Macrofossil biotas in the Late Ediacaran-Cambrian boundary interval of South China and stratotype correlation

In the Ediacaran-Cambrian transition, there existed a major mutation in the geological history of the Earth, during which a series of geological and biological events occurred along with the environment changes and life evolution. New materials of important macrofossil biota from South China show that, across the boundary formations of Precambrian-Cambrian, there probably existed a hyperactive biological evolution characterized by a qualitative leap mainly from soft-bodied metazoans to shelled animals, and hence the research on the phylogenetic and stratigraphic correlation of the major groups has important significance. Eastern Yunnan is located on the southwestern margin of Yangtze region, and during the Precambrian-Cambrian transition period there was an environment from open platform to slope of shallow water, which preserved typical and continuous deposits of Upper Ediacaran to Cambrian bottom, and also contained a candidate stratotype of China’s Sinian and Cambrian boundary. In recent years, researchers discovered macrofossil algae, trace fossils and possible Ediacaran-type fossils with more sophisticated content (“Jiangchuan Biota”) as well as numerous long-striped macrofossil Shaanxilithes that occur beneath the bottom of phosphate layer of Early Cambrian. Relevant boundary sections from Dengying Formation to the bottom of phosphate sediments (Zhongyicun Member) reveal continuous deposition, and diverse macrofossil records (assemblage zones) can be used for the division of the Dengyingxian Stage of the Upper Ediacaran, and are associated with Jinningian Stage and Meishucunian Stage of the lowermost Cambrian by a potential standard stratotype section. The authors emphatically studied the standard sections and Meishucun stratotype in Jingning of eastern Yunnan where there occur macrofossil assemblages including Jiangchuan Biota, then made a comparative investigation of other neighboring supplementary sections and typical successions of Upper Ediacaran and Lower Cambrian phosphorite sediments containing early animal fossils with phosphate mineral shell in South China, and also conducted an in-depth study of biostratigraphy and evolutionary biology for the macrofossils and their assemblages so as to build the chronostratigraphic stage of Late Ediacaran, contrast and establish stratotype, and provide more desirable index macrofossils to define the worldwide boundary between Precambrian and Cambrian.