Kaili Formation

The Kaili Formation (simplified Chinese: 凯里组; traditional Chinese: 凱里組; pinyin: Kǎilǐ zǔ) is a special layer of rock formed a very long time ago, during the Lower and Middle Cambrian — about 513 to 506 million years ago. This layer is about 200 metres (660 feet) thick and was named after the city Kaili in the Guizhou province of southwest China.

Scientists are still learning about where and how this rock layer was created. There are two main ideas. One idea is that it may have formed close to the shore in ocean water with normal air levels. The other idea is that it could have formed farther from the shore, in deeper water where air was not available below the top layers of the sediment. The marks left by small sea creatures in this rock suggest it was below the reach of waves and had enough air to support life.

Fossils

The Kaili Formation has many different kinds of ancient animals, with about 110 groups from 11 main animal families. Some of these groups are also found in famous places like the Burgess Shale and the Maotianshan Shale. The most common fossils are trilobites and eocrinoids, which have hard shells that are easy to preserve. But we also find animals that only had soft bodies.

One special part of the Kaili Formation, called the Oryctocephalus indicus Zone, has many well-preserved fossils known as the Kaili Biota. This group of fossils is from a time between two very important fossil sites: the Maotianshan Shale in China and the Burgess Shale in Canada.

Other interesting fossils from Kaili include possible invertebrate eggs and embryos, trace fossils called Gordia, and animals like Naraoia, Microdictyon, Wiwaxia, and Marrella. There is also a possible fossil of a very early land plant called Parafunaria, but scientists are not sure if it is really a moss.

The Kaili Formation is divided into three zones based on trilobite fossils:

• Bathynotus holopygous–Ovatoryctocara granulata Zone
• Oryctocephalus indicus Zone
• Olenoides jialaoensis Zone

Paleobiota

Animals

Other taxa

Animals
Genus	Species	Higher taxon	Images
Skania?	"S." sundbergi	Acercostraca
Olenoides	O. paraptus	Dorypygidae
Alicaris	A. kailiensis	Arthropoda
Pseudoarctolepis	P. semicircularis	Hymenocarina
Tuzoia	T. bispinosa	Tuzoiidae
Forfexicaris	F. reticulata	Megacheira?
Leanchoilia	L. sp	Megacheira
Fuxianhuiida indet?	Unapplicable	Deuteropoda
Mollisonia	M. sinica	Mollisoniida
Ursulinacaris	U. cf. grallae	Hurdiidae
Ottoia	O. guizhouensis	Archaeopriapulida
Haplophrentis	H. carinatus	Hyolithida
Nisusia	N. guizhouensis, N. granosa	Kutorginida
Kailidiscus	K. chinensis	Edrioasteroidea
Globeocrinus	G. globulus	Eocrinoidea
Sinoeocrinus	S. lui	Eocrinoidea
Turbanicystis	T. inflata	Eocrinoidea
Pararotadiscus	P. guizhouensis	Eldoniidae
Dinomischus	D. isolatus?	Dinomischidae (stem-Ctenophora)
Angulosuspongia	A. sinensis	Vauxiidae (Demospongiae)
Allonnia	A. phrixothrix, A. erjiensis	Chancelloriidae
Archiasterella	A. anchoriformis	Chancelloriidae
Chancelloria	C. zhaoi, C. eros	Chancelloriidae

Other taxa
Genus	Species	Higher taxon	Images
Parafunaria	P. sinensis	Bryophyta?
Parallelphyton	P. tipica	Viridiplantae?
Walcottophycus	W. gyges	Bryopsidales?

GSSP for the Cambrian Series 3

An outcrop of the Kaili Formation, called the Wuliu-Zengjiayan section, was considered for marking the start of the 5th stage of the Cambrian period. Scientists suggested using the first appearance of two trilobites, Oryctocephalus indicus and Ovatoryctocara granulata, to define this important boundary. These trilobites help connect this formation to similar rock layers in places like Siberia and China. In 2018, this formation was officially chosen to mark the beginning of the Miaolingian series, also known as Cambrian Series 3, and the Wuliuan stage.