Gosau group

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The Gosau Group is a lithostratigraphic group in the Northern Limestone Alps and in the Eastern Central Alps.

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The Muttekopf in the Lechtal Alps near Imst, the highest Gosau deposit at 2,774  m

After the first peak of mountain formation in the Middle Cretaceous (around 100 million years before today), the Gosau sediments were deposited discordantly (irregularly) on the roof and fold building of that time.

The Gosau sediments are the result of a transgression (sea advance) that began in the Upper Cretaceous - after a layer gap for the Turonian - in the Coniacian , about 90 million years ago. The sediments of the Gosau group reach in the Paleogene to the lower Eocene , around 40 million years before today. The deposits of the Gosau group were formed during the mountain formation in the Cretaceous, the Cretaceous orogenesis , which had affected the Eastern Alps. Large areas of the archipelago- like landscape protruded from the sea and therefore the sediments only cover parts of the Northern Limestone Alps. Gosauian or related sediments can be found next to the Northern Limestone Alps and occasionally in the Eastern Central Alps, according to Alexander Tollmann also in the Southern Alps , Carpathians , Dinarides and even further south-east in the Mediterranean region.

According to the formation in different basins, the thickness of the Gosau sediments fluctuates strongly, at Gosau they reach a thickness of 2600 meters, at Gams and Grünbach the Gosau group is up to 2200 meters thick.

Research history

The name Gosau as a stratigraphic term was introduced by J. Bohadsch in 1782 . In 1829 the British geologists A Sedgwick and RJ Murchison created a first rough outline of the Gosau in their two works On the Overlying Deposits of the Vale of Gosau in the Salzburg Alps and On the Tertiary Formations which range along the Flanks of the Salzburg and Bavarian Alps; being a continuation of the memoir "On the Valley of Gosau" . In the years 1930 and 1931 her work A Sketch of the Structure of the Eastern Alps followed; with Sections through the Newer Formations on the Northern Flanks of the Chain, and through the Tertiary Deposits of Styria, & c. & c- With Supplementary Observations, Sections, and a Map . Building on the work of the two Brits, August Emanuel von Reuss published his articles on the characteristics of the chalk layers in the Eastern Alps, especially in the Gosauthale and Wolfgangsee .

The type locality is the Gosau basin around Gosau in the Upper Austrian Salzkammergut.

Occurrence

There are Gosau deposits in the Northern Limestone Alps in the area of ​​the Lechtal Alps west of Imst , the so-called Muttekopfgosau , in the Tyrolean Unterland in the area of ​​the Brandenberger Valley , in the Wörgl area and near Kössen , in the area of ​​the city of Salzburg to Bad Reichenhall and in the state of Salzburg in the area Lake Wolfgang , in Upper Austria near Gosau in the Salzkammergut, in the Windischgarsten area , near Laussa to Großraming in the Reichraminger Hintergebirge , in Styria near Wörschachwald on the southern edge of the Dead Mountains , near Gams near Hieflau and in the Mariazeller basin . In Lower Austria there are Gosau deposits at Grünbach am Schneeberg / Neue Welt and at Gießhübl . There are also numerous small and very small Gosau deposits. In the central alpine area there is the Kainacher Gosau west of Graz and the Krappfeldgosau in Carinthia .

Due to tectonic processes and erosion , today's Gosau deposits no longer correspond to their original extent.

Breakdown

The sedimentation of the Gosau sediments in different basins complicates a lithostratigraphic assignment of the respective units, which were also often deposited at different times. There are formations that are limited to just one or a few Gosau occurrences, while other formations, such as the conglomeratic Kreuzgraben formation or the Nierental formation on the basin slope, are formed in several Gosau occurrences.

The group is divided into a lower Gosau subgroup and an upper Gosau subgroup (obsolete Tiefere / Höhere Gosau ), which are separated by a phase of renewed uplift and erosion, called the Intragosau phase .

At the beginning of the Gosau Transgression, mostly in the Coniacium (90–86 million years ago), a basic conglomerate, the Kreuzgraben formation, formed . In some locations, such as Grünbach, the first transgression took place later, in the following Santonium (86–84 million years). These conglomerates are usually followed by fossil-rich sandstones, marls and limestone from a shallow water facies, this Lower Gosau is also called Flachwassergosau . Sometimes coal seams can also be found, such as in the Gosau von Grünbach. The lower Gosau subgroup thus includes terrestrial to shallow marine deposits.

After the uplift phase, the Limestone Alps in the upper Campanium (around 80 million years ago) began to sink rapidly. The sediments of the Upper Gosau, such as the Zwieselalm Formation , the Gießhübl Formation or the Brunnbach Formation , are therefore often deep-water formations that were partially formed below the calcite compensation depth . Therefore, sometimes the term is for the upper Gosau deepwater Gosau or flysch gosau used.

For the lower Gosau period around 4–5 million years are to be assumed, for the intragosau uplift around 8 million years, and for the upper Gosau period around 7–10 million years. The upper Gosau is also often discordant on the lower Gosau. The Zwieselalm formation of Gosau, as the latest layer, is today at around 1500 meters above sea level, so it was lifted over 4 km.

Sequence of the Gosau group at some locations:

Type locality Gosau

In the Gosau Basin - Pass Gschütt - Abtenau Basin area :

The type localities of these layers can also be found here in the room.

