Wetterstein lime

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Wetterstein limestone and Wetterstein dolomite are the most common names for a carbonate rock from the Middle Triassic , the Ladin period, comparable to the German stage of shell limestone .

The rock is widespread throughout the Alps , in some places as limestone ( calcium carbonate ), in some places as dolomite with an additional proportion of magnesium . Since the fossil traces are largely erased by the recrystallization during dolomitization, the fossils in the weather stone dolomite are even worse, even in a thin section they are hardly recognizable. Wetterstein dolomite is seldom as bituminous and therefore mostly much purer and lighter colored than the typical main dolomite . Otherwise there are no known fundamental differences to the lime of the same name.

It was named after the Wetterstein Mountains because the Wetterstein limestone forms particularly mighty mountains here. However, it has its main distribution area in the Karwendel . In some areas there is a narrow alternation of limestone and dolomite facies.

The sub-forms include knife- edged lime , Schlern dolomite , Marmolatakalk , stone-alm lime and lower Ramsaudolomite .

The Martinswand near Zirl is made of massive Wetterstein reef limestone
Banked Wetterstein limestone in the Karwendel

construction

At least for the areas where the Wetterstein limestone is thick, the following layer sequence should generally apply:

  • The lower Wetterstein limestone is banked and dark in color ; it often still contains echoes of the clayey Partnach strata or the pebbly Reifling limestone or alpine shell limestone .
  • The middle Wetterstein limestone is a light, non-stratified reef limestone , it forms the summit area around the Laliderer tip .
  • The upper Wetterstein Limestone is also light-colored, but again very clearly banked, with a similarity to the Lofer cyclothemes of the Upper Triassic. Its clear banks form the summit of the Birkkarspitze and Kaltwasserkarspitze , for example .
  • In the uppermost parts of the Wetterstein limestone there are occasionally layers in which there are approximately lentil-sized, flat cavities in the limestone, the cavities being oriented in all directions. This variant is also known as knife lime . The assumption was made that originally there were gypsum crystals instead of the cavities, whereby the gypsum can later be dissolved by seepage water or, after the following reaction, converted into lime with the help of natural gas:
CaSO 4 + CH 4 = CaCO 3 + H 2 O + H 2 S

Mark

The Wetterstein limestone is characterized by its high purity and its resistance to erosion, which is why it is extremely steep and huge rock faces such as B. the Hochwanner north face in the Wetterstein (1400 m thick) forms.

In terms of mountaineering, it is therefore a special attraction for both climbers and mountain hikers, because many classic climbing routes are in the Wetterstein limestone. Extremely attractive mountains such as Zugspitze , Alpspitze , Birkkarspitze , Lamsenspitze , Scheffauer and Säuling consist of Wetterstein limestone. Also typical is the widespread karst formation , which manifests itself in the occurrence of sinkholes , caves and cart fields .

Another consequence of its high resistance to erosion is the conservation of old surfaces from the Tertiary, i.e. H. high-altitude, relatively flat areas that have not yet been cut (crushed) by river erosion , which means that an old landscape form from the Tertiary has been well preserved to this day. Good examples of this are the Zugspitzplatt , the Leutascher Platt and the Höllentalkar . In most areas, the plains, which were widespread in the tertiary era, have been converted into ridges and valleys by being cut by water.

Occurrence

In all of the northern and southern Limestone Alps, either peaks or in the underground of the mountains. He is summit-forming in:

In the Southern Alps especially:

Local names

  • In the southern Alps, the rock series is mostly dolomitized and is mostly given the name Schlern dolomite .
  • But especially on the Queen of the Dolomites , the highest mountain Marmolada , the rock is more calcareous and is called Marmolata limestone there . However, this name remains purely local because dolomite is consistently present in the neighboring mountains.
  • In parts of the Northern Limestone Alps , in some areas there is a very close alternation and also a shingling of the limestone facies with the dolomite facies. The Karnische level has remained without any sediment, so that the limestone and dolomite of Ladiniums of which Noriums practical contexts. There is no difference to be seen between the Wetterstein dolomite (Ladin, Middle Triassic) and the main dolomite of the (Norium, Upper Triassic), which is why both levels are combined there as Ramsaudolomite , whereby in the latter only the lower part is identical to the Wetterstein dolomite . This summary is provided for the convenience of the mapping geologist.
  • In parts of the Northern Limestone Alps, a rock very similar to Wetterstein limestone with diplopores as fossils can already be found at the beginning of the Middle Triassic (anisian stage). If this limestone is followed by another rock in front of the Wetterstein dolomite, it can be separated from the Wetterstein dolomite and is called Steinalm limestone , after the Steinalm near Saalfelden .

In the 19th century it was referred to as Lower Alpine Limestone , referring to the fact that another very mighty pile of carbonate rocks (lime or dolomite) from the Upper Triassic was or was once stored above.

Fossils

Dasycladaceae ( whorl algae ) with the typical species Diplopora annulata with a growth form similar to a horsetail and with a calcareous skeleton around the stem . The fossils are macaroni-like lime tubes of different sizes, notched on the outside and inside, so that the stem parts look like rolls of money from the outside, i.e. ringed (annulata) . A closer microscopic examination shows that the tubes are perforated by fine channels. These channels fork into two branches from the inside to the outside, hence the name "Diplopora".

The diplopores built up entire reefs, so that they are still occasionally preserved in the stone in an upright position. Together with calcareous sponges , they were the only reef builders, as the coral trunk had suffered so much from the mass extinction at the turn of the Permian Triassic that reef-building corals were not yet available again.

Ore deposits

Mineralization with lead and zinc ( galena and zinc blende ) is typical of the Wetterstein limestone and is spread over almost all of the northern and large areas of the southern limestone Alps. Most famous are the ore deposits of Bad Bleiberg west of Villach in Carinthia , Raibl in Friuli and Mesica in eastern Slovenia . In the northern Alps, a deposit in the Karwendel ( Lafatsch , near the Kastenalm in the Hinterautal ) was investigated in the 1950s, but was not mined due to insufficient mineralization and insufficient supplies. In the past, many other deposits were worth building, such as the Rauschberg near Ruhpolding , the Staufen near Reichenhall etc. In the Karwendel, Wettersteingebirge and in the Mieminger Mountains , as well as on the Heiterwand, there were quarries (St. Veit, Nassereith, Dirstentritt). In the late Middle Ages / early modern times, in addition to the lead, which was used to extract silver from the copper ores of Schwaz, the relatively low silver content of the lead luster (approx. 100–200 g / tonne of lead; cf. approx. 0, 5% silver in the Schwazer Fahlerz). Mineralization of the Wetterstein limestone / dolomite with ankerite (weathered limonite) was used as iron ore on the Säuling. In the years around the First World War, molybdenum deposits (wulfenite) were important in the same ores, here the mines near Bleiberg and Mies (Mesica) are particularly worthy of mention, while the trial mining in the Hell Valley of the Wetterstein did not lead to any significant amounts of ore despite great efforts. The mineralization must essentially have arisen practically synsedimentary, i.e. while the Wetterstein limestone or, at the latest, the Raibler layers were being deposited, since the higher-lying limestone or dolomite of the Noric level are never reached by the veins.

Web links

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