The Messinian Erosional Surface (MES), commonly correlated with the “desiccation” phase and the deposition of deep evaporites during the apogee of the event, is generally interpreted as a subaerial feature. In the Gulf of Lions, it is a complex diachronic polygenic erosional surface observed at the base of the prograding Plio-Quaternary sequence beneath the shelf and slope; it extends downslope beneath the deep basin Upper Evaporites and the Salt, and possibly correlates conformably with the base of the so-called deep Lower Evaporites. The whole morphology of the MES reflects a buried drainage pattern, supporting the interpretation of fluvial erosion driven by a substantial drop in sea level. Our results also suggest that large submarine gravity flows occurred prior to any significant accumulation of Salt in the basin and prior to the Upper Evaporites. Consequently, interbedded clastic deposits may partly account for the parallel reflectors of the Lower Evaporites. Since river erosion persisted throughout the MSC, the Salt and Upper Evaporite units may also contain a large amount of detrital sediments.
The good quality of the new seismic data clearly reveals fan-shaped Messinian deposits in the downstream part of the main Messinian valleys (i.e., the Nile, Var, and Spanish rivers). The depositional scenarios generally involve a substantial sea-level fall coupled with deltaic/prodeltaic accumulations. A chaotic seismic unit (Unit D) filling Messinian lows and extending beneath the Salt within the study area is interpreted as a Messinian clastic unit. We propose a polyphase scenario of detrital fan deposition involving pre-, syn-, and post-Salt deposition in subaqueous/subaerial environments.
In the Gulf of Lions, a late Miocene tectonic phase that affected the western shelf also played an important role in controlling (a) the pattern of the Messinian fluvial network, (b) the location of maximum erosion on the shelf, and (c) the location of the detrital fan depocentre downslope.