Main dolomite
The main dolomite is a lithostratigraphic unit of the Alpid mountains that is up to 2200 meters thick and is primarily composed of dolomite . The rocks were mostly in shallow lagoon areas in the period of the late Karniums and Noriums (both Upper Triassic deposited before about 230-200 million years ago).
Research history
The term 'main dolomite' comes from the German geologist Carl Wilhelm von Gümbel , who first used it in 1857 in his treatise Investigations in the Bavarian Alps between Isar and Salzach . Richard Lepsius, the son of Karl Richard Lepsius , introduced the name in 1876 for the southern Alpine area. The name Dachstein dolomite was partly used as a synonym for main dolomite . Today the upper parts of the main dolomite are called Dachstein dolomite .
Lithostratigraphic classification
Despite its often great thickness, the main dolomite is not subdivided on many geological maps and shown as a gray area. In the description of the Stratigraphic Commission of Italy, the main dolomite, known in Italy as the Dolomia Principale, is given the rank of formation . For the northern alpine area there is a proposal to view the main dolomite, which is up to 2200 meters thick, as a group . The geological map of the Republic of Austria 1.50.000, sheet Zirl, which was published back in 1992 , shows various sub-units within the main dolomite, but without explicitly using the stratigraphic terms group or formation .
Educational area and age
The formation area of the main dolomite is generally the northwest of the Neotethys , which penetrated into the Pangea , which breaks up in Gondwana (here later Africa) and Laurasia (Europe) . In more recent research, the Meliata Ocean is assumed here, the character of which as an independent ocean, marginal sea of the Tethys or transitional sea to the breaking Atlantic Ocean is still unclear.
The main dolomite is a formation of very shallow and wide lagoon regions and shallow water zones , some of which were temporarily dry areas of the Wadden Sea (tidal facies).
The main dolomite is generally underlain by Raibler strata ( Raibl Formation i. E. S., Lunz Formation in the limestone foothills), which emerged from a climatic event that took place in the middle of Carnival ( July 230 million years ago). However, the lithographic demarcation is not always sharp. In the Lunz facies area , which extends roughly across southeastern Upper Austria and parts of southern Lower Austria, the main dolomite begins above the marine Opponitz Formation , but can also reach deeper in place of it.
The bituminous rocks of the Seefeld Formation were created in embedded basins, bays and colo-like depressions in the lagoon. Keuper can be laterally interlocked - terrestrial-lacustric (freshwater-bound) deposits of the Vindelizo-Bohemian Land further north in the Germanic Triassic, which are present as red to colorful clay or schisty inclusions. On the lagoon side, the Dachstein formation appears either interlocked (in Dachstein lagoon facies) or superimposed (as Dachstein reef limestone). The Noric limestone can act as a transitional facies here. This is followed by the fossil-rich shallow water deposits of the Kössen Formation of the Upper Triassic.
Tectonically, the main dolomite in the Alps belongs to the Oberostalpin , in the Northern Limestone Alps it can be found in the Bajuvarikum as well as in the Tirolikum .
properties
The main dolomite is a dolomitized limestone (enrichment of magnesium instead of calcium). The rock is light gray or brownish-gray in color with a clearly layered structure and strong fissures . It is extremely brittle and hard. The fissures are often subsequently healed with calcite , recognizable by white veins in the rock.
geomorphology
Because of its high resistance to erosion, the main dolomite is one of the main peaks in the western Eastern Alps . There it is interspersed with an intensive folding with small-scale changing directions of the cleft , which is why there are usually no mighty, very steep rock faces (exception e.g. Trettachspitze ), but rather complex, brittle ravines, small rock faces, debris above approx. 2000 m , Ribbons and episodic water-bearing channels crisscrossed with craggy walls and ridges decorated with small turrets are typical. Due to its strong fissures, the main dolomite is the strongest debris builder in the Alps. Huge rubble slopes and flat rubble areas in the valley area (such as the Wimbachgries am Watzmann) are evidence of this. Lower mountains in the main dolomite, on the other hand, are often clumsy, less impressive mountains overgrown with forest or mountain pines.
