Identification of MIS 11 Interglacial tufa deposit in the Somme valley (France): new results from the Saint-Acheul fluvial sequence

• Published in: Quaternaire
• Main Authors: Antoine, Pierre, Limondin-Lozouet, Nicole
• Format: Article in Journal/Newspaper
• Language: French
• Published: Association Française pour l'Etude du Quaternaire 2004
• Subjects: Tuf calcaire; St 1 1; malacofaunes; France du Nord.; dépôts fluviatiles; vallée de la Somme; interglacial; Calcareous tufa; fluvial deposits; Northern France.; MIS 11; malacofaunas; Somme valley; geo; envir; Arctic
• Online Access: https://doi.org/10.3406/quate.2004.1753; https://www.persee.fr/doc/quate_1142-2904_2004_num_15_1_1753

Recently a new cleaned profile at Saint-Acheul in the Somme valley (type section for the Lower Palaeolithic Acheulean industry), has provided an opportunity to undertake malacological analysis and ESR dating on a tufa deposit at the top of the fluvial sequence. The context of the basal alluvial sheet within the terrace system of the Middle Somme valley allows attribution of the fluvial deposits of Saint-Acheul to the Garenne Formation (Formation V of the system), which has been previously allocated to MIS 12 and 11. The upper part of the Saint- Acheul sequence (slope deposits) is mainly composed of Upper Saahan loess, overlain by Upper Pleistocene deposits and soils, separated from the fluvial beds by erosion and a long hiatus. The Upper Pleistocene succession includes an arctic brown soil horizon (the so-called «Sol de Saint Acheul»), representing the results of pedogenesis throughout the Weichselian Middle Pleniglacial (MIS 3). Chronostratigraphic interpretation of the underlying fluvial deposits is now consolidated by an ESR age determination on quartz (403 ± 73 kyrs BP), consistent with a MIS 11 allocation. Malacofaunas recovered from the tufa deposit are rich and diversified (60 taxa) and the presence of no less than 23 forest species point unequivocally to climatic optimum conditions. Fluvial taxa are represented by 17 aquatic species of slow-flowing water. Terrestrial habitats consist of open-grassland, as demonstrated by the strong development of Pupilla, Vallonia and Trichia species, and of wooded areas. Among the forest molluscs several species are out of their modern ranges (Platyla polita, Ena montana, Ruthenica filograna, Clausilia pumila, Macrogastra ventricosa, Perforatella bidentata, P. incarnata, H. limbata). Most noteworthy of all is the occurrence of the extinct Zonitid Retinella (Lyrodiscus) skertchlyi. These species belong to the particular «Lyrodiscus biome» recognised in several tufa deposits from north-west Europe, all allocated to MIS 11. Finally, these results reinforce the ...