Sedimentary features in the Rhône River Prodelta from radionuclide analysis and bathymetric evidences

Titre du congrès :ASLO Summer Meeting Ville du congrès :Saint-Jacques-de-Compostelle Date du congrès :19/06/2005

Sediment cores were collected from 30 m in the Rhône River prodelta shortly after the centennial Rhône River flood of December 2003 (1st - 4^), in the framework of the EUROSTRATAFORM program. The cores were analyzed for radionuclide depth profiles in order to characterize the sédimentation rates during flood conditions. It appears that Rhône River flood deposits correspond with a 10 cm-thick depositional layer over a 5 d period, compared to the 0.65 cm.y-1 sédimentation rates previously measured at thèse depths. In addition, bathymétrie investigations in waters from 0 to 20 m, performed before and just after the December flood indicated that an estimated 7.8 million m3 of river-borne sédiments were deposited, corresponding to a 60 to 100 cm-thick wedge at 20 m deep. Thèse bathymétrie profiles permit to draw an accumulation-thickness map. This work shows the benefit of adding bathymétrie to radionuclide data in order to better illustrate and to constrain the low time scale Rhône River events.