Despite its fissures, it tends to become less karstified than most limestones due to its lower solubility , which is why more clearly structured ridges and slopes with a more uniform slope angle emerge in the northern Alps, and irregular, undulating plateaus are less common than in limestone areas.
In the Dolomia Principale of the Southern Alps, where the rock is less folded, impressive mountains with repeatedly vertical walls can develop, such as the famous Three Peaks , if the gaps are favorable .
Fossil guide
The main dolomite is generally considered to be low in fossil rock. At macro fossils are found algae as Gyropella or Dasycladaceen , Megalodonten or worm as Worthenia . The microfauna is also relatively poor. However, foraminifera can occur locally in large numbers . However, the fish faunas of the Seefeld layers are known .
Hydrogeology
Despite the comparatively low level of karstification, the rocky rock is also important for the supply of drinking water . If its stratifications have been folded into larger hollows by the alpine mountain formation, the course of the groundwater follows them ; in this way, the underground catchment area can be estimated even in unclear source areas.
Occurrence
The main dolomite is found in the Alps as well as in the Carpathian and Dinarides .
Northern Limestone Alps
Overall, the main dolomite is the most important rock in the Northern Limestone Alps . It is high alpine peaks especially in the western area, for example in the Lechtal Alps , the Lechquellen Mountains and the Allgäu Alps with well-known mountains such as Hochvogel or Mädelegabel . The highest main dolomite summit in the Northern Limestone Alps is the 2889 m high front lake peak in the Lechtal Alps. In the Karwendel, the Erlspitz group in particular consists of main dolomite. The greatest known thickness of the main dolomite of 2200 meters was measured at the Rappenspitze in the southeastern Karwendel. The main dolomite also occurs frequently further to the east, especially in the northern areas of the Limestone Alps, but it also reappears on the southern edge. In the Upper Austrian Limestone Alps, it mainly forms the Limestone Pre-Alps , and the Dachstein Limestone the High Limestone Alps. It is no longer as thick as in the Karwendel, for example, in the Ötscher blanket in south-western Lower Austria it is around 500 meters thick.
There are more precise subdivisions of the main dolomite for the Seefeld area and the Lechtal Alps.
- In the Erlspitz group near Seefeld, the formations lower main dolomite (Schloßbach formation), middle main dolomite (freeing formation), Seefeld layers ( Seefeld formation ) and upper main dolomite (Dachstein dolomite) are distinguished.
- In 1970, W. Müller-Jungbluth divided the main dolomite into three sections in the eastern Lechtal Alps, a lower, middle and upper main dolomite . The lower main dolomite with a thickness of 250 to 350 meters is characterized by finely layered, dark bituminous and pyrite-containing dolomites. The central main dolomite is 400 to 900 meters thick, it is lighter, finely to densely banked and rich in detritus . The upper main dolomite reaches about two thirds of the thickness of the middle main dolomite. There is a greater variety of rocks such as breccia layers , algae stromatolites or oncolites . In addition to a richer fossil record (Dasycladaceae and megalodonts), there are also dry cracks or traces of rain.
Central Eastern Alps
In the central Eastern Alps, main dolomite can be found in various sediment layers on the crystalline basement, for example in the Kalkkögeln or in the Radstädter Tauern , as well as in various windows such as the Semmering window .
Western Eastern Alps
In the western Eastern Alps ( Arosa Dolomites , Montafon Mountains, Lower Engadine Dolomites ) the main dolomite is only comparatively thin. These are deposits on the crystalline basement of the Silvretta Nappe . The rocks are often folded, sheared and shattered by transporting the roof.
Southern alps
While in the area east of Lake Maggiore the mid-Triadic sediments merge directly into Jurassic sediments, the main dolomite begins in eastern Lombardy and extends as far as Slovenia . In the Italian Southern Alps, the main dolomite, referred to here as the Dolomia Principale , reaches a thickness of up to 3000 meters. Nonetheless, he is led here as a formation. However, some members are defined locally, such as the Membro di Malga Flavona, which is characterized by breccias in the Brenta . As in the Northern Alps, the main dolomite is generally underlain by Carnic sediments, in Lombardy by the Formazione di Castro Sebino , further east by Raibler layers.
