Conodont faunal dynamics across the Middle and Upper Ordovician boundary in the Yichang area, western Hubei Province, South China

Abstract

A total of 6094 conodont specimens, assigned to 18 genera and 27 species, have been recovered from the uppermost Kuniutan and Miaopo formations, spanning the latest Darriwilian – early Sandbian in age, at the Jieling section, Yichang, Hubei Province. Three conodont zones have been recognized, i.e., in ascending order, the Pygodus serra Zone, the Pygodus anserinus – Yangtzeplacognathus jianyeensis Zone, and the Baltoniodus alobatus Zone. The conodont biodiversity in the Miaopo Formation shows a decreasing trend at Jieling. Multivariate statistical analysis of the conodont fauna from the Jieling section shows that the Baltoniodus and Periodon biofacies are present in the uppermost Kuniutan Formation, and the Periodon and Scabbardella biofacies can be recognized in the Miaopo Formation.

Biostratigraphy and palaeoecology of Middle and Late Ordovician conodonts from the Hulo and Yenwashan formations, western Zhejiang, south‐eastern China

“…In South China, the P. anserinus Biozone was first reported by X. F. Wang, Ni, and Zhou () from the Miaopo Formation, Yichang area. Since then, the spatial and temporal distribution of P. anserinus on the Yangtze Platform has been debated by several authors (An, ; An & Ding, ; An, Du, & Gao, ; X. Chen, Bergström, Zhang, Goldman, & Chen, ; M. J. Chen & Zhang, , ; Ni, ; Ni & Li, ; Wu, Stouge, Zhan, Liu, & Liang, ; Zeng et al, ). Bergström () subdivided the P. anserinus Biozone into two subbiozones, with its lower subbiozone characterized by the co‐occurrence of P. anserinus and Baltoniodus prevariabilis and the upper subbiozone marked by the appearance of B. variabilis .…”

“…Yangtzeplacognathus jianyeensis is important for correlation on the Yangtze Platform. It has been widely documented from the lower portion of the Miaopo and Datianba formations, of which the age falls within the P. anserinus Biozone (An, ; An et al, ; An et al, ; Bagnoli & Qi, ; M. J. Chen & Zhang, ; Wu, Stouge, Zhan, Liu, & Liang, ; J. H. Zhang, ). An et al () and An et al () proposed the Y .…”

“…Later, An () revised the definition of Y. jianyeensis Biozone, of which the base is characterized by the disappearance of P. anserinus and its upper boundary is marked by the FAD of Baltoniodus alobatus . However, subsequent studies showed that Y. jianyeensis normally co‐occurred with P. anserinus on the Yangtze Platform (Bagnoli & Qi, ; M. J. Chen & Zhang, ; Wu et al, ; J. H. Zhang, ). Based on the material from the Datianba Formation in the Lower Yangtze Platform, M. J. Chen and Zhang () established the P. anserinus–Y.…”

“…Bergström () argued that C. pugionifer ranges from the upper P. anserinus Biozone to lower Amorphognathus tvaerensis Biozone on Baltica. C. pugionifer is normally recorded in the lower part of Miaopo and Datianba formations on the Yangtze Platform (An, ; M. J. Chen & Zhang, ; Wu et al, ). In this study, few elements of this species are recorded from the lower Yenwashan Formation in the P. anserinus Biozone, supporting the correlation of the present P. anserinus Biozone with the upper P. anserinus Biozone of Baltica.…”

“…In the Hengdu section, the conodont fauna in this biofacies is dominated by Pygodus , Periodon , and Protopanderodus with the lithology characterized by the grey nodular mudstone/wackestone in the Yenwashan Formation (Figure ). In South China, Wu et al () documented the equivalent conodont fauna from Miaopo Formation from Yichang area, palaeogeographically located in the inner Yangtze Platform, where the yield of Pygodus is low. Other deeper water genera are also very common in the lower Yenwashan Formation, such as Dapsilodus and Costiconus (Figure ).…”