The Valais Ocean is a subducted

oceanic basin In hydrology, an oceanic basin (or ocean basin) is anywhere on Earth that is covered by seawater. Geologically, ocean basins are large  geologic basins that are below sea level. Most commonly the ocean is divided into basins foll ...

which was situated between the continent

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

and the

microcontinent Continental crustal fragments, partly synonymous with microcontinents, are pieces of continents that have broken off from main continental masses to form distinct islands that are often several hundred kilometers from their place of origin. Caus ...

Iberia The Iberian Peninsula (), ** * Aragonese and Occitan: ''Peninsula Iberica'' ** ** * french: Péninsule Ibérique * mwl, Península Eibérica * eu, Iberiar penintsula also known as Iberia, is a peninsula in southwestern Europe, defi ...

or so called

Briançonnais microcontinent Briançonnais may refer to: *the people of Briançon *, a natural region of France *Briançonnais zone, a piece of continental crust See also

*Republic of the Escartons, sometimes called the Briançonnais {{dab ...

. Remnants of the Valais ocean are found in the western Alps and in tectonic windows of the eastern Alps and are mapped as the so-called "north

Penninic The Penninic nappes or the Penninicum, commonly abbreviated as Penninic, are one of three nappe stacks and geological zones in which the Alps can be divided. In the western Alps the Penninic nappes are more obviously present than in the eastern ...

" nappes.

Tectonic history

After the breakup of

Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...

in the early

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...

age, the continents of Africa,

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...

, Europe and

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

began to move away from each other. The breaking up, or

rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...

ing, did not take place along one unbroken line; thus, at the southern edge of the European plate the microcontinent Iberia also began to break away from Europe. In the western part of the rift that separated the two landmasses, oceanic crust was formed in what is at present the Gulf of Biscay, while in the eastern part the Valais Ocean was formed. When in the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

period Africa again began to move towards Europe, the Valais Ocean became sandwiched between the two continents. To the east, the Valais oceanic crust, together with a piece of Iberian

continental crust Continental crust is the layer of igneous, sedimentary, and metamorphic rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called ''sial'' be ...

(called the Briançonnais terrane),

subducted Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...

beneath the

Apulian plate The Adriatic or Apulian Plate is a small tectonic plate carrying primarily continental crust that broke away from the African Plate along a large transform fault in the Cretaceous period. The name Adriatic Plate is usually used when referring ...

, a part of the African

tectonic plate Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...

that had begun to move independently. This process eventually led to the formation of the

Alps The Alps () ; german: Alpen ; it, Alpi ; rm, Alps ; sl, Alpe . are the highest and most extensive mountain range system that lies entirely in Europe, stretching approximately across seven Alpine countries (from west to east): France, Sw ...

. To the west, no subduction took place, but the Iberian plate moved against the European plate along a large

transform fault A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subductio ...

, which led to the formation of the

Pyrenees The Pyrenees (; es, Pirineos ; french: Pyrénées ; ca, Pirineu ; eu, Pirinioak ; oc, Pirenèus ; an, Pirineus) is a mountain range straddling the border of France and Spain. It extends nearly from its union with the Cantabrian Mountains to C ...

. Fragments of Valais oceanic crust have been obducted and can be found as

ophiolite An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks. The Greek word ὄφις, ''ophis'' (''snake'') is found i ...

s in the

Penninic nappes The Penninic nappes or the Penninicum, commonly abbreviated as Penninic, are one of three nappe stacks and geological zones in which the Alps can be divided. In the western Alps the Penninic nappes are more obviously present than in the eastern ...

of the Alps.

Name

The Valais Ocean was named after the

Swiss Swiss may refer to: * the adjectival form of Switzerland * Swiss people Places * Swiss, Missouri * Swiss, North Carolina *Swiss, West Virginia * Swiss, Wisconsin Other uses *Swiss-system tournament, in various games and sports *Swiss Internation ...

canton

Valais Valais ( , , ; frp, Valês; german: Wallis ), more formally the Canton of Valais,; german: Kanton Wallis; in other official Swiss languages outside Valais: it, (Canton) Vallese ; rm, (Chantun) Vallais. is one of the cantons of Switzerland, 26 ...

Occurrences

In the eastern

remnants of the Valais are confined to tectonic windows and the northern margin of the Alps. They include oceanic sediments (e.g.

radiolarite Radiolarite is a siliceous, comparatively hard, fine-grained, chert-like, and homogeneous sedimentary rock that is composed predominantly of the microscopic remains of radiolarians. This term is also used for indurated radiolarian oozes and ...

turbidite A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean. Sequencing Turbidites were ...

s) and oceanic crust (e.g.

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

pillow lava Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava underwater, or ''subaqueous extrusion''. Pillow lavas in volcanic rock are characterized by thick sequences of disconti ...

). The windows in the overlying

Austroalpine nappes The Austroalpine nappes are a geological nappe stack in the European Alps. The Alps contain three such stacks, of which the Austroalpine nappes are structurally on top of the other two (meaning they were thrust over the other two). The name Aust ...

reveal the underlying

. In the Engadin window, remnants are found in the Pfundser zone and in the

Tauern window The Hohe Tauern window is a geological structure in the Austrian Central Eastern Alps. It is a window (in German ''fenster'') in the Austroalpine nappes where high-grade metamorphic rocks of the underlying Penninic nappes crop out. The structu ...

the "Obere Schieferhülle"; at the northern margin of the Alps the remnants are called Rhenodanubic flysch. In the western

, remnants of the Valais crop out in many areas of

Switzerland ). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are installed in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel ...

and

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...

. This includes the Cheval noir unit, the Versoyen unit, the Sion-Courmayeur Zone, the Niesen nappe, the

Schlieren flysch Schlieren ( ; , ) are optical inhomogeneities in Transparency and translucency, transparent optical medium, media that are not necessarily visible to the human eye. Schlieren physics developed out of the need to produce high-quality lenses devoi ...

, the Antrona unit, the Wägital flysch and the Prätigau Bündnerschiefer.

References

{{Reflist Geology of the Alps Historical oceans Geology of Austria Geology of Germany Geology of Switzerland