Lantian formation

from Wikipedia, the free encyclopedia

The Lantian Formation is a 150-meter-thick, transgressive geological stratification in southeast China , which represents about 60 million years of geological history and was deposited during the Ediacarian . The formation is known for its complex macrofossils ( algae and possible metazoa ), which are considered to be the oldest large fossil forms to date.

Type locality and first description

The type locality of the Lantian Formation is located in the eponymous town of Lantian in southern Anhui , about 30 kilometers northwest of Huangshan (Southeast China). The fossils were first scientifically described by Xing and colleagues in 1989.

stratigraphy

The 100 to 150 meters thick Lantian Formation, belonging to the Sinium, begins with a so-called hat dolomite ( English cap dolostone ), which marks the end of the Marino Ice Age - recognizable by the diamictites of the underlying Leigongwu Formation ( Cryogenium ) - and at the same time the beginning of the Features Ediacariums. Above the hat dolomite follow black slate clays , which contain the fossils of the Lantian fauna. Layers of dolomite , shale and limestone lay on top . The formation ends with black shale clay. In the hanging wall, the dolomitic-siliciclastic Piyuancun formation joins, followed by fossil-bearing Cambrian shales (with trilobites ).

The Lantian formation can be divided into four members: Member 1 is formed by the almost 10 meter thick hat dolomite. Member 2 consists of 40 meters thick black schists , with the top 15 meters containing the fossils of the Lantian fauna. Member 3 is a 40-meter-thick alternation of Dolomites, black slate and a limestone-dolomite layer in the hanging wall. The final 25-meter-thick Member 4 is again built from black slate.

Deposit conditions

The sediments of the Lantian Formation were deposited in a shallow sea below the storm wave base, the water depths are likely to have ranged between 50 and 200 meters. They were still in the euphotic zone , but anoxic conditions must have prevailed. Paleogeographical reconstructions point to the edge of a platform or to a locally limited, restrictive environment.

Fossils

Judging by the many adhesive discs, the fossils are in the majority of benthic organisms in the still water environment . Their presence is limited to several, maximally only 20 centimeters thick sections in the black slate. They usually start with a horizon of thalli of various multicellular algae. The organisms can be interpreted as fan-shaped algae, branched seaweed or even as possible primitive multicellular cells (Metazoa) with a cup shape or a cone shape. The alleged Eumetazoa have tentacles and organ structures in the body cavity, which in modern Hohltiere (coelenterates) or Bilateria remember. The very small fossils - the fan shapes that open at an angle of 12 to 32 °, such as Flabellophyton, are only 1.5 to 3.5 centimeters in size - are randomly scattered on the layer surfaces. They were obtained as carbon-rich coatings, including the taxa Doushantuophyton cometa and Enteromorphites siniansis , which are also found in the Doushantuo formation . Its conservation mode is similar to that of the Burgess slate , but differs very clearly from that of the Ediacaran fauna .

Of the around 50 originally described taxa, only 12 to 15 are now recognized as independent species, including the pyritized Chuaria circularis (Chuaridae). Other taxa besides the fossils already mentioned are Anhuiphyton lineatum , Baculiphyca , Flabellophyton lantianensis , Flabellophyton strigata , Huangshanophyton fluticulosum , Konglingiphyton erecta and Orbisiana .,

Age

The Lantian Formation was originally placed in the Cambrian , but is now correlated with the Doushantuo Formation of the Ediacarian due to the fossil record. Their sedimentation should have taken place in the period 635 to 577 mya ; the Lantian biota are probably around 600 million years old.

meaning

In summary, it can be said that the fossils of the Lantian fauna document the transition to an ecosystem in which macroscopic, complex, multicellular eukaryotes played an increasingly important ecological role. This change of fauna is possibly associated with a gradually increasing oxygen content at the earth's surface, which can be recognized by the increased sulphate concentration in the Lantian Formation. At that time, the oxygen content should have been between the values ​​of the previous Proterozoic and the current values. However, it was not yet sufficient to enrich the deep sea with oxygen. This did not occur until around 580 mya with the appearance of the Avalon Fauna Community in Newfoundland. It is likely that the organisms lived in generally anoxic conditions, as evidenced by their in situ preservation. However, occasional influx of oxygen-rich water ensured their survival.

literature

  • Steiner, M .: The neoproterozoic mega-algae of southern China . In: Berlin Geoscientific Treatises . tape 15 , 1994, pp. 1-146 .

Individual evidence

  1. ^ Narbonne, GM: Evolutionary biology: when life got big . In: Nature . tape 470 (7334) , 2011, pp. 339-340 , doi : 10.1038 / 470339a .
  2. ↑ Xing, Y., Gao, Z., Liu, G. et al .: The Upper Precambrian of China (Chinese) . In: The Stratigraphy of China . Volume 3. Geological Publishing House, Beijing 1989, p. 1-150 .
  3. ↑ Yuan, X., Chen, Z., Xiao, S., Zhou, C. and Hua, H .: An early Ediacaran assemblage of macroscopic and morphologically differentiated eukaryotes . In: Nature . tape 470 (7334) , 2011, pp. 390–393 , doi : 10.1038 / nature09810 .
  4. ↑ a b Yuan, X., Li, J. Cao, R .: A diverse assemblage metaphyte from the Neoproterozoic black shales of South China . In: Lethaia . tape 32 , 1999, p. 143-155 .
  5. ↑ Wan, Bin, Yuan, Xunlai, Chen, Zhe, Guan, Chengguo, Pang, Ke, Tang, Qing, Xiao, Shuhai and McIlroy, Duncan: Systematic description of putative animal fossils from the early Ediacaran Lantian Formation of South China . In: Palaeontology . tape 59 (4) , 2016, ISSN  0031-0239 , p. 515-532 , doi : 10.1111 / pala.12242 .
  6. ↑ Yuan, X., Xiao S., Li, J. et al .: Pyritized chuarids with excystment structures from the late Neoproterozoic Lantian Formation in Anhui, South China . In: Precambrian Research . tape 107 , 2001, p. 251-261 .
  7. ↑ Yuan, XL, Chen, Z., Xiao, SH et al: The Lantian biota: A new window onto the origin and early evolution of multicellular organisms . In: Chinese Science Bulletin . tape 58 , no. 7 , 2013, p. 701-707 , doi : 10.1007 / s11434-012-5483-6 .
  8. ↑ Shen, Yanan, Tonggang Zhang, and Paul F. Hoffman: On the coevolution of Ediacaran oceans and animals . In: PNAS . tape 105 , no. 21 , 2008, p. 7376-7381 , doi : 10.1073 / pnas.0802168105 .