The Messinian/Zanclean boundary in the Northern Apennines

TheMiocene-Pliocene boundary in the Northern Apennine was the object of several studies prior to the definition of the GSSP of the Zanclean stage in the Eraclea Minoa section (Sicily, Italy). This definition came at the end of the ’90s, after an accurate and Mediterranean wide high resolution biostratigraphic study of the basal Pliocene deposits. Since then calcareous plankton biostratigraphy allows to correlate the very base of the Zanclean through the occurrence of two consecutive sinistrally coiled Neogloboquadrina acostaensis influxes, respectively placed within the 1st/2nd cycle and the 2nd/3rd cycle from the base astronomically dated at 5.33Ma (insolation peak 510). Besides these bioevents, the classical Spheroidinellopsis spp. acme interval, the base of subchron Thvera and the cyclic signal of both biota and lithology help recognize the base of the Zanclean stage. Several sections and boreholes were studied in an east (Marche region) to west (Emilia region) transect along the Northern Apennine. Despite different sampling resolution, the two N. acostaensis sinistral influxes were recognized in each sites except the Montepetra borehole were the definition of the Zanclean base was achieved through cyclostratigraphic features. Some nannofossil bioevents, such as the drop of abundance of D. variabilis and the beginning of a paracme interval of R. pseudoumbilicus, revealed to be useful for a better constraining of the basal Zanclean. Thus the sedimentary succession across the Messinian – Zanclean boundary was recognized to be continuous and the base of the Zanclean stage coeval to its GSSP at Eraclea Minoa, thus dated at 5.33 Ma. This demonstrates that the Zanclean restoration of marine condition that ended the Messinian salinity crisis was a synchronous event, geologically speaking within the present resolution power, throughout the entire Mediterranea region.