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)是地球历史上一个环境和生物不稳定的时期，其特点是与反复发生的海洋变化有关的许多大规模灭绝事件。这一资助项目的目标是确定与志留纪最严重的大灭绝有关的海洋和环境变化的机制。该项目将利用新开发和成熟的地球化学方法，详细记录这段时间内海洋中氧气水平的历史。重要的是要了解古代海洋中氧浓度的历史，因为氧水平的变化影响海洋生物、海洋和大气中的关键生物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，支持对地球科学中代表性不足群体的培训，并支持一名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。该项目将针对三个研究目标：建立高分辨率的硫和碳同位素分析，以及一套氧化还原替代物(铁形态、痕量金属浓度、铊同位素、I/Ca比值)，以及对三个不同古大陆上的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这次志留纪晚期大灭绝事件和相关的大的正13C漂移的原因有关的现有假说。其次，新的高分辨率沉积地球化学数据将通过数字地层学方法(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升降记录之间可能存在的因果联系。第三，地球化学模拟将被用来进一步评估关于晚志留纪期间局部环境变化、生物灭绝和恢复以及全球海洋氧化还原条件波动之间的联系的假设。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.