Kaili-Formation

The Kaili Formation (凯里 组Chinese, Pinyin Kǎilǐ zǔ ) is a lithostratigraphic formation from the southwestern People's Republic of China, which ranges from the Upper Cambrian to the Lower Middle Cambrian and part of the regional Taijiang stage of China. Embedded in it is a Konservatlagerstätte from the Lower Middle Cambrian fossils with many well-preserved - usually known as Kaili fauna (凯里 生物 群, Kǎilǐ Shengwu Qun ). The up to 222 meters thick layers are mainly deposited sediments of the inner and outer shelf area ( calcareous mudstones and shales ) and in the period 513 bis 501 million years BP. Age default, the Kaili Formation is therefore to be between two of the most important and best-known Cambrian Konservatlagerstätten: the Burgess Shale (~ 505 million years BP) and the Maotianshan slate ( with the associated Chengjiang Faunengemeinschaft, 525 - 520 million years BP).

Etymology and type locality

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

Stratigraphy

Lithostratigraphy

The Kaili Formation, the sediments were deposited on the sign board of the Yangtze craton, immediately following the Qingxudong formation, sometimes with abnormal contact.

The formation can be divided into three parts, the sediments reflect an almost complete cycle in the deposition conditions of near-coastal shallow water to deep water ( 150 to 200 m water depth) and back to shallow water. Its lower section is lithologically from a 55 meter thick alternation of gray to dark gray, thin - to mittelbankigen limestones and calcareous siltstones. The 123 meter thick midsection leads gray to green calcareous, silty mudstones, are interposed in the feinschichtige siltstone. The upper 44 m thick section consists of medium to fairly dense limestones with scattered Riffstotzen and performs a rich fauna of trilobites and well-preserved Medusenähnlichen.

The Kaili Formation is overlain by the Jialao lineup.

The actual Kaili fauna belongs to the middle portion of the formation and is located in feinschichtigen mixed layer from the low energy Turbiditsedimenten ( suspension flows ) of the outer shelf area.

Biostratigraphy

The Kaili Formation can be biostratigraphically divided into three Trilobitenzonen:

• The Cambrian Ovatoryctocara granulata - Bathynotus holopygus zone. Corresponds to the lower Flachwasserfazies. Contains the Taijiang fauna.
• The mittelkambrische Oryctocephalus indicus Zone. Contains the Kaili fauna.
• The mittelkambrische Oryctocephalus jialaensis zone. Corresponds to the upper Flachwasserfazies.

GSSP

The Wuliu - Zengjiayan profile of the Kaili Formation is a promising candidate for the GSSP of the start of the third series of the Cambrian ( former border Cambrian - Middle Cambrian, 510 million years BP), marked by the first occurrence of the trilobite Oryctocephalus indicus and numerous acritarchs. This time is also accompanied by a sudden rise in sea level that led to the extinction of benthic Trilobitenarten and had already occurred about 800 000 years ago,. This is one of the most important turning points of the Phanerozoic, underlined by a very significant negative carbon isotope anomaly with a simultaneous increase of the strontium isotope ratio.

Fossil content

The fossil content in the Kaili Formation is highly diversified and includes 110 genera in 11 tribes. Of these, 40 genera overlap with the Burgess Shale and 30 genera with the Maotianshan slate. Most commonly get are hard Schaler as trilobites and Eocrinoideen, but there are quite many species of animals with soft body preservation present. As an example Parvancorina be cited from the Neoproterozoic - an arthropod with similarities to the Ediacaran Fauna of South Australia. Noteworthy are findings in Kaili, which are interpreted as eggs and embryos of invertebrates, further Naraoiidae, Chancelloridae and Marrella splendens.