Dachstein Limestone
The Dachstein Limestone is a series of carbonate layers that occurs mainly in the Northern Limestone Alps and the Eastern Southern Alps ( Julian Alps ). They are light gray to whitish, sometimes reddish and relatively pure limestones . The Dachstein limestone is divided into two different facies , the bank limestone and the reef limestone .
The Dachstein pioneer and natural scientist Friedrich Simony first described the rock in the 19th century and named it after the Dachstein made of this rock .
Age
The Dachstein limestone was formed around 217 to 200 million years ago in the Upper Triassic . Lime material up to a layer thickness of one kilometer was deposited over a period of around 10 to 15 million years. The formation of this rock began in Carnation ; in general, however, the main sedimentation did not begin until the north , so that it corresponds to the upper two thirds of the upper Alpine limestone . Its sedimentation ended towards the end of the Rhät around 200 million years ago at the turn of the Triassic-Jurassic. After the Dachstein limestone was deposited, the seabed was broken up by expansion tectonics and younger red limes from the lower Jurassic period were deposited in the crevices in the seabed, known as “ Neptunian Dikes ”. These crevice fillings occur frequently within the Dachstein Limestone and are very noticeable due to their purple-red color.
Occurrence
In the Northern Limestone Alps, the Dachstein limestone can be found in all the higher mountain ranges from the eastern border of Tyrol to the east. The summit areas of wide mountain ranges are built from this rock , such as Loferer and Leoganger Steinberge , Watzmann , Steinernes Meer , Hochkönig , Hagengebirge , Tennengebirge , Dachstein Mountains , Totes Gebirge , Gesäuse or Hochschwab . In the western part of the Northern Limestone Alps, however, the same old main dolomite is found instead of the Dachstein limestone .
In the Southern Alps, Dachstein limestone occurs only in the Julian Alps ; further to the west there is the same old series of rocks dolomitized and referred to as the Dachstein dolomite or the main dolomite. Between the individual mountains of Dachstein limestone, there are very often layer sequences with a different formation at the same age, the Hallstatt limestone , so that the occurrence is interrupted.
Outside of Austria, rocks from Hungary are known as Dachstein limestone, which opens up to the Danube in the mountain range north of Lake Balaton ( Balaton felvidék , upstream chain of the Bakony Mountains ). Other rocks similar to the Dachstein Limestone are mentioned from western Sicily , northern Calabria , the southern Balkans and southern Turkey; for example the Aladaglari north of Adana as the highest mountain group of the Middle Taurus .
In New Guinea , the Carstensz pyramid , the highest mountain on the Australian continental plate at almost 5000 meters above sea level, is made of limestone of the Dachstein limestone type.
Bank lime
The most widespread facies of the bank limestone or the banked Dachstein limestone is a very clearly stratified limestone with a very coarse deposit structure in the meter to ten meter range. These are the remains of living things in a lagoon area . In particular, the Noric transition facies to the main dolomite (tidal facies of the Carnian) are also known as plate limestone .
The bank limestone is the most powerful layer of the Dachstein limestone, it is very resistant and firm. The massive limestone banks up to about 20 meters thick are made of lime with a grain size ranging from sandy to muddy (tenths of a millimeter to a micrometer range). They often contain the remains of very large mussels, the megalodonts . Short-term changes in the deposition conditions, such as increased flooding of clayey and finest-grained material through the rivers, lead to fine disturbances in the otherwise compact mass: These form mechanical or mineralogical structural boundaries in the recarbonation of the lime mass, which solidifies homogeneously through dissolution and precipitation under pressure.
The "separating joints" of the limestone banks consist of ½ to 1 meter thick intermediate layers of dolomite (magnesitic carbonates) with a millimeter-fine layering, sometimes of thin-plate breaking limestone (repetition of the deposit structure on a small scale) and in places marls . The different mechanical behavior of these more fragile intermediate layers leads to the stepped structure of the mountains.
Shortly after the sedimentation, cavities and crevices formed in some places, these are filled with breccia and sometimes very noticeable brick-red to ocher-colored clay or red-colored lime.
Due to their thickness and the clear delimitation of the individual benches from one another, the layered slabs of limestone can be seen from a great distance. This clearly defined stratification structure is created by the rhythmic alternation of the various types of rock in the limestone. The rhythmic alternation of individual layers ( cyclothema ) in the Dachstein limestone was described by the American geologist Alfred G. Fischer as the Lofer cyclothema . He explains the Lofer cyclotheme by means of sea level fluctuations in the rhythm of several 1,000 years.
The originally horizontal stratification can be found, for example, in the compact limestone stocks of the Dachstein massif or the Dead Mountains , elsewhere it can be tilted, steeply positioned and folded or discarded .
Reef limestone
The second type of rock in the Dachstein limestone is reef limestone . It is the same age as the bank limestone and is also known as high mountain coral limestone . In reef limestones comes to coral reefs that have sea side consist of the lagoons.
This type is not as widespread as the bank lime and occurs mainly on the south or south-east side of some mountain ranges, such as the Hochkönig , the Hohen Göll , the Tennen- and Hagengebirge and the western edge of the Dachstein Mountains.
Most of the apparently unstratified reef limestone ("mass limestone") consists of reef debris, which can be recognized by the disordered position of many of the coral sticks and reef-forming algae mats. The fossils were socialized in the reef before they were deposited , were broken off by surf or earthquakes and were cemented in larger, contiguous blocks in the reef debris further down in front of the reef debris. Only in a few areas of the reef are the reef builders preserved in their living position. These areas are called reef cores and represent the remains of the original reef complex. In the Göll massif, the transition from the fore reef to the banked reef back to the lagoon facies can be documented.
