新元古代与寒武纪之交,即伊迪卡拉纪—寒武纪过渡期,是地球历史上一个重大的地质突变期,出现了一系列地质环境变化事件和生物快速演化事件.云南东部位于扬子地区西南缘,在前寒武纪—寒武纪过渡期属于开放式浅水台地至台缘斜坡环境,是中国伊迪卡拉(震旦)系顶部与底寒武统基本连续沉积的典型地区,也曾是中国震旦系与寒武系界线层型候选剖面所在地.近年来,在此新发现了更为丰富的宏体藻类化石、遗迹化石和伊迪卡拉生物群的疑似后生动物化石等(江川生物群),以及大量以条带状Shaanxilithes为代表的宏体化石层.相关剖面自下而上从灯影组至磷矿沉积层(中谊村段)出露有连续的宏体化石记录,研究后可以细分伊迪卡拉系顶部灯影峡阶的化石带,并与底寒武统晋宁阶、梅树村阶对接,具有作为标准层型剖面的较大潜力,为伊迪卡拉纪末期年代地层单位的建阶分层、对比及确立层型剖面,以及与寒武纪最早期年代地层的界线划分提供了更为理想的标准.%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 impor-tant 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 envi-ronment from open platform to slope of shallow water, which preserved typical and continuous deposits of Upper Ediacaran to Cam-brian bottom, and also contained a candidate stratotype of China's Sinian and Cambrian boundary. In recent years, researchers discov-ered macrofossil algae, trace fossils and possible Ediacaran-type fossils with more sophisticated content ("Jiangchuan Biota") as well asnumerous 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 deposi-tion, and diverse macrofossil records (assemblage zones) can be used for the division of the Dengyingxian Stage of the Upper Edia-caran, 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.
展开▼
