华南埃迪卡拉纪-早寒武世成磷过程记录的海洋环境

During Ediacaran-Early Cambrian transition period, the occurrence of large scale phosphorite deposits in the worldwide is on behalf of the first global largest scale phosphogenesis in geological history. In South China, Ediacaran-Early Cambrian phosphogenesis was well preserved in Yangtze platform. The period phosphogenesis created major phosphate resource in China. At the same time, the occurrence of these phosphorite deposits in South China is coincided with the muti-cellular organism radiation and appearance of metazoan, and oxygenation of ocean and atmosphere, in the term of time. Previous studies suggested that these pristine phosphorites can record the primary changes in the marine environment, such as productivity, temperature and redox condition, and so on. However, the primary marine environmental information recorded in these pristine phosphorites has not been accurately estimated. Recently, Zn, Fe isotopes and oxygen isotope of phosphate would provide new idea to solve this issue. To trace the primary productivity, temperature and redox condition of seawater, Zn, Fe isotopes and oxygen isotope of phosphate of the major phosphorites during Ediacaran-Early Cambrian transition from South China, will be measured in this project. Then the relationship among the primary productivity, temperature and redox condition will be estimated. Finally, the causal relation between the changes in marine environment and phosphogenesis during Ediacaran-Early Cambrian transition will be discussed in detail.

埃迪卡拉纪-早寒武世过渡时期，世界范围内大型磷矿床的广泛出现代表了地质历史时期第一次全球性最大规模的成磷事件。华南扬子地台完整记录了埃迪卡拉纪-早寒武世的成磷事件，这一时期的成磷作用造就了我国主要的磷矿资源。同时，这些磷矿床在时间上与多细胞生物演化和大气-海洋氧化事件相对应，因此原生沉积的磷块岩记录了重要的海洋环境信息（如生物产率、温度、氧化还原环境等），然而这些重要的海洋信息一直没有被准确地评价。锌、铁同位素和磷酸盐氧同位素的发展将为解决这个问题提供新的思路。本项目将以华南埃迪卡拉纪-早寒武世原生沉积磷矿床为研究对象，利用原生沉积磷块岩的锌、铁同位素和磷酸盐氧同位素示踪成磷过程海洋生物产率变化，恢复海水温度，反演海洋氧化还原环境，揭示生物活动、海水温度和氧化还原环境之间的内在联系，综合评价成磷过程记录的海洋环境，并探讨海洋环境变化与大规模成磷作用的因果关系。

埃迪卡拉纪-早寒武世过渡时期，世界范围内大型磷矿床的出现代表了地质历史时期第一次全球性最大规模的成磷事件。华南扬子地台完整记录了埃迪卡拉纪-早寒武世的成磷事件，这一时期的成磷作用造就了我国主要的磷矿资源。同时，这些磷矿床在时间上与多细胞生物演化和大气-海洋氧化事件相对应，因此原生沉积的磷块岩记录了重要的海洋环境信息（如生物产率、温度、氧化还原等），然而这些重要的海洋信息一直没有被准确地评价。为了更好的理解埃迪卡拉纪-寒武纪过成磷时期海洋生物产率、海水温度和氧化还原状态的变化，本项目完成了磷块岩及其他赋存地层样品的铁同位素组成、锌同位素组成和磷酸盐氧同位素组成的测试。不规律的铁同位素组成变化趋势显示，大规模的磷矿沉积可能与整体的海洋氧化环境有关，而不均一的空隙水的氧化还原状态可能促使磷矿中稀土元素的富集。磷块岩呈现重的锌同位素组成，而深水页岩呈现轻的锌同位素，暗示磷块岩可能代表重锌同位素的重要储库之一。另外，生物活动对锌和磷的控制作用在寒武纪早期更为明显。磷酸盐氧同位素组成的系统变化，指示从陡山沱组到寒武纪早期南华盆地的水温一致升高，可能与华南陆块的古纬度变化及海洋有机质埋藏减少密切相关。