Guizhou Cambrian Kaili Formation

The Kaili Formation is a lithostratigraphic unit spanning the lower-middle Cambrian boundary,and is very thick(＞200 m) and dominated by mudstones in the Danzhai-Jianhe area of easten Guizhou.It is underlain by the Qingxudong Formation which is comprised limestone,gray dolomite,dolomitic mudstone,and gray to black dolomite.The Kaili Formation is overlain by the Jialao Formation which is comprised of gray bioclastic limestone,medium-bedded dolomite,and sandstone.The Kail Formation contains a rich fauna containing both benthonic and planktonic trilobites.The Kaili Formation is divided into three biostratigraphic zones based on trilobites;from lower to upper,these are①the Ovatoryctocara granulata—Bathynotus holopygus zone,②the Oryctocephalus indicus zone,and③the Olenoides jialaoensis—Oryctocephalus orientalis zone.The third series of the Cambrian is marked by the First Apperance Datum(FAD) of Oryctocephalus indicus,which is abundant in the Kaili Formation.Because the FAD of O.indicus is well represented in the Kaili Formation,the Wuliu-Zengjiaya section of the Kaili Formation at Balang is a potential stratotype section and point (GSSP) for the boundary of the second and third series of the Cambrian.The Jianshan section of the Kaili Formation at Chuandong is a supplementary section to the Wuliu-Zengjiaya section.In this area,the Kaili Formation contains a rich diversity and abundance of fossils,including a famous Burgess Shale-type Biota,"The Kaili biota",which occurs in the middle to upper part of the formation,just above the FAD of Oryctocephalus indicus.Thus,the Kaili Formation in the area not only contains a famous Burgess Shale-type biota but is also a candidate section for a GSSP marking the boundary of the second series and the third series of the Cambrian.This research concerns additional sections of the Kaili Formation in the Yuping-Tongren area and the Danzhai-Jianhe area.The Kaili Formation was deposited in an inner shelf sedimentary environment lying offshore of a carbonate platform.In the Tongren areas, the Kaili Formation is mostly comprised of mudstone and shale,but the diversity of fossils is not as great as in the Balang area.The dominant trilobites in the Yuping and Tongren areas are Nangaops sp.,Eosoptychoparia guizhouensis,and Peronopsis,and the green and black colored mudstones are similar to the third series of the Cambrian in the Balang area.Hence,the Kaili Formation of the Tongren area does not span the lower-middle Cambrian boundary,but instead belongs entirely to the lower part of the third series of the Cambrian.