Middle–Late Ordovician cephalopod faunas from western Hunan and Hubei provinces, South China
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Abstract:
In the middle Yangtze region, continuous and well-exposed Middle to Upper Ordovician strata yield abundant cephalopod fossils. This paper describes the systematic palaeontology and biostratigraphy of cephalopods of the Middle–Late Ordovician age based on specimens from the Kuniutan, Datianba/Miaopo, Pagoda and Linhsiang formations at the Chenjiahe section in Yichang, Hubei Province, and the Maocaopu section in Taoyuan, Hunan Province. From a collection of more than 1000 specimens, 46 species in 24 genera have been identified. Among them, six new species belonging to five genera have been systematically described here, and their biostratigraphy has been discussed and redefined. In light of the Middle–Late Ordovician cephalopod faunas, two cephalopod biozones, in ascending order, the Sinoceras chinense and the Richardsonoceras simplex biozones, have been recognized in the Pagoda and Linhsiang formations at the Chenjiahe section. Four biozones, including the Proterovaginoceras incognitum, the Ancistroceras undulatum, the Cyclolituites and the Sinoceras chinense biozones, have been defined in the Kuniutan, Datianba and the lower part of the Pagoda formations at the Maocaopu section. Based on the new results and redefinition of the previously established biozones, a total of five cephalopod biozones in the Dawan (middle part), Kuniutan, Datianba (or Miaopo), Pagoda and Linhsiang formations in South China are proposed. These are, in ascending order, the Proterovaginoceras incognitum, the Meitanoceras-Ancistroceras, the Lituites-Cyclolituites, the Sinoceras chinense, and the Richardsonoceras simplex biozones.
