A bio-chronostratigraphic study of the upper Miocene from the northern Caltanissetta Basin, Sicily (core 3AGN2S04). Implications for dating the Messinian Salinity Crisis onset

The late Miocene deposits from core 3AGN2S04, located in the northern Caltanissetta Basin (Sicily), display the pre-Messinian Salinity Crisis (MSC) and the MSC events. The present study describes the entire core in terms of lithology, biostratigraphy and magnetostratigraphy and aims to enlighten the relationship between MSC evaporite cyclicity and astronomical forcing. The lithological and micro-/macro-paleontological descriptions document the MSC record, with Stage 1 (onset and Calcare di Base member), Stage 2 (Messinian Erosional Surface) and part of Stage 3 (Upper Gypsum and Lago Mare). Detailed micro-fossil analyses of the pre-evaporites reveal several biostratigraphic events that permit correlations to the well-dated Mediterranean planktonic foraminiferal biostratigraphic zonation of the late Tortonian and Messinian. An integrated bio-cyclostratigraphic analysis allows bed-to-bed correlations of core 3AGN2S04 with the reference sections of Falconara/Gibliscemi (Sicily) and Sorbas (Spain), but also with various other sections from the Caltanissetta Basin. Our cyclostratigraphic correlations show a stratigraphical gap in the core between the late Tortonian Terravecchia Formation and the pre-evaporitic Messinian Tripoli Formation. This hiatus is probably related to the tectonically active geological setting of the northern Caltanissetta Basin. Finally, we show that the repercussions of the paleoenvironmental evolution towards evaporitic deposition and the MSC onset seem to have been diachronous throughout the various perched basins on Sicily characterized by different paleobathymetries. In particular, the onset of the Calcare di Base took place around 40-100 ka before the deposition of the first gypsum bed of the Primary Lower Gypsum units.