Erosional processes and paleo-environmental changes in the Western Gulf of Lions (SW France) during the Messinian Salinity Crisis
|Lofi Johanna1, 2, Gorini Christian3, Berne Serge2, Clauzon Georges4, Dos Reis A.Tadeu5, Ryan William6, Steckler Michael6
|1 : Univ Perpignan, Cefrem, F-66860 Perpignan, France.
2 : IFREMER, DRO GM Technopole Brest Iroise, F-29280 Plouzane, France.
3 : Univ Lille 1, F-59655 Villeneuve Dascq, France.
4 : CEREGE, Europole Arbois,F-13545 Aix En Provence, France.
5 : UERJ, Dept Oceanog, BR-20550090 Rio De Janeiro, RJ, Brazil.
6 : Lamont Doherty Earth Observ, Palisades, NY 10964 USA.
|Marine Geology (0025-3227) (Elsevier), 2005-05 , Vol. 217 , N. 1-2 , P. 1-30
|WOS© Times Cited
|Fluvial erosion, Eustasy, Tectonism, Detrital deposits, Erosional surface, Messinian Salinity Crisis, Gulf of Lions
|Current interpretation of the Messinian Salinity Crisis (MSC) involves partial "clesiccation" of the Mediterranean Sea coupled with the deposition of thick evaporites in the deep basins. New sets of seismic reflection profiles in the western part of the Gulf of Lions confirm the basinward extension of the Messinian erosion and enable the mapping of distinctive seismic markers indicating the Messinian Erosional Surface (or Messinian unconformity), the basin-margin detrital deposits, and the deep evaporite sequence. The geometrical relationship between these three elements and their relationship to the paleogeography of the margin during the MSC provide new information about the evolution of the study area during the Messinian. 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-Quatemary 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.