Collaborative Research: Anatomy of a Greenhouse World: The Early Eocene of the Green River Basin, Wyoming

过去环境变化的地质记录为了解地球自然系统的行为提供了一个有启发性的机会。古湖泊中形成的沉积物在这方面特别有用，原因如下：它们对气候变化高度敏感；它们通常含有相对完整的地质档案，裂缝相对较少；它们可能被用来记录对人类有意义的时间尺度上发生的变化。美国西部的绿河组提供了一个特别有价值的记录，记录了最近一段时间的长期温室条件，大约发生在5000万至5300万年前的始新世时期。它以丰富的脊椎动物、昆虫和植物化石组合以及世界上最大的纯碱和油页岩商业矿床而闻名。该研究项目将通过研究河道如何变化、湖泊内沉积的类型以及古代土壤发育和化学的变化，重点研究这段时间内反复出现的快速变暖事件的证据。同样重要的是，这项研究将为这些重要的沉积物建立一个前所未有的精度和精度的时间尺度，基于湖中火山灰的新辐射测定日期，地球磁场变化的年代学，以及由地球自转和轨道的周期性振荡驱动的沉积模式。该提案的更广泛影响将包括为初中和高中学生开展当地2小时的实地考察，并通过使用便携式设备上的创新数据可视化技术得到加强。早始新世气候最佳期（EECO）是一个全球持续变暖的时期，其原因尚未完全确定。绿河组的湖泊沉积物保存了丰富的、以前未开发的记录，与海洋沉积物中的记录相补充，并提供了提高始新世早期时间尺度的精度和准确性的机会。这个项目是一个综合的，多学科的调查，集中在世界上最丰富和研究最好的古湖泊地层系统之一。该研究将调查三个主要问题：1。陆地变暖的时间与从海洋记录中推断出来的时间和地球轨道变化的预测模式相比如何？放射性同位素定年的最新进展可以用来直接测试变暖事件与地球轨道变化的关系，并校准大约5000万年前的太阳系动态引力模型。2. 在EECO期间，陆地上的温度、季节、水文循环和风化是如何演变的？一种假设是，相对于海洋，变暖在大陆上被放大了，并且伴随着全年更均匀的温度，而降水的季节性和强度则增加了。3. 北美西部复杂的构造和岩浆演化如何影响EECO气候信号的保存？该研究将验证构造活动高地内重复的、逐步的排水重组改变了始新世湖泊环境的水文平衡和沉积沉积及其对轨道变化的响应的假设。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 geologic record of past environmental change offers an illuminating glimpse into the behavior of Earth's natural systems. The deposits formed in ancient lakes are particularly useful in this regard for several reasons: they are highly sensitive to climate change; they often contain relatively complete geologic archives with relatively few gaps; and they can potentially be used to document changes that occurred over time scales meaningful to humans. The Green River Formation in the western U.S. offers an especially valuable record of the most geologically recent period of prolonged greenhouse conditions, which occurred approximately 50-53 million years ago during the Eocene Epoch. It is famous for its rich assemblages of fossil vertebrates, insects, and plants, and for containing the world's largest commercial deposits of soda ash and oil shale. This research project will focus on evidence for repeated rapid warming events during this time, by examining how river courses changed, the types of sediment that accumulated within the lake, and variations in ancient soil development and chemistry. Equally important, this study will build a time scale of unprecedented accuracy and precision for these important deposits, based on new radiometric dates of volcanic ash in the lake, the chronology of changes in the Earth's magnetic field, and sedimentation patterns that were driven by periodic oscillations in the Earth's rotation and orbit. Broader impacts of this proposal will include development of local 2-hour field trips for middle and high school students, enhanced through the use of innovative data visualization technology on portable devices. The Early Eocene Climatic Optimum (EECO) was a time of persistent global warmth, of which the cause remains incompletely determined. Lake deposits of the Green River Formation preserve a rich and previously untapped record that complements that contained in marine sediments, and present an opportunity to advance the precision and accuracy of the Early Eocene timescale. This project is an integrated, multidisciplinary investigation focused on one of the world's richest and best studied systems of ancient lake strata. The research will investigate three principal questions: 1. How did the timing of terrestrial warming compare to that inferred from the marine record, and to predicted patterns of the Earth's orbital variations? Recent advances in radioisotopic dating can be used to directly test the relationship of warming events to Earth's orbital changes, and calibrate dynamic gravitational models of the solar system back to ca. 50 million years. 2. How did temperatures, seasonality, hydrologic cycling, and weathering on land evolve during the EECO? One hypothesis is that warming was amplified on continents relative to the oceans and was accompanied by more equable temperatures year-round, whereas precipitation seasonality and intensity increased. 3. How did the complex tectonic and magmatic evolution of western North America impact the preservation of EECO climate signals? The research will test the hypothesis that repeated, stepwise drainage reorganizations within the tectonically-active uplands modified the hydrologic balance and sedimentary deposits of the Eocene lake environment and its response to orbital changes.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.