Geological history of Lower Austria
Precambrian to Jurassic
The oldest geological relic in Lower Austria is the Dobra gneiss in the Bohemian Massif in the Waldviertel - dated to 1377 mya - but in which no fossils can yet be found. It is also the oldest exposed rock formation in Austria . Only in the vicinity of the Variscan central gneiss cores of the Zillertal Alps and the eastern Hohe Tauern are parts of the Proterozoic supercontinent Rodinia from 1000 mya.
In the ancient times (541 to 252 mya ) the area of today's Lower Austria was covered by the great Caledonian and Variscan mountain formations, which in Lower Austria today mainly the rocks of the Bohemian Massif (Waldviertel) testify. As a result of the Variscan mountain formation, large packets of rock were sunk in the depths, melted, rose up and solidified as "South Bohemian Pluton ", which in the Waldviertel includes, for example, the extensive Weinsberg granite . The area of today's Alps was initially on the seabed off the coast in the Rheic Ocean of the south-eastern subduction zone of Laurussia , from which volcanic islands - the Hun Terrans - emerged at times. As a result of the Variscan mountain formation, the (older) rocks of today's Alps were also lifted above sea level and incorporated into the thousands of kilometers long high mountain system in the middle of the supercontinent Pangea (the younger alpine rocks only emerged afterwards). In the later Paleozoic Era, today's Central and Western Europe was part of Pangea in the tropical climatic zone, i.e. in the immediate vicinity of the equator. At the beginning of the Permian at about 5 ° south latitude, these areas shifted in the course of 50 million years in the course of the continental drift towards the 10th north latitude. During this time there was a relatively frequent change between humid (damp) and arid (dry) phases.
In the early Middle Ages , the Triassic (252 to 201 mya ), Lower Austria and Vienna were temporarily a peninsula in the Tethys , on the fault line between Laurasia and Gondwana of the disintegrating Pangea, roughly at the level of the Tropic of Capricorn . All of Central Europe, with the exception of the Variscan Mountains , was submerged in the flat water, the Germanic Sea and the Alpine Shelf (where the rocks of the later Northern Limestone Alps were deposited). After the Atlantic opened up in the Jura - 201 to 145 mya - Lower Austria (with the exception of the Waldviertel belonging to the Vindelizian threshold ) sank again into the sea and remained there until the Middle Cretaceous (100 mya) when the first phase of the Alpid mountain formation began .
Chalk and Paleogene
In the Cretaceous Period (145 to 66 mya) the Alps slowly began to rise due to the collision between Africa and Europe. In a first phase, the later Northern Limestone Alps rose as island chains (comparable to today's Dalmatian coast ), which were separated from one another by the Gosau Basin .
While extensive coral reefs thrived on the northern edge of the Mediterranean Sea , a much more monotonous fauna spread on the northern edge of the emerging Alps . In the narrow Tiefseerinne the north formed the surging Alps, black were clays and submarine sand flows deposited later to flysch rocks solidified and today Flyschzone build. The water circulation in the deep sea was poor and therefore led to a lack of oxygen ( hypoxia ) in deeper water layers.
Around the time of the Cretaceous-Paleogene transition (66 mya), the first islands also formed in the region of the Pennine Ocean and the westernmost part of the closing Tethys .
In the Eocene and Oligocene , from around 50 mya, the northern part of the western Tethys was finally separated from the southern part by the piling up of the Alpid mountain ranges, while the flysch channel was closed and the flysch rocks were now pushed north by the limestone Alps. The northern sea trough, which runs from east to west, is known as the Paratethys (the southern part of the former western Tethys developed into today's Mediterranean).
The end of the Eocene (34 mya), the northern foothills of the Alps and parts began the Bohemian Massif under the burden of the south by covering, towering Alps descend quickly. The sea cover - moving from the Rhone region to the east - soon spread to the Lower Austrian Alpine foothills, which now formed the western part of the Paratethys, which at that time extended to the Caspian Sea . Eroded material, which came from the young Alps on the one hand and from the Bohemian Massif on the other, was deposited in the form of clay, sand and gravel in these western foothills of the Paratethys, the so-called Molasse Sea . The oldest deposits of the Molasse Sea can be found in Austria in the Salzburg - Upper Austrian Alpine foothills .
In the late Paleogene (25 mya) the western part of the Molasse Sea fell temporarily dry and, following today's course of the Danube, reached east to Munich , while the section in present-day Austria was still completely covered by the sea.
