Sedimentary record and Holocene environment of the Giessen alluvial plain (Scherwiller, Bas-Rhin, Alsace)

National audienceSEDIMENTARY RECORD AND HOLOCENE ENVIRONMENT OF THE GIESSEN ALLUVIAL PLAIN (SCTIERWILLER, BAS-RHIN, ALSACE) Geological and geomorphological studies performed during an operation of preventive archaeology (Pare d'Activites Economiques Intercommunal du Giessen, Scherwiller, Bas-Rhin. 2008 on paleochannels of a vosgian river, the Giessen, provide new insight on the formation, the evolution and the interactions between man and environment in this area during the Holocene. The approach was based on the field observation and data from sedimentology, chronostratigraphy and palynology. During the early and middle Holoene, the studied zone was crossed by three channels: they are respectively dated from the Boral (10200-8900 cal. BP) early Atlantic (8900-6800 cal. BP) recent Atlantic 16800 - 5700 cal. BPI and Subboreal (5700-2600 cal. BPl. They migrated step by step to the northward to the course of the present river. The presence of an artificial antic pool, around which Gallo-Roman farm activity was developed has allowed the recording and anlysis of the recent Holocene sequences. No deposit by the Giessen in the 111(th) Century is recorded. The alluvial plain alterated between wet and drier zones. From the IVth Century. Gallo-Roman occupation and the Giessen River seem to have migrated away from the pool, and the depression was filled by the deposition of suspended overflow material. From the VIIIth century until the contemporary period, the area was covered by deposits of Giessen overflow. The diversity of sedimentary facies underlines the large potential of the Giessen divagations. This increase of the deposits is associated with a constant land-clearing