Inland aeolian deposits of south-west France: Facies, stratigraphy and chronology

Archaeological investigations undertaken along a proposed highway together with the compilation of available geological and pedological data made it possible to give a first overview of the distribution of Pleistocene aeolian deposits in south-west France. A chronological framework for deposition has been obtained using both radiocarbon (n=24) and luminescence (n=26) dating. It shows that aeolian transport was very active during the Late Pleniglacial, between 15 and ~23ka, leading to sand emplacement over a 13 000-m² area at the centre of the basin. The Pleniglacial coversands are typified by extensive fields of small transverse to barchanoid ridges giving way to sandsheets to the east. Subsequent aeolian phases, at ca. 12ka (Younger Dryas) and 0.8-0.2ka (Little Ice Age), correspond to the formation of more localized and higher, mainly parabolic dunes. At the southern and eastern margins of the coversand area, aeolian dust accumulated to form loess deposits, the thickness of which reaches ~3m on the plateaus. Luminescence dates together with interglacial-ranking palaeoluvisols between the loess units clearly indicate that these accumulations built up during the last two glacial-interglacial cycles. The chronology of sand and loess deposition thus appears to be consistent with that already documented for northern Europe. This suggests that it was driven by global climate changes in the northern hemisphere. The relatively thin aeolian deposits (and particularly loess) in south-west France is thought to reflect both a supply-limited system and a moister climate than in more northern and continental regions.