Baltica (continent)
Baltica , in German also Baltika , was a continent in the history of the earth that originated in the uppermost Neoproterozoic (approx. 570 to 550 mya ). In Llandovery (approx. 440 to 430 mya), the older section of the Silurian , it collided with the geological continent Laurentia and thus became an essential part of the geological continent Laurussia .
Naming
Baltica consisted of areas that in the older geological literature were also known as Fennosarmatia (composed of Fenno for Finland and Sarmatia ) or Fennoskandia , in older German usage also as Ureuropa .
A group of authors around Alfred M. Ziegler suggested the name Baltica in 1977. It quickly found its way into the literature and replaced the older terms Fennosarmatia, Fennoskandia and Ureuropa , which, however, are basically not synonyms , as they represent structural or regional geological terms. However, in the case of Laurentia , an older structural geological term was also used for the geological continent.
Geographical expansion
In total, the area that once formed the geological continent of Baltica covers around 8 million km². At the time of its maximum size, Baltica consisted of most of northern and eastern Europe as far as the Urals .
The boundaries of the geological continent of Baltica today consist of geosutures or major faults , some of which only arose from much later tectonic activities. This means that the borders of Baltica, as they are today, have been greatly changed compared to the original borders at the time of the existence of the geological Baltica. Therefore, the geological Baltica can only be described very roughly using today's geography.
- In the Caledonian folded West Scandinavia , the border runs within the Caledonian ceiling pile .
- In the north-east belonged the Timan Ridge and the continental shelf that adjoins it today to the north with the Spitsbergen Archipelago and the Franz Joseph Land . These areas were welded to the continent during Baltica's independent history.
- In Central Europe , the western border is roughly formed by the northwest-southeast running trans-European suture zone .
- In the south, the border is even less clear, as it has been severely deformed several times by later orogenes . It runs from the Trans-European Suture Zone, starting roughly from Moldova , north of the Black Sea to the Urals.
Geological structure and early history
Baltica consisted or consists of three old cores: Fennoskandia, Sarmatia and Volgo-Uralia. Fennoskandia can, in turn, be divided into two parts: an archaic core in the northeast and a southwestern zone with Proterozoic rocks that are 2,500 to 1,700 mya old.
The gneisses of the Kola peninsula, which is part of the archaic core, are the oldest rocks in Europe at 2,700 to 3,500 ma. They may come from the first archaic supercontinent Ur . Only a few rocks on earth are older (4,300 - 3,800 mya), such as the Acasta gneiss and the Nuvvuagittuq greenstone belt of Canada or the Isua gneiss of Greenland .
Around 1,900 mya, Fennoskandia was merged with the recently united Volgo-Uralia and Sarmatia. Around 1100 to 1000 mya the area became part of the supercontinent Rodinia . Baltica first became tangible when the supercontinent Rodinia broke up about 800 million years ago . Baltica was probably still connected with Laurentia at that time and together with him formed a major continent, a forerunner of the later Laurussia . However, Baltica was rotated 120 ° clockwise compared to the position later assumed in Laurussia.
Baltica as an independent geological continent
Presumably around 580 mya, the Iapetus Ocean opened between the combined Laurentia / Baltica and Gondwana . At 570 to 550 mya the spreading moved further north between Laurentia and Baltica; this is how the northern part of the Iapetus Ocean was created and Baltica had become an independent continent, which at that time lay between about 30 ° and 60 ° south latitude.
Around 550 mya, various small terranes were welded to today's northeastern edge of Baltica and formed the Timanids . The Timan Ridge lies north of the Urals and is the remainder of this mountain formation . The continental shelf north of the Timan Mountains to Svalbard also belonged to these areas accredited at this time . At that time, this part of Baltica formed the southeastern tip of Baltica, due to the later 120 ° counterclockwise rotation. Neoproterozoic tillites found in this region agree well with a location in high southern latitudes.
Gondwana and Baltica were separated by a relatively narrow ocean area, which geologists Ebbe Hartz and Trond Helge Torsvik named Ran Ocean in 2002 . The Aegir Ocean had opened between Baltica and Siberia , which lay east of Baltica . The northern edge of Gondwana, which was then formed by Avalonia and Armorica or the Hun superterran , was recorded between 650 and 550 ma by the Cadomian orogeny .
A transgression to the fringes of Baltica began in the highest Ediacarium . The relief seems to have been relatively flat. The facies areas in the Cambrian are relatively uniform over great distances and a large part of the continent was covered by shallow seas. The thicknesses are relatively small and indicate a low sediment supply and thus in turn a low relief in the hinterland. In the Upper Cambrian, today's north-western edge of Baltica was covered by the Finnmark orogeny (approx. 505 to 500 mya), which is probably related to the subduction of the Aegir Ocean. In the Cambrian, Baltica began to rotate counterclockwise by 120 degrees.
In the Lower Ordovician , Avalonia broke away from the northern edge of Gondwana and drifted north towards Baltica, opening up the Rheic Ocean . In the upper Ordovician, Avalonia collided with the Baltica, which has now rotated into its current position.
In the course of the Silurian, Baltica / Avalonia finally collided with Laurentia to form the new major continent Laurussia . In Europe this collision caused the Caledonian orogeny and in North America the Taconian orogeny . This ended the history of Balticas as an independent continent in the history of the earth.
In the Carboniferous the western part of Gondwana collided with Laurussia, in the Lower Permian Sibiria and Laurussia came together and the actual Pangea was formed.
literature
- L. Robin M. Cocks, Trond H. Torsvik: Baltica from the late Precambrian to mid-Palaeozoic times: The gain and loss of a terrane's identity. In: Earth Science Reviews. 72, Amsterdam 2005, pp. 39-66. ISSN 0012-8252 doi: 10.1016 / j.earscirev.2005.04.001
- Alfred M. Ziegler, KS Hansen, ME Johnson, MA Kelly, Christopher R. Scotese, Rob van der Voo: Silurian Continental Distributions, Paleogeography, Climatology, and Biogeography. In: Tectonophysics. 40, Amsterdam 1977, pp. 13-51. ISSN 0040-1951
- Ebbe H. Hartz, Trond H. Torsvik: Baltica upside down: A new plate tectonic model for Rodinia and the Iapetus Ocean. In: Geology. 30 (3), Boulder 2002, pp. 255-258.
Web links
- Shadows of old continents ( Memento from August 28, 2011 in the Internet Archive )
- The history of the Scandinavian mountains
- palaeos.com: Baltica (engl.)
- palaeos.com: Development in Devon (Engl.)
Individual evidence
- ^ R. Schönenberg, J. Neugebauer: Introduction to the geology of Europe. 7th edition. Rombach Science, Freiburg i. Br. 1997, ISBN 3-7930-9147-3 .