Reconstruction of the paleoenvironmental changes around the Miocene-Pliocene boundary along a W-E transect across the Mediterranean

Abstract

In order to reconstruct the environmental changes at the end of the Messinian salinity crisis, a multidisciplinary study has been carried out with a high sampling resolution of the late Messinian-early Zanclean (Zone MPl 1) sediments along a West-East Mediterranean transect. The studied examples comprise sections from southern Spain (Vera/Almanzora), Balearic Basin (ODP Site 975), Tyrrhenian Basin (ODP Site 974), Sicily (Eraclea Minoa), Zakynthos (Kalamaki), Corfu (Aghios Stefanos), Crete (Aghios Vlasis). Previously analyzed sections from the Levantine Basin (Cyprus and ODP Sites 968 and 969) are used for comparison. The sections have been correlated using planktonic foraminiferal assemblages, sedimentological and stable isotope variations, and compared to the astronomical cyclicity defined in the Miocene-Pliocene boundary stratotype of Eraclea Minoa, Sicily. Variations of CaCO3 content, stable isotopes of carbonates (δ18O, δ13C), and foraminiferal assemblages indicate similar environmental transition at the Miocene-Pliocene boundary in all of the investigated sections. The latest Messinian deposits are barren of fossils or characterized by only reworked planktonic foraminifers, except for the sporadic presence of Ammonia tepida, brackish or lacustrine ostracods and brackish mollusks typical of the "Lago-Mare" facies. The oxygen and carbon isotopic compositions of carbonates usually exhibit large variations with dominantly low δ values indicating freshwater dilution. The earliest Pliocene (MPl 1, cycle 1) shows a rapid and progressive increase of the δ18O values, which indicates the restoration of marine conditions after the Lago-Mare event. Normal marine environments were definitely established and stabilized at the top of cycle 1. These data confirm that the inflow of marine waters occurred contemporaneously within the whole Mediterranean at the base of Pliocene, although stable marine conditions occurred only about 20 kyrs later.