Stromatoporoids of the upper Hirnantian (Upper Ordovician) Shiqian Formation of South China: implications for environmental interpretation and the Ordovician–Silurian stromatoporoid transition

Abstract

The diversification of Palaeozoic stromatoporoid sponges was interrupted by the Late Ordovician glaciation, which caused the first of the five major extinctions during the Phanerozoic. Glaciation and the subsequent expansion of anoxia during deglaciation are interpreted to have resulted in a persistent scarcity of stromatoporoids during the Hirnantian. Previously, Hirnantian stromatoporoids were only known from two regions: Estonia in Baltica and Anticosti Island in eastern Laurentia. Here we report stromatoporoids from the upper Hirnantian Shiqian Formation of South China, adding to the rare fossil record of Hirnantian stromatoporoids. Three new stromatoporoid taxa are identified: Ecclimadictyon ancipitum Jeon sp. nov., Camptodictyon contortus Jeon & Kershaw sp. nov., and Cystostroma rallus Jeon sp. nov. The appearance of these stromatoporoids in South China is stratigraphically later than solitary rugose corals, but coincides with tabulate corals in the aftermath of the end-Ordovician mass extinction. Compared to the wider palaeogeographical and environmental distributions of rugose and tabulate corals during the Hirnantian, stromatoporoids presumably had a narrower environmental tolerance. The stromatoporoid assemblage in South China during the Hirnantian is dominated by clathrodictyids, which exhibit similar faunal patterns to those found in Baltica and Laurentia during the same period. The rise of clathrodictyid-dominated assemblages began in the middle to late Katian of the Late Ordovician, particularly in peri-Gondwanan regions, and rapidly expanded worldwide during the subsequent Hirnantian and Silurian onwards. The Late Ordovician glaciation significantly hastened the global Ordovician–Silurian stromatoporoid transition, as evidenced by the disappearance of numerous labechiid-type stromatoporoids and the expansion of clathrodictyid-type stromatoporoids in the Hirnantian and the subsequent Silurian. http://zoobank.org/urn:lsid:zoobank.org:pub:8DDBDBE2-D193-4689-BC8A-840EF88752A8

Keywords:

• Late Ordovician glaciation
• Hirnantian
• end-Ordovician mass extinction
• South China
• stromatoporoids
• Ordovician–Silurian stromatoporoid transition

Acknowledgements

This study derived from the first author’s PhD dissertation under the direction of Prof. Y.-D. Zhang. Funding support was provided by the National Natural Science Foundation of China (Grant No. 42030510) and the Chinese Academy of Sciences (Grant No. XDB26000000) to Y.-D. Zhang. U. Toom received funding from the Estonian Research Council under Grant No. PUTJD1106. J. Jeon was supported by the ANSO Scholarships for Young Talents, the 2020 Nanjing Municipal Government International Students Scholarship and National Research Foundation of Korea (2021R1A2C1009687). We would like to extend our gratitude to Jia-Yu Rong, Guang-Xu Wang (both from NIGPAS), and Jeong-Hyun Lee (Chungnam National University) for their valuable and constructive feedback. Additionally, we are grateful to the two reviewers, Carl Stock and Lucy Muir, for providing helpful comments. S. Kershaw thanks André Desrochers for hosting a visit to the Ellis Bay Formation on Anticosti Island in 2007. This paper is a contribution to IGCP 735 ‘Rocks and the Rise of Ordovician Life: Filling knowledge gaps in the Early Palaeozoic Biodiversification’. Finally, this paper is dedicated to the memory of Yue Li, whose life’s work was devoted to the study of Phanerozoic reef systems in China. Yue Li was particularly renowned for his invaluable research on the recovery of coral-stromatoporoid reef development following the end-Ordovician mass extinction event in South China. This study was inspired by the innovative ideas and steadfast support of the esteemed Yue Li, whose invaluable guidance shaped the fieldwork and scientific discourse underlying this research. We are deeply honoured to build on the remarkable legacy of this pioneering scholar, whose tireless efforts have profoundly advanced our understanding of this critical period in Earth’s history.

Disclosure statement

No potential conflict of interest was reported by the authors.

Associate Editor: Ken Johnson