Miocene

The Miocene is a geological history in the stratigraphic series of the Neogene, formerly of the Tertiary. It started about 23.03 million years ago and ended about 5.333 million years. Before the Miocene is the series of the Oligocene, which is the youngest part of the Paleogene. After the Miocene, the series follows 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 " her.

Definition and GSSP

The lower limit of the Miocene (and also the level of Aquitaniums ) is defined by the following events in Earth's history: the basis of magnetic polarity chronozone C6Cn.2n, first appearance of foraminiferal species Paragloborotalia kugleri and through the extinction of calcareous nannoplankton - type Reticulofenestra bisecta (base of nannoplankton zone NN1 ). The upper limit ( and at the same time the upper limit of the Messinian stage or the lower limit of Zancleum stage) is the top of magnetic polarity chronozone C3R ( about 100,000 years before the Thvera normal - polar Subchronozone C3n.4n ). Just above the border of the calcareous nannoplankton Aussterbehorizont Type Triquetrorhabdulus is rugosus (base of CN10b zone) and the first appearance of calcareous nannoplankton - type Ceratolithus acutus. The GSSP ( global calibration point ) for the base of the Miocene ( Aquitanian and the stage) is located near Carrosio, north of Genoa in Italy.

Subdivision

The Miocene is currently divided into three chronostratigraphic sub-series and in six stratigraphic levels:

  • Series: Miocene ( 23.03 to 5.333 mya ) Subseries: Upper Miocene (or Upper Miocene ) Level: Messinian ( 7.246 to 5.333 mya )
  • Level: Tortonian ( 11.62 to 7.246 mya )
  • Level: Serravallium ( 13.82 to 11.62 mya )
  • Level: Langhium ( 15.97 to 13.82 mya )
  • Level: Burdigalium ( 20.44 to 15.97 mya )
  • Level: Aquitanian ( 23.03 to 20.44 mya )

In the Miocene massive sediment masses were deposited in Europe's tectonic basin. As these deposits are often very difficult to correlate with the international levels, own regional levels have been proposed for the area of the central Paratethys and the North German Tertiary basins. For the central Paratethys is the step outline:

  • Pontium (roughly corresponding to the Messinian )
  • Pannonium (corresponds to the Tortonian )
  • Sarmatian (upper part of Serravallium )
  • Badenian ( Langhium and lower part of the Serravallium )
  • Karpatium (upper part of Burdigalium )
  • Ottnangium (middle part of the Burdigalian )
  • Eggenburgium (lower part of Burdigalium )
  • Egerium (still includes the upper part of the Chattiums )

For the North German Tertiary basins following regional levels have been proposed ( and used ):

  • Syltium (roughly corresponding to the Messinian )
  • Gramium ( ranging from the upper Serravallium to the Tortonian )
  • Langenfeldium (middle part of the Serravallium )
  • Reinbekium (largest part of the Langhium to lower part of the Serravallium )
  • Hemmoorium (upper part of the Burdigalian - level to the lowest part of the Langhium )
  • Vierlandium ( Aquitanian to Burdigalian )

The sub- series terms used for the classification of the sediments of the North German Tertiary basins, "Lower Miocene ", "Middle Miocene " and "Upper Miocene " not in accordance with the international subdivision of the Miocene series.

Paleogeography

Since the Mesozoic, the continents had drifted apart, initially had Laurasia separated from Gondwana southern continent, and finally both land masses further broke into the present continents. Already in the early Oligocene to Antarctica from Australia and South America was separated, resulting in a circumpolar ocean current allowed. So were in the Miocene South America, Africa, Australia and Antarctica independent island continents. The Miocene was marked in contrast of rock formations that were caused by the collision of continental plates. So pressed the fragment of India, which had hit the Asian continent since the early Eocene, in the middle Miocene increasingly to the north, causing the Himalayas was unfolded. This can be seen for instance from the sedimentary formations in the Indian Ocean. At the same time, the African plate pushed since the early Miocene epoch, to the north, resulting in the reduction of the Tethys Sea and mountain formation of the Zagros Mountains and the Alps. Also in North America, where the Rocky Mountains raised, the Miocene was a period of mountain building.

Climate, sea level and vegetation

The climate in the Miocene was globally still warm, although a gradual cooling announcing the impending ice age of the Pleistocene. Overall, it was subjected to relatively strong fluctuations. At the end of the preceding Oligocene the climate was relatively cool. In this case, even an Antarctic ice sheet had formed. Since the beginning of the Miocene, the climate warmed again and the polar cap disappeared at times completely, causing the sea level rose. This large parts of southern Europe, such as the Rhone basin and the Tagus Basin were flooded by shallow seas. This meant that Europe partially disintegrated into smaller islands. There was also a connection from the Mediterranean to the Indian Ocean. Before 14 to 16 million years ago, a climatic optimum was reached at which the water temperature of the deep sea to 7 ° C had increased (from a previous 3 ° C). Already in the early Miocene in northern latitudes ruled until a warm- temperate to subtropical climate. The plant communities of the early Miocene, which are preserved in the lignite layers in Brandon (Vermont, USA), suggest that the average annual temperature in this area at that time was approximately 17 ° C. Today, the average temperature is in Vermont at only 7.6 ° C. The annual rainfall amounts were significantly higher. In the Canadian Arctic, up to 75 ° north latitude, where today is dominated by permafrost and tundra, the climate in the early Miocene was also significantly milder than today. On Devon Iceland vegetation seems to have consisted of forests kühlgemäßigter widths, corresponding to an average annual temperature of 11 ° to 15 ° C. In the Rocky Mountains and in the region of the Great Basin prevailed in the early Miocene, a shrub or forest landscape in front, at Anchorage, Alaska thrived nettle trees, oaks, walnut trees, magnolias and other tree species. In the other parts of the world the climate in the early and middle Miocene was much warmer and wetter than it is today, but also warmer than at the end of the Oligocene. In Europe, dominated by evergreen broad-leaved forests of oak, laurel family, magnolias, pines, figs and Rattanpalmen that point to a subtropical climate. In the coastal areas, which dominated the European islands, mangroves grew. In the warm seas that are likely to have had a temperature of about 25 to 27 ° C, established themselves again coral reefs that were temporarily disappeared in the Oligocene. The Antarctic ice sheet is pulled back and pollen analyzes show that the ice-free zones of the Antarctic found significant vegetation.

After a climatic optimum about 15 million years ago the climate during the middle Miocene was again noticeably cooler and drier. Here, an Antarctic ice sheet, which already reaching its current proportions formed.

Fauna and Flora

During the Miocene the first time spread large savanna areas on the earth. The wildlife began in the Miocene already clearly the approaching today. The land bridge ( isthmus ) between North and South America did not exist, and the South American fauna was still isolated, while developed the forefathers of today's wolves, cats, horses, deer and camels on other continents. The mammoths flourished. In addition, in the Miocene, there were now extinct animal groups, such as the Chalicotherien and Barbourofeliden.

Economic Importance

The sedimentary rocks of the Miocene are for hydrocarbon production and the energy industry is of great importance. Especially in the area of the Paratethys petroleum and natural gas deposits are bound to sandstones of the Miocene.

Ries

Before 14.3 to 14.5 million years ago by a meteorite impact the Ries. After the impact, the Ries Lake, which was made up of Miocene sediments formed.

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