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In geological history, the Miocene is a chronostratigraphic series of the Neogene , before the systemic division it was part of the Tertiary . It started about 23.03 million years ago and ended about 5.333 million years ago. Before the Miocene lies the series of the Oligocene , the youngest section of the Paleogene . After the Miocene comes the series of the Pliocene .
Naming and history
The name was proposed by Charles Lyell in 1847 and is derived from the Greek μείων meiōn "smaller, less, less" and καινός kainos "new, unusual".
Definition and GSSP
The lower limit of the Miocene (and also the Aquitaine level ) is defined by the following events in the history of the earth: Basis of the magnetic polarity Chronozone C6Cn.2n, first appearance of the foraminifera species Paragloborotalia kugleri and extinction of the calcareous Nannoplankton species Reticulofenestra bisecta (Basis the nannoplankton zone NN1). The upper limit (and at the same time the upper limit of the Messinium stage or the lower limit of the Zancleum stage) is marked by the upper end of the magnetic polarity chronozone C3r (around 100,000 years before the Thvera normal-polar subchronozone C3n.4n). The extinction horizon of the calcareous nannoplankton species Triquetrorhabdulus rugosus (base of the CN10b zone) and the first appearance of the calcareous nannoplankton species Ceratolithus acutus lie just above the border . The GSSP (global calibration point) for the Miocene (and Aquitanium stage) base is located near Carrosio north of Genoa in Italy .
- Series: Miocene (23.03-5.333 mya)
- Sub-series: Upper Miocene or Upper Miocene
- Sub-series: Middle Miocene or Middle Miocene (formerly also Helvetian )
- Sub-series: Lower Miocene or Lower Miocene
In the Miocene, huge series of sediments were deposited in the sea basins of Europe . Since some of these sequences are very difficult to correlate with the international levels due to their special ( endemic ) macrofossil fauna, separate regional ones were created for the central Paratethys ( Vienna Basin and Pannonian Basin ) and for the Northwest European Tertiary Basin (North Sea Basin in other words) Stages with corresponding key fossils suggested. For the central Paratethys, the classification is as follows:
- Pontium (corresponds roughly to the Messinium )
- Pannonium (corresponds to the Tortonium )
- Sarmatium (upper part of the Serravallium )
- Badenium ( Langhium and lower part of the Serravallium )
- Carpathian (upper part of the Burdigalium )
- Ottnangium (middle part of the Burdigalium )
- Eggenburgium (lower part of the Burdigalium )
- Egerium (upper part of the Chattian and Aquitanium ; consequently beginning already in the Oligocene , 25.8 mya)
For the Northwest European Tertiary Basin, the following structure was proposed (and used):
- Upper Miocene:
- Middle Miocene:
- Lower Miocene:
Since the Middle Ages, the continents had drifted apart, with Laurasia initially separated from the southern continent of Gondwana and finally both land masses broke up into today's continents. In the late Eocene , Antarctica separated from Australia and subsequently from South America. This created the strongest ocean current on earth in the Southern Ocean , the Antarctic Circumpolar Current , which from now on orbited Antarctica in a clockwise direction, cut off the continent from the supply of warmer seawater and created the basis for the formation of the Antarctic Ice Sheet. In the Miocene, South America, Africa, Australia and Antarctica were already independent island continents.
The Miocene is considered to be the age of mountain formation, caused by the merging of different continental plates. The Indian plate , which collided with the Eurasian plate in the early Eocene , moved further and further north during the Miocene. The process of the Himalayan unfolding extends into the geological present and will continue in the future. The same applies to the African plate , which also shifted further north in the Miocene. This led to the shrinking of the Tethys Sea and the emergence of the Zagros Mountains and the Alps . In North America, too, the Miocene was the climax for the time being in relation to the Rocky Mountains and the conclusion of an intensive phase of mountain formation.
