Relative sea-level variations and basin evolution during the Messinian Salinity Crisis (Crotone and Rossano Basins - North Calabria)

An integrated analysis of subsurface dataset and outcropping successions permitted to define a stratigraphic and paleogeographic evolutionary model of the wedge-top Rossano and Crotone Basins during the Messinian Salinity Crisis (MSC). The presence of complete sea-level controlled successions, indicate the dominance of the eustatic signal in the basin evolution, in comparison with the synsedimentary tectonic input, which played only a secondary role consisting in the strong basinward shift of facies caused by fast decreasing in the accommodation space. In particular, during the late Tortonian - early Messinian the studied basins were characterized by open normal marine conditions, as suggested by the widespread deposition of deep-water claystones followed by diatomites (Tripoli Fm). The first basin restriction occurred during the early Messinian at ca. 5.96 Ma, as a consequence of the sea-level relative still stand, that triggered the deposition of a carbonate platform system (Calcare di Base Fm - CdB). The latter was characterized by sabkha to shallow-water environments, dominated by microbial carbonate and evaporite deposition, passing into a gentle slope to basin setting in which resedimented and pelagic deposits occurred. A successive regional sea-level drop, dated at ca. 5.60 Ma, induced a general exposure of the CdB platform system and the creation of a marked erosional surface generally known as the Messinian Erosional Surface (MES). Consequently, during the early LST, a thick prograding wedge deposited and, due to the reduction of the connections with the open sea, new more severe restricted conditions of the basins took place. Later, during the late LST, the massive deposition of salt dominated bodies reshaped the basin paleotopography and the depocentres were filled, thus sealing the previous irregularities of the paleo-seascape and creating roughly flat plains without deep depozones. Afterwards, a renewed transgression phase (TST) inundated again the basins, causing firstly the sedimentation of clay dominated deposits, and later, during a further HST, the reestablishment of evaporitic conditions and the deposition of widespread shallow-water sulphate deposits. Lastly, a new severe relative sea-level drop (LST) exposed again all the previous deposits, as testified by the superimposition of alluvial conglomerates along paleovalleys incised into the underlying HST sulphates. This event marks the transition to the so-called Lago-Mare event that typifies the last stage of the MSC, which definitely terminates with the reflooding of the Mediterranean at the Pliocene transition (ca. 5.33 Ma).