In the Southern Alps, large parts of the Brenta, the upper floor of the Sella and the Three Peaks consist of main dolomite.
Apennines
In the Apennines , the Dolomia Principale occurs in the central and southern part. In the Gran Sasso d'Italia massif , it reaches a thickness of around 600 meters.
use
The main dolomite is used as a building material (e.g. as a substrate for road construction ) because it is cheap and a little harder than lime , and it is also known as gravel for sidewalks. However, the brittleness of the rock allows only a few applications as ballast in the technical sense.
See also
literature
- 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 .
- Jürg Meyer: Geology and rocks. In: Manfred Hunziker: Ringelspitz / Arosa / Rätikon, Alpine Touren / Bündner Alpen , Verlag des SAC 2010, ISBN 978-3-85902-313-0 , p. 31 ff.
- Martin Fellehner: The main dolomite as an aquifer in the Northern Limestone Alps. Dissertation, Philipps University of Marburg, 2003 ( abstract and PDF , uni-marburg.de).
Map series:
- Stratigraphic table of Austria 2004 (pdf, 381 kB; on geologie-ist-alles.at)
Web links
- Main dolomite. In: geopal.at (excerpts from reference works)
Individual evidence
- ^ Carl Wilhelm von Gümbel: Investigations in the Bavarian Alps between Isar and Salzach. In: Yearbook of the Geological Reichsanstalt. JG 7, pp. 146-151.
- ^ R. Lepsius: Classification of the Alpine Triassic and its relationship to the Ausseralpinen. In: Yearbook of Min. Geol. Paleont. Stuttgart 1876, pp. 742-744.
- ↑ Donato A. Donofrio, Rainer Brandner , Werner Poleschinski: Conodonts of the Seefeld formation. A contribution to the bio- and lithostratigraphy of the main dolomite platform (Upper Triassic, western Northern Limestone Alps, Tyrol). In: Geol. Paleont. Mitt. Innsbruck 2003, Volume 26, pp. 91-107. PDF file
- ↑ cf. Nikolaus Froitzheim: Geology of the Alps. Part 1: General and Eastern Alps. 2.1 Opening and Closing of the Meliata Ocean. Lecture notes, University of Bonn (2011, online at uni-bonn.de).
- ↑ Andreas Ebert: The development of the Alps: Pre-Alpine development and Mesozoic development in Southeastern Europe . Excerpt from a diploma thesis, May 2001 (author's private website).
- ↑ a b ops. cit. Froitzheim: Geology of the Alps. Part 1. Fig. 3-2: Permian and Triassic of the Northern Limestone Alps: kp - hd - dkl (in section 3.3. Tectonics of the Northern Limestone Alps ).
- ↑ Spectacular fossil finds in Switzerland. swissinfo, October 10, 2007 3:38 pm (accessed March 2, 2015).
- ^ Project Dinosaurs grischuns ; accessed on March 2, 2015.
- ^ Erich Thenius: Lower Austria. Geology of the Austrian federal states in brief individual representations. 2nd expanded edition, Vienna 1974, p. 120.
- ↑ Donato A. Donofrio, Rainer Brandner , Werner Poleschinski: Conodonts of the Seefeld formation. A contribution to the bio- and lithostratigraphy of the main dolomite platform (Upper Triassic, western Northern Limestone Alps, Tyrol) In: Geol. Paläont. Mitt. Innsbruck 2003, Volume 26, pp. 91-107 ( uibk.ac.at PDF).
- ^ R. Assereto and P. Casati: Revisione della stratigrafia permo-triassica della Val Camonica meridionale (Lombardia) . In: Riv. It. Paleont. Strat. From 71 to 4. Milano 1965, p. 999-1097 .