The onset of the Messinian Salinity Crisis recorded by a new marginal basin succession in the Caltanissetta Basin (Sicily, IT).

The fresh new cores 3AGN2S02 and 3AGN2S04 located in the deformed foredeep of the Gela Thrust System, locally known as Caltanissetta Basin, represent an opportunity for a better comprehension of the Messinian events, as well as for the reconstruction of the Sicilian evaporitic Basin architecture. The entire ‘early Messinian stage’ (7.2-5.96Ma) preceding the Messinian Salinity Crisis (MSC) has been already investigated in the Caltanissetta Basin. Even though the Tripoli Formation and ‘Calcare di Base’ (‘CdB’) have been widely studied for a long period of time, many aspects remain unclear. The ‘CdB’ has been commonly considered to represent the first evaporitic unit of the Messinian succession in Sicily. Different ages obtained in the underlying Tripoli deposits from various Sicilian outcrops display a diachronous onset of the MSC (Rouchy & Caruso, 2006). However, Manzi et al. (2011) propose an alternative interpretation for the ‘CdB’, suggesting that it does not belong exclusively to the onset of the MSC, but it is made of three carbonate facies belonging to different MSC stages. A detailed sedimentological, geochemical and petrographic study of the two cores allowed us to evidence the paleoceanographic changes that affected the central Mediterranean Sea during the transition from marine to restricted conditions, up to the onset of the MSC, and to observe the differences between the marginal and the deep basins of the Caltanissetta Basin, enhanced by the ongoing regional tectonics. Facies characterization made it possible to confirm the nature of the sediments of the cores, reflecting distinct depositional environments. A lithological transition passing from the Tripoli Formation to the complex ‘CdB’ carbonates alternating with shales is observed (3AGN2S04). This CdB appears to be laterally equivalent to gypsum and salts at site 3AGN2S02. In the brecciated facies of the ‘CdB’, evaporite pseudomorphs are also present, implying early stage diagenesis. Furthermore, our analyses gave us insights of strong oscillations in hypersaline conditions with freshwater inputs controlled by Milankovitch’s cycles. Moreover, the 3AGN2S04 core is characterized by the repetition of sedimentary successions due to the later development of a thrust system, which can be an important hint concerning the morphological and structural evolution of the Caltanissetta Basin. These new data are fundamental for stratigraphic reconstructions, comparing them with the already well-calibrated reference section of Falconara-Gibliscemi but also with other outcrops located in the various depocenters of the Caltanissetta Basin. The local transition from the uppermost part of the Tripoli cycles to the ‘CdB’ reflects the worsening of the marine connections, implying that during late Messinian broadly constant stressed environmental conditions existed in the central Mediterranean shelves. We conclude that since the onset of the MSC, marine inputs were not important enough to balance the effects of the climate fluctuations and the evaporation/precipitation budget in the individualized semi-closed settings.