ESR dating of the Clain alluvial deposits at Saint-Georges-Lès-Baillargeaux (Vienne, France). Geological and archaeological implications

The establishment of a system of at least four fossil alluvial terraces staged during the Quaternary is attested in the valley of the Clain, a tributary of the Vienne, and several witnesses are still visible in the landscape. Alluvial deposits from one of these terraces are located in the commune of St Georges-les-Baillargeaux, at the place called "la Gratteigne" in a Clain palaeomeander. Due to its relative altimetry, this vestige of the alluvial sheet has been attributed to the Fx sheet of the Alluvial system. It was exploited as a sandpit for nearly a century and many lithic industries were discovered throughout the extraction work. These industries, both Acheulean, were saved and studied by an amateur researcher, Maurice Taillet, and are today deposited in the Sainte-Croix Museum in Poitiers. This alluvial formation was the subject of a geological and archaeological study between 2015 and 2018, as part of an operation led by Jean Airvaux and David Herisson. The dating results show that the Clain paleomeander alluvial deposits at St Georges-les-Baillargeaux were deposited in several phases that can be globally attributed MIS8. The first phase (Fluvial 1: US 14 to 12), with ages between 261 and 337 ka (maximum age range given by the uncertainty domains of samples 2016-1 and 2016-2), seems to correspond to the transition between MIS 9 and MIS 8. The second phase ( Fluvial 2: US 11 to 9) corresponds to the MIS 8, with a Alluvial activity end of record around 247 ka. These alluvial deposits are surmounted by important red interglacial soils whose the two lowest levels (US 8 and 7) correspond, according to OSL dating and litho-stratigraphy, to MIS 7. These data make it possible to attribute an age of between 300 and 247 ka for the installation of the Fx (MIS 9/8) of Clain terrace and to make it correspond to the first phase of the Saalian.