The last 1 Ma record from the fluvial terraces system of the River Somme Valley (Northern France) and the background of the earliest Acheulean occupation of Northwestern Europe

Following the discovery at the end of the 19th century of the famous Palaeolithic sites of Abbeville “Moulin-Quignon” and Amiens “Saint-Acheul” (type-site of the Acheulean), the River Somme valley has been for a long time recognized as the “cradle of Prehistory” in Europe. It is also the place where the first approach combining geology and prehistory, known as “archaeogeology”, was conceptualised by Boucher de Perthes (1850). Modern research or “geoarchaeology”, combining geology, geomorphology, sedimentology, pedology, palaeontology and archaeology was later developed in the valley, especially during the pioneering works by Bourdier in the 1970s. During the last 30 years, the study of the Quaternary sequences of the Somme basin, coupled with the development of absolute dating methods (ESR on fluvial quartz, ESR/U-series on large mammal teeth, TIMS U-series on calcareous tufa, OSL on sediment and TL on heated flints), has made the Somme terrace system an international reference for both Pleistocene geology and archaeology. It is presently one of the best locations in Europe for the evidencing of the response of river systems to glacial-interglacial climatic cycles during the last Ma. This system, fully incised in the Cretaceous bedrock, is made up of 10 stepped alluvial formations spread over 55 m of relative altitude. The resulting fluvial staircase is covered by thick slope deposits (loess-palaeosol sequences up to 8 m thick), the complexity of which increases with the age of the underlying fluvial sequence. Researches are completed by investigations undertaken on the present valley infilling in which systematic radiocarbon dating allows an accurate correlation between the various units of the morpho-sedimentary sequence and climatic events during the last Glacial-Interglacial cycle. Recent discoveries such as the Gravettian site of Amiens-Renancourt (2013) or the rediscovery of the emblematic Acheulean site of Abbeville Moulin Quignon now dated ca 670 ka (2016) have reinforced the importance of the Somme valley in current researches. This work is thus a fundamental and still evolving contribution to the study of the relationship between Europe's earliest human settlements and climatic and environmental variations and new investigations are planned for 2023 in the frame of the “Lateurope” ERC project