RESUME New isotopie results on bulk carbonate and mollusc (gastropods and bivalves) samples from Lake Geneva (Switzerland), spanning the period from the Oldest Dryas to the present day. are compared with pre-existing stable isotope data. According to preliminary calibration of modern samples. Lake Geneva endogenic calcite precipitates at or near oxygen isotopie equilibrium with ambient water, confirming the potential of this large lake to record paleoenvironmental and paleoclimatic changes. The

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... onset of endogenic calcile precipitation at the beginning of ihe Allerod biozone is clearly indicated hy ihe oxygen isotopie signature of bulk carbonaie. A large change in S1 'C values occurs during the Preboreal. This carbon shift is likely to be due to a change in bioproductivity and/or to a "catchment effect", the contribution of biogenic CO: from ihe catchment area to the dissolved inorganic carbon reservoir of the lake water becoming significant only during Ihe Preboreal. Ciastropods are confirmed as valuable for studies of changes in paleotemperature and m paleowater isotopie composition, despile the presence of a Les évidences minéralogiques indiquent une augmentation de l'influence détritique sur la sédimentation à partir du Subboreal. D'autre coté, des mesures isotopiques préliminaires sur des sédiments carbonates subatlantiques ont des valeurs comparables à celles de la calcite endogène pure et des gastéropodes (en considérant l'effet vital). Cet apparent contraste reste difficile a expliquer.