Collaborative Research: Assessing the Sensitivity of High-altitude Environments to Global Increased Temperature as Recorded by Lacustrine Microbialite Carbonates

该项目将重建约7000万至5000万年前全球暖期的高海拔环境。尽管现代高海拔地区似乎对气候的快速变化高度敏感，但研究人员对过去全球气温升高时期的高海拔地区知之甚少。我们的研究重点是羊口组，它被解