La séquence loessique Pléistocène moyen à supérieur d'Etricourt-Manancourt (Picardie, France) : un enregistrement pédo-sédimentaire de référence pour les derniers 350 ka

In this study, we describe a new Middle Pleistocene loess-palaeosol sequence uncovered during a preventive excavation at Étricourt-Manancourt (Somme, France; fig. 1). The full 12-m-thick sequence exhibits five stacked glacial-interglacial cycles and integrates five in situ Palaeolithic levels and remarkably one Acheulean level dated by TL on burned flints at about 280 - 300 ka.Detailed field stratigraphic approach has been completed by (1) a high-resolution sedimentological study (grain size, TOC) based on a set of more than 380 5-cm-thick samples collected from continuous sampling columns covering the entire units, (2) more than 110 micromorphological block samples for thin sections analysis (fig. 3) and (3) a set of 37 sub-samples for the study of heavy minerals. Despite specific samples (tubes) having been extracted for future OSL dating, the geochronological control is mainly based on TL dating of heated (archaeological) flints, completed by IRSL dating on K-feldspars.The archaeological excavation, located on the slope of a dry valley, was opened over more than 4500 m² and led to the discovery of two deep sinkholes developed in the chalk bedrock (fig. 6). The bottom of the deepest one is located at more than 11 m from the surface of the topsoil and 5 m below the average chalk surface. The study of four reference profiles distributed throughout the excavation (figs. 6-9), and their correlation using well defined pedological level marks led to the definition of a ca. 12-m-thick cumulative loess-palaeosols succession including eighteen main stratigraphic units. This approach allowed building a global pedosedimentary sequences for the Étricourt site that presently serves as a reference for northern France (fig. 14 & tab. 2).Here we focus mainly on the detailed description and analysis of palaeosols. The Étricourt sequence includes five luvisols attributed to full interglacial conditions and allocated to MIS 11 (unit 17), MIS 9 (unit 14), MIS 7 (units 8b and 8a) and MIS 5 (unit 5). Two luvisols are thus identified for MIS 7. The pedosedimentary records corresponding to MIS 9 and MIS 5 are represented by well-developed pedocomplexes corresponding to the superimposition of a truncated luvisol and a humic soil complex that includes systematically a grey forest soil (greyzem).During MIS 9e, a luvisol developed on loessic deposits. The truncation of this Bt horizon (unit 14), and its degradation by hydromorphy and solifluction, indicate a phase of climatic degra