In contrast to the bank limestone, the reef limestone is criss-crossed by steep fractures and fissures , which geomorphologically leads to the construction of towers and the rugged ridges following the reef course ( Mandl walls on the Hochkönig, Gosaukamm and Bischofsmütze ).
Deposition environment
When the Dachstein Limestone was deposited, the Eastern Alps were a flat sea area set apart from the mainland coast in subtropical latitudes on the southern edge of the western Tethys . The Eastern Alps offered ideal living conditions for the formation of reefs and a rich lagoon fauna due to the tropical location at that time - roughly comparable to today's Caribbean.
Both types of facies of the Dachstein Limestone originated in a relatively shallow sea area ( epipelagial ) with euphotic conditions. The occurrence of living shallow water fossils in the entire layer complex of the Dachstein Limestone testifies that sunlight reached the sea floor in substantial quantities. The subsoil must have continuously sunk during the deposition of the Dachstein limestone, because the lowest layer of the kilometer-thick pile of rock was also formed in the shallow sea. These sedimentation conditions, which have been comparatively stable over millions of years, result in the homogeneous structure of the Dachstein masses.
There are transitions between the two types of facies, banks of the lagoons and reef structures; The same applies to the facies of the Hallstatt limestone ( epipelagial basin) that formed in deeper water and the facies of the main dolomite , which probably marks areas of the Wadden Sea (tidal facies): the transition facies from the main dolomite that can still be assigned to the north is the plate limestone . In the Hochschwab on the eastern edge of the Dachstein Formation, the transition from the reef over the scree slope of the fore reef to a basin facies to the south ( Aflenzer Kalk ) is very well preserved. The Aflenz limestone is dark, thin-banked, marly and pebbly, and like the part of the Hallstatt limestone of the same age is not referred to as Dachstein limestone.
The Gosau strata - erosion sediment of the Upper Cretaceous that is baked into the Limestone Alps - prove that the Limestone Alps have been lifted again in the meantime and protruded out of the sea like an archipelago, before another shallow water phase follows with the Juvavikum . The beginning of this uplift phase should mark the end of the Dachstein limestone building.
Fossils
Typical fossils in the bank limestone are the so-called megalodonts , a group of giant clams known as Dachstein bivalves , which is represented by several genera such as Neomegalodus and Conchodus . They are popularly referred to as cow steps, as the two shells are generally still together and therefore show a hoof-like or heart-shaped cross-section on the rock surface. The group of corals formerly named Thecosmilia , which is now divided into several genera (including Thecosmilia , Retiophyllia ) , is also common and known among collectors . The most common type has stems about the size of a pencil and sometimes forms several decimeter tall sticks. The coral is common in reef limestone, but is rarely found in bank limestone. Many other fossils have been described from the Dachstein Limestone, including snails and fish remains. A dinosaur skeleton was found in the Dead Mountains, which is exhibited in a museum in Bad Ischl . The exact biostratigraphy of the Dachstein Limestone is carried out using foraminifera .
Karst hydrology
Due to its compact, up to 2 kilometers thick masses, the Dachstein limestone today forms massive mountain massifs , some with pronounced high plateaus . Bank and reef limestone, with their primarily horizontal and vertical faults, form a highly complex three-dimensional network of waterways. Due to the water solubility of the lime these are worked out in many ways. Therefore, the summit corridors of the Dachstein Limestone Mountains are largely without surface water, i.e. extremely karstified , and the stocks are criss-crossed by extensive and varied cave systems . These include several of the most extensive cave systems in the Alps: Schönberg cave system in the Totes Gebirge (longest cave in Austria), Hirlatz cave in the Dachstein, Dachstein Mammut cave , Lamprechtsofen in the Leoganger Steinberge (deepest cave in Austria), monster cave -Kolkbläser-System in the Steinernes Meer, Eisriesenwelt in the Tennengebirge - all of the 50 deepest / longest known cave systems on earth. Eisriesenwelt (largest ice cave in the world) and Dachstein ice cave are just as remarkable as the powerfully pouring Koppenbrüller cave in the Dachsteinstock.
literature
- Heinrich Zankl: The High Göll. Structure and life picture of a Dachstein limestone reef in the Upper Triassic of the northern limestone Alps . Treatises of the Senckenberg Natural Research Society, Volume 519, 123 pages, 74 illustrations, 15 plates. Frankfurt 1969
- Alfred G. Fischer: The Lofer Cyclothems of the Alpine Triassic ; Kansas Geol. Surv. Bull. 169, pp. 107-149. Topeka 1964
Web links
- The formation of the Alps
- The position of the continents shortly after the end of the Dachstein limestone sedimentation
- Original article by AG Fischer on the bank lime facies of the Dachstein limestone (en.)
Individual evidence
- ↑ In some areas this designation is even preferred; so in the Bajuvarikum of the Upper Austrian Pre-Alps, which are highly lagoon, thinner banked and have different fossil content than the actual Dachstein Limestone: Michael Moser: Report 2014 on geological recordings of the Hirschwaldstein range of the Ternberg Nappe between Micheldorf and Molln on sheet 4201 Kirchdorf an der Krems. In: Yearbook of the Federal Geological Institute. 154, 2014, p. 357, column 2 "Regarding the address as Plattenkalk ...", full article, p. 354–357 ( PDF on ZOBODAT ).
- ↑ Lit. Zankl 1969
- ↑ Upper Triassic reef fauna from the Quesnel terrane, central British Columbia ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. . Evaluation at The Paleobiology Database (en.). Retrieved December 10, 2007.
- ↑ The longest and deepest caves in the world. Researched by Martin Roubal (Regional Association for Speleology in Vienna and Lower Austria), status January 1999, accessed at schulen.eduhi.at in September 2013 - Austrian caves are marked in red; added.
