Ordovician chitinozoans of the Miaopo Formation at Zhenjin, Upper Yangtze Platform, South China

Chitinozoan investigations on the late Middle to early Late Ordovician in South China are limited. Documented chitinozoan occurrences are mainly from the Miaopo Formation on the Upper Yangtze Platform. The present study reports new data from the Miaopo Formation at the Zhenjin section in the Yichang area. In total, 13 genera and 33 species are recognised, and three new species are described: Spinachitina? coronifera sp. nov., Lagenochitina yichangella sp. nov. and Pellichitina confragosa sp. nov. The Baltoscandian index species, Laufeldochitina striata, is documented in the lowermost part of the formation. This is the first report of this species in South China. The L. striata Biozone is suggested for the basal part of the formation due to the presence of the eponymous species. The index species of the Laufeldochitina stentor Biozone, the Armoricochitina granulifera and Cyathochitina megacalix subzones adopted in the Jieling section, are also observed in the Zhenjin section. However, according to the new data obtained at Zhenjin, the first appearance datum of C. megacalix and A. granulifera coincides with that of L. striata. Therefore, the C. megacalix Subzone is kept but moved to the L. striata Biozone. Armoricochitina granulifera has stable occurrences in almost the entire Miaopo Formation, corresponding to the Nemagraptus gracilis graptolite biozone. It is slightly older than Baltic records but could be useful for recognising this time interval in South China.

Automated summary

Chitinozoan investigations in South China during the late Middle to early Late Ordovician are limited. This study presents new data from the Miaopo Formation at the Zhenjin section in the Yichang area, including the identification of 13 genera, 33 species, and the description of three new species. The presence of the Baltoscandian index species, Laufeldochitina striata, is documented for the first time in South China. The results suggest the reassignment of the C. megacalix Subzone to the L. striata Biozone based on concurrent first appearance datum, and the recognition of Armoricochitina granulifera as a useful marker for this time interval in South China.