Fabienne Orszag-Sperber

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

Abstract The study of the late Messinian–Early Pliocene sediments in south Cyprus (Pissouri and Polemi basins) and the comparison with the offshore coeval deposits drilled in the ODP Leg 160 boreholes, provide new data illustrating the 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 change indicated by sharp variations in lithology, sedimentology, microfaunal assemblages and stable isotope composition. The latest Messinian interval is dominated by the ‘Lago-Mare’ oligo-mesohaline environments. The most striking feature in the Pissouri Basin is the intercalation between the uppermost gypsum bed and the base of the Zanclean deposits of four main horizons of paleosols interbedded with carbonates and conglomerates. Paleosols indicate periods of subaerial exposure long enough to permit pedogenesis to develop. Conglomerates indicate intense erosion of the Troodos Massif and its sedimentary cover as a result of the water level drop, tectonic activity and more humid climatic conditions. Thus, several subaerial exposure phases occurred in the marginal areas like the Pissouri Basin whereas shallow oligohaline 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 Erathostenes Seamount the late Messinian paleosols are directly overlain by the lowermost Pliocene sediments deposited in well-oxygenated deep marine conditions. This drastic change of water depth shows that the water level of the late Messinian saline to brackish lakes dropped far below that of the world ocean, at least more than several hundred meters. Both these base level fluctuations and the oligohaline conditions caused intensive erosion–karstification of the upper gypsum beds as also reported from many other Mediterranean regions. Moreover, the study of the Polemi sections shows that oligohaline conditions had already started during the deposition of the upper gypsum sub-unit. Typical brackish and fresh water assemblages are present in the last two gypsum layers and intergypsum beds. This indicates that freshwater dilution, i.e. the Lago-Mare conditions, resulted from a progressive change of the hydrological budget which started during deposition of the upper evaporites and climaxed after the deposition of the uppermost gypsum layer (classical Lago-Mare facies). During this time, periods of increased evaporation over precipitation led to deposition of the uppermost gypsum layers. This evolution is interpreted as being due both to the severance from the open ocean and to the increasing contribution of the runoff–precipitation versus marine inputs in the hydrological budget of the Mediterranean.

The onset of the Messinian salinity crisis in the Eastern Mediterranean (Pissouri Basin, Cyprus)

The Pissouri Basin in Cyprus contains one of the most suitable sedimentary successions with which to study the onset of the Messinian Salinity Crisis in the Eastern Mediterranean. Exposures along the new Paphos^Limassol motorway near Pissouri exhibit distinct cyclic bedding which permits the construction of a chronology based on orbital tuning. Biostratigraphic results reveal 10 planktonic foraminifera events that have been astronomically dated in other Mediterranean sections, and as such provide an excellent first-order age control. Magnetostratigraphic results are in good agreement with the biostratigraphic data and show that all magnetic chrons between C4n.1n and C3An.1n are present. The pattern of sedimentary cycles generally fits well with the insolation curve. Astronomical tuning of the succession shows that the first gypsum bed at Pissouri overlies a 40^60 kyr stromatolite-bearing transitional interval and correlates with the amplitude increase in insolation at 5.96 Ma, as in the western Mediterranean. This indicates that the onset of evaporite precipitation was synchronous right across the entire Mediterranean Basin. fl 2002 Elsevier Science B.V. All rights reserved.

Tectonic and sedimentary evolution of the Gulf of Suez and the northwestern Red Sea

Abstract The structural pattern of the Gulf of Suez and Red Sea Rift is inherited from the basement tectonics. N140 faults (clysmic direction), parallel to the regional elongation of the rift, are associated with submeridian (Aqaba direction) and sub-E-W faults (Duwi direction) that also play an important role in the rifting processes. The pre-rift sedimentary cover includes Cretaceous and Eocene platform deposits. It was slightly deformed prior to rifting. The syn-rift sedimentary sequence comprises four major units (groups A to D) delimited by unconformities: Group A (Oligocene to Early Burdigalian), continental to restricted subaquatic deposits; Group B (Burdigalian to Middle Miocene), open marine sediments; Group C (Middle to Upper? Miocene), major evaporitic episode; and Group D (Plio-Pleistocene) which returns to an open marine environment. Four majors stages of structuration are recorded: an initial stage of compressive deformation (direction of shortening close to NW-SE) characterized by strike-slip movements and associated drag folds (early Group A); a tilted block stage (late Group A) corresponding to the period of highest extensional rate; a horst and graben stage (Group B) resulting in the cutting out of the tilted blocks by numerous synthetic faults; Group B corresponds to the period of highest subsidence rate when a flexuration stage of the margin, expressed by a centripetal evolution of the subsidence, is associated with major periferal uplift.

La transition Messinien–Pliocène en Méditerranée orientale (Chypre) : la période du Lago-Mare et sa signification

Abstract The transition between the Messinian evaporites and the Lowermost marine Pliocene in the Mediterranean records a major environmental change (‘Lago-Mare’). In Cyprus, this period is characterised by fresh-water to brackish fauna, palaeosols and the dissolution/erosion of the Upper Gypsum Unit, which can be correlated with a general erosional episode in the Mediterranean. These conditions had already begun during the deposition of Upper Gypsum Unit. Thus, during this period, very shallow and episodically desiccated saline lakes were located in the Mediterranean area, below the world sea-level, in response to a major change of the hydrological budget forced by a climate variation and tectonics.

Quaternary changes in the Egyptian shoreline of the Northwestern Red Sea and Gulf of Suez

Abstract On the NW, Egyptian, shoreline of the Red Sea, remarkably preserved Pleistocene-Holocene marine (reefs, beaches, mangrove swamps, gypsum-salinas) and non marine (alluvial fans and wadi terraces) deposits are located within a complex Neogene rift frame. The Early and Middle Pleistocene reefs are uplifted to a maximum of 40 m, subsequent movement being limited to a few metres (except on the S Gulf of Suez shores) which suggests a decreasing tectonic activity of the northern part of the rift. A new series of radiometric dates and precise levelling have demonstrated a short-lived, low stand of relative sea level during the Last Interglacial high stand (5e). At that time, flooding of the Isthmus of Suez has enabled exchanges between Mediterranean and Indian Ocean faunas and the biogeographic limit was temporarily located in the Southern Gulf of Suez, thus explaining the Late Quaternary introduction of Potamides conicus into the Indian Ocean subprovince.