The Messinian pre-salt carbonate/evaporite platform system of the Central Mediterranean (Calcare di Base Fm - North Calabria)

The Calcare di Base (CdB) Fm is a carbonate/evaporitic unit formed during the onset of the Messinian Salinity Crisis in the the central Mediterranean region, before the deposition of massive halite and sulphate bodies. An integrated facies and stratigraphic analysis of the CdB was performed along the neogenic basins of north Calabria, that allowed to propose a sedimentary and evolutionary model in which the CdB consists of a carbonate, with minor evaporites, platform-to-slope system, formed during a general cold and arid climate period, characterized by precession-forced more humid intervals. The inner platform setting was generally characterized by a sabkha-type environment with scattered lakes and coastal lagoons grading into a shallow-marine unrimmed shelf. In particular, as the general aridity, restricted conditions frequently established, inducing hypersalinity and local anoxia. Such general stressed environmental conditions favored the thriving of extensive lithifying microbial-mats dominated by sulfur bacteria, that acted as the main carbonate factory along the whole shelf, producing widespread microbial carbonate deposits, associated with precipitation of gypsum-dominated evaporitic deposits. During the more humid periods an increasing in the runoff provoked the substantial reduction of the carbonate production, the interruption of the evaporitic sedimentation, the input of fine to coarse silicilcastic sediments, and the formation of dissolution breccias. The slope setting is inferred with a general low-angle profile and was typified by breccias and disorganized floatbreccias commonly developing along the inner slope, and by slides, slumps and channelized turbidites forming along the mid-to-outer slope to basin. During the arid periods the resedimentation processes were generally limited and characterized by monomictic (carbonate) debrites. In comparison, during the humid phases, the enhanced erosion and the consequent mixed carbonate/evaporite/terrigenous sediment exportation towards the basin, resulted in the formation of thicker polymictic breccia and megabreccia bodies.