Paratethys

Paleogeography of the Tethys ocean in the Rupelian age (33.9-28.4
million years ago). Black lines indicate present day coastlines.[1]

The Paratethys ocean, Paratethys sea or just Paratethys was a large shallow sea that stretched from the region north of the Alps over Central Europe to the Aral Sea in Central Asia. The sea was formed during the Oxfordian stage of the Late Jurassic as an extension of the rift that formed the Central Atlantic Ocean and was isolated during the Oligocene epoch (about 34 million years ago).[2] It was separated from the Tethys Ocean to the south by the formation of the Alps, Carpathians, Dinarides, Taurus and Elburz mountains. During its long existence the Paratethys was at times reconnected with the Tethys or its successors, the Mediterranean Sea or Indian Ocean. From the Pliocene epoch onward (after 5 million years ago), the Paratethys became progressively shallower. Today's Black Sea, Caspian Sea, Aral Sea, Lake Urmia and others are remnants of the Paratethys Sea.

Name and research

The name Paratethys was first used by V. D. Laskarev in 1924.[3] Laskarev's definition included only fossils and sedimentary strata from the sea of the Neogene system. This definition was later adjusted to also include the Oligocene series. The existence of a separated water body in these periods was deduced from fossil fauna (most importantly molluscs, 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.

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

Paratethys realm at 17-13 mya.

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 (Eurasia and North America) and Gondwana (Africa, India, Antarctica, Australia and South America) when the supercontinent Pangea broke up during the Triassic (200 million years ago).

The boundary between the Eocene and Oligocene epochs was characterized by a big drop of the global (eustatic) 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 Turgai Sea), the North Sea Basin and Atlantic Ocean (in the form of a strait north of the Carpatians) also closed in the Early Oligocene.[4] However, it is possible connections with the Rhônegraben (and the Mediterranean) and the Hessen Strait (that connected the Molasse Basin with the North Sea Basin) still kept open.

The Early Miocene (around 20 million years ago) 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 the Mediterranean fell dry during the Messinian salinity crisis (about 6 million years ago) there were phases when Paratethys water flowed into the dry Mediterranean basins. During the Pliocene epoch (5,33 to 2,58 million years ago) the former Paratethys was divided in 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.

See also

References

  1. ↑ Rögl, F.; 1999: Mediterranean and Paratethys. Facts and hypotheses of an Oligocene to Miocene paleogeography (Short Overview), Geologica Carpathica 50(4), p. 339– 349.
  2. ↑ Stampfli, Gérard. "155 Ma - Late Oxfordian (an. M25)" (PDF). University of Lausanne.
  3. ↑ Laskarev, V.; 1924: "Sur les equivalents du Sarmatien superieur en Serbie". In: Vujević, P. (ed.), Recueil de travaux offert à M. Jovan Cvijic par ses amis et collaborateurs. Drzhavna Shtamparija, Beograd, pp. 73–85.
  4. ↑ Schulz, H.-M.; Vakarcs, G. & Magyar, I.; 2005: The birth of the Paratethys during the Early Oligocene: From Tethys to an ancient Black Sea analogue?, Global and Planetary Change 49(3-4), p. 163-176.

Further reading

External links

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