Événements éoliens rapides dans les loess du Pléniglaciaire supérieur weichselien : L'exemple de la séquence de Nussloch (Vallée du Rhin-Allemagne) / Rapid aeolian events within the Weichselian upper pleniglacial loess: The example of the Nussloch sequence (Rhine valley, Germany)

Variations of detailed grain size and magnetic susceptibility records in the Nussloch loess sequence (Rhine Valley), where the sedimentation rate is especially high (1 to 2m per ka on more than 10 m) are presented. This study leads to evidence more or less cyclic variations of these indices between about 30 and 17 ka. These variations, especially well expressed by the evolution of the IGR (% 20-50μm / % <20μm), are considered to be an indirect measurement of the aeolian dynamic intensity and of the sedimentation rate during loess deposition (high ratio in typical unweathered loess (Loess events L1 to L8) / low ratio in tundra gleys horizons G1 to G8 (reduction or stop of the sedimentation, permafrost development...). On the basis of OSL, and of 14C dates on loess organic matter, we show that during the Upper Pleniglacial the loess deposition was especially fast and discontinuous, and resulted from a succession of rapid deposition phases, separated by stops or strong reduction of the aeolian flux sedimentation during some centuries. A temptative correlation with the Greenland dust record (GRIP) is proposed. In addition we can observe a parallel between Henrich 2 event and one of the main period of loess deposition around 22-23 ka. Finally, the comparison with the magnetic susceptibility record and the grain-size data show that the period characterized by a high grain-size index, are also underlined by an increase in the amount of ferromagnetic minerals reworked from the Rhine alluvial plain located at the foot of the site (enhancement in the frequency of the storms from N-NW).