RAPID AEOLIAN EVENTS WITHIN THE WEICHSELIAN UPPER PLENIGLACIAL LOESS : THE EXAMPLE OF THE NUSSLOCH SEQUENCE (RHINE VALLEY, GERMANY).
International audience Vanations 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 vanations of t...
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|Summary:||International audience Vanations 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 vanations of these indices between about 30 and 17 ka. These vanations, especially well expressed by the evolution of the IGR (% 20-50um / % <20um), are considered to be an indirect measurement of the aeohan dynamic intensity and of the sedimentation rate dunng loess deposition (high ratio in typical unweathered loess (Loess events LI to L8) / low ratio in tundra gleys horizons Gl to G8 (reduction or stop of the sedimentation, permafrost development.). On the basis of OSL, and of I4C dates on loess organic matter, we show that dunng 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 aeohan flux sedimentation dunng some centunes. 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 penod of loess deposition around 22-23 ka. Finally, the companson with the magnetic susceptibility record andthe grain-size data show that the period charactenzed 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). L'étude des variations de la granulométrie et de la susceptibilité magnétique dans la séquence de Nussloch (Vallée du Rhin), où le taux de sédimentation est particulièrement élevé (1 à 2 m/ka sur plus de 10m), débouche sur la mise en évidence de variations plus ou moins cycliques entre 30 et 17 ka environ. Ces vanations, particulièrement bien soulignées par l'évolution du rapport % 20- 50um / % <20 um (indice IGR), sont ...|