Climate, Oceans and Vegetation
In the Miocene, the global climate was warm, but it was subject to relatively strong fluctuations. In the climatic optimum of the Miocene 17 to 15 million years ago, which was most likely forced by the long-lasting CO 2 emissions of the Columbia Plateau basalt , the then Antarctic ice sheet , which existed since the transition from the Eocene to the Oligocene , lost part of its mass, without completely melting away. Simulations, including the atmospheric conditions at the time, indicate that the core areas of the East Antarctic Ice Sheet were hardly affected by the warming phase in the Middle Miocene. At the height of the climatic optimum, the atmospheric CO 2 content rose briefly from 350 ppm at the beginning of the epoch to 500 to 600 ppm. In the course of global warming, large parts of southern Europe, such as the Rhone Basin and the Tagus Basin, were flooded by shallow seas. As a result, parts of Europe disintegrated into smaller islands. There was also a connection from the Mediterranean to the Indian Ocean. During this time, the water temperatures in the deep sea rose to 7 ° C (previously around 3 ° C).
As early as the early Miocene, warm-tempered to subtropical climatic zones extended to northern latitudes. The plant communities of the early Miocene, which are passed down in the brown coal strata in Brandon ( Vermont , USA), indicate annual average temperatures in this area of about 17 ° C. Today the average temperature in Vermont is only 7.6 ° C. In the Canadian Arctic, up to 75 ° north latitude, where permafrost and tundra dominate today, the climate in the early Miocene was also significantly milder than it is today. On Devon Island the vegetation consisted of forests of cool temperate latitudes, which would correspond to an average annual temperature of 11 to 15 ° C. In the Rocky Mountains and in the area of the Great Basin in the western part of today's USA, shrubbery and forest landscapes dominated in the early Miocene, while hackberry trees , oaks, walnut trees, magnolias and other tree species flourished near Anchorage in Alaska . In the rest of the world, too, the climate in the early and middle Miocene was much warmer and more humid than it is today. Evergreen deciduous forests of oak, laurel family , magnolias, pines, figs and rattan palms grew in Europe, suggesting a subtropical climate. Mangroves flourished on the coasts of the European island world , and coral reefs that had temporarily disappeared in the Oligocene were reestablished in the warm seas, which had a surface temperature of around 25 to 27 ° C.
Under the influence of strong erosion and weathering processes, the CO 2 concentration sank below 400 ppm at the end of the Miocene climatic optimum 14.8 million years ago, and a cooler climatic phase began with renewed growth of the Antarctic ice sheet . However, 14 to 12.8 million years ago, the temperatures in Antarctica were still 25 ° C to 30 ° C above current levels before the region was hit by a cold snap.
In the further course of the Miocene, large parts of Europe had a relatively mild and dry climate. However, in the period from 10.2 to 9.8 million years ago and then from 9.0 to 8.5 million years ago, two "laundry room phases" developed in which the climate became significantly more subtropical and more humid (with annual rainfall of some over 1500 mm).
fauna and Flora
During the Miocene, large savannah areas emerged for the first time under predominantly arid conditions. Linked to this was the global distribution of the C 4 plants adapted to these conditions (especially grasses ), which require considerably less carbon dioxide for photosynthesis than the C 3 plants, which are historically older .
In the Miocene, the animal world began to approach that of today. The land bridge (isthmus) between North and South America did not yet exist, and South American wildlife continued to be isolated, while the ancestors of today's wolves , cats, horses , deer, and camels evolved on other continents . The proboscis also flourished. In addition, groups of mammals that were extinct today existed in the Miocene, such as the Chalicotheria and Barbourofelids, as well as the Phorusrhacidae and Brontornithidae in South America and finally the Dromornithidae in Australia, a gigantic avifauna .
The sedimentary rocks of the Miocene are important for the energy industry . Thus, in the field of Paratethys (u. A. In the German Alpine foothills and in the Vienna Basin ) conventional oil and gas deposits in sandstones of the Miocene bound , and Southern Caspian Basin organic-Miocene sediments are (including the "Maykop suite" майкопская свита) as the most important bedrocks for the conventional deposits there. In addition, the economically most important brown coal deposits in Germany, the Rhenish brown coal and the Lusatian brown coal , are of the Miocene age.
The Nördlinger Ries was formed about 14.6 million years ago after a meteorite impact . The meteorite, about 1500 meters in diameter, which evaporated almost completely when it hit the earth's surface, left an impact crater about 20 × 24 kilometers in size. After the impact, the 400 km² Ries lake was formed, which was gradually filled with Miocene sediments.
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