Morphological and sedimentary evolution of an alluvial floodplain in an urban area: geoarchaeological approaches and applications (Tours, France)

International audience; Urban zones on alluvial plains offer considerable geoarchaeological potential for understanding river dynamics over large time spans and their relationship with land use, because of the extensive subsoil data that is available. In the alluvial plain of Tours, lying between the Loire and the Cher, multidisciplinary studies of the relationships between societies and environment have been conducted as part of an archaeological research programme launched in the 1960s. A sedimentary database containing data for 1309 surveys has been compiled and assembled in a geographic information system to produce geostatistical models of valley bottom geomorphology. The stratigraphy and chronology of alluvial filling have also been studied with information and C14 and OSL dating obtained during archaeological operations. Taken together, the results offer a new interpretation of the morphological evolution of the alluvial plain of Tours from the Weichselian to the present day, by providing new information that either validates or invalidates previous hypotheses: bedrock incision prior to the end of the Weichselian Upper Pleniglacial, coarse sedimentation during the Lateglacial, relative morphological stability up to the late Holocene. The morphological context of the first human settlements, which are not concentrated on the low alluvial reliefs, and the role of urbanization conditions on the present morphology of the valley floor are also presented. This applied study shows the relevance of combining different methodological approaches.