Bündner schist

The Bündnerschiefer are chalky - clayey sediments of the Alps, which have been deposited during the Jurassic and Early Cretaceous in the Penninic Valais trough, a marine basin of intermediate depth and in the oceanic region of the Alpine Tethys. However, subsequent Alpine metamorphism, these are today at lime, clay, mica or Kalkglimmerschiefer. The name is derived from the Swiss canton of Grisons, where they are particularly common. In France they are called Schistes lustres (, gloss slate '), in Italy they are a part of the broader conceptual calcescisti, as they also occur in the Apennines. Were deposited Graubunden slate in the Penninic ocean, which was located between the southern edge of the Eurasian plate and the Apulian and was closed during the Alpine orogeny.

Rocks

The bulk of the Bündnerschiefer consists of dark, fine-grained mudstones with varying sand and lime that shine often silky by tectonic deformation and formed during the metamorphism mica. Together with the Grison shales are mainly in the southern Penninic frequently radiolarites and ophiolites. This association suggests that the Bündnerschiefer were deposited for the most part on oceanic crust. It is typical of the Penninic and has been described among others by Gustav Steinmann, after which she was named Steinmann Trinity. Within the slate by, while chaotic sliding masses containing large blocks and tangled masses of Flyschsedimenten. The thickness of the layers is difficult to determine because of the intense deformation, it is in some areas several thousand meters.

Depositional environment

The depositional environment of the slate was divided into two parts: in the south Graubunden slate were deposited in the Piedmont - Ligurian ocean, which is also called the Alpine Tethys. Here the deposition took place almost entirely on oceanic crust instead, and ophiolites are common. In the north, the sedimentation in the Valais Ocean played out, which also had oceanic crust at least in its southern range. A high area lay between these oceanic areas with continental crust, the Briançonnais, from the sediment material was delivered in the oceanic areas again and again.

Tectonics

Since the Bündnerschiefer consist of relatively easily deformable rocks, they were strongly affected by the thrust of the Alpine nappes. You have thereby partially experienced an intense tectonic deformation, are usually strongly geschiefert, disturbed and verfaltet. Near the ceiling tracks they are as mylonites, in the Boudin other rocks are adjusted, usually ophiolites and marbles.

Within the Pennine units Graubunden slate are limited according to their original depositional environment mainly on the ceiling of the Nordpenninkums and Südpenninikums. They frequently appear as disconnecting device between the crystalline ceiling on ( so-called ceiling Scheider).

The metamorphosis of Bündnerschiefer is always clear. Widely used are evidence of a high-pressure metamorphism, which is the result of the subduction of the oceanic areas under the Apulian plate and their anticipatory accretionary prism.

Occurrence

Typical rocks of Penninikums occur Bündnerschiefer, in greater numbers to the west of Switzerland -Austrian border in the entire Western Alps arc on.

In Austria they are only known from the Rechnitz window, the Tauern window and the Engadine window, everywhere else there they are eclipsed by the Austroalpine nappes. The slate of Rhenodanubian Flysch, which accompanies most of the way between Lake Constance and the Alps Wien front are referred to by some authors as being Bündnerschiefer.

In Switzerland, the soft limestone and shale of the Bündnerschiefer for example, form the mountains between Brig and Nufenenpass. They form the framework of the Bedretto Valley, the Safiental and the background the Rhine valley, and the valleys Domleschg, Schanfigg and Prättigau are sunk into it. They also occur in the southern and eastern area of the Gotthard Massif, such as Zermatt and Saas Fee. Here they also occur across the border in Italy. In France, they set out to be Schistes lustres continued that stretch over Savoie to the south.