Daohugou layers

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The Daohugou layers ( Chinese  道 虎 沟 化石 层 , Pinyin Dàohǔgōu huàshícéng ) are a very fossil-rich sedimentary sequence in the northeast of the People's Republic of China south of Chifeng ; They were named after the village Daohugou the community Shantou ( 山头乡 ) in the district of Ningcheng on the southeastern margin of the Ningcheng basin ( 宁城盆地 ). The layers consist essentially of gray, fine layered sandy shales , in the tuffhaltige layers are interposed; it was deposited in inland lakes probably during the period from the upper Dogger to the lower Malm , that is, in the period 168 - 152 Ma BP ( Bathonian - Kimmeridgian ).

Fossil content

The Daohugou layers contain well-preserved fossils of dinosaurs , pterosaurs , salamanders , insects and other invertebrates , as well as plant remains of conifers , ginkgos , cycads , horsetail and ferns - even the first known gliding mammal, Volaticotherium and the primeval mammal, Castorocauda , were made discovered here. All of these organisms together form the Daohugou Biota ( 道 虎 沟 生物 群 , Dàohǔgōu shēngwù qún ), an ecosystem of Northeast Asia specific to the Jura. The tuff content of individual layers suggests a volcanic area in which heavy ash showers came down during volcanic eruptions. The landscape at that time was probably shaped by mountain streams and deep lakes, framed by gymnosperm forests . Previously it was assumed that the Daohugou biota represent an early form of the Jehol biota ; However, recent studies have shown that the two biota are different from one another.

stratigraphy

The Daohugou strata have a sometimes quite complicated geological structure, they are folded and their strata has been disturbed by volcanic activity. According to Liu et al. a. (2006) the Daohugou biota occur not only in the Daohugou strata, but also in the Tiaojishan and Lanqi formations. They were also able to show that the Jiulongshan formation is older ( Dogger ) and the Tuchengzi formation ( 土城 子 組 , Tǔchéngzǐ zǔ ) younger ( Malm ). Terrain surveys published in 2006 illustrated the extensive extent of the strata - from western Liaoning to the district of Nincheng in Inner Mongolia (Nei Mongol, Nèi Měnggǔ).

Dating

The exact age of the Daohugou strata remains a matter of dispute. Several different dating methods have been used, but the results are very conflicting. The fossils were given an age that extends from the Dogger to the Lower Cretaceous (period 169 - 122 Ma BP).

Scientific age regulations

In their 2004 work, He u. a. a sub-Cretaceous age for the Daohugou layers, only a few million years older than the overlying Yixian formation with the Jehol biota. The starting point here was the radiometric determination of the age of a tufa layer in the Daohugou strata. A subsequent paper by Gao & Ren disputed this result because of what they believed to be faulty working methods. Rather, they advocate a biostratigraphically determined age from the Middle Jurassic (using key fossils ) .

One in 2006 by Wang et al. a. published study came to the result that the Tiaojishan Formation has an age of 164 -159 Ma BP ( Callovium - Oxfordium ) and the Daohugou layers under- and not overlaid. In contrast to the earlier study by Gao and Ren, they found a broad correspondence in the fossil content of the Daohugou strata with that of the Yixian formation:

"Vertebrates such as Liaoxitriton , Jeholopterus and pinnate Manoraptoria show a great resemblance to their conspecifics from the Yixian formation. Despite the lack of Lycoptera - a fish genus that characterizes the Jehol group - the vertebrates of the Daohugou strata are in their composition most comparable to the biota of the sub-Cretaceous Jehol group. "

Wang et al. a. concluded from this that the Daohugou biota probably represent a very early stage of development of the Jehol biota and therefore "are to be counted as belonging to the same volcanic sedimentary cycle like the Yixian formation from the Jehol group". In the same year, Liu et al. a. their dating of the Daohugou strata using the U-Pb method; A key fossil horizon with salamanders embedded in volcanic deposits was examined. Liu et al. a. found an age of 164 and 158 Ma BP (Callovium and Oxfordium) for the two volcanogenic layers.

The Daohugou Biota

The forests of the Daohugou biota grew under warm and humid to moderately humid climatic conditions and were dominated by naked samers. Including but found themselves Ginkgophyta such. B. Ginkoites , Ginkgo , Baiera , Czekanowskia and Phoenicopsis . The conifers were represented by Pityophyllum , Rhipidiocladus , Elatocladus , Schizolepis and Podozamites . In addition, bear moss plants such as Lycopodites and Sellaginellities , horsetail ( Equisetopsida ) with Equisetum , cycads such as z. B. Anomozamites and ferns ( Filicopsida ) such as Todites and Coniopteris .

fauna

Amphibians
dinosaur
Pterosaurs
insects
Mammaliaformes
Mammals

Individual evidence

  1. ↑ Liu, Yongqing, Liu, Yanxue, Ji, Shu'an, Yang, Zhiqing (2006) "U-Pb zircon age for the Daohugou Biota at Ningcheng of Inner Mongolia and comments on related issues" Chinese Science Bulletin Vol.51 no. 21, pp. 2634-2644. doi : 10.1007 / s11434-006-2165-2
  2. ↑ Tan, Jingjing, Ren, Dong, Shih, Chungkun "New Cupedids from the Middle Jurassic of Inner Mongolia, China (Coleoptera: Archostemata)" Annales Zoologici 2006, 56 (1): 1-6z
  3. ↑ a b Wang, X., Zhou, Z., He, H., Jin, F., Wang, Y., Zhang, J., Wang, Y., Xu, X. & Zhang, F. (2005) . "Stratigraphy and age of the Daohugou Bed in Ningcheng, Inner Mongolia." Chinese Science Bulletin , 50 (20): 2369-2376
  4. ↑ Ren, D. et al. (2002). "On the biostratigraphy of the Jurassic fossil beds at Daohugou near Ningcheng, Inner Mongolia." Geol. Bull. China 21 , 584-591
  5. ↑ He, H., Wang, X., Zhou, Z., Zhu, R., Jin, F., Wang, F., Ding, X. and Boven, A. (2004). "(^ 40) Ar / (^ 39) Ar dating of ignimbrite from Inner Mongolia, northeastern China, indicates a post-Middle Jurassic age for the overlying Daohugou Bed." Geophysical Research Letters 31 , L20609
  6. ^ Gao, K., and Ren, D. (2006). "Radiometric dating of ignimbrite from Inner Mongolia provides no indication of a post-Middle Jurassic age for the Daohugou Beds." Acta Geologica Sinica English Edition , 80 (1): 42-45 (February 2006)
  7. Jump up ↑ Liu, Y., Liu, Y., and Zhang, H. (2006). "LA-ICPMS zircon U-Pb dating in the Jurassic Daohugou Beds and correlative strata in Ningcheng of Inner Mongolia." Acta Geologica Sinica (English Edition) , 80 (5): 733-742
  8. ↑ Zhang, Kuiyan, Yang, Ding, Ren, Dong. (2006) "The first snipe fly (Diptera: Rhagionidae) from the Middle Jurassic of Inner Mongolia, China" Zootaxa 1134: 51-57 (2006) z

See also