华北中元古代氮同位素组成的时空变化及其对真核生物和海洋水化学演化的启示

Early Mesoproterozoic (>1300 Ma) was a stasis in the evolutionary history of eukaryotic diversity. It has been supposed that crisis in nitrogen cycle due to deficient in trace metal in the Mesoproterozoic sulfidic ocean would be a possible mechanism. However, it is unclear about the characters of the Mesoproterozoic nitrogen cycle up to date, which will be the target of this project. On the basis of well preserved and low metamorphosed Mesoproterozoic strata in North China, this project will analyze the spatial-temporal variation pattern of nitrogen isotopic composition of different nitrogen fraction including bulk nitrogen, kerogen nitrogen and nitrogen trapped in clay minerals, oceanic geochemistry (mainly trace metal composition) and redox condition from the Chuanlinggou Formation (about 1650 Ma) to the Xiamaling Formation (about 1350 Ma). Based on these data, this project will analyze the spatial variation pattern of nitrogen cycle and temporal evolution of nitrogen cycle in the early Mesoproterozoic, unravel the variation pattern of some important steps in nitrogen cycle, such as nitrogen fication, denitrification, anaerobic ammonia oxidation and nitrogen assimilation and their relationship to the oceanic geochemistry and redox condition. Finally, this project will try to answer the question that how did the crisis in nitrogen cycle affect the biological evolution.

中元古代早期（>1300 Ma)是真核生物演化史上的一个停滞期。有学者认为海洋中微量元素匮乏所引起的氮循环异常可能是中元古代早期真核生物演化缓慢的主要原因。然而目前对中元古代氮循环的认识还非常不足，这是本项目拟解决的重大问题。为此，本项目将以我国华北地区出露良好、变质程度较低的中元古代早期地层为研究对象，重点分析从常州沟组到下马岭组（时间跨度约300 Ma）不同沉积环境和不同组分氮（全岩、干酪根和粘土矿物）的氮同位素组成的时空变化特征，古海洋水化学和氧化还原状况，分析这一时期氮循环的空间分布和时间演化特征，查明氮循环过程主要环节（固氮作用、反硝化作用、氨的厌氧氧化作用和氮的同化作用）的变化特征及其与古海水化学和氧化还原环境之间的关系，重点探讨这一时期氮循环的变化特征与生物演化之间的关系。