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This paper represents a synthetic overview of the main results of the CNRS Programme " Palaeoenvironments and Hominids ". This project focused on the study of interactions between human occupation and environmental modification, between 500 and 10 kyrs BP, based on multidisciplinary and diachronic studies of key sites in the Somme Basin. The main analytic results concern ESR, TL-IRSL and 14C dates, which reinforce the chrono-stratigraphical interpretation of the various Palaeolithic sites. At the same time, bioclimatic analyses of fluvial sediments (palynology, malacology, analysis of Coleoptera), combined with the measurement of δ13C variations of organic carbon, and of the low-field magnetic susceptibility in loess and fossil soils, allowed the restitution of the various Pleistocene environments, and especially of the full Interglacials, to be refined. The main conclusions of the synthesis of archaeological, chronostratigraphical and environmental data are the following. 1) The earliest human occupations in the Somme Basin are no older than 500-450 kyrs BP and are straight away represented by well evolved Acheulean industries (beginning of MIS 12, according to the data from modern excavations). 2) During the last climatic cycle, human occupation of the Somme Basin was clearly discontinuous and strongly influenced by climatic and environmental modifications: maximum during the Early-Glacial, some occupations during the Lower and Middle Maximum Glaciations, rare occurrences around 23-24 kyrs (14C), total abandonment of the area between 23 and 13 kyrs, then reoccupation with the beginning of the Lateglacial climatic improvement. 3) Although the data are less numerous, the model of the last climatic cycle seems to apply during the Middle Pleistocene for the end of the Saalian (occupation at the end of MIS 7 or at the transition MIS7/MIS6, and desertion of the area during the cold maximum of MIS 6). 4) Finally, between 500/450 and 200 kyrs human settlements mainly occurred during periods of climatic transition (Early or Lateglacial). From a general point of view, the human occupation of the Somme Basin during the Middle Pleistocene was therefore discontinuous and strongly influenced by climatic and environmental factors.

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