Miocene
The deposits from the early and middle Miocene - 23 to 13 mya - are of particular importance for eastern Austria, as a large number of particularly beautiful fossils have been preserved from this period . Some periods of this epoch are named after Lower Austrian locations, in whose surroundings the deposits in question are particularly diverse and scientifically well processed. The Eggenburgium covers the period from 20.5 to 19 mya, the Badenium the period before 16.5 to 13 mya.
The transition from the Oligocene (end of the Paleogene) to the Miocene (beginning of the Neogene ) took place in the Alpine foothills of Austria without major geological changes. Therefore, there is a separate name for this transition period - the Egerium (28 to 20.5 mya) - which covers the period of the Younger Oligocene and the oldest Miocene. In the Egerium there was already better aeration of the deep sea basins, but it was only with the Eggenburgium that a new development began.
In the early Miocene - around 23 to 18 mya - a wide sea route opened up via what is now Iran to the Indian Ocean . On earth, no land masses obstructed ocean currents around the equator. Favored by this unimpeded circumequatorial flow, after a relatively cool beginning in the climatic optimum of the Middle Miocene, there was a worldwide temperature increase, probably also influenced by the massive outgassing of the Columbia Plateau basalt (main activity 16.7 to 15.9 mya). This development is also shown in the Paratethys by the sudden advance of large tropical mussels; the corresponding time stage is named after the fossil-rich sediments around Eggenburg Eggenburgium .
Shallow bays and rugged rocky coasts along the Bohemian Massif offered a habitat for a variety of marine organisms. In the Horner Basin , the rise in sea level pushed the freshwater river system of the Ur kamp , which was formed during the Oligocene, back north. A mixed area between fresh water and sea water was created on a north-south facing, 10 km long and 4 km wide area. This area was characterized by a variety of habitats, the salinity of which changed several times depending on the sea or freshwater advances.
Carpathian and Badenian
After a phase of sea retreat, the sea level rose again during the warm phase of the Middle Miocene, the Carpathian Mountains - 17 to 16 mya . The Paratethys extended in the west to Lower Austria and was limited in the east by the growing Carpathian arch. This part of the Paratethys was quickly repopulated by marine animals. The deposits of this time in the Korneuburg Basin have been examined particularly well ; Over 650 plant and animal species can be identified here. In the fossil world of the Weinviertel you can also visit the largest accessible fossil oyster reef on earth. The terrestrial fauna was also characterized by a high level of biodiversity during the Middle Miocene, and in Central Europe (including the northern Alpine foothills) it included scaled reptiles, belted lizards, alligators and turtles.
Due to tectonic movements, the earth's crust was torn between the Alps and the Carpathian Mountains, the surface of the earth subsided and warping basins formed that reached deep into the body of the Alps and were flooded by the sea. This is how the Vienna Basin and the Graz Basin were formed . At the same time a connection to the Mediterranean was created again .
The water temperatures remained very warm in the Badenium , small patch reefs and coral carpets formed. Calcareous red algae covered the shallow seabed and lined shallows and islands such as the Steinberg near Zistersdorf or the Leithagebirge ; they are handed down as white Leithakalk . The tropical temperatures and the broad connection to the Mediterranean and Indian Ocean were prerequisites for the highest diversity of organisms in the Paratethys. The hardly manageable number allows the image of today's Red Sea or the Indian Ocean to emerge in the mind of the beholder . In fact, the closest relatives of the inhabitants of the Paratethys can still be found there today.
Sarmatian and Pannonian
At the transition from the Middle to the Younger Miocene, the Sarmatian - 12.7 to 11.6 mya - there was a brief marine transgression at 12.5 mya, before the Paratethys was cut off again from the open oceans. The now isolated inland sea extended from the Vienna Basin to the Aral Sea . Due to the limited water exchange with the Mediterranean Sea, the alkalinity increased significantly, so that a large part of the marine organisms disappeared. Very few adaptable animal species survived this crisis.
From the meager remnant of the former abundance, only around 120 species developed in the Pannonian - 11.6 to 7.2 mya - which colonized the many ecological niches of the great inland sea. 11.5 mya the Paratethys Sea retreated far to the east. Instead, a large brackish lake , the Pannon Lake , was created in the west . The sweetening of the water led to the extinction of the Sarmatian fauna. A few species of mussels and snails have now taken their place. The triangular clams of the genus Congeria found little competition from other species on the muddy sea floor and spread in large numbers. Something similar with the snails : Species of the genus Melanopsis penetrated from the estuaries into the shores of Lake Pannon. In a short time, numerous new forms emerged from the original species that lived exclusively in Lake Pannon.
