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

Abstract

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.