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Alpine flysch deposits in the Northern Carpathians. In the upper center of the picture, layers of gray mudstone or marl clay alternating with roughly equally thick yellowish or reddish layers of coarser material can be seen.

In geology, flysch [ ˈfliːʃ ] denotes a marine sedimentary facies , which is mostly represented by an alternation of claystones and coarse-grained rocks (typically sandstones ). These sediments are often subsequently deformed ( folded ), e.g. Sometimes so intense that it is metamorphic rocks . Flysch series arise during mountain-building processes and the coarse-grained rocks represent the eroded material of the mountain range being formed. Since this material usually enters the deposit area in the form of suspension flows , the geology of flysch is often referred to as turbidites .


The term was first used in geological literature in 1827 by Bernhard Studer , who used it to designate rock formations in the Simmental and Saane valley in the Swiss Alps , made up of “predominantly sandy or marly, black or gray slate and very hard and dense sandstones with calcareous and dark gray cement ”. The term 'flysch' comes from the local dialect in the Simmental and describes slatey, easily split, easily eroded rock material that has weathered into platelets. Studer himself later associated the word with the originally Low German word ' Flöz ', which in turn is related to various old words of the Germanic language family , all of which mean something like 'flat' or 'level'. Thus, the name 'Flysch' is likely to go back to the schisty nature of the rocks that are so called in Simmental Swiss German .


Banded Kulm clay schist from a distal flysch facies, NW Harz.
Fold in the mighty Kulm-Grauwackenbanks of a proximal flysch facies, NW Harz.
Alpine flysch series in the western Pyrenees, near Deba and Zumaia, Basque Country.

In modern geology, flysch is the term used to describe sequences of marine clastic sediments . a. by slipping from previously on the continental shelf deposited sediments output over the continental slope into the deep arise. This sliding usually takes place in the form of avalanche-like turbidity or suspension flows. Since such landslides are repeated relatively frequently during a mountain formation that takes millions of years, characteristic sequences arise in which layers of claystone alternate with layers of coarser-grained material. The latter often have a very mixed mineral composition. Like sandstone, they consist mainly of quartz grains, but usually also contain large amounts of lime or clay. Furthermore, various minerals, u. a. Glauconite , mica and / or feldspar may be included.

The layers of coarse material that are deposited by the suspension streams within a few hours or days are also referred to as turbidites with regard to their formation. The claystone layers in between are the result of an extremely slow, continuous sedimentation of clay particles (so-called background sedimentation) in the deep sea.

The term flysch thus designates a special sedimentary facies and a distinction can be made between a distal and a proximal facies, the transition between the two facies being fluid. In the typical distal flysch, the turbidites are represented by thin silt bands , which in the rock are characterized by a different weathering color than by a grain size difference that is visible to the naked eye. In the typical proximal flysch, the turbidites are characterized by z. Sandstone banks, some more than 1 meter thick, may even contain remains of plants. Another characteristic of proximal flysch are unlayered brecciated sediment masses ( olisthostromes ) . A flyschlage with such a chaotic structure is called a wildflysch .

The initial sediments of the flysch can be unconsolidated mud or sands , but already consolidated rocks can also be included in a landslide and turned into a sandstone-mudstone sequence as a wildflysch. The rocks ( olistholiths ) contained in wild flysch, which mostly differ from the flysch sediments facially, can e.g. T. house size and reach more (olisthoplaka) , and in some areas kilometer-sized slipped clods (olisthothrymmata) can be detected. The transport route of such foreign rocks can be more than 100 kilometers long, even with the Olisthothrymmata.

The composition of the Flysch Turbidite is very different, as the starting material comes from various sources and is strongly mixed. As a result of the deposition in the foreland of a mountain in the process of being formed, the sequence of deformation processes that take place in the areas of origin of the parent rock can in many cases be reconstructed from the composition of the flysch. In the course of time, other rocks come under the influence of the mountain-forming processes, are eroded and relocated, so that they are ultimately also found in the flysch deposits. Due to their position close to mountain-forming processes, flysch rocks are often included in these after being deposited and are then strongly tectonically deformed.


Flysch is found worldwide both in old mountain hulls and in young fold mountains . Geologically relatively young occurrences include:

In Germany, Variscan flysch is found as part of the Kulm facies with their typical Grauwacken in the Rhenish Slate Mountains , in the Harz and in the Thuringian-Franconian-Vogtland Slate Mountains . The flysch in the axial zone of the Pyrenees is also Variscan.

See also

Individual evidence

  1. KJ Hsü, U. Briegel: Geology of Switzerland: A textbook for getting started. 1991, pp. 65-67.
  2. The information in the paragraph on etymology is taken from the following literature:
    • KJ Hsü, U. Briegel: Geology of Switzerland: A textbook for getting started. 1991, pp. 65-67.
    • J. Früh: On the etymology of "Flysch". 1904.
  3. ^ Richter: General Geology. 1986, p. 342.
  4. Scholz: Building and Becoming the Allgäu Landscape. 1995, p. 74 f.


  • Heinrich Bahlburg, Christoph Breitkreuz: Fundamentals of geology. 3. Edition. Spectrum Academic Publishing House, 2008, ISBN 978-3-8274-1811-1 .
  • J. Früh: On the etymology of “Flysch” (m.), “Fliesse” (f.) U. "Flins" (m.) . In: Eclogae Geologicae Helvetiae . tape 8 , issue 1, 1903, pp. 217–220 , doi : 10.5169 / seals-156273 .
  • Rudolf Hohl (ed.): The history of the development of the earth. 6th edition. Werner Dausien Verlag, Hanau 1985, ISBN 3-7684-6526-8 .
  • Kenneth J. Hsü, Ueli Briegel: Geology of Switzerland: A textbook for getting started and dealing with the experts. Birkhäuser, 1991, ISBN 3-7643-2579-8 .
  • Dieter Richter: General Geology. 3. Edition. De Gruyter Verlag, Berlin / New York 1985, ISBN 3-11-010416-4 .
  • Herbert Scholz: Construction and development of the Allgäu landscape. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 1995, ISBN 3-510-65165-0 .

Web links

Commons : Flysch  - album with pictures, videos and audio files