The Geological origins and paleoceanographic history of the Mediterranean region: Tethys to Present

The Mediterranean we presently see is the result of a long geological history of rifting, spreading, subduction and collision of plates and microplates since the Mesozoic (Fig. 1). At the beginning of that time, a wide ocean, the Tethys, was encased between the continental masses of the Pangea, forming a large gulf, wedging to the west into this supercontinent. The subsequent geological history brings to the modern Mediterranean through the collision between African and Eurasian continents almost consuming all the former oceanic crust of the Tethys. Nowadays, it is possible to distinguish the Western Mediterranean from the Eastern, separated by the Sicily channel and characterized by different age and setting. The Eastern Mediterranean includes the oldest portion of oceanic lithosphere preserved from subduction in two remnants: the Ionian and Herodotus abyssal plains, at present among the deepest portion of the Mediterranean. They consists of an old oceanic lithosphere, possibly of pre-Jurassic to Cretaceous age that is subducting under the Eurasian plate. This subduction forms the Mediterranean Ridge, an accretionary prism of deformed rocks, scraped off from the subducting plate. Associated with this subduction are some features that characterize the entire Eastern Mediterranean: the opening of the Aegean sea, a back-arc basin created by stretching of the upper (Eurasian) plate, due to the retreat of the subducting plate. The Anatolian microplate started drifting to the west at the same time of the Aegean spreading, i.e. around 23 My ago, basically driven by the collision of Arabia against Eurasia, and the occurrence of a free boundary to the west, i.e the Aegean opening. Toward the northwest, the Ionian oceanic lithosphere subducts again part of the Eurasian plate, with the accretionary prism affecting a wide area known as Calabrian arc (see Fig. 1). The Adriatic Sea is a relict epicontinental sea formed by patches of carbonate platforms and intervening basins, whose most prominent are the Apulian platform and the Umbro-Marchean-Adriatic basin. The sea is bordered by active margins, documenting the subduction of the Adriatic plate to the northeast under the Dinarides, as well as to the southwest under the Apennines. The Western Mediterranean is much younger with respect to the Eastern (Fig. 1). It developed as the now consumed oceanic crust of the African plate (the so-called Neo-Tethys, or Alpine Tethys) was subducted under Eurasia. The retreat of this oceanic crust forced the upper (Eurasian) plate to stretch and open back-arc basins, that developed in relatively short time periods, as is the case of the Ligurian-Provençal basin, started around 20 My and stopped at 15, the Alboran and Algerian basins (between 16 and 8 My) and the Tyrrhenian (between 7 and 2 My). The Corsica – Sardinia block was rifted off from Eurasia and drifted to the present-day setting by the opening of the Ligurian-Provençal basin. Also the Apenninic chain was rifted and rotated by the opening of the Tyrrhenian Sea.