Kaili formation

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The Kaili Formation ( Chinese  凯里 组 , Pinyin Kǎilǐ zǔ ) is a lithostratigraphic unit with the rank of a formation in the southwest of the People's Republic of China . The Kaili Formation extends from the Upper Lower Cambrian to the Lower Central Cambrian and belongs to the regional Taijiang level of China. Embedded in the Kaili Formation is a conservatory deposit from the Lower Central Cambrian with many well-preserved fossils - commonly known as Kaili fauna ( 凯里 生物 群 , Kǎilǐ shēngwù qún ). The layer sequence, which is up to 222 meters thick, consists mainly of sediments from the inner and outer shelf area (calcareous mudstones and shale clays ) and was deposited between 513 and 501 million years ago. In terms of age, the Kaili Formation is therefore between two of the most important and well-known Cambrian conservation deposits: the approx. 505 million year old Burgess Shale and the 525–520 million year old Maotianshan Shale (with the associated Chengjiang Fauna Community ).

Etymology and type locality

The formation was named after the nearby town of Kaili in Guizhou Province . Type locality is the north of the village Balang in a circle on a ridge Jianhe preferred Wuliu-Zengjiayan profile.

stratigraphy

Lithostratigraphy

The Kaili Formation, the sediments of which were deposited on the shield table of the Yangtze River Kraton , immediately follows the Qingxudong Formation , occasionally with abnormal contact.

The formation can be subdivided into three parts, the sediments of which reflect an almost complete cycle in the deposition conditions from shallow water close to the coast to deep water (150 to 200 meters water depth) and back to shallow water again. Its lower section consists lithologically of a 55 meter thick alternation of gray to dark gray, thin to medium- bank limestone and calcareous siltstone . The 123-meter-thick central section has gray to green calcareous, silty clay stones with fine-layered siltstones in between. The upper, 44-meter-thick section consists of medium to thick-bank limestone with isolated reef stumps and has a rich fauna of trilobites and well-preserved medusa - like species .

The Kaili Formation is overlaid by the Jialao Formation .

The actual Kaili fauna belongs to the middle section of the formation and is located in fine-layer alternating layers of low- energy turbidite sediments (suspension flows) of the outer shelf area.

Biostratigraphy

The Kaili Formation can be divided biostratigraphically into three trilobite zones:

GSSP of the Miaolingium and Wuliuums

The type locality of the Kaili Formation also serves as a GSSP for the lower limit of the Miaolingian , the third series / epoch of the Cambrian and for its lowest level / age , the Wuliuum (former border Lower Cambrian-Middle Cambrian, approx. 510 million years before today), marked by the first occurrence of the Trilobiten Oryctocephalus indicus and numerous acritarchs . This is immediately preceded by a sudden rise in sea level, which led to the extinction of numerous benthic trilobite species and manifests itself geochemically as a clearly negative carbon isotope anomaly with a simultaneous increase in the strontium isotope ratio. This is one of the most important turning points of the Phanerozoic.

Fossil content

The fossil content in the Kaili Formation is highly diversified and includes 110 genera in 11 tribes . Of these, 40 types overlap with the Burgess Shale and 30 types with the Maotianshan slate. Hard-shelled shells such as trilobites and eocrinoids are the most commonly preserved , but there are also many species of soft-body preservation present. An example of this is Parvancorina from the Neoproterozoic - an arthropod with similarities to the Ediacaran fauna of South Australia. Finds in Kaili, which are interpreted as eggs and embryos of invertebrates, are remarkable, as are Naraoiidae , Chancelloridae and Marrella splendens .

Individual evidence

  1. ↑ Zhang, Xinliiang, Zhao, Yuanlong, Yang, Ruidong and Shu, Degan: The Burgess Shale Arthropod Mollisonia (M. sinica new species): New Occurrence from the Middle Cambrian Kaili Fauna of Southwest China . In: Journal of Paleontology . 76, No. 6, 2002, pp. 1106-1108. doi : 10.1666 / 0022-3360 (2002) 076 <1106: TBSAMM> 2.0.CO; 2 .
  2. ↑ Zhao, YL., Huang, YZ. and Gong, X.-Y .: Echinoderm fossils of Kaili Fauna from Taijiang, Guizhou . In: Acta Palaeontologica Sinica . 33, 1994, pp. 305-324.
  3. ↑ a b Lin, JP, Gon, SM; Gehling, JG; Babcock, LE; Zhao, YL; Zhang, XL; Hu, SX; Yuan, JL; Yu, MY; Peng, J .: A Parvancorina-like arthropod from the Cambrian of South China . In: Historical Biology . 18, No. 1, 2006, pp. 33-45. doi : 10.1080 / 08912960500508689 .

swell

  • Lin, J. et al .: Silicified egg clusters from a Middle Cambrian Burgess Shale-type deposit, Guizhou, south China . In: Geology . 34, No. 12, 2006, pp. 1037-1040. doi : 10.1130 / B23006A.1 .
  • Zhao, Yuanlong, Parsley, Ronald L., Peng, Jin: Middle Cambrian short-stalked eocrinoids from the Kaili Biota: Guizhou Province, China . In: Journal of Paleontology . 82, No. 2, 2008, pp. 415-422. doi : 10.1666 / 06-041.1 .

Web links

  • Fossils - The Key to the Past. Images and texts about the Kaili, Taijiang and Balang Biota. Bureau of Science and Technology, Autonomous Prefecture of Miao and Tong Nationalities (PDF file; 21 MB; Chinese / English)