Reconstruction of the sediment transport conditions in the Urumqi alluvial fan (northeastern Tian Shan, China)
Résumé
Alluvial fans must contain information about the physical parameters of palaeo-rivers that built them. In particular, their grain-size evolution is partly related to water discharge and granulometry of the sediment supply. However, the temporal framework of deposits could also influence this grain size evolution. In order to discriminate the respective influence of the short-and long-term sedimentation dynamics on the grain-size organization of alluvial fans, we used a coupled experimental and field 99 approach. The experiments show that aggradation is a local and short-term process, whereas progradation is a more long-term and regional one. Moreover, progradation is clearly related to time through a power law, which indicates a progradation rate lowering. Accordingly, the progradation rate seems to be a good proxy to reconstruct the overall evolution of fans. The field measurements performed on the Quaternary deposits of the Uumqi River shows that it is possible to observe a progradation rate lowering associated with a natural fan growth, and to document and quantify this lowering on a single vertical section using a granulometric approach. This example shows that granulometric studies could be a good manner to characterize the long-term and regional fan dynamics and, we hope soon, the associated transport conditions.
Domaines
GéomorphologieOrigine | Accord explicite pour ce dépôt |
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