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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. [ABSTRACT FROM AUTHOR]

This work deals with Messinian deposits belonging to the Neogene infill of the Rossano and Belvedere Basins, respectively developed along the fore-arc and the back-arc areas of the north Calabria accretionary wedge. The main goal is to characterize the carbonate and evaporitic sedimentation during the Messinian Salinity Crisis, in the general framework of the basin architecture and the interplay between eustatic vs tectonic controlled sea-level variations. Fieldwork integrated with seismic lines and well logs interpretations led to the revision of the general stratigraphy of the basins and the proposal of a new sequential stratigraphic model driven by cyclic sea-level variations. Each cycle, repeated at least two times during the Messinian Salinity Crisis time frame, begins with a relative sea-level fall responsible for the emplacement of prograding wedges composed of terrigenous and evaporitic deposits that, subsequently, evolve in the deposition of primary basin-fill evaporites. This phase is followed by open marine transgression due to relative sea-level rise that terminates the evaporite formation and predates the development of microbial dominated carbonate platforms associated with shallow-water evaporites. Both basins experienced intense tectonic activity during the Messinian, which could be responsible for huge basinward sediments exportation and fast decreasing in the accommodation space. However, this did not substantially influence the development of the systems tracts that, considering the basinal architecture, have been mainly controlled by eustatic sea-level variations. In fact, two major sea-level drops associated with basin restriction and aridity (cold) conditions seem to have caused the origin of two main evaporitic units as basin-fill evaporites, while consequent sea-level rises and less stressed condition, account for two carbonate units with limited evaporites and terrigenous deposition. • Messinian salinity crisis is well recorded in North Calabria (Italy) basins. • Messinian carbonate/evaporitic deposits are organized in 3 depositional sequences. • Despite active tectonics, sea-level variations drive system tracts formation. • Peritidal evaporites and microbial carbonate shelves formed during High Stands. • Two main basin fill evaporites (Halite or Sulphate) formed during Low Stands. [ABSTRACT FROM AUTHOR]

A multi-scale analysis of sedimentary carbonate facies and post-sedimentary diagenetic features of the Calcare di Base Formation, the precursor to evaporites in Upper Messinian successions of Northern Calabria and Central Sicily, has revealed their microbial bio-mediated origin. Massive to laminated microbial boundstones represent the most common sedimentary facies forming flat to low relief cm to m scale stromatolitic and thrombolitic bodies. The fabric of the micrite varies from peloidal to aphanitic, and almost always preserves filamentous bacteria which characterized the original microbial mat. The mat was dominated by sulphur-oxidizing bacteria belonging to the Thiotrichaceae, but there is evidence for a more complex community with sulphate- and/or nitrate-reducing bacteria, all being responsible for the mediation of the carbonate precipitation. Microbial boundstones are rich in pseudomorphs of Ca-sulphate and halite, which formed during the deposition of the microbial carbonate. Layers of primary gypsum are interbedded locally with carbonates suggesting the presence of restricted marine conditions. The stable O and C isotopic composition of the carbonates, that vary from dolomite to aragonite and calcite, suggests a complex interplay between arid to humid climatic changes, expressed cyclic interbedding of the carbonate with marl-marlstone. Later diagenetic events mainly consist of phreatic meteoric recrystallization and cementation. Although considered as diachronous, the microbial carbonates can be mapped out over a distance of more than 500 km across southern Italy; this indicates near-constant environmental conditions upon the central Mediterranean shelf at the beginning of the salinity crisis. Deposition of the extensive subaqueous microbial deposit that largely comprises the Calcare di Base is envisaged to have taken place across a shallow to moderate depth platform with local slopes into deeper water areas, where some resedimentation occurred. [ABSTRACT FROM AUTHOR]