放射虫起源、早期演化及其环境背景研究

Radiolarians were frequently recovered from the early Cambrian strata recently and the structures of their tests are complex, which indicate the possibility that radiolarian had gone through a long evolutional process before the Cambrian. They are important parts in the explorations of the “Cambrian explosion” in deep-water ecosystem and the deep-root of the eukaryote to research on seeking the ancestor of radiolarian and to investigate the origin and early evolution of radiolarian. In this project, the radiolarian fossils will been researched widely and the paleo-environments will been analysed in high-resolution in the Ediacaran-early Cambrian strata composed by dark siliceous-mudstone rocks and calcareous-mudstone rocks in the Guizhou-Hunan-Guangxi area ( southren marginal of Yangtze block), West Zhejiang-South Anhui area (southeastern marginal of Yangtze block), and South Shanxi-West Hubei area (northern marginal of Yangtze block). The aim of this research are: 1) exploring the origin of the radiolarian, the formation and evolution of its siliceous skeleton, and the early evolution and radialization of different radiolarian groups; 2) inquisition on the biotic assemble of the deep-water face, reconstraction of the deepwater ecosystem, and calculation on primary productivity by the of micro fossils and geochemcial data, which help us to understand the food chain and nutrition level in the marine during the “Cambrian explosion”; 3) investigation on the evolution of the siliceous organisms and the process of silica cycle for knowing the relationship between the paleo-environment and the orginal and evolution of radiolarian in the view of geobiology. The results from the proposal project will be a contribution to understanding of “Cambrian explosion” and to building the evolution tree of the eukaryote.

近年来国内外研究表明，寒武纪早期地层中放射虫化石已经比较常见，其壳体结构较分化，指示可能存在更早期的演化过程。追索放射虫祖先，探索放射虫起源，研究放射虫早期演化，是深水生态系寒武纪大爆发研究和真核生物深根研究的重要组成部分。在扬子板块南缘黔湘桂相邻地区、东南缘的浙西-皖南地区和北缘的陕南-鄂西地区，选择埃迪卡拉纪和寒武纪早期暗色硅泥质、钙泥质岩系地层，开展系统的放射虫化石调查、深入的分类学研究、精细的古海洋环境分析。调查放射虫的起源、壳体结构的形成和演化，揭示放射虫各类群的早期演化和辐射规律；全面调查深水相古生物组合，恢复深海生态系结构，利用微体古生物和地球化学资料计算古生产力，阐述古生产力演变对寒武纪大爆发的作用；调查硅质骨骼生物兴衰演化规律，揭示硅循环过程，从地球生物学角度探讨放射虫起源和演化与古海洋环境的相互作用关系；为全面认识寒武纪大爆发和重建真核生物演化树提供放射虫古生物学依据.

追索放射虫祖先，探索放射虫起源，研究放射虫早期演化，是深水生态系寒武纪大爆发研究和真核生物深根研究的重要组成部分。本项目以地球生物学研究思路为指导，对华南地区埃迪卡拉系顶部-寒武系下部地层，开展了放射虫、海绵骨针古生物学和古海洋环境研究，主要研究成果如下：1）采用锆石U-Pb 年代学、碳同位素地层学、生物地层学的方法，对多条含放射虫化石的地层进行了年代地层学的综合研究，查明了埃迪卡拉系-寒武系的界线位置，弥补了深水相年代地层学研究的薄弱环节，为了厘定放射虫动物群地质时代提供了依据。2）在幸运阶和筇竹寺阶地层中，发现保存很好的放射虫化石，建立6属7种（含未定种），首次对寒武纪早期放射虫化石从表面形态到内部结构开展系统研究和描述，查明其分类位置，提出寒武纪幸运阶就出现了泡沫虫类放射虫，揭示了该放射虫动物群与奥陶纪放射虫之间的可能演化关系，这些研究成果在国内外均属首次报道。3）在多条剖面，发现丰富的海绵骨针化石，查明其地层分布和演化规律：在埃迪卡拉系顶部地层中仅发现形态简单的单轴形海绵骨针化石，其长度在150-400 µm之间，这些细小骨针组成海绵岩；从寒武系底向上，出现形态较复杂的十字形和三轴形海绵骨针化石，首次证实埃迪卡拉系顶部存在海绵骨针化石。4）对含放射虫剖面，进行了沉积学、沉积地球化学和古生态群落研究，查明古海洋环境演变阶段，分析了古环境变化对生物群演变的控制关系，以及生物群演化对环境的改造作用，从地球生物学角度探讨了放射虫起源和演化与古海洋环境的相互作用关系。发表研究论文22篇（其中SCI源刊论文17篇），会议论文16篇，培养博士研究生10人、硕士研究生14名。本项目研究成果为全面认识寒武纪大爆发提供了深水浮游生态系古生物学和地球生物学资料。