Oberalm formation

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Oberalm formation, Wildgößl, Totes Gebirge . You can see the chert layer on which the map lichen ( Rhizocarpon geographicum ) grows.

The Oberalm Formation , formerly also Oberalmer layers or Oberalmer Kalk, is a lithostratigraphic formation in the Northern Limestone Alps . The formation can be found in the higher, southern parts of the Northern Limestone Alps and marks the Jura - Chalk border area there.

history

It is named after the Austrian town of Oberalm in Salzburg's Tennengau . The term Oberalmer Klassen was coined by Marko Vincenc Lipold in 1954. B. Plöchinger and S. Prey used the name Wurzener Kalk synonymously in 1968 . There was also the term Rettenbachkalk , this term encompassed several layers, including those of the Oberalm formation.

definition

The formation is underlain by the Tauglboden and Sillenkopf Formations and partially overlaid by the Schrambach Formation . It interlocks with the Ammergau and Tressenstein limestone formations . It is dated to the Kimmeridgian , Tithonian and Berriasian , that is, it was formed between 157.3 and 139.3 million years ago. It is mainly developed in the Salzburg area and Upper Austria and occurs only in the Northern Limestone Alps (Eastern Alpine nappes). At the type locality near Hallein , it is 500 to 600 meters thick. Its westernmost occurrence is in the Berchtesgaden Alps , to the east there are occurrences up to the eastern edge of the Limestone Alps. The formation in the Osterhorn group is the strongest . It occurs extensively in the Salzkammergut . It reaches its maximum thickness of 800 meters.

Lithology

The Oberalm Formation consists of pelagic sediments, mainly clayey, well-banked, micritic limestone. In addition, lime-rich, bio-debris-bearing limes also occur. Connected to the formation are turbiditic limestone banks, which were created by turbid currents from neighboring carbonate platforms and which contain numerous chert stones. Banks made of turbiditic deposits with greater thickness are called Barmstein limestone , after the Barmstein in the northernmost part of the Haselgebirge between Oberalm and the Dürrnberg.

Fossils

In addition to calcareous algae and silica sponge skeletal elements , microfossils contain radiolarians , foraminifera and calpionella .

Economical meaning

In Salzburg, the thin limestone of this formation is used as an important natural building block for garden slabs and building walls.

Individual evidence

  1. ↑ PDF file Benno Plöchinger, Siegmund Prey: Profiles through the Windischgarstener fault zone in the Windischgarsten area - St. Gallen, Jb.Geol. BA, vol. 111, Vienna 1968, p. 194.
  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, p. 356.
  3. ^ R. Oberhauser, FK Bauer: The Geological Structure of Austria, Springer-Verlag, Vienna 1980, ISBN 978-3-211-81556-4 , p. 230f. PDF , accessed June 27, 2009.
  4. ↑ Peter Faupl: Historical Geology , 2nd edition, Facultas University Press, Vienna 2003S. ISBN 3-8252-2149-0 , p.159.
  5. ↑ Helfried Mostler: A contribution to the development of phyllotriaen megasclera from Upper Jurassic basin sediments (Upper Alm layers, northern Limestone Alps) PDF , accessed on June 27, 2009.
  6. ↑ Tom McCann: The Geology of Central Europe, Volume 2, Mesozoic and Cenozoic, Geological Society Publishing House 2008, ISBN 9781862392656 , pp. 970f .. PDF , accessed June 27, 2009.