Paleoenvironmental changes at the Messinian-Pliocene boundary in the eastern Mediterranean (southern Cyprus basins): significance of the Messinian Lago-Mare

The study of the late Messinian-Early Pliocene sediments in south Cyprus (P issouri and Polemi basins) and the comparison with the offshore coeval depo sits drilled in the ODP Leg 160 boreholes, provide new data illustrating th e environmental changes which occurred in the eastern Mediterranean at the end of the salinity crisis. The Messinian-Pliocene transition is marked by a very rapid environmental c hange indicated by sharp variations in lithology, sedimentology, microfauna l assemblages and stable isotope composition. The latest Messinian interval is dominated by the 'Lago-Mare' otigo-mesohaline environments. The most st riking feature in the Pissouri Basin is the intercalation between the upper most gypsum bed and the base of the Zanclean deposits of four main horizons of paleosols interbedded with carbonates and conglomerates. Paleosols indi cate periods of subaerial exposure long enough to permit pedogenesis to dev elop. Conglomerates indicate intense erosion of the Troodos Massif and its sedimentary cover as a result of the water level drop. tectonic activity an d more humid climatic conditions. Thus. several subaerial exposure phases o ccurred in the marginal areas like the Pissouri Basin whereas shallow oligo haline conditions persisted in the deeper parts of the basin, as indicated at ODP Site 968. Both in the Pissouri Basin and on the flank of the Erathos tenes Seamount the late Messinian paleosols are directly overlain by the lo wermost Pliocene sediments deposited in well-oxygenated deep marine conditi ons. This drastic change of water depth shows that the water level of the late M essinian saline to brackish takes dropped far below that of the world ocean , at least more than several hundred meters. Both these base level fluctuat ions and the oligohaline conditions caused intensive erosion-karstification of the upper gypsum beds as also reported from many other Mediterranean re gions. Moreover, the study of the Polemi sections shows that oligohaline condition s had already started during the deposition of the upper gypsum sub-unit. T ypical brackish and fresh water assemblages are present in the last two gyp sum layers and inter-gypsum beds, This indicates that freshwater dilution, i.e. the Lago-Mare conditions, resulted from a progressive change of the hy drological budget which started during deposition of the upper evaporites a nd climaxed after the deposition of the uppermost gypsum layer (classical L ago-Mare facies). During this time, periods of increased evaporation over p recipitation led to deposition of the uppermost gypsum layers. This evoluti on is interpreted as being due both to the severance from the open ocean an d to the increasing contribution of the runoff-precipitation versus marine inputs in the hydrological budget of the Mediterranean. (C) 2001 Elsevier S cience B.V. All rights reserved.