Yixian-Formation

The Yixian Formation (义县 组, Yixian zǔ ) is a geological formation in Liaoning in the northeast of the People 's Republic of China, which is known for its fossil wealth. It is named after the Yi County (义县, Yi Xiàn ) of the prefecture-level city of Jinzhou named in the southwest of the province.

The Yixian Formation originated in the Lower Cretaceous and is the elder of two formations, which together form the Jehol Group. Your geochronologisches ( absolute geological ) Age is not yet clear, but is approximately in the period 130-120 mya ( Barremian / Aptian lower ). It is overlain by the younger Jiufotang lineup. Your fossil wealth was first manifest when the Japanese Empire, the deer (also called " Jehol " ) - a large province in Manchuria ( Northern China) - had occupied. Already during the occupation several Japanese scientists had the fossil remains of extinct fish and reptile species, including possibly Choristodera (water- living reptiles) discovered. With the Japanese defeat at the end of World War II in 1945, but these discoveries were forgotten. In 1949, the region came under the administrative authority of the Communist Party of China; since only studied the rich fossil fauna Chinese scientists. In the 1990s, unique fish and dinosaur fossils have been found. In 1996, in Yixian, a number of dinosaur fossils to light that have revolutionized the understanding of these animals, such as the discoveries of feathered dinosaurs. 2011 has been described with Leefructus mirus an extinct plant of the family Ranunculaceae scientifically possessed in the same year with a blood-sucking insect Pseudopulex magnus, 2013, the enantiornine bird Sulcavis geeorum, the grooved teeth.

Dating

The Yixian Formation was originally placed in the border of Upper Jurassic - Lower Cretaceous, ie 145 mya. New radiometric studies have found younger age, their period of deposition is therefore 125 - dated 121 mya; Zhou et al. found a minimum age from 128.2 to 121.6 mya, corresponding to Barremian to lower Aptian (middle Cretaceous ).