EVOLUTION OF THE ALLUVIAL PLAIN IN THE ``RIED NORD'' AREA: PALEOENVIRONMENT AND ANTHROPIC INTERACTIONS SINCE BRONZE AGE TO ANTIQUITY/EARLY MIDDLE AGE (ROESCHWOOG, BAS-RHIN, ALSACE)

Résumé : Geomorphological studies led in the natural region of ``Ried nord'' allowed to comprehend its hydrological mechanisms and evolutions from the Bronze Age to the Antiquity / Early Middle Age. Livelihood in this area has also been assessed. During the Bronze Age (2 859-2 757 cal. BP; 3 441-3 264 cal. BP), the site is occupied by an active meander of the Rhine. The surrounding landscape is covered by an alluvial forest. Clearing evidences are observed, probably located on the terrace of Haguenau. Then, step by step, the channel is filled. During Hallstatt-Early Tene period (2 759-2 378 cal. BP), the area evolves towards a paludal environment and clearing activities are identified in the surroundings; first evidence of anthropisation and fanning are recorded. After this paludal episode, the ``Ried nord'' shows hydrological activity taking back and alluvial forests cover again the landscape. However on-going farming evidences are recorded. Around 2 296-1 999 cal. BP, the channel is active again and the stream flow raises regularly. Over this period, pollen grains are not preserved. Progressively, the size of the channel seems to decrease until its permanent closure at the beginning of the Antiquity. In the Early Middle Ages the ground is stable enough to allow the settlement implementation.