The onset of the Messinian Salinity Crisis in the central Mediterranean recorded by pre‐salt carbonate/evaporite deposition

The Calcare di Base is a carbonate/evaporitic unit formed before the deposition of the massive halite bodies in the main depozones of the Mediterranean region, and has been at the centre of a fiery debate between different ‘schools of thought’ about its genesis, environmental conditions and timing of deposition. It crops out extensively in Southern Italy, across Neogene basins located on the Tyrrhenian and Ionian margins of northern Calabria, where it was studied through a detailed facies and stratigraphic analysis that revealed the presence of a continental/shallow-marine to slope system, active during the onset of the Messinian Salinity Crisis. During the Calcare di Base deposition, an arid climate regime with intermittent humid phases occurred with a precession forced cyclicity, facing an overall generally cold climatic period. During arid periods, stressed environmental conditions permitted the establishment of widespread microbial-mediated carbonate production, frequently associated with evaporitic (gypsum-dominated) deposition, along a sabkha-type environment with extensive salinas and hypersaline coastal lagoons grading seaward into a carbonate/evaporite shallow-marine shelf. This is testified to by microbial boundstones and dissolution breccias commonly associated with nodular gypsum and arenites affected by desiccation, typically forming metre-scale shallowing-upward peritidal cycles. Seaward, gravity flow deposits are interpreted as re-sedimented shelf limestones, defining a slope apron. Mixed carbonate/evaporite megabreccias and disorganized floatbreccias were deposited along the upper slope, whereas soft deformation with slides, slumps and channelized turbidites further developed along the lower slope to basin. During the humid climate episodes, that affected the platform system with a precession-forced cyclicity, the carbonate production was reduced together with the evaporitic deposition, leading to the widespread deposition of marlstones and fine to coarse siliciclastic deposits.