Résumé
The EOLE project focuses on the impact of millenial climatic variations (Dansgaard/Oeschger) and abrupt events (Heinrich), on the loessic environments of Western and Central Europe between 30 and 15ka BP (50 degrees N transect between 2 degrees and 17 degrees E). The evidence of rapid climatic events in the loess sequences is based on their physical (grain-size, CaCO3, Iron, magnetic susceptibility) and biogeochimical (molluscs, organic carbon, d13C) characterisations, within the best-developed sequences (high-resolution 1 sample/5 cm; 10 to 15 m in thickness). The main results have been obtained in the Nussloch reference sequence (Rhine valley, Germany) where cyclic variations appear within the Upper Pleniglacial from high-resolution grain-size and MS analyses. These variations are mainly underlined by the %20-50mu m/%<20mu m ratio (grain-size index GSI) which is interpreted as an indirect proxy of the aeolian dynamics: high values within pure typical loess ("L?ss Events" L1 to L8)/ low values in the various tundra gley layers G1 to G8. Our investigations show that, during the Upper Pleniglacial, the loess deposition is basically characterised by a succession of rapid sedimentation phases (especially during Heinrich events 2 and 3), separated by stops (or strong reduction) in the aeolian flux. According to OSL and 14C dating, a correlation between GSI index and the dust record from GRIP or GISP II ice cores is proposed. In addition, the cyclicity of the loess record seems to represent the expression, in continental environments, of the 1500 years cycles described in North Atlantic sediments. In parallel, the analysis of the 13C of loess organic matter and of the malacological assemblages at Nussloch shows a close correspondence with the d18O from GRIP. Finally these results show that the high frequency climatic variability that characterises the North Atlantic and Greenland records during the LGM had a strong impact on aeolian sedimentation and on terrestrial environments of Western and Central Europe.