Flysch zone
In geology, the flysch zone or Rhenodanubian flysch is a comparatively narrow rock unit stretching north of the Eastern Alps and the Carpathian Mountains . Geographically, it is part of the transition area between the Alps and the northern Alpine foothills . It consists mainly of clay and sandstone , which is why it was also known as a sandstone zone in the past .
Occurrence
As a unit that is particularly widespread in the Eastern Alps , the flysch rocks of the flysch zone on the northern edge of the Alps form gentle hill shapes . In the Swiss area, their rocks can only be detected in isolated isolated occurrences on the northern edge of the Alps.
The flysch zone is most pronounced at the western end of its main distribution area, where it forms the Bregenzerwald east of Lake Constance . Further to the east it no longer forms any noteworthy mountain formations - just like the underlying Helvetian nappes , which are still peaks in the Allgäu . On long stretches vanishes here among them about donating rocks of the Northern Limestone Alps .
Only east of Salzburg is the flysch zone several kilometers wide again ( Salzburg Pre-Alps , hills of the Salzburg Lake District ). It also forms the northern zone of the Upper Austrian Pre-Alps and the Eisenwurzen and on the northeastern edge of the Alps the northern or Flysch- Wienerwald .
With the Bisamberg and the Waschbergzug, it continues beyond the Danube, runs over the cliff zone ( Steinitz Forest ) far beyond the Alps and accompanies the Carpathian Mountains on its north and east side in a zone up to 100 km wide , especially as a Carpathian flysch . The last foothills of the flysch zone disappear north of Bucharest under the molasses sediments of the Carpathian pre-depth .
Surface shape
The mountains of the flysch zone are heavily influenced by the glaciers and periglacial processes of the ice ages , as the flysch rocks that build them up are easily weathered, often lacking great internal cohesion and still tend to flow today ( Swiss German : flyschen ). There are gentle hill formations and rounded mountain tops .
The peaks of the northern limestone alps adjoining it to the south, like those of the Helvetic nappes, sometimes set themselves off quite suddenly as a stick , karst plateau or wall against the significantly lower mountains of the flysch zone.
Formation and rocks
Geologically, the rhenodanubian flysch formed during the folding of the Alps from the deposits in the northern half of the Pennine area of the ancient Mediterranean, the Tethys , to the south of Europe . Both temporally and in the geographical sequence of the nappe systems, it stands between the Helvetic nappes , which originate from the original European continental shelf, and the northern limestone Alps (the tectonically deepest layer of which is the Tirolean ), which come from the northern edge of the Adriatic plate belonging to Africa . In the Alpine region, the rocks of the flysch zone are associated with the other flysch rocks of the western Alpine Penninic, such as the Bündner schist , which were also formed as flysch rocks in the Penninic Ocean.
The Flysche formed from the Lower Cretaceous to the Eocene , ie in the period of roughly 150–50 million years, and are thus younger than the typical Triassic (around 250–200 million years old) Alpine Limes. At this time the Alps began to unfold in depth.
The rocks the Flyschzone are predominantly in deep sea below the carbonate compensation depth (3000-5000 m) deposited Turbidite sequences - so sediments submarine landslides - of sandstones , siltstones , marls and shales , partly calcareous and sometimes kieselig that at their base can also contain scree layers , and are closed off at the top by the finest-grained settlement layers. Fossils washed in with the turbidites can only be found more frequently in the lower part of each layer sequence . These mass movements from the continental shelf at that time are likely to have been triggered by earthquakes, for example, and have been repeated many times and the flysch zone has built up up to 2000 m thick.
The strata of the Limestone Alps and the strata of the Pennine Ocean that were originally in front of them to the north were pushed up and over a large area in the course of the mountain formation on the Helvetian shelf belonging to the European continent. The Rhenodanubian flysch forms the lowest layer in this nappe pile lying on the layers of the Helveticum. When it was pushed onto the European continental margin, it was pushed in front of the ceiling stack and was the first part of the stack to be pushed onto the European shelf. Later in the course of the further collision, the Limestone Alps slowly slipped northwards from their position further south and higher in the pile of nappies when the pile of nappes bulged and slid over the flysch.
As a result, they form a comparatively narrow zone of evacuated layer sequences on the northern edge of the Alps, which quickly plunge into the depths towards the south. During deep drilling, the continuations of the now exposed flysch layer under the limestone Alps were found at around 5500 m ( Berndorf , Molln / Breitenau - only a dozen kilometers south of the edge of the Alps). In some places the flysch is still exposed in the middle of the Kalkalpen ( flysch window , for example in Windischgarsten in the Kalkalpen National Park).
Like the Flyschzone also dome-building and morphologically often similar Subalpine Molasse (Molasse), which follows today north of the Flyschzone has arisen in its main mass under very different geological conditions, mainly erosion sediment from the already soaring Alps in the Paratethys -Flachmeer, the final phase of the Thetys north and east of the Alps, which lasted from the Eocene to the Miocene only about 15 million years ago.
Literature and maps
- Johann Egger: On the paleogeographical position of the Rhenodanubian flysch (Neocom-Eocene) of the Eastern Alps. In: Jahrbuch der Geologische Bundesanstalt Volume 133 / Issue 2, 1990, pp. 147–155 ( pdf , geologie.ac.at).
- Geological map of Bavaria 1: 500000, explanations . Bavarian Geological State Office, Munich, 4th edition 1996.
- SM Schmid, B. Fügenschuh, E. Kissling, R. Schuster: Tectonic map and overall architecture of the Alpine orogen. In: Eclogae geologicae Helvetiae 97 (2004), pp. 93–117, PDF
Individual evidence
- ↑ Schmidt et al. 2004, p. 109.
- ↑ a b The Flysch Zone: Mudslides in the Deep Sea ( Memento of the original from January 30, 2013 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. . In the Federal Geological Institute: RockyAustria (geologie.ac.at, link no longer available)
- ↑ Sandstone balls - a specialty in the flysch zone. Granzer mineral and fossil collection (granzer.at).
