Yixian formation

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

The Yixian Formation originated in the Lower Cretaceous and is the older of two formations which together make up the Jehol Group . Their geochronological (absolute geological) age has not yet been clarified, but is approximately in the period 130 to 120 mya ( Barremium / lower Aptian ). It is overlaid by the younger Jiufotang formation . Their wealth of fossils first became apparent when the Japanese Empire called the Deer (also "Jehol") - a large province in Manchuria(Northeast China) - held occupied. During the occupation, several Japanese scientists discovered the fossil remains of extinct fish and reptile species, possibly including choristodera (aquatic reptiles). However, with the Japanese defeat at the end of World War II in 1945, these discoveries were forgotten. In 1949 the region came under the administrative authority of the Chinese Communist Party ; since then, only Chinese scientists have studied the rich fossil fauna. Exceptional fish and dinosaur fossils were found in the 1990s . In 1996 a number of dinosaur fossils came to light in Yixian that revolutionized the understanding of these animals, such as the finds of feathered dinosaurs . 2011 was leefructus an extinct species of the family of the cock foot scientifically described, the same year with pseudopulex magnus a blood-sucking insect, 2013 enantiornine bird sulcavis geeorum , the grooved teeth possessed.

Dating

The Yixian Formation was originally placed on the Upper Jurassic - Lower Cretaceous border ; H. 145 mya . New radiometric examinations have shown a younger age, their deposition period has therefore been dated 125–121 mya ; Zhou et al. found a minimum age of 128.2 to 121.6 mya, this corresponds to Barremium to Lower Aptium (middle Lower Cretaceous).

See also

Individual evidence

  1. ↑ Swisher, Carl. C., Wang, Yuan-qing, Wang, Xiao-lin, Xu, Xing, Wang, Yuan. (1999). "Cretaceous age for the feathered dinosaurs of Liaoning, China". Nature 400, July 1, 1999, pp. 58-61.
  2. ↑ Zonghe Zhou, Paul M. Barrett and Jason Hilton. (2003). "An exceptionally preserved Lower Cretaceous ecosystem". Nature 421, Feb. 20, 2003, pp. 807-814.

Coordinates: 41 ° 32 '  N , 121 ° 14'  E