Present-day rhythmic deposition in the grand Rhone prodelta (NW Mediterranean) according to high-resolution pollen analyses

A high-resolution pollen study (136 samples) has been performed on the KTR05 core (738 cm long) located in the modern Grand Rhone prodelta. The objectives were (1) to evaluate the palynological and sedimentological record quality of a prodelta in comparison with fluvial inputs (2) and to quantify lost sediment (resuspensions) in this area. The core covers more than the last thirty years. By comparison with the modern pollen rain both in the Rhone delta and in the mid-drainage basin (Lyon), a seasonal forcing in pollen deposition has been demonstrated. Monthly pollen successions can be evidenced in a well preserved sequence, providing an estimate of the true sedimentation rate (60 cm.yr(-1)). Importance of disturbed or incomplete sequences suggests that most of the sediment first deposited in the prodelta (around 2/3) has been resuspended. Sedimentological and palynological data record not only seasonal but fluvial impact. The progressive shift of the prodelta has been evidenced firstly with sedimentology and secondly with palynology. Despite high fluvial impact, pollen grains in the KTR05 core are representatives of the vegetation of the Rhone drainage basin. The apparent homogeneity of the pollen spectra evidences the high reliability of palynology applied on prodeltaic area, at least in a microtidal environment.