A staged geogenetic approach to underwater archaeological prospection in the Port of Rotterdam (Yangtzehaven, Maasvlakte, The Netherlands): A geological and palaeoenvironmental case study for local mapping of Mesolithic lowland landscapes

This study presents the geogenetic approach to detect presently drowned archaeological sites in the transgressive palaeoenvironment of the Holocene Rhine-Meuse delta. A staged and practical approach is advocated in which subsurface archaeological predictions are based on geological mapping and palaeoenvironmental reconstruction of the underwater location. The study area is located in the Maasvlakte harbour extension of the Port of Rotterdam, formerly a part of the southern North Sea. Prior to construction works, it was suggested that dredging of the new harbour (Yangtzehaven) would disturb the subsurface stratigraphy to around-21m below present mean sea level, a zone which is known to contain archaeological remains. The staged approach makes use of geological data starting from a conceptual model that indicates the depths of layers that could be rich in Upper Palaeolithic/early Mesolithic artefacts. This initial model is used to determine the strategy of the subsequent phases of investigation, such as whether to proceed with dredging as part of the engineering work, down to 17m water depth, to remove the upper (younger) sands and thereby improve the opportunities for underwater survey of fluvio-deltaic layers of Mesolithic age. Following the development of the initial site model, a full-area investigation was carried out using geophysics and coring, the latter providing material for palaeoenvironmental analysis. This allowed the reconstruction of the long-drowned former landscape, which included inland dune areas and local drainage systems and provided the physiographic context for the geoprospection of Mesolithic archeology. This predictive modeling identified two areas in the harbour for detailed investigation, again employing geophysics and coring at higher resolutions, allowing fine tuning of the palaeolandscape models at the localities of presumed highest archeological potential. Cores from one of the selected areas, an inland dune area within the Early Holocene wetland region, yielded in-situ evidence of Mesolithic occupation of this site in what is now the southern North Sea. These finds and the palaeolandscape context created with the data from the prospection phases were critical in the decision to undertake an underwater archaeological excavation using a large, boat-mounted grab sampling system. This paper provides an account of the geological and palaeoenvironmental work undertaken in the prospective phases leading up to the discovery of the site, highlighting the importance of the staged geogenetic approach for informing sampling strategies and securing high-quality information on landscape contexts, which in turn, informed archaeological decision-making and geoprospection strategies. Such an approach has wider generic application for palaeolandscape reconstruction and mapping at regional scales. © 2014 Elsevier Ltd and INQUA