The land mammals
As the sea recedes, the sediments increasingly contain fossils of land mammals . The alpine foothills were of river landscapes, u. a. the original Danube , shaped and housed a wide range of fauna. Willows, alders, elms, maples and oaks grew in the extensive forests on the banks of Lake Pannon, but also bald cypresses, celcios, wingnuts and sweetgum trees.
The largest inhabitant of the alluvial forests was the "tusk elephant" Deinotherium . The saber-toothed cat Sansanosmilus presented Hirsch piglets , muntjac -Hirschen, claws animals and pony big "three toe horses " Hippotherium after. Five tiny to giant-sized species of flying squirrels lived in these forests. Since flying squirrels that are still alive today do not hibernate and only have limited food supplies, this suggests frost-free winters and a rainy, warm climate.
At 9 mya the Pannon Lake began to withdraw from the Vienna Basin. From the forests on the freshwater lakes and pools near Neufeld and Zillingdorf, mighty lignite deposits have been handed down.
For more than 500 million years, the history of Lower Austria and Austria was a history of oceans and seas; Only with the end of the Paratethys Sea and the Pannon Sea did the marine past of Lower Austria 8 mya come to an end and 2.5 mya ended in the Quaternary Glaciation .
See also
Web links
- Shadows of old continents: The oldest parts of Austria ( Memento from January 2, 2013 in the Internet Archive )
- International Chronostratigraphic Chart 2020/03 (Regularly updated chronostratigraphic chart of the International Commission on Stratigraphy )
source
- Materials from the special exhibition Sea beach at the edge of the Alps , Lower Austria State Museum in Sankt Pölten , 2005.
Individual evidence
- ↑ Stefan M. Schmid, Daniel Bernoulli, Bernhard Fügenschuh, Liviu Matenco, Senecio Schefer, Ralf Schuster, Matthias Tischler, Kamil Ustaszewski: The Alpine-Carpathian-Dinaridic orogenic system: correlation and evolution of tectonic units . (PDF) In: Swiss Journal of Geosciences . 101, March 2008, pp. 139-183. doi : 10.1007 / s00015-008-1247-3 .
- ↑ Jennifer Kasbohm, Blair Schoene: Rapid eruption of the Columbia River flood basalt and correlation with the mid-Miocene climate optimum . (PDF) In: Science Advances . 4, No. 9, September 2018. doi : 10.1126 / sciadv.aat8223 .
- ^ Madelaine Böhme : The Miocene Climatic Optimum: evidence from ectothermic vertebrates of Central Europe . (PDF) In: Palaeogeography, Palaeoclimatology, Palaeoecology . 195, No. 3-4, June 2003, pp. 389-401. doi : 10.1016 / S0031-0182 (03) 00367-5 .
- ↑ Fred Rögl, Stjepan Ćorić, Mathias Harzhauser, Gonzalo Jimenez-Moreno, Andreas Kroh, Ortwin Schultz, Godfrid Wessely, Irene Zorn: The Middle Miocene Badenian stratotype at Baden-Sooss (Lower Austria) . (PDF) In: Geologica Carpathica . 59, No. 5, October 2008, pp. 367-374.
- ^ Holger Gebhardt, Irene Zorn, Reinhard Roetzel: The initial phase of the early Sarmatian (Middle Miocene) transgression. Foraminiferal and ostracod assemblages from an incised valley fill in the Molasse Basin of Lower Austria . (PDF) In: Austrian Journal of Earth Sciences . 102, No. 2, 2009.
- ^ Mathias Harzhauser, Gudrun Daxner-Höck, Ursula B. Göhlich, Doris Nagel: Complex faunal mixing in the early Pannonian palaeo-Danube Delta (Late Miocene, Gaweinstal, Lower Austria) . (PDF) In: Annals of the Natural History Museum in Vienna. Series A for Mineralogy and Petrography, Geology and Paleontology, Anthropology and Prehistory . Volume 113, 2011, pp. 167-208.
- ↑ Kati Huttunen: Deinotheriidae (Proboscidea, Mammalia) dental remains from the Miocene of Lower Austria and Burgenland . (PDF) In: Annals of the Natural History Museum in Vienna. Series A for Mineralogy and Petrography, Geology and Paleontology, Anthropology and Prehistory . Volume 103, 2001, pp. 251-285.
- ↑ Madelaine Böhme, August Ilg, Michael Winklhofer: Late Miocene “washhouse” climate in Europe . (PDF) In: Earth and Planetary Science Letters . 275, No. 3-4, November 2008, pp. 393-401. doi : 10.1016 / j.epsl.2008.09.011 .