The Egergraben ( Ohře Graben , Oherský příkop ) is a geographical and regional geological spatial unit in the north-west of the Czech Republic and in northern Bohemia . It is oriented northeast-southwest, runs parallel to the Ore Mountains ( Krušné Hory ) to the south and is linked to it in terms of its formation.
The part of the Egergraben, formed morphologically as a lowland , is located entirely in the Czech Republic, roughly between the towns of Cheb in the southwest and Ústí nad Labem (Aussig) in the northeast. Its southwestern section is traversed by the eponymous river Eger ( Ohře ) and separates the Ore Mountains from the Imperial Forest ( Slavkovský les ) and Duppau Mountains ( Doupovské hory ). In the northeast the lowlands recognized as North Bohemian Basin in the valley of Biela continued and there separated the Ore from the Bohemian Uplands ( České středohoří ), while the Eger flows around the Bohemian Highlands south and Litomerice flows (Litoměřice) into the Elbe.
The Egergraben in the geological sense includes, depending on the definition, a z. Sometimes much larger area than the river valleys of Eger and Biela. In any case, the Duppau Mountains and the Bohemian Central Mountains are also included.
The Egergraben can be seen as a paleo-rift , i.e. H. as a largely inactive rift valley today. It belongs to the so-called European Cenozoic Rift System and was formed by the long-distance effects of the formation of the Alps in the Tertiary . The northern drift of the African continental plate caused increased tensions in the earth's crust in Central Europe. These tensions were reduced by renewed tectonic movements at faults in the leveled Variscan Basement, which is largely covered by thick layers of sediment . Along such, northeast-southwest (Erzgebirgisch) trending fracture zones and correspondingly northwest-southeast (hercynian) oriented transverse disorders decreased from Eozän or early Oligozän until late Miozän , about 40 and 35 to 9 million years ago, the Eger Graben in the North Western part of the Bohemian mass and thereby separated the Erzgebirgsscholle from the rest of the Bohemian mass. Subsequently, the Ore Mountains were also highlighted. Since the uplift took place mainly in the fracture zone between the Erzgebirge and Egergraben ( Erzgebirge demolition ), the Erzgebirge rises only very gradually on its northwest flank in Saxony, but falls steeply to the southeast on the flank facing the Egergraben. Because of this geometry, one speaks of a Pultschollengebirge . The most important southern peripheral fault of the Egergraben is the low mountain range (named after the Bohemian low mountain range ), also known as the Litoměřice fault. During the main phase of the tectonic movements in particular, large amounts of basaltic magma rose where the main faults of the Ore Mountains and Hercynics meet, which led to extensive volcanism on the surface of the Eger Trench . Since the resulting volcanic rocks are relatively resistant to erosion , they now form the mountains of the Duppau Mountains and the Bohemian Central Mountains.
The volcanic complexes divide the Egergraben together with some Hercynian-oriented main faults into several sub-basins: the geologically relatively young Eger basin (Cheb basin) in the south-west, the North Bohemian basin (Most basin) in the north-east and the relatively narrow Falkenau basin ( Sokolov Basin) in between. In principle, the Mitterteicher Basin in northeast Bavaria as well as the Zittauer and Berzdorf-Radmeritzer Basins in the border triangle of Germany, the Czech Republic and Poland can also be counted as south-western or north-eastern foothills of the Egergraben system.
As subsidence areas, the Egergraben and its sub-basins were important deposition areas in the Tertiary . There were extensive river, lake and marsh landscapes in which today's North Bohemian lignite deposits were formed. B. at Chomutov in the must basin or at Bogatynia in the Zittau basin. The sediment layers also contain a diverse flora and fauna. The Dolnice fossil deposit in the Cheb Basin is famous for its abundance of snakes, lizards and amphibians from the early Miocene , as these vertebrate groups are much rarer in most fossil sites of the same geological age. Another important early Miocene vertebrate site is "Merkur-Nord" in the Nástup – Tušimice open-cast mine near Chomutov in the North Bohemian Basin.
In some areas of the Egergraben high geothermal gradients of 5.5 ° C / 100 m have been observed, which shows that the volcanic activity in the area has not yet completely died out. Late volcanic phenomena include the mofettes in the Soos moorland and the numerous thermal springs , which are among the hottest springs in Europe, such as the Karlovy Vary Hot Spring (Vřídlo) with an outlet temperature of 72 ° C. The occurrence of weak but noticeable earthquakes in the south-western section of the Egergraben, especially in the area of the Marienbader fault on the eastern edge of the Cheb basin, shows that the tectonic movements have not yet completely stopped.
- J. R. Kasiński: Tertiary Lignite-Bearing Lacustrine Facies of the Zittau Basin: Ohře Rift System (Poland, Germany and Czechoslovakia). In: P. Anadon Ll. Cabrera, K. Kelts: Lacustrine Facies Analysis. Special Publication no. 13 of the International Association of Sedimentary Geologists, 1991, pp. 93-108 doi : 10.1002 / 9781444303919.ch5
- Peter A. Ziegler: European Cenozoic rift system. Tectonophysics. Vol. 208, 1992, No. 1-3, pp. 91-111 doi : 10.1016 / 0040-1951 (92) 90338-7
- Wolfram H. Geissler: Seismic and Petrological Investigations of the Lithosphere in the Swarm-Earthquake and CO 2 Degassing Region Vogtland / NW-Bohemia. Dissertation to obtain the academic degree doctor rerum naturalium (Dr. rer. Nat.) Of the Faculty of Geosciences at the Free University of Berlin. Scientific Technical Report STR05 / 06, GeoForschungsZentrum Potsdam, 2004 ( PDF 15.3 MB)
- K. Reicherter, M. Froitzheim, N. Jarosiński, J. Badura, H.-J. Franzke, M. Hansen, C. Hübscher, R. Müller, P. Poprawa, J. Reinecker, W. Stackebrandt, T. Voigt, H. von Eynatten, W. Zuchiewicz: Alpine Tectonics north of the Alps. In: T. McCann (Ed.): The Geology of Central Europe. Volume 2: Mesozoic and Cenozoic. Geological Society, London 2008, pp. 1233-1286, p. 1255 in the Google book search
- Zbigniew Szyndlar: Snakes from the Lower Miocene Locality of Dolnice (Czechoslovakia). Journal of Vertebrate Paleontology. Vol. 7, 1987, No. 1, pp. 55-71 doi : 10.1080 / 02724634.1987.10011637
- Zbyněk Roček: Lizards (Reptilia: Sauria) from the Lower Miocene locality Dolnice (Bohemia, Czechoslovakia). Rozpravy Československé Akademie věd, řada matematických a přírodních věd. Vol. 94, 1984, No. 1, pp. 3–64 ( PDF 5.9 MB)
- Martin Ivanov: The oldest known Miocene snake fauna from Central Europe: Merkur-North locality, Czech Republic. Acta Palaeontologica Polonica. Vol. 47, No. 3, 2002, pp. 513-534 ( PDF ( 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. 1 , 2 MB)
- Maria Hammerich Maier: The furniture began to creak - earthquake in the Eger Trench. Online article on Radio Praha from September 9, 2008