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The Messinian Salinity Crisis in the Mediterranean basin: a reassessment of the data and an integrated scenario
No full textAfter a long period of controversial debate about the interpretation of the Messinian salinity crisis (MSC), a near consensus
existed since the ODP Leg 42A for a model keeping the major lines of the deep basin-shallow water model initially proposed by
Hsü et al. (1973). The knowledge of the crisis was improved since the 1995s by the availability of a very accurate astronomically
calibrated timescale. The debate about its interpretation was then reactivated by several new scenarios that questioned most the
major aspects of the previous classical models. The updated re-examination of the most salient features along with consideration of
the hydrological requirements for evaporite deposition allow us to assess the viability of the new models. We propose an integrated
scenario that revives the key points of the previous model with new statements about the chronology, depositional settings,
hydrological mechanisms, consequences and correlations with the global changes. A model implying two main stages of evaporite
deposition that affected successively the whole basin with a slight diachronism matches better the whole dataset. The distribution of
the evaporites and their depositional timing were constrained by the high degree of paleogeographical differentiation and by the
threshold effects that governed the water exchanges. It is assumed that the central Sicilian basin was a deep basin located in a
marginal position with regard to the deepest central basins. The restriction of the Mediterranean was predominantly under a tectonic
control, but the complex development of the evaporitic crisis implied the interplay of both glacio-eustatic changes and fluctuations
of the circum-Mediterranean climate.
The first evaporitic stage (lower evaporites) that includes the deposition of the thick homogeneous halite unit with K–Mg salt
interbeds in the deepest basins is correlated with the major evaporative drawdown and higher aridity, and occurred during the
glacial period recorded in the ocean sediments between 6.3 and 5.6Ma. The deposition of the potash in Sicily is tentatively linked
to the two major glacial peaks TG 20 and TG 22, while the end of this first stage is linked to the peak TG 12. The second stage
(upper evaporites) correlates with the interval of warming and global sea level rise recorded in the ocean since 5.6–5.5Ma onwards.
During this second stage, freshwater contribution increased and culminated by the latest Messinian dilution, i.e. the Lago-Mare
event, as the result of the worsened tectonically driven closure of the Atlantic gateways combined to an evolution towards wetter
climate conditions at least on the mountainous peripheral areas. In fact, reduced inputs of seawater continued to enter at least
episodically the basin through the MSC explaining the sporadic presence of marine organisms. These inputs reached their lowest
value and practically ceased during the latest Messinian dilution, just before the abrupt restoration of stable open marine conditions
at the beginning of the Zanclean.
A polyphased erosional surface affected the Mediterranean margins during the MSC with several critical episodes. The major
episode related to the greatest water level fall, more than 1000m, occurred during the deposition of the lower evaporites, from the
onset of the evaporite deposition till the end of the first stage. Erosional processes remained active during the second evaporitic
stage especially whenever the basin dried-up and a last important event marked by the karstification of the evaporites developed
during the latest Messinian dilution just before the Early Zanclean reflooding that filled the erosional morpholog
Paleoenvironmental changes during the calcare di base deposition a prelude to the Messinian salinity crisis.
No full textPaleoenvironmental changes heralding the Messinian Salinity Crisis in central Sicili: The Tripoli formation of the Falconara-Gibliscemi composite section
No full textHigh resolution stratigraphy and stable isotopes at the Messinian/Zanclean boundary. In the Mediterranean basins. Paleoceanographic reconstruction
No full textNew insights on the onset of the Messinian salinity crisis in Cyprus (East Mediterranean)
No full textDepositional and diagenetic environments of the Messinian Calcare di Base and sulfur-bearing carbonates from Sicily and Calabria
No full textPaleoenvironmental evolution of the eastern Mediterranean during the Messinian: Constraints from integrated microfossil data of the Pissouri Basin (Cyprus)
No full textIntegrated data of calcareous nannofossils, as well as planktonic and benthic foraminifera from the Pissouri Motorway section on Cyprus allow the reconstruction of surface- and bottom-water paleoenvironments of the eastern Mediterranean during the interval preceding the Messinian salinity crisis (MSC). Contrary to deeper-water locations, where benthic foraminifera faunas are suppressed or absent just after the Tortonian-Messinian boundary, sediments deposited at intermediate water depths do contain benthic assemblages. From the earliest Messiman onwards, a development towards increasingly unfavourable paleoenvironments is reflected in the planktonic and benthic microfossil records of the Pissouri section and proceeds with rather discrete time steps that can be correlated to sequences throughout the Mediterranean. Shortly after the Tortonian-Messinian boundary a transition is recorded in the sedimentology and the open marine, deeper-water taxa disappear from the benthic foraminifera assemblages; subsequently, the diversity of all fauna groups diminishes. The changes recorded at species level in both surface-water and sea-floor dwelling taxa suggest decreasing circulation of the bottom waters, associated with changes in the surface waters, most likely due to increasing stratification. From similar to 6.73 Ma onwards, our data indicate a prominent change to more restricted conditions and increasing salinity at the sea floor together with intermittently rising surface water salinity. The dominance of oligotypic and monospecific assemblages and the frequent shifts in assemblage compositions of all microfossil groups indicate severely stressed environments after similar to 6.4 Ma, probably related to increased salinity. The major changes in palcoenvironmental conditions, including oxygen deprivation due to stagnation and hypersalinity, can be explained by hydrographical changes in the Mediterranean basin, which are probably caused by tectonic movements in the Rif Corridor acting in concert with astronomical cyclicity. Evaluation of the paleodepth proxies indicates that the depth of the Pissouri Basin remained rather constant at similar to 300-500 in, with a minimum of 200 in, until deposition of the "barre jaune", the transitional interval towards the evaporites and that early shallowing to neritic depths, as was proposed before, is highly unlikely
Paleoenvironmental changes at the Messinian/Pliocene boundary in the Alboran Area: The example of the Melilla Basin, NE Marocco
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