The name Paratethys was first used by Vladimir D. Laskarev in 1924. Laskarev's definition included only fossils and sedimentary stratafrom the sea of the Neogenesystem. This definition was later adjusted to also include the Oligocene series. The existence of a separated water body in these periods was deduced from fossilfauna. In periods in which the Paratethys or parts of it were separated from each other or from other oceans, a separate fauna developed which is found in sedimentary deposits. In this way the paleogeographical development of the Paratethys can be studied. Sedimentary strata from the Paratethys are difficult to correlate with those from other oceans or seas because at times it was totally separated from them. Stratigraphers of the Paratethys therefore have their own sets of stratigraphic stages which are still used as alternatives for the official geologic timescale of the ICS.
Paleogeographical development
The Paratethys spread over a large area in Central Europe and western Asia. In the west it included in some stages the Molasse basin north of the Alps; further east the Vienna Basin and the Pannonian Basin; the basin of the current Black Sea; and from there it spread eastward until the current position of the Aral Sea. During the Jurassic and Cretaceous periods, this part of Eurasia was covered by shallow seas that formed the northern margins of the Tethys Ocean. However, because Anatolia, the southern boundary of the Paleo-Tethys, is a part of the original Cimmerian continent, the last remnant of Paleo-Tethys Ocean might be oceanic crust under the Black Sea. The Tethys Ocean formed between Laurasia and Gondwana when the supercontinentPangeabroke up during the Triassic. The boundary between the Eocene and Oligocene epochs was characterized by a big drop of the global sea level and a sudden steep cooling of global climates. At the same time the Alpine orogeny, a tectonic phase by which the Alps, Carpathians, Dinarides, Taurus, Elburz and many other mountain chains along the southern rim of Eurasia were formed. The combination of a drop in sea level and tectonic uplift resulted in a large regression of the sea and a barrier was formed between the Tethys and Paratethys domains. Connections with the Arctic Ocean, the North Sea Basin and Atlantic Ocean also closed in the Early Oligocene. However, it is possible connections with the Rhônegraben and the Hessen Strait still kept open. The Early Miocene saw a phase of marine transgression. During this period the Paratethys was well connected with the Mediterranean again. This trend was reversed halfway in the Miocene, and parts of the Paratethys were often separated from each other. When parts of the Mediterranean fell dry during the Messinian salinity crisis there were phases when Paratethys water flowed into the deep Mediterranean basins. During the Pliocene epoch the former Paratethys was divided into a couple of inland seas that were at times completely separated from each other. An example was the Pannonian Sea, a brackish sea in the Pannonian Basin. Many of these would disappear before the start of the Pleistocene. At present, only the Black Sea, Caspian Sea and Aral Sea remain of what was once a vast inland sea.
