Global trends in nutrient dynamics during the Ediacaran / Cambiran period as revealed in nitrogen isotope signatures

埃迪卡拉纪和寒武纪记录了地球上非常重要的环境变化，人们认为这些变化与地球历史上最突出的生物辐射有关。向完全氧化的表层环境的转变发生在新元古代晚期，并被认为影响了氮循环，因为初级生产力中还原(NH4)或氧化(NO3)形式的氮的有效性不同。与这些变化相吻合的是广泛分布的富含磷矿和有机质的巨型沉积物(黑色页岩)，尤其是在中国。前一个项目的重点是创建~635 Ma至~500 Ma区间的详细的15N记录。它记录了早寒武世中国南部大部分研究剖面的强烈负氮同位素漂移。这次漂移可能与较老的小壳化石组合和后来的典型化石组合(包括三叶虫、软体动物、棘皮动物、海绵和其他“现代”类型化石)的转换有关。基于这些结果，该项目旨在详细研究中国南部三个暴露良好和有充分记录的埃迪卡拉纪至早寒武世剖面的页岩和其他沉积岩的氮同位素记录，并与其他地球化学子项目密切合作，以多代理的方式将其用作重建前寒武纪-寒武纪过渡期间生物地球化学和古环境变化的关键剖面。此外，使用来自哈萨克斯坦、西班牙和纳米比亚的来自哈萨克斯坦、西班牙和纳米比亚的中国西北塔里木区块的相同代用品的样品将被纳入这项研究，以进行全球生物地球化学对比，尽管分辨率较低。首先，西班牙剖面的结果表明，早寒武世存在与南中国剖面记录的氮同位素负漂移。我们还将与中国合作伙伴合作，分析碳酸盐存在的地区的有机和碳酸盐碳同位素组成。新数据将与现有记录相结合，与古生物学和地层学的结果相结合，以评估它们在印刷电路板全球辐射事件中的可能作用。

The Ediacaran and the Cambrian periods record remarkably important environmental changes on Earth which are believed to be relevant for the most prominent bioradiation in Earth's history. The transition to a fully oxygenated surface environment occurred during the late Neoproterozoic and is believed to have influenced the nitrogen cycle in terms of the variable availability of nitrogen in reduced (NH4) or oxidised (NO3) forms for primary productivity. Coincident with these variations was the widespread deposition of giant phosphorite- and organic-rich sediments (black shales), notably in China. The previous project has focused to create detailed 15N records of the ~635 to ~500 Ma interval. It documented a strong negative nitrogen isotopic excursion in most of the studied sections from South China during the earliest Cambrian. This excursion is probably linked to the switch between the older small shelly fossil assemblages and the later "typical" fossil association including trilobites, molluscs, echinoderms, sponges and other "modern" type fossils.Based on these results, the proposed project aims to study in detail the nitrogen isotope record of shales and other sedimentary rocks from three well-exposed and well-documented Ediacaran to Early Cambrian sections in South China, closely cooperating with the other geochemical subprojects in a multi-proxy approach so that they can be used as key sections for the reconstruction of biogeochemical and paleoenvlronmental changes during the Precambrian-Cambrian transition. Additionally, samples using the same proxies from the Tarim block of NW China, from Kazakhstan, Spain and Namibia will be integrated in this study for global biogeochemical correlation, albeit at a lower resolution. First results from the Spanish sections indicate the existence of a negative nitrogen isotope excursion during the early Cambrian comparable to that documented from the South China sections. We will also analyze, in cooperation with our Chinese partners, organic and carbonate carbon isotope composition where carbonates are present.The new data, in combination with the existing records, will be integrated with results from paleobiology and stratigraphy to assess their possible role in "feeding" the global radiation event at the PCB.