The depositional environment of the Kaili Formation is not entirely known, and there are two hypotheses for its formation. It may have been a nearshore marine environment with 'normal' levels of oxygenation; or it may have been a deeper water environment further from the shore, on the open continental shelf; in this setting oxygen would not be available below the surface layers of the deposited sediment.[1] The trace fossil assemblages in the formation suggest that it was below the wave base and was reasonably well-oxygenated.[1]
Fossils
The faunal assemblage is highly diverse, comprising some 110 genera among 11 phyla; of these, some 40 genera are also found in the Burgess Shale, and some 30 are also found in the Maotianshan Shale. Trilobites and eocrinoids with hard parts that are easily preserved are the most common fossils, but many animals with only soft tissues are also preserved. For example, the arthropodSkania similar to the EdiacaranParvancorina of the Neoproterozoic age Ediacara Hills of South Australia has been found at the Kaili site.[2]
The middle part of the Kaili Formation, the Oryctocephalus indicus Zone, contains a Burgess Shale-type Lagerstätte with many well-preserved fossils known collectively as the Kaili Biota. In terms of age, this biota is located between the two most important and famous Cambrian Lagerstätten: the middle Lower Cambrian Maotianshan Shale (containing the Chengjiang Biota), also from China: and the Middle Cambrian Burgess Shale, known from Canada.[3][4]
Some other notable fossils discovered at Kaili are putative invertebrate eggs and embryos,[5] trace fossils of the genus Gordia (not to be confused with the Gordian worms),[1] as well as Naraoia, chancellorids, Microdictyon, Wiwaxia, and Marrella.[4] Furthermore, the possible moss Parafunaria is also known, marking the earliest likely fossil of land plants.[6] However this fossil has been disputed, as its Cambrian age means more conclusive proof is needed to determine whether it truly is a moss.[7]
The Kaili Formation is subdivided into three trilobite zones:
An outcrop of the Kaili Formation, the Wuliu-Zengjiayan section, was a candidate for the GSSP for the beginning of the 5th stage of the Cambrian. The FAD of two trilobites from the formation are proposed to be the official stage boundary, Oryctocephalus indicus and Ovatoryctocara granulata. Both can be correlated with formations of similar age in Siberia and China.[13] In 2018, GSSP for the Miaolingian series (Cambrian Series 3, "Middle" Cambrian[14]) as well as the Wuliuan stage was finally defined in this formation.[15]
References
^ abcWang, Y.; Lin, J. P.; Zhao, Y. L.; Orr, P. J. (2009). "Palaeoecology of the trace fossil Gordia and its interaction with nonmineralizing taxa from the early Middle Cambrian Kaili Biota, Guizhou Province, South China". Palaeogeography, Palaeoclimatology, Palaeoecology. 277 (1–2): 141–148. Bibcode:2009PPP...277..141W. doi:10.1016/j.palaeo.2009.02.017.
^ abLin, J. P.; Gon, S. M.; Gehling, J. G.; Babcock, L. E.; Zhao, Y. L.; Zhang, X. L.; Hu, S. X.; Yuan, J. L.; Yu, M. Y.; Peng, J. (2006). "A Parvancorina-like arthropod from the Cambrian of South China". Historical Biology. 18 (1): 33–45. Bibcode:2006HBio...18...33L. doi:10.1080/08912960500508689. S2CID85821717.
^Legg, D.A. (30 September 2015). "The morphology and affinities of Skania fragilis (Arthropoda) from the middle Cambrian Burgess Shale". Bulletin of Geosciences: 509–518. doi:10.3140/bull.geosci.1532.
^ abcYuan, Jinliang; Peng, Jin; Zhao, Yuanlong (August 2011). "New Bivalved Arthropods from Mid‐Cambrian Kaili Biota of Southeastern Guizhou, Southwest China". Acta Geologica Sinica - English Edition. 85 (4): 758–764. doi:10.1111/j.1755-6724.2011.00481.x.
^Wen, Rong-Qin; Zhao, Yuan-Long; Peng, Jin (March 2015). "Morphology and ontogeny of Tuzoia bispinosa from the Kaili Biota (Cambrian Stage 5) of eastern Guizhou, China". Palaeoworld. 24 (1–2): 61–70. doi:10.1016/j.palwor.2014.12.005.
^Yang, Xinglian; Zhao, Yuanlong; Babcock, Loren E.; Peng, Jin (November 2017). "A new vauxiid sponge from the Kaili Biota (Cambrian Stage 5), Guizhou, South China". Geological Magazine. 154 (6): 1334–1343. doi:10.1017/S0016756816001229.
^Arne Thorshøj Nielsen, Per Ahlberg (2019). "The Miaolingian, a new name for the 'Middle' Cambrian (Cambrian Series 3): identification of lower and upper boundaries in Baltoscandia". GFF. 141 (2): 162-173. Bibcode:2019GFF...141..162N. doi:10.1080/11035897.2019.1621374.
