High-frequency cyclicity in the Mediterranean Messinian evaporites: evidence for solar-lunar climate forcing

The deposition of varved sedimentary sequences is usually controlled by climate conditions. The study of two Late Miocene evaporite successions (one halite and the other gypsum) consisting of annual varves has been carried out to reconstruct the paleoclimatic and paleoenvironmental conditions existing during the acme of the Messinian salinity crisis, ~ 6 Ma, when thick evaporite deposits accumulated on the floor of the Mediterranean basin. Spectral analyses of these varved evaporitic successions reveal significant periodicity peaks at around 3-5, 9, 11-13, 20-27 and 50-100 yr. A comparison with modern precipitation data in the western Mediterranean shows that during the acme of the Messinian salinity crisis the climate was not in a permanent evaporitic stage, but in a dynamic situation where evaporite deposition was controlled by quasi-periodic climate oscillations with similarity to modern analogs including Quasi-Biennial Oscillation, El Ni\~no Southern Oscillation, and decadal to secular lunar- and solar-induced cycles. Particularly we found a significant quasi-decadal oscillation with a prominent 9-year peak that is commonly found also in modern temperature records and is present in the contemporary Atlantic Multidecadal Oscillation (AMO) index and Pacific Decadal Oscillation (PDO) index. These cyclicities are common to both ancient and modern climate records because they can be associated with solar and solar-lunar tidal cycles.Comment: 13 pages, 10 figures, 1 Tabl

Tribocorrosion Properties of PEO Coatings Produced on AZ91 Magnesium Alloy with Silicate- or Phosphate-Based Electrolytes

In this work, the tribocorrosion behavior of plasma electrolytic oxidation (PEO)-coated AZ91 samples was studied. In particular, two different coatings were produced and compared. One was obtained with an alkaline electrolyte containing sodium phosphate, whereas the other one was produced with an alkaline electrolyte containing sodium silicate. The coatings were characterized with SEM-EDS and XRD techniques, and after the tribocorrosion tests, the wear scars were analyzed with SEM-EDS. The tribocorrosion behavior was evaluated measuring the OCP during a pin on disk test performed in an aggressive environment. Moreover, potentiodynamic polarization and electrochemical impedance spectroscopy tests were performed, to evaluate the corrosion resistance of the different samples in the absence of wear phenomena. The behavior of all the PEO-treated specimens was compared with the one of the untreated sample. A remarkable increase in the tribocorrosion performances after the PEO treatments was observed. Moreover, the samples obtained with the electrolyte containing silicates showed higher tribocorrosion performances

The Messinian salinity crisis in Cyprus: a further step towards a new stratigraphic framework for Eastern Mediterranean

A revised stratigraphic framework for the Messinian succession of Cyprus is proposed demonstrating that the three-stage model for the Messinian salinity crisis recently established for the Western Mediterranean also applies to the Eastern Mediterranean, at least for its marginal basins. This analysis is based on a multidisciplinary study of the Messinian evaporites and associated deposits exposed in the Polemi, Pissouri, Maroni/Psematismenos and Mesaoria basins. Here, we document for the first time that the base of the unit usually referred to the 'Lower Evaporites' in Cyprus does not actually correspond to the onset of the Messinian salinity crisis. The basal surface of this unit rather corresponds to a regional-scale unconformity, locally associated with an angular discordance, and is related to the erosion and resedimentation of primary evaporites deposited during the first stage of the Messinian salinity crisis. This evidence suggests that the 'Lower Evaporites' of the southern basins of Cyprus actually belong to the second stage of the Messinian salinity crisis; they can be thus ascribed to the Resedimented Lower Gypsum unit that was deposited between 5.6 and 5.5\ua0Ma and is possibly coeval to the halite deposited in the northern Mesaoria basin. Primary, in situ evaporites of the first stage of the Messinian salinity crisis were not preserved in Cyprus basins. Conversely, shallow-water primary evaporites deposited during the third stage of the Messinian salinity crisis are well preserved; these deposits can be regarded as the equivalent of the Upper Gypsum of Sicily. Our study documents that the Messinian stratigraphy shows many similarities between the Western and Eastern Mediterranean marginal basins, implying a common and likely coeval development of the Messinian salinity crisis. This could be reflected also in intermediate and deep-water basins; we infer that the Lower Evaporites seismic unit in the deep Eastern Mediterranean basins could well be mainly composed of clastic evaporites and that its base could correspond to the Messinian erosional surface

The Messinian salinity crisis: open problems and possible implications for Mediterranean petroleum systems

Abstract: A general agreement on what actually happened during the Messinian salinity crisis (MSC) has been reached in the minds of most geologists but, in the deepest settings of the Mediterranean Basin, the picture is still far from being finalized and several different scenarios for the crisis have been proposed, with different significant implications for hydrocarbon exploration. The currently accepted MSC paradigm of the ‘shallow-water deep-basin’ model, which implies high-amplitude sea-level oscillations (> 1500 m) of the Mediterranean up to its desiccation, is usually considered as fact. As a consequence, it is on this model that the implications of the MSC events on the Mediterranean petroleum systems are commonly based. In fact, an alternative, deep-water, non-desiccated scenario of the MSC is possible: it (i) implies the permanence of a large water body in the Mediterranean throughout the entire Messinian salinity crisis, but with strongly reduced Atlantic connections; and (ii) envisages a genetic link between Messinian erosion of the Mediterranean margins and deep brine development. In this work, we focus on the strong implications of an assessment of the petroleum systems of the Mediterranean and adjoining areas (e.g. the Black Sea Basin) that can be based on such a non-desiccated MSC scenario. In particular, the near-full basin model delivers a more realistic definition of Messinian source-rock generation and distribution, as well as of the magnitude of water-unloading processes and their effects on hydrocarbon accumulation