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

The deposition of varved sedimentary sequences is usually controlled 22 by climate conditions. The study of two Late Miocene evaporite 23 successions (one halite and the other gypsum) consisting of annual 24 varves has been carried out to reconstruct the palaeoclimatic and 25 palaeoenvironmental conditions existing during the acme of the 26 Messinian salinity crisis, ~6 Ma, when thick evaporite deposits 27 accumulated on the floor of the Mediterranean basin. Spectral analyses of these varved evaporitic successions r 28 eveal significant periodicity 29 peaks at around 3-5, 9, 11-13, 20-27, 50-100 yr. A comparison with 30 modern precipitation data in the western Mediterranean shows that 31 during the acme of the Messinian salinity crisis the climate was not in a 32 permanent evaporitic stage, but in a dynamic situation where evaporite 33 deposition was controlled by quasi-periodic climate oscillations with 34 similarity to modern analogs including Quasi-Biennial Oscillation, El 35 Niño Southern Oscillation, decadal to secular lunar and solar induced 36 cycles. Particularly we found a significant quasi-decadal oscillation with 37 a prominent 9-year peak that is commonly found also in modern 38 temperature records and is present in the contemporary Atlantic 39 Multidecadal Oscillation (AMO) index and Pacific Decadal Oscillation 40 (PDO) index. These cyclicities are common to both ancient and modern 41 climate records because they can be associated with solar and 42 solar/lunar tidal cycles. 43 During the Messinian the Mediterranean basin as well as the global 44 ocean were characterized by different configurations, than at present, in 45 terms of continent distribution, ocean size, geography, hydrological 46 connections and ice-sheet volumes. The recognition of modern-style 47 climate oscillations during the Messinian suggests that, although local 48 geographic factors acted as pre-conditioning factors turning the Mediterranean Sea into a giant brine pool, external climate forcings, 50 regulated by solar/lunar cycles and largely independent from local 51 geographic factors, modulated the deposition of the evaporites.