Flysch - AbsoluteAstronomy.com

Flysch is a sequence of sedimentary rock

Sedimentary rock

Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

s that is deposited in a deep marine

Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

facies in the foreland basin

Foreland basin

A foreland basin is a depression that develops adjacent and parallel to a mountain belt. Foreland basins form because the immense mass created by crustal thickening associated with the evolution of a mountain belt causes the lithosphere to bend, by a process known as lithospheric flexure...

of a developing orogen. Flysch is typically deposited during an early stage of the orogenesis. When the orogen evolves the foreland basin becomes shallower and molasse

Molasse

The term "molasse" refers to the sandstones, shales and conglomerates formed as terrestrial or shallow marine deposits in front of rising mountain chains. The molasse is deposited in a foreland basin, especially on top of flysch, for example that left from the rising Alps, or erosion in the Himalaya...

is deposited on top of the flysch. It is therefore called a syn-orogenic

Orogeny

Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...

sediment (deposited contemporaneously with mountain building).

Sedimentological properties

Flysch consists of repeated sedimentary cycles with upwards fining

Particle size (grain size)

Particle size, also called grain size, refers to the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which is the size of a single crystal inside the...

of the sediments. At the bottom of each cycle are sometimes coarse conglomerates

Conglomerate (geology)

A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...

or breccia

Breccia

Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....

s, which gradually evolve upwards into sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

and shale/claystone

Shale

Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...

. Flysch typically consists of a sequence of shales rhythmically interbedded with thin, hard, graywacke-like sandstones. Typically the shales do not contain many fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s, the coarser sandstones often have fractions of mica

Mica

The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition...

s and glauconite

Glauconite

Glauconite is an iron potassium phyllosilicate mineral of characteristic green color with very low weathering resistance and very friable.It crystallizes with a monoclinic geometry...

.

Flysch is formed under deep marine circumstances, in a quiet and low-energetic depositional environment. The coarser layers (which require higher energy) are disruptions in these circumstances, caused by pulsewise flows of mass transport from the forming orogenic wedge

Accretionary wedge

An accretionary wedge or accretionary prism is formed from sediments that are accreted onto the non-subducting tectonic plate at a convergent plate boundary...

. In many cases the mass transports are represented in the record by turbidite

Turbidite

Turbidite geological formations have their origins in turbidity current deposits, which are deposits from a form of underwater avalanche that are responsible for distributing vast amounts of clastic sediment into the deep ocean.-The ideal turbidite sequence:...

Tectonics

Flysch deposits form at convergent plate boundaries

Convergent boundary

In plate tectonics, a convergent boundary, also known as a destructive plate boundary , is an actively deforming region where two tectonic plates or fragments of lithosphere move toward one another and collide...

at the stage of continental collision

Continental collision

Continental collision is a phenomenon of the plate tectonics of Earth that occurs at convergent boundaries. Continental collision is a variation on the fundamental process of subduction, whereby the subduction zone is destroyed, mountains produced, and two continents sutured together...

, often in remnant ocean basins that are present along the same boundary. The sedimental material in the flysch is derived from the forming mountain

Mountain

Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...

s and deposited along the axis of the new mountain chain into remnant ocean basin. The same ocean basin is in the process of subducting

Subduction

In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

under the orogenic wedge. As subduction continues, the flysch sediments are scraped off the down-going oceanic plate and are accreted

Accretion (geology)

Accretion is a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features.-Description:...

onto the orogenic wedge. As a result, flysch deposits are often highly deformed by thrust fault

Thrust fault

A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...

ing and folding

Fold (geology)

The term fold is used in geology when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Synsedimentary folds are those due to slumping of sedimentary material before it is lithified. Folds in rocks vary in...

Name and use

The name flysch was introduced in geologic literature by the Swiss

Switzerland

Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....

geologist Bernhard Studer

Bernhard Studer

Bernhard Studer , Swiss geologist, was born at Büren, near Bern.Although educated as a clergyman, he became so interested in geology at the university of Göttingen that he devoted his life to its pursuit...

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

Alps

The Alps is one of the great mountain range systems of Europe, stretching from Austria and Slovenia in the east through Italy, Switzerland, Liechtenstein and Germany to France in the west....

. The name comes from the German

German language

German is a West Germanic language, related to and classified alongside English and Dutch. With an estimated 90 – 98 million native speakers, German is one of the world's major languages and is the most widely-spoken first language in the European Union....

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 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 foreland

Foreland

Foreland is the easternmost point of the Isle of Wight. It is located three miles east of the town of Brading, and due south of the city of Portsmouth on the British mainland. It is characterised by a pub called the Crab and Lobster and various beach huts plus a beach cafe and a coast guard...

s of the Pyrenees

Pyrenees

The Pyrenees is a range of mountains in southwest Europe that forms a natural border between France and Spain...

and Carpathians and in tectonically similar regions in Italy

Italy

Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

, the Balkans

Balkans

The Balkans is a geopolitical and cultural region of southeastern Europe...

and on Cyprus

Cyprus

Cyprus , officially the Republic of Cyprus , is a Eurasian island country, member of the European Union, in the Eastern Mediterranean, east of Greece, south of Turkey, west of Syria and north of Egypt. It is the third largest island in the Mediterranean Sea.The earliest known human activity on the...

. In the northern Alps, the Flysch is also a lithostratigraphic

Lithostratigraphy

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...

unit.

Sedimentological properties

Tectonics

Name and use

Further reading