The Muschelkalk is the middle of the three lithostratigraphic groups of the Germanic Triassic . This tripartite division, which gave the Triassic system its name , is only developed in the area north of the Alps (Germanic Triassic super group). Similar to the two other lithostratigraphic units of the Triassic, the underlying Buntsandstein and the overlying Keuper , the term Muschelkalk is very confusing for non-experts. In the past it was used on the one hand as a rock term ("lime that contains mussel shells or is made up of mussel shells"), on the other hand as a term ("shell limestone time") in the sense of a stage . Today the term is mostly used in the sense of a rock unit of lithostratigraphy. The international chronostratigraphic stages (or time intervals) of the Triassic were defined in the Alpine Triassic .
The name goes back to Georg Christian Füchsel , who first used it in 1761. In 1834 Friedrich August von Alberti introduced the Triassic system. At that time, shell limestone was already a firmly established term used by v. Alberti was already divided into the Lower Muschelkalk, the anhydrite group and the Upper Muschelkalk. In the further course of research into shell limestone, it was subdivided into ever greater detail. Since the 1990s, the Muschelkalk has been divided into lithostratigraphic formations, the lower limits and distribution of which are defined.
The lower limit of the Muschelkalk is defined today in Germany with the lower edge of the border yellow limestone. The upper limit in southern Germany is the so-called Muschelkalk-Keuper-Grenzbonebed. This bank is no longer available further north from Thuringia; here the line is drawn with the first Keupersandstone. The lower limit of the shell limestone is now dated in the lower anisium . However, the lower limit of the international chronostratigraphic level of the anisium has not yet been decided. The upper limit is in the Lower Ladinium (Upper Triassic).
The geographic deposition area of the shell limestone is the Germanic Basin , which in the Triassic extended over large parts of what is now Central Europe . At the time when the shell limestone was deposited, this basin was covered by a shallow sea in which mainly carbonate sludge and flaky sediments settled, which were later solidified into limestone. In contrast to its Upper Permian counterpart, the Zechstein Sea , which was connected to the ocean to the north, the Muschelkalkmeer was connected to the ocean ( Tethys ) to the south . The corresponding sea routes are called the Burgundian Gate , the Silesian-Moravian Gate and the Eastern Carpathian Gate .
Contrary to what the name “Muschelkalk” suggests, the fossil-rich rocks of this unit contain not only mussels , but also, above all, the armpods (Brachiopoda) that look similar to mussels . In many layers they are even more common than clams. In some intervals of the shell limestone, remains of echinoderms are also very common. For a layer member of the Upper Muschelkalk, the " Trochitenkalk " and today Trochitenkalk formation (according to the Trochiten designated, often individually distributed in the rock fossil stalk members of sea lilies ) they were even eponymous.
The period of deposition of the shell limestone extends to about 243 to 235 million years before today (each with an uncertainty of about 2 million years). This corresponds to the international stage anisium and the lower section of the ladinium of the Middle Triassic .
The shell limestone is divided into three subgroups:
The Lower Muschelkalk consists mainly of limestone, limestone marl and clay marl. In Germany today it is divided into six formations: Jena formation , Rüdersdorf formation , Udelfangen formation , Freudenstadt formation and Eschenbach formation .
The Middle Muschelkalk, on the other hand, contains predominantly evaporites ( gypsum , anhydrite and rock salt ). It is divided into three formations: Karlstadt formation , Heilbronn formation and Diemel formation . The Grafenwoehr Formation , which extends into the Upper Muschelkalk, was deposited in the peripheral areas .
The Upper Muschelkalk is characterized by limestone, marl and dolomite. It is divided into six formations: Trochitenkalk , Meißner-Formation , Warburg-Formation , Quaderkalk-Formation , Rottweil-Formation , Schengen-Formation , Irrel-Formation , Gilsdorf-Formation and Grafenwoehr-Formation, which forms the eastern peripheral facies of the Muschelkalk .
Geomorphology and Soils
In parts of the wine-growing regions of Württemberg , Franconia, Baden, Thuringia and Saxony-Anhalt ( Saale-Unstrut ), shell limestone forms the basis of the soil and is often rocky. The often extremely steep locations are difficult to manage and are built in terraced form from limestone dry stone walls . The weathering layer of the shell limestone is thin and prone to erosion.
In places where there are limestone rocks, sinkholes are now forming . These sinkholes tend to occur where, over time, the limestone in the subsoil is leached out by water (surface water, groundwater) ( karstification ). There are also karst caves in the Muschelkalk . Well-known examples are the Eberstadt stalactite cave discovered in 1971 in the building land (Baden-Württemberg) and the Bleßberg cave in Thuringia, discovered in 2008 , both in the Lower Muschelkalk.
Shell limestone in mining
The middle shell limestone (mm) in Baden-Württemberg in a strip from Heilbronn to the Swiss border contains an evaporite group with rock salt , under- and overlaid with anhydrite ( converted to gypsum or leached near the surface ). While the mostly locally operated gypsum mining no longer plays a role (previously mostly used as fertilizer gypsum), rock salt is still mined in large quantities in mines near Heilbronn, Bad Friedrichshall and Haigerloch . On the Upper Rhine , rock salt is extracted from the middle shell limestone at Rheinfelden ( Aargau , Switzerland) and Schweizerhalle by leaching and, after evaporation, covers Switzerland's salt needs (with the exception of the canton of Vaud : salt production in Keuper near Bex ). No more brine is extracted on the German side of the High Rhine .
In some regions the layers of the Upper and Lower Muschelkalk contain ore-containing inclusions (so-called " calamine ", oxidized zinc and sometimes lead ores ). Mainly lead, silver and / or zinc ores are involved. These raw materials , which used to be very popular, were a. Silver used for minting coins . Numerous archaeological finds from former stone mills and lime kilns have historically proven the mining and use of shell limestone. The evidence goes back to the 1st century AD.
Economic meaning and definition of terms
Even today, shell limestone rocks are mined and used economically (e.g. in road construction, as track ballast, production of cement). The high-quality Elm limestone was extracted as a building material in the Elm ridge in Lower Saxony , which was built from shell limestone .
In architectural contexts, the term shell limestone or square limestone is used differently as a material designation. This is understood to be a fossil-bearing limestone with pronounced stratification. This type of stone was mined , for example, in Lower Franconia near Würzburg and in Thuringia in the Jena area. Often it is a question of the economic use of the Terebratelbänke . In older literature, these rock designations often appear in material contexts and thus primarily do not provide reliable lithostratigraphic information. That has to be judged according to the respective context. The use of these terms in their dual meaning continues to the present day.
Muschelkalk soils, which are particularly suitable for Burgundy (Pinot), as well as for Silvaner and Riesling vines, are of agricultural importance, namely in viticulture . Muschelkalk soils occur in France mainly in Burgundy, and in southern Germany in Franconia , Baden and the Palatinate.
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