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 fol ...
which was situated between the continent
Europe 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.
Cau ...
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, def ...
or so called
Briançonnais microcontinent. 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" 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 Cretace ...
age, the continents of Africa,
South America, 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 C ...
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-graben wi ...
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'' bec ...
(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, 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 subduction ...
, which led to the formation of the
Pyrenees.
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 ...
s in the
Penninic nappes 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 Internatio ...
canton
Canton may refer to:
Administrative division terminology
* Canton (administrative division), territorial/administrative division in some countries, notably Switzerland
* Township (Canada), known as ''canton'' in Canadian French
Arts and ente ...
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 26 cantons forming the Sw ...
.
Occurrences
In the eastern
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 ...
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 ...
s,
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,
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 reveal the underlying
Penninic nappes. 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 stru ...
the "Obere Schieferhülle"; at the northern margin of the Alps the remnants are called
Rhenodanubic flysch.
In the western
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 ...
, 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. This includes the
Cheval noir unit, the
Versoyen unit, the
Sion-Courmayeur Zone, the
Niesen nappe, the
Schlieren flysch, the
Antrona unit, the
Wägital flysch and the
Prätigau Bündnerschiefer.
See also
*
Piemont-Liguria Ocean
The Piemont-Liguria basin or the Piemont-Liguria Ocean (sometimes only one of the two names is used, for example: Piemonte Ocean) was a former piece of oceanic crust that is seen as part of the Tethys Ocean. Together with some other oceanic basi ...
*
Pannonian Sea
References
{{Reflist
Geology of the Alps
Historical oceans
Geology of Austria
Geology of Germany
Geology of Switzerland