湖北峡东地区早寒武世黔东统水井沱生物群及其与古氧相协同演化研究

No consensus has been reached so far on the co-evolution between the metazoan-biotas and the palaeo-environment during the Cambrian Explosion, although lots of attentions were paid on this issue in the decades. The lower Cambrian Qiandongian successions of the Eastern Yangtze Gorges are generally complete and continuous. However, the explorations on the metazoan biotas of this work area are quite weaker compared to the same aspects in Yunnan and Guizhou Provinces. .The metazoan-biotas in Shuijingtuo Formation in Zigui County will be studied in this project. We have found abundant and relatively highly diversified metazoan-biotas in the study area in the previously work. Based on that, we plan to figure out their characters and replenish the Shuijingtuo biota. In addition, we attempt to conduct the comparisons among the Shuijingtuo biota and other famous biotas or faunas such as the Chengjiang Biota, Niutitang biota (including the lower Songlin fauna and upper Zunyi biota), Guanshan and Balang faunas. On the one hand, an integrated paleontology, sedimentology, geochemistry and pyrite morphology studies will be done. This proposal not only provides oceanic redox fluctuations, but also offers the co-evolution characters between the biota and paleo-oxygenation transitions in the early Cambrian of Three Gorges area, South China.

寒武纪大爆发过程中后生生物如何与环境协同演化长期以来一直是学者们尚未弄清的热点问题。峡东地区下寒武黔东统地层出露齐全且连续，对后生生物的研究却相对同期滇黔地区较为薄弱。本项目以峡东地区下寒武统水井沱组为研究对象，在申请者业已发现大量后生生物化石的基础上试图探讨生物群的组成特征、完善该时期水井沱生物群的面貌；并进一步与其他著名生物群如澄江生物群、牛蹄塘生物群（包括松林动物群和遵义生物群）、关山和耙榔动物群进行对比得出其时空分布规律。另一方面，通过古生物学、沉积学和地球化学、以及草莓状黄铁矿形态学方面的证据研究该地区早寒武世的古氧相变迁历史，从而探讨研究区古氧相与生物群的协同演化特征。

为了研究峡东地区水井沱生物群与古氧相的协同演化关系，项目组以峡东地区岩家河组、水井沱组及石牌组为研究对象，对一些代表化石如放射虫、海绵动物、腕足动物、刺细胞动物等多个门类进行鉴定并统计，并进行沉积学、地球化学分析和草莓状黄铁矿形态学研究，以识别该地区水井沱组生物群及古氧相的时空演化特征及其协同演化关系。获得的主要结果如下： . 1、在岩家河组中发现了目前为止最古老的疑似放射虫?Blastulospongia sp.和确切海绵骨针的化石记录。在水井沱组发现并建立了一些放射虫新属种，如Paraantygopora porosa gen. et sp. nov.、Paraantygopora parva gen. et sp. nov.、Tetrasphaera yichangensis sp. nov.等。在水井沱组也发现了大量形态各异的海绵骨针以及保存完整的海绵体化石。这些放射虫和海绵的出现和快速繁盛与同期海洋中的大规模硅事件可能有耦合关系。. 2、在岩家河组至石牌组发现了大量可能的刺细胞动物，共鉴定出四属九个种，包括Cambrorhytium gracilis sp. nov.，Cambrorhytium cf. C. major，Cambrorhytium minor；Sphenothallus songlingensis，Sphenothallus taijiangensis?，Sphenothallus kozaki，?Sphenothallus sp.；?Byronia sp.和?Mackenzia sp.。认识到从伊迪卡拉纪至寒武纪，此类锥管状刺细胞化石的形态演化以为个体变大以及广泛矿化为特征，可能与该时期氧含量升高以及捕食压力有关。. 3、在时间上，水井沱组以阶段性的缺氧程度波动为特征，顶部比下部环境有较大改善。水井沱组上部原位保存的底栖类动物多样性也比下部明显要高；在空间上，发现刺细胞和海绵动物在较深的台盆更繁盛，而腕足类在较浅外陆架更富集。从外陆架向台内盆地，峡东地区底层水氧含量有着非常明显的梯度。因此，底栖类生物的分布特征应当是受研究区甚至华南氧含量梯度的控制的。