Conference:
Scientific Workshop ” What happened in southern Romania and Black sea when the Mediterranean Sea desiccated 5.6 Ma ago”, Bucarest, Romania, 29 February – 1 March 2008, Abstract volume, Pages 33-35.
Authors:
Jean-Pierre Suc, Georges Clauzon, Speranta-Maria Popescu, Mihaela Carmen Melinte-Dobrinescu, Frédéric Quillévéré, Sophie A. Warny, Séverine Fauquette, Jean-Loup Rubino.
Abstract:
Since Gautier et al. (1994) first published a magnetostratigraphy of deposits encompassing the Messinian Salinity Crisis, systematic ecostratigraphic (pollen, dinocysts) and biostratigraphic studies (nannoplankton and planktonic foraminifers) performed around the Mediterranean and adjacent basins (Eastern Paratethys) have enabled the development of a detailed succession of Messinian events and associated paleogeographic changes.
Pollen records established that drastic climatic change was not the cause of the desiccation of the Mediterranean Sea (Suc and Bessais, 1990; Fauquette et al., 2006). However, the influence of cooling cannot be discarded. It may have caused, in conjunction with the tectonic narrowing of the Rifian Corridor (Warny et al., 2003; see also: Drinia et al., 2007), a context of minor sea-level fall in the Mediterranean, which was prevalent in the marginal basins because of their relative isolation by sills. At Bou Regreg (i.e. the Atlantic outlet of the Rifian Corridor), the large fluctuations in abundance of Operculodinium israelianum, a neritic dinoflagellate cyst, indicates that glacio-eustatic variations mostly controlled the water-depth changes in the Rifian Corridor before and after the Antarctic glacials TG 22 and TG 20. These conditions continued up to 5.6 Ma, i.e. during the progress of narrowing of the corridor not only indicated by increasing neritic conditions according to dinocysts but also by the transition from distal to coastal conditions according to a severe decrease of Pinus in the pollen record (Warny et al., 2003).
Only the erosional surface which cuts the uppermost marginal evaporites is the Messinian Erosional Surface overlain by Zanclean deposits and corresponds to the peak of the Salinity Crisis, i.e. deposition of evaporites in the almost desiccated central basins (Clauzon et al., 1996). This feature has been observed everywhere around the Mediterranean (for example: Clauzon, 1973; Chumakov, 1973; Delrieu et al., 1993; Poisson et al., 2003) and also in the Eastern Paratethys (Dacic Basin: Clauzon et al., 2005, submitted; Black Sea: Gillet et al., 2003, 2007). In Sicily, an erosional phase is intercalated between the Lower and Upper Evaporites and is often considered as the Messinian Erosional Surface (Butler et al., 1995; Krijgsman et al., 1999). As this erosion is expressed at the foot of the Nebrodi Mountains, in a similar relief context as in Tunisia (El Euch – El Koundi et al., in revision) where it is overlain by the Messinian Erosional Surface itself, we consider that it has been caused by tectonic uplift and has only a local significance. Some marginal localities simulate an apparent continuity between Messinian and Zanclean deposits but show in fact a clear discontinuity caused by a weak erosion in an interfluvial context: Cava Serredi in the Livorno region (Popescu et al., in press), Eraclea Minoa in Sicily (Popescu et al., in press), Intepe in the Dardanelles Strait (Melinte-Dobrinescu et al., in progress).
In many places (Sorbas; Vera, Dardanelles Strait, Orb Valley), an older erosional surface coeval with the marginal evaporites is evident, and this surface corresponds to the first step of the crisis (Clauzon et al., 1996). The marginal evaporites significantly preceded the central deep basin ones.
In many places (Marches: Popescu et al., 2007; Sicily: Popescu et al., in press; northern Morocco: Cornée et al., 2005; Dacic Basin: Clauzon et al., submitted; Dardanelles Strait: Melinte Dobrinescu et al., in progress), the Zanclean reflooding precedes the “official” base of Zanclean. Zanclean reflooding seems to have occurred in two steps (collapse of the Gibraltar Strait at 5.480 Ma, widening of the Gibraltar Strait at 5.332 Ma).
The Mediterranean region s.l. was marked by severe upheavals during the 6-5 Ma time-interval which encompasses the Messinian Salinity Crisis, forced both by tectonics and sea-level changes. Their deciphering depends on a finer chronological evaluation and more detailed paleogeographic reconstructions.