中国科学院南京地质古生物研究所机构知识库

埃迪卡拉纪是地球第二次大规模成磷时期,全球各大陆均有这次成磷事件的记录。目前对于该时期成磷事件的形成尚未有广泛接受的地球化学模型解释。而磷酸盐的沉积受海水氧化还原条件的控制,因此通过该时期磷块岩沉积与海水氧化还原条件演变之间关系的研究可为全球大规模成磷事件的沉积地球化学模型建立提供验证。文章通过对扬子板块埃迪卡拉纪不同相区磷块岩中碳酸盐组分稀土元素分析,结果表明磷块岩形成时底层海水处于次氧化—接近氧化的不稳定状态,氧化还原界面沿浅海—大陆架呈现动态变化的特征,为磷块岩的大规模形成提供最佳沉积地球化学条件。合适的海水化学条件及丰富的磷质来源,大大增加了磷块岩沉积的空间和机会,导致了地质历史时期第二次全球规模成磷发生。

Large accumulations of phosphorite in the Ediacaran worldwide witnessed the second phosphogenic event in the Earth history. However, there is no generally acknowledged geochemical model for this event so far. Given that precipitation of phosphate is controlled by seawater redox conditions, explore the cause-and-effect relationship between the phosphorite deposits and seawater chemistry is critical to testify the model of sedimentary geochemistry. This can help to understand the large scale phosphorite deposits worldwide across this transitional time interval. In this study, the REE+Y data of phosphorite-associated carbonates from different facies demonstrate that the Doushantuo phosphorites were deposited in suboxic conditions with intermittent oxidization. The redox condition of the Ediacaran seawater was unstable and the redox boundary dynamically fluctuated from shallow to deep water conditions.This greatly increased the space and opportunity for the deposition of phosphorite, leading to the great phosphogenic event during the Ediacaran-Cambrian transition.