华南伊迪卡拉纪宏体生物群的古地理分布及意义

Palaeogeography and palaeoecology of the Ediacaran(Sinian) macrofossil biota in South China

伊迪卡拉纪(635—542,Ma)是前寒武纪全球大规模末次冰期(Marinoan)结束后至寒武纪"生命大爆发"之前一段重要的地质时期,由于受到新元古代气候和环境剧变的影响,真核生物乃至多细胞生物迅速演化、分异,出现显著的适应辐射。中国华南的伊迪卡拉系——震旦系陡山沱组和灯影组及其相当地层代表着这一特殊地史时段的沉积,地层记录完整,岩相环境多样,化石产出丰富,是深入研究伊迪卡拉(震旦)纪(Ediacaran/Sinian)地层划分及全球对比、探讨早期多细胞生物起源和辐射的理想地区之一。其中,扬子台地边缘相地层中出露丰富的宏体化石材料,分异显著,具有较为独特的组合面貌。近年取得的研究成果表明华南宏体化石群中也含有澳洲伊迪卡拉生物群和俄罗斯白海生物群的典型分子。作者总结了前人关于华南伊迪卡拉纪岩相古地理的研究成果;重点展示了近年来开始研究的贵州江口"翁会生物群"、云南"江川生物群"的宏体化石;简要记述了华南伊迪卡拉系中以"庙河生物群"为代表的若干宏体生物群的古地理位置及其宏体化石组合特征,据此提出了华南伊迪卡拉纪丰富多样的宏体生物群基本发育在扬子台地边缘碎屑岩至碳酸盐岩相的过渡带和斜坡带;各生物群宏体化石的组合面貌受沉积微相的制约,存在一定的变化规律。宏体化石记录表明在这一时期,伴随着显著的气候和环境变化,不仅发生了一系列重要的生物演化事件,比如:多细胞藻类和后生动物普遍开始出现多样化发展,为寒武纪生命的演化辐射奠定了生态基础;而且在华南地区已经形成了一个全新的浅海生态系统,以浮游和底栖真核藻类为主的海洋初级生产者大量繁盛,尤其是丰富的多细胞藻类可能成为前寒武纪末期至寒武纪早期主要的生烃植物类群。

Ediacaran （635 -542 Ma） is the important geological period between the last global glaciation （Marinoan） and the Cambrian ＂explosion of life＂. As a result of the tremendous changes of Neoproterozoic climate and environment, rapid evolution and diversity of many eukaryotic lives, including multicellular organisms arise to adapt significant radiation. The Sinian Doushantuo and Dengying Formations in South China and their coeval strata represent the deposition of this special geological time. The complete stratigraphic record, diverse depositional environments and abundant micro- and macrofossils make South China to be one of the ideal areas for further studies on the Ediacaran （Sinian） stratigraphic division and global correlation, and to explore the early origin and radiation of multieellular organisms of the areas of radiation. In particular, the more abundant macrofossils occurring in the Ediacaran （Sinian） strata in the Yangtze platform marginal facies, contain the more distinct assemblages with significant diversity. The recent researches indicate that the Sinian maerofossil assemblages in South China also include a couple of typical fossils of the Ediacaran Biota in Australia and the White Sea biota in Russian. We synthesize in this paper the previous researches in recent years on the Sinian lithofacies and Palaeogeography in South China; mainly displays some newly collections of the ＂Wenghui Biota＂ from Jiangkou, Guizhou and the ＂Jiangchuan Biota＂ from Jiangchuan, Yunnan; briefly describe the palaeogeographic locations and several Sinian macrofossil assemblages including ＂Miaohe Biota＂. And hereby we conclude that a variety of Sinian macrofossil assemblages in South China were living and buried in the transitional/slope zone of carbonate rocks and clastic rocks at the margin of the Yangtze platform, the characteristics of each macrofossil assemblage were constrained by its sedimentary microfacies and went on changes regularly. The macrofossil records suggest that in this period, accompanied by significant climatic and environmental changes, a series of important evolution events took place, many macroalgae and metazoan generally appeared a diverse developments and laid an ecological foundation for the huge Cambrian radiation of early animal; and in the southern China, a brand new neritic ecosystem had been formed, the dominant planktonic and benthic eukaryotic algae were very prosperous to be the marine primary producers, especially the abundant multicellular macroscopic algae might be main plants of hydrocarbon generation in the transitional period of Precambrian-Cambrian.