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International audience; A 2 m profile of organic sediments, interbedded between two tills, was taken from the Evian high plateau at Hameau de Maravant, 860 m a.s.l. (Haute-Savoie, Western Alps, France). Pollen, plant macrofossils and insect remains were used to reconstruct the local palaeoenvironment, which consisted of a moss and Carex mire, surrounded by a dense Abies and Picea mixed forest. Pollen and macrofossil data indicate that this peat layer was deposited at the end of the Eemian interglacial. The lower till should therefore be assigned to the penultimate glaciation and the upper till to the maximum extent of the Rhône glacier during the Würm. A comparison of the results with previous studies carried out in the Geneva area and other alpine valleys has yielded a detailed reconstruction of the past fluctuations of the Rhône glacier: 1. a first Early/Lower Würmian advance, reaching the region around Lyon; 2. a subsequent retreat of ice; 3. a second moderate readvance, restricted to the surroundings of Geneva, followed by a final deglaciation. A continuous lacustrine sequence has been obtained from the nearby Roseire peat-bog (890 m a.s.l). Pollen and radiometric results show the establishment of a former palaeolake during the Upper Pleniglacial, probably before ca. 22 450±850 cal years BP, thus implying that the high plateau was ice-free from that time. These new data appear to suggest that the maximal extension of the Rhône glacier occurred prior to the Last Glacial Maximum (OIS 2) and, according to a well-documented geomorphological context, probably during the Lower Würmian Pleniglacial.

La réalisation récente de sondages carottés sur l’ensemble du versant d’Evian permet de réaliser des observations détaillées des dépôts détritiques d’épaisseur hectométrique. Ceux-ci sont constitués de sédiments hétérogènes de type glacio-lacustre, glaciaire de fond, glaciaire latéral, avec de nombreux dépôts ligneux et tourbeux. Trois complexes sont mis en évidence, du plus ancien au plus récent :• un complexe inférieur, à dominante glacio-lacustre, mis en place avant 30 000 ans, mais après le maximum glaciaire würmien,• un complexe dit du « Plateau de Gavot », de marge glaciaire active, accumulé entre 30 000 et 27 000 BP. Il enregistre une quinzaine d’oscillations latérales du glacier du Rhône dont certaines de plus d’un kilomètre,• un complexe emboîté, riche en sédiments glacio-lacustres, mis en place entre 25 000 et 21 000 ans BP. Il correspond vers l’aval, à Thonon, à la limite entre les hautes et les basses terrasses de kame. Recent corings have been carried out in the Evian area, allowing us to describe in details new hectometric profiles of detritical sedimentary deposits. Various sediments have been observed throughout the Quaternary sequences: glacio-lacustrine facies, basal and lateral till, and organic-rich layers (including lignite and peat). Three major stratigraphical units have been identified:• The “Complexe Inférieur”, mainly composed of glacio-lacustrine sediments, dated before 30 000 yr B.P. and prior to the L.G.M.• The “Complexe du Plateau Gavot”, deposited between 30 000 and 27 000 yr B.P., in the sedimentological context of active glacial margin.Therefore, this unit recorded at least fifteen lateral fluctuations of the Rhône glacier margin. Some oscillations could have exceeded one kilometer of extension in latitude,• The “Complexe emboîté”, mainly composed of glacio-lacustrine sediments, deposited between 25 000 and 21 000 yr. BP. This Unit fits well with the boundary between high and low kame terraces located in the surroundings of Thonon-Les-Bains.