Salzburg - Bad Reichenhall

Northwest continuation beyond the Salzach:

Laussa - Großraming

Gosau der Weyrer Bögen , east of Windischgarstener Gosau: Deeper Gosau is missing in sections, post-Intragosau strata are only present in small areas, therefore Upper Gosau strata, especially Brunnbach strata, often lie directly on the pre-Gosau main dolomite. The south-north relationship is particularly interesting here.

Lower Gosau:

  • Bauxite (terrestrial-subtropical erosion relief, Turon)
  • Basal red conglomerates ( cross ditch formation , alluvial-fluvatil, up to 100 m thick)
  • Freshwater limestone, marl (gray-brown to black, partly bituminous, up to 20 m thick)
  • in the north (Ramingstein):
  • Lime sandstone (marinate to neritic , occasionally bearing scree, up to a few tens of meters thick, middle to lower conacium)
  • in the south (white water area):
    • Conglomerate, sandstone and silty marl (maritime margins with delta sediments and storm schill, occasionally coal-bearing, up to 260 m thick, Oberturon – Mittelconiac)
    • Rudist limestone sandstones (lagoon with reef structures, up to 50 m thick)
  • Gray, partly very silty limestone marl ( white water formation - local, shelf up to 150 m sea depth of a transgression, in the north Conac, not very thick; in the south Santon, up to 150 m thick)

Upper Gosau:

  • Turbiditic carbonate breccia, sand-lime brick ( Spitzenbach formation - local;> 150 m thick); Limestone conglomerate ( Hieselberg Formation - local, probably subformation of the Spitzenbach layers , submarine rubble flows from the main dolomite,> 200 m thick)
  • Turbidic succession of carbonate breccia, sandstone, colored marl ( Brunnbach formation - local; deep-marine fan sediments, up to 1000 m thick, probably to be placed in the Nierental formation)

Fossil guide

Gastropod-rich sandstone in a small Gosau deposit in the Seebachtal near Lunz am See
Three specimens of approximately the same size of Trochactaeon conicus (Actaeonellidae) in different planes from the Gosau layers of Russbach am Pass Gschütt .

The Gosau Group has become known not least for its sometimes extraordinary wealth of fossils . As a result of the discovery of a giant ammonite of the species Parapuzosia seppenradensis almost one meter tall in 1971, an ammonite has graced Gosau's coat of arms since 1979.

In addition to ammonites, actaeonelles, nerinees and other gastropods as well as various corals are particularly common as fossils. Mussels like rudists , especially hippuritoids, sometimes occur to a reef-forming extent. Foraminifera are valuable microfossils with regard to zoning .

Natural resources

A witness of the former hard coal mining in Grünbach

At the base of the Gosau group there is bauxite in some places , which was formed in the turonium under tropical conditions. The best known is the bauxite deposit near Unterlaussa , which was mined until 1964.

In regression phases , coal formed in some places in the Northern Limestone Alps but also in the Central Alps . The (meanwhile exploited) Gosau coal from Grünbach am Schneeberg was the most important coal deposit in Austria.

Individual evidence

  1. ↑ a b Peter Faupl: Historical Geology. 2nd Edition. Verlag UTB, 2009, ISBN 978-3-8252-2149-2 , pp. 185 ff.
  2. ↑ a b Alexander Tollmann: Analysis of the classical north Alpine Mesozoic. Stratigraphy, fauna and facies of the Northern Limestone Alps. Part II of the monograph of the Northern Limestone Alps , Verlag Deuticke, Vienna 1976, ISBN 3-7005-4412-X , p. 400 ff.
  3. ^ O. Adrian Pfiffner: Geology of the Alps. Haupt Verlag, Bern 2009, ISBN 978-3-8252-8416-9 , p. 284.
  4. ^ Klaus Dorsch: Geological mapping of the Gosau basins of Rigaus and Schorn; Tennengau / Salzburger Land. Summary of the diploma mapping, undated (1996; originally on lrz-muenchen.de ( Memento from February 25, 2010 in the Internet Archive )).
  5. ↑ Harald Lobitzer: The exploration of the Gosau occurrence from Rußbach at the Gschütt pass from the 18th century until today. In: Reports of the Federal Geological Institute. Volume 72, 2008 ( PDF , geologie.ac.at).
  6. ↑ Stratigraphic table of Austria 2004 ( PDF ( Memento of the original from April 24, 2018 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this note. , Geology- ist-alles.at). @1@ 2Template: Webachiv / IABot / www.geologie-ist-alles.at
  7. ↑ Michael Wagreich: The grave Bach formation (Gosau Group, Santonian - Lower Campanian) in the Lattengebirge (Germany): lithostratigraphy, biostratigraphy and strontium isotope stratigraphy. In: Werner E. Piller: Stratigraphia Austria. Publishing house of the Austrian Academy of Sciences, Vienna 2003, ISBN 3-7001-3180-1 , p. 141.
  8. ^ Geological map of the Republic of Austria 1: 50,000, sheet 69, Großraming, Geologische Bundesanstalt 1999; 55–46 Gosau Group ( explanations 2011, p. 42 ff).
  9. ↑ Peter Faupl: The flysch facies in the Gosau of the Weyerer arches (Upper Cretaceous, Northern Limestone Alps, Austria). In: Jb. Geol. B.-A. Volume 126, Issue 2 (1983), pp. 219-244, especially sections 2., 3. ( PDF on ZOBODAT ).
  10. ^ The recovery of the giant ammonite from Gosau , gosaunet.at; Retrieved August 12, 2009.
  11. ↑ ops cit. Tollmann 1976, p. 413 ff.