Discerning Mechanisms of Environmental and Climatic Changes Associated with the Late Silurian (Ludfordian) Extinction Event

志留纪（4.19亿至4.43亿年前）是地球历史上环境和生物不稳定的时期，其特征是与海洋变化有关的许多大规模灭绝事件。该资助项目的目标是确定与志留纪最严重的大规模灭绝相关的海洋学和环境变化的机制。该项目将利用新开发的和成熟的地球化学方法，详细研究这一时期海洋中氧含量的历史。了解古代海洋中氧浓度的历史很重要，因为氧含量的变化影响海洋生物、海洋和大气中的关键地球化学过程以及经济碳氢化合物和矿藏的形成和保存。该项目将为本科生和研究生提供有意义的实地和实验室经验，支持在地球科学中代表性不足的群体的培训，并支持高中科学教师进行前沿研究，这将为他们自己的课堂上的新活动提供动力。该项目将涉及三个研究目标：建立硫和碳的高分辨率同位素分析，沿着一套氧化还原代用指标（铁形态、微量金属浓度、铊同位素、I/Ca比值），以及通过三个独立古大陆上多个洋盆的晚志留世地层进行详细的沉积相分析。这将使研究小组能够直接测试与志留纪晚期大规模灭绝事件及其相关的大的正13 C漂移的原因有关的现有假设。其次，新的高分辨率沉积地球化学数据将通过数值地层学方法（CONOP）与已知的古生物记录相结合，以限制碳循环扰动，海洋灭绝事件和海平面变化记录之间可能的因果关系。第三，地球化学建模将被用于进一步评估有关当地环境变化，生物灭绝和恢复，以及在晚志留世期间海洋中波动的全球氧化还原条件之间联系的假设。该奖项反映了NSF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 Silurian (419 to 443 million years ago) was an environmentally and biologically volatile interval of Earth history, which was characterized by numerous mass extinction events that are linked to reoccurring oceanographic changes. The goal of this funded project is to determine the mechanisms responsible for oceanographic and environmental changes associated with the most severe mass extinction in the Silurian. This project will utilize both newly developed and well-established geochemical approaches to develop a detailed history of oxygen levels in the oceans during this time interval. It is important to understand the history of oxygen concentrations in ancient oceans because changes in oxygen levels impact marine life, critical biogeochemical processes in the oceans and atmosphere, and the formation and preservation of economic hydrocarbon and mineral deposits. The project will provide meaningful hands-on field and laboratory experiences for undergraduate and graduate students, support the training of underrepresented groups in the geosciences, and support a high school science teacher to conduct cutting-edge research, which will provide motivation for new activities in their own classrooms. The project will address three research objectives: construct high-resolution isotopic analyses of sulfur and carbon, along with a suite of redox proxies (Fe-speciation, trace metal concentrations, thallium isotopes, I/Ca ratios), and detailed sedimentary facies analyses through late Silurian strata from multiple ocean basins on three separate paleocontinents. This will allow the research team to directly test existing hypotheses related to the causes of this late Silurian mass extinction event and associated large positive 13C excursion. Second, new high-resolution sedimentary geochemical data will be integrated with known paleobiological records via numerical stratigraphic methods (CONOP) for constraining possible causative connections between carbon cycle perturbation, marine extinction event, and eustatic sea-level records. Third, geochemical modeling will be used to further evaluate hypotheses regarding the links of local environmental changes, biotic extinction and recovery, and fluctuating global redox conditions in the oceans during the late Silurian.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.