Paratethys Megalake Infographic 23X 2 EN

The Paratethys sea, Paratethys ocean, Paratethys realm or just Paratethys (meaning "beside Tethys"), was a large shallow inland sea that covered much of mainland Europe and parts of western Asia during the middle to late Cenozoic, from the late Paleogene to the late Neogene, and is regarded as the largest inland sea in history. At its greatest extent, it stretched from the region north of the Alps over Central Europe to the Aral Sea in Central Asia.

Paratethys formed about 34 Mya (million years ago) at the beginning of the Oligocene epoch, when the northern region of the Tethys Ocean (Peri-Tethys) was separated from the Mediterranean region of the Tethys realm due to the formation of the Alps, Carpathians, Dinarides, Taurus and Elburz mountains. Paratethys was at times reconnected with the Tethys or its successors (the Mediterranean Sea or the Indian Ocean) during the Oligocene and the early and middle Miocene times, but at the onset of the late Miocene epoch, the tectonically trapped sea turned into a megalake from the eastern Alps to what is now Kazakhstan. From the Pliocene, Caspian Sea, Aral Sea, Lake Urmia, Namak Lake and others are remnants of the Paratethys Sea.

Name and research

The name Paratethys was first used by Vladimir Laskarev in 1924. Laskarev's definition included only fossils and sedimentary strata from the sea of the Neogene system. This definition was later adjusted also to include the Oligocene series. The existence of a separate water body in these periods was deduced from the fossil fauna, including mollusks, fish and ostracods. 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.
Laskerev's description of the Paratethys was anticipated much earlier by Sir Roderick Murchison in chapter 13 of his 1845 book.

One of the key characteristics of the Paratethys realm, that is differentiating it from the Tethys Ocean, is the widespread development of endemic fauna, adapted to fresh and brackish waters like those that still exist in recent waters of the Caspian Sea. This distinctive fauna in which univalves of freshwater origin such as ''Limnex'' and ''Neritinex'' are associated with forms of Cardiacae and Mytili, common to partially saline or brackish waters, makes the geologic records from Paratethys particularly difficult to correlate with those from other oceans or seas because their faunas evolved separately at times. 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.

Palaeogeographic evolution

Paratethys was peculiar due to its paleogeography: it consisted of a series of deep basins, formed during the Oxfordian stage of the Late Jurassic as an extension of the rift that formed the Central Atlantic Ocean. During the Jurassic and Cretaceous periods, this part of Eurasia was covered by shallow seas that formed the northern margins of the Tethys Ocean. These basins were connected with each other and the global ocean by narrow and shallow seaways that often limited water exchange and caused widespread long-term anoxia. The Paratethys descends directly from the Peri-Tethys, the northwestern arm of the Tethys Ocean, which was separated from the rest of the ocean via the Alpide orogeny.

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; the Vienna Basin, the Outer Carpathian Basin