Collaborative Research: Tracking Middle-late Paleozoic Global-ocean Redox Conditions Using U Isotopes in Marine Carbonates

合作研究：利用海洋碳酸盐中的U同位素追踪中晚古生代全球海洋氧化还原条件

基本信息

批准号：
1733641
负责人：
Jennifer Morford
金额：
$ 10.26万
依托单位：
Franklin and Marshall College
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-09-01 至 2023-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1733641&HistoricalAwards=false
关键词：
Collaborative Research Tracking Middle late

项目摘要

The goal of the funded proposal is to determine the relative amounts of oxygen dissolved in ancient oceans during a unique geologic time interval (300 to 420 million years ago) when three major mass extinctions occurred and the Earth was significantly warmer than today. Understanding the history of oxygen levels in ancient oceans is important because oxygen concentrations influence all marine animal life, control the formation and preservation of petroleum and many economic mineral deposits, and affect important biochemical reactions in the oceans and atmosphere. This project utilizes the relatively new geochemical tool of uranium isotopes to develop the most detailed history of changing ocean oxygen concentrations to date. The funding supports the training of the next generation of Earth scientists, will provide hands-on field and laboratory experience for first-generation college students, and will support multiple primary school science teachers to conduct real-world science to gain confidence and provide new ideas for their own classrooms. The project goal is to develop a global-ocean redox curve using U isotopes from Devonian-Mississippian marine carbonates. The ~100 million year study interval, which bridges the transition between poorly oxygenated Precambrian-Early Paleozoic oceans and well-oxygenated Late Paleozoic-Recent oceans, is important because of: 1) a doubling of atmospheric pO2 levels, 2) a transition from greenhouse to icehouse climate and intensifying ocean circulation, 3) the occurrence of three mass extinctions, two of which are attributed to marine anoxia, and 4) multiple large positive &#61540;13C excursions. The U-isotope composition of marine carbonates has the potential to record mean global-ocean redox conditions owing to the long residence time (~500 thousand years) of U in seawater. Samples will be collected from biostratigraphically well-dated successions in Nevada and Utah at spacings ranging from ~100 thousand years/sample to 20 thousand years/sample through specific event intervals. To assess samples for local redox influences, we will analyze redox-sensitive metals, Fe-speciation, and Corg:P ratios. To verify the global nature of the composite curve, we will sample and compare to selected shorter stratigraphic intervals on other continents.

资助的提案的目的是确定在独特的地质时间间隔（300至4.2亿年前）中溶解在古老海洋中的氧相对量（当时发生了三个主要的批量灭绝），并且地球比今天更加温暖。了解古老海洋中氧气水平的历史很重要，因为氧气浓度会影响所有海洋动物生命，控制石油和许多经济矿物质的形成和保存，并影响海洋和大气中的重要生化反应。该项目利用铀同位素的相对较新的地球化学工具来开发迄今为止改变海洋氧气浓度的最详细历史。这笔资金支持对下一代地球科学家的培训，将为第一代大学生提供动手实践和实验室经验，并将支持多位小学科学教师进行现实科学以获得信心并提供新的想法为他们自己的教室。项目目标是使用来自泥盆纪密西西比州海洋碳酸盐的U同位素来开发全球 - 海洋氧化还原曲线。约1亿年的研究间隔桥接了氧化不良的前寒武纪 - 古生代海洋与氧化良好的晚期古生代焦点海洋之间的过渡很重要，因为：1）大气PO2级别的两倍，2） 3）出现三种大规模灭绝的海洋循环，其中两种归因于海洋缺氧，而4）多个大型正面＆＃61540; 13c偏移。海洋碳酸盐的U-同位素组成有可能记录由于海水中U的长期停留时间（约50万年），因此有可能记录平均的全球氧化还原条件。通过特定的事件间隔，将从内华达州和犹他州的生物地层学良好的继任和犹他州的距离收集样本，从约1万年/样本到20千年/样品。为了评估局部氧化还原影响的样品，我们将分析对氧化还原敏感的金属，Fe-Speciation和CORG：P比率。为了验证复合曲线的全球性质，我们将采样并与其他大陆上选定的较短地层间隔进行比较。