Collaborative Research: Calibrating the end-Ediacaran Extinction with U-Pb Geochronology & Chemostratigraphy at a New Precambrian-Cambrian Boundary Site in Namibia & South

在寒武纪（约5.4亿年前）初期，复杂的多细胞动物首次出现并迅速多样化，这无疑是地球生命进化过程中最重要的一段时期，因为它为今天存在的绝大多数生命形式奠定了最初的蓝图。了解寒武纪“大爆发”的驱动机制一直具有挑战性，因为在之前的埃迪卡拉纪占主导地位的生命形式只有很少的化石记录。此外，保存了埃迪卡拉纪-寒武纪过渡时期的海相沉积岩现在分散在大陆上，阻碍了在地质历史的这个关键节点上对生命和环境的明确重建。这项研究的重点是埃迪卡拉-寒武纪海相沉积物的关键露头，在纳米比亚-南非边境附近的一个以前未开发的地区，这些沉积物具有壮观的化石和高潜力的精确同位素定年。这些结果将为这一关键时期的古环境和海洋化学变化速率提供新的见解。除了公开演讲和学术出版物外，还计划了一个全面的教育、培训和推广活动计划。本项目采用野外测绘、沉积学、化学和生物地层学的综合方案，对纳米比亚和南非奥兰治河两岸新发现的富含碳酸盐和化石的埃迪卡拉-寒武纪海相剖面进行了研究，这些剖面具有丰富的适合U-Pb地质年代学的夹层火山灰层。它将提供高分辨率的记录，有助于揭示元古代末期生物和同期环境变化的模式和速度。这一结果将在验证全球同步的环境扰动与埃迪卡拉纪-寒武纪边界上的生物转换遗传相关的假设方面迈出重要一步，并将使人们更好地理解寒武纪辐射的驱动机制。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The first appearance and rapid diversification of complex, multicellular animals at the dawn of the Cambrian (~540 million years ago) is conceivably the single most significant episode in the evolution of life on Earth, as it laid out the initial blueprints for the vast majority of life forms that exist today. Understanding the driving mechanisms of the Cambrian 'explosion' have been challenging because life forms that dominated the preceding period, the Ediacaran, have a sparse fossil record. In addition, the marine sedimentary rocks that preserve the Ediacaran-Cambrian transition are now scattered across the continents, hampering an unequivocal reconstruction of life and the environment at this crucial junction of the geologic history. This study focuses on key outcrops of the Ediacaran-Cambrian marine deposits with spectacular fossils and high potential for precise isotopic dating in a previously unexplored region near the Namibia-South Africa border. The results will provide new insights into the rates of paleoenvironmental and ocean chemical change during this critical time interval. In addition to public presentations and scholarly publications, a comprehensive program of educational, training, and outreach activities are planned.This project employs an integrated program of field mapping, sedimentology, chemo- and bio-stratigraphy on newly discovered marine carbonate-rich and fossiliferous Ediacaran-Cambrian sections on either side of the Orange River in Namibia and South Africa with abundant intercalated ash beds suitable to U-Pb geochronology. It will provide a high-resolution record that will help to unravel the mode and rates of biotic and coeval environmental changes at the close of the Proterozoic. The results will be a major step forward in testing the hypothesis that there were globally synchronous environmental perturbations that were genetically associated with biotic turnover across the Ediacaran-Cambrian boundary, and will lead to a better understanding of the driving mechanisms of the Cambrian radiation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.