Preservation potential of Cambrian small shelly fossils in different microfacies, North China

Abstract

Small shelly fossils (SSFs) have long been recognized as important to the studies of both metazoan evolution and the onset of biomineralization during the Cambrian radiation. The marked decline in the occurrence, diversity and abundance of SSFs in the middle to late Cambrian, when compared with the early Cambrian, has often been regarded as a result of the closure of a phosphatization window. Despite this, there have been numerous and consistent reports of SSFs from the middle Cambrian and younger deposits. To identify possible factors influencing SSF preservation, five microfacies including bioclastic limestone, flat-pebble conglomerates with bioclasts, hummocky cross-stratified grainstone with bioclasts, bioclastic grainstone in hardgrounds and glauconite bioclastic wackstone-packstone, from Cambrian Series 2 to Miaolingian in North China are compared to assess how differences in lithology impact the preservation potential of SSFs. Our results, based on 35,161 SSF specimens from deposits across six sections, suggest that there are still abundant and diverse SSFs in the middle Cambrian of North China preserved in ways not exclusively reliant on the presence of phosphate and that SSF preservation can be linked to the differences in microfacies in the early to middle Cambrian of North China.

Keywords

Small shelly fossils / Shell structure / Glauconite / Phosphatization window

CRediT authorship contribution statement

Yazhou Hu: Writing - original draft, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. Timothy P. Top-per: Writing - review & editing, Investigation, Formal analysis. Luke C. Strotz: Writing - review & editing, Methodology, Formal analysis. Yue Liang: Writing - original draft, Formal analysis. Fan Liu: Writing- review & editing, Formal analysis. Rao Fu: Writing - review & edit-ing, Data curation. Baopeng Song: Writing - review & editing. Zhao Wang: Writing - review & editing, Formal analysis, Data curation. Bing Pan: Writing - review & editing, Methodology, Data curation. Zhifei Zhang: Writing - review & editing, Supervision, Resources, Funding acquisition, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing finan-cial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was financially supported by the National Key Research and Development Program of China (Grant No. 2023YFF0803600) and National Natural Science Foundation of China (Grant Nos. 42302009, 42072003, and W2441016). HYZ thanks the Shaanxi Province postdoctoral research project and China Scholarship Council (202306970031). We also thank the Department of Science and Technology of Shaanxi Province (2022TD-11). TPT also acknowledges the Swedish Research Council (VR2017-05183 and VR2021-04295). This is also a contribution to the project of Theory of Hydrocarbon Enrichment under Multi-Spheric Interactions of the Earth (THEMSIE04010106). We extend our appreciation to the editor Prof. Damian Nance, Dr. Sarah Jac-quet and two anonymous reviewers for their help, constructive suggestions that improved the manuscript greatly. We are also very grateful to Dr. Chen Yanlong, Ms. Zhai Juanping and Ms. Zhang Qian for their kind help and assistance in laboratory and fieldwork.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.gsf.2025.102108.

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