Soil archives of a Fluvisol: subsurface analysis and soil history of the medieval city centre of Vlaardingen, the Netherlands – an integral approach

The medieval city of Vlaardingen (the Netherlands)was strategically located on the confluence of three rivers,the Maas, the Merwede, and the Vlaarding. A church of the early 8th centuryAD was already located here. In a short period of time, Vlaardingen developedin the 11th century AD into an international trading place and into one ofthe most important places in the former county of Holland. Starting from the11th century AD, the river Maas repeatedly threatened to flood thesettlement. The flood dynamics were registered in Fluvisol archives and wererecognised in a multidisciplinary sedimentary analysis of these archives. To secure the future of these vulnerable soil archives an extensiveinterdisciplinary research effort (76 mechanical drill holes, grain sizeanalysis (GSA), thermo-gravimetric analysis (TGA), archaeological remains,soil analysis, dating methods, micromorphology, andmicrofauna) started in 2011 to gain knowledge on the sedimentological and pedologicalsubsurface of the settlement mound as well as on the well-preserved nature of thearchaeological evidence. Pedogenic features are recorded with soildescription, micromorphological, and geochemical (XRF – X-ray fluorescence) analysis. The soilsequence of 5 m thickness exhibits a complex mix of "natural" as well as"anthropogenic" layering and initial soil formation that enables us to makea distinction between relatively stable periods and periods with activesedimentation. In this paper the results of this interdisciplinary projectare demonstrated in a number of cross-sections with interrelated geological,pedological, and archaeological stratification. A distinction between naturaland anthropogenic layering is made on the basis of the occurrence of thechemical elements phosphor and potassium. A series of four stratigraphic and sedimentary units record the period beforeand after the flooding disaster. Given the many archaeological remnants andfeatures present in the lower units, in geological terms it is assumed thatthe medieval landscape was submerged while it was inhabited in the 12thcentury AD. In reaction to a final submersion phase in the late 12th centuryAD, the inhabitants started to raise the surface of the settlement. Withinarchaeological terms the boundary between natural and anthropogenic layers isstratigraphically lower, so that in the interpretation of archaeologists, the living ground was dry during the 12th and the 13th centuriesAD. In this discussion, the geological interpretation will be compared withalternative archaeological scenarios