ISOTOPIC CHARACTERIZATION (O, C, SR) OF THE GLACIAL FLUXES FROM THE LAKE ANNECY BASIN (EASTERN FRANCE)

The Annecy depression infill is essentially reflected by the clastic s ediments related to the dynamics of the Warmian glaciation. The marine Mesozoic carbonates and the non-marine Cenozoic molassic complex, whi ch form the palaeo-watershed bedrock of the Annecy glacial lake, provi ded a large part of the till material deposited by glacial fluxes. Iso topic characterization (O-18, C-13, Sr-87/Sr-86) of the different sedi ment components enables restoration of their depositional processes. T he till and molasse silicate fractions show, through Rb-Sr isotopic re lationships, mechanical mixing involving mineral phases that resulted from tardi-Hercynian and pre-Alpine tectonic events. Multi-isotopic me asurements of the carbonate fractions show that the glacial sedimentat ion can be explained by a mixing between Mesozoic carbonates and the C enozoic molassic complex. The convergence of basic field data and isot opic signatures from the carbonate fractions of ice-related sediments leads to the reconstruction through time and space of the genesis of t hese poorly differentiated surface deposits.