Abstract:

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 Niño 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 also found 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.

During the Messinian the Mediterranean basin as well as the global ocean were characterized by different configurations than at present, in terms of continent distribution, ocean size, geography, hydrological connections, and ice-sheet volumes. The recognition of modern-style climate oscillations during the Messinian suggests that, although local geographic factors acted as pre-conditioning factors turning the Mediterranean Sea into a giant brine pool, external climate forcings, regulated by solar–lunar cycles and largely independent from local geographic factors, modulated the deposition of the evaporites.

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