-accurate resolution in the cm-scale. We aim to evaluate the potential of direct push sensing in wetland (geo)archaeology. We focus on depth-accurate recording of buried archaeological structures and on the high-resolution detection of different facies types in wetlands. Within an integrated multidisciplinary approach, minimally invasive direct push techniques are combined with a large set of geophysical and (geo)archaeological methods. Direct push techniques will be applied in three different spatial dimensions: a) medium-scale detection of the lateral extents of archaeological sites, b) small-scale detection of wetland stratigraphies including their depth-accurately vertical dimension, and c) high-resolution micro-scale reconstruction of archaeological features. Our Pestenacker-specific objectives focus on the analysis of the lateral extent of the pile dwellings and their intercalation with the Neolithic water body, on the depth-accurate reconstruction of the site's vertical extent including the probable discovery of an earlier phase of foundation, and on minimal-invasive, micro-scale reconstruction of previous not-excavated pile dwellings. Our Fossa Carolina-specific objectives focus on the detailed reconstruction of buried Carolingian canal structures in zones of high groundwater-table. As archaeological excavations are difficult to conduct there, we will evaluate direct push sensing as an alternatively concept.