Early Sandbian (Late Ordovician) conodonts from the Yenwashan Formation, western Zhejiang, South China

Abstract

Zhen, Y.Y., Zhang, Y.D. & Percival, I.G., June, 2009. Early Sandbian (Late Ordovician) conodonts from the Yenwashan Formation, western Zhejiang, South China. Alcheringa 33, 133–161. ISSN 0311-5518.

Conodonts are documented from the basal Yenwashan Formation at the Huangnitang Section (the GSSP section for the base of the Darriwilian), exposed near Changshan County town in western Zhejiang. The fauna consisting of 14 species is dominated by Pygodus anserinus, Periodon aculeatus, Protopanderodus cooperi, Costiconus ethingtoni and Dapsilodus viruensis. Both P. anserinus and P. cooperi are revised as having a septimembrate apparatus. The Pa element of P. anserinus has a morphology that varies from the primitive form with node-like denticles of the fourth row only developed on the distal part of the platform, to the advanced form with a well-developed fourth row of denticles. Association of these two morphotypes of P. anserinus, and the absence of P. serra and P. xinjiangensis in the basal Yenwashan Formation, suggests correlation of this level with the upper part of the P. anserinus Biozone (earliest Late Ordovician). This age determination agrees with the FAD of Nemagraptus gracilis immediately below in black shales intercalated with thinly bedded limestones at the very top of the underlying Hulo Formation, and provides new data for correlation with the graptolite biozone.

Key words:

• Conodonts
• Late Ordovician
• Sandbian
• Yenwashan Formation
• South China

Acknowledgements

Study of the conodont fauna by YYZ was supported by the CAS/SAFEA International Partnership Program for Creative Research Teams. Fieldwork by YYZ in Zhejiang was undertaken with the support of the Australian Academy of Sciences and the Academia Sinica. Professors Zhiyi Zhou and Jiayu Rong (Nanjing Institute of Geology and Palaeontology, Academia Sinica, Nanjing, China) are thanked for their assistance during the fieldwork in China (NSFC projects 40272001, and Major Basic Research Projects of MST, China G2000077703). Gary Dargan (Geological Survey of New South Wales, Londonderry) assisted with acid leaching and residue separation. Scanning electron micrographs were prepared in the Electron Microscope Unit of the Australian Museum (Sydney). IGP publishes with permission of the Director (Geological Survey), NSW Department of Primary Industries. Stig Bergström and Viive Viira are thanked for their careful and constructive reviews of the manuscript. This is a contribution to IGCP Project 503: Ordovician Palaeogeography and Palaeoclimate.