Flysch () is a sequence of

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

layers that progress from deep-water and turbidity flow deposits to shallow-water shales and

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s. It is deposited when a deep basin forms rapidly on the continental side of a mountain building episode. Examples are found near the North American Cordillera, 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, Swi ...

, 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 ...

and the

Carpathians The Carpathian Mountains or Carpathians () are a range of mountains forming an arc across Central Europe. Roughly long, it is the third-longest European mountain range after the Urals at and the Scandinavian Mountains at . The range stretches ...

Sedimentological properties

Flysch consists of repeated sedimentary cycles with upwards fining of the sediments. There are sometimes coarse conglomerates or

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...

s at the bottom of each cycle, which gradually evolve upwards into

and shale/mudstone. Flysch typically consists of a sequence of shales rhythmically interbedded with thin, hard,

graywacke Greywacke or graywacke (German ''grauwacke'', signifying a grey, earthy rock) is a variety of sandstone generally characterized by its hardness, dark color, and poorly sorted angular grains of quartz, feldspar, and small rock fragments or lit ...

-like sandstones. Typically the shales do not contain many

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s, while the coarser sandstones often have fractions of micas and

glauconite Glauconite is an iron potassium phyllosilicate ( mica group) mineral of characteristic green color which is very friable and has very low weathering resistance. It crystallizes with a monoclinic geometry. Its name is derived from the Gre ...

Tectonics

In a continental collision, a

subducting 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 ...

tectonic plate pushes on the plate above it, making the rock fold, often to the point where

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

s form, and a mountain chain rises. On the upper plate, the land between the mountains and the undeformed continent bends downward, forming a foreland basin. If the basin forms slowly, as in the northern

Appalachians The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They ...

, it fills with shallow-water sediments. If it forms rapidly, as in the east side of the North American Cordillera, then sea water may rush in, and the first sedimentary deposits are deep water deposits. If the mountain slope is steep enough at the edge of the basin, it will shed material in rapidly moving sedimentary flows called

turbidity current A turbidity current is most typically an underwater current of usually rapidly moving, sediment-laden water moving down a slope; although current research (2018) indicates that water-saturated sediment may be the primary actor in the process. T ...

s, resulting in

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 wer ...

deposits. As the basin fills up, shallow-water sandstones and continental deposits form. Most of the resulting rocks have little deformation, but near the edge of the mountain chain they can be subject to folding and thrusting. After the basin fills up, continental sediments (

molasse __NOTOC__ The term "molasse" () refers to sandstones, shales and conglomerates that form as terrestrial or shallow marine deposits in front of rising mountain chains. The molasse deposits accumulate in a foreland basin, especially on top of flysc ...

) are deposited on top of the flysch.

Name and use

The name flysch was introduced in geologic literature by the Swiss geologist

Bernhard Studer Prof Bernhard Studer HFRSE (August 21, 1794May 2, 1887), was a 19th-century Swiss geologist. Biography He was born at Buren an der Aare near Bern in Switzerland on 21 August 1794. He was educated to become a clergyman, but his interests later ...

in 1827. Studer used the term for the typical alternations of sandstone and shale in the foreland of the

. The name comes from the

German German(s) may refer to: * Germany (of or related to) ** Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...

word ''fliessen'', which means ''to flow'', because Studer thought flysch was deposited by rivers. The insight that flysch is actually a deep marine sediment typical for a particular

plate tectonic 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 ...

setting came only much later. The name flysch is currently used in many mountain chains belonging to the Alpine belt. Well-known flysch deposits are found in the forelands of the

and

and in tectonically similar regions in

Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...

, the

Balkans The Balkans ( ), also known as the Balkan Peninsula, is a geographical area in southeastern Europe with various geographical and historical definitions. The region takes its name from the Balkan Mountains that stretch throughout the who ...

and on

Cyprus Cyprus ; tr, Kıbrıs (), officially the Republic of Cyprus,, , lit: Republic of Cyprus is an island country located south of the Anatolian Peninsula in the eastern Mediterranean Sea. Its continental position is disputed; while it is ge ...

. In the northern Alps, the Flysch is also a

lithostratigraphic Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igneou ...

unit.

Sedimentological properties

Tectonics

Name and use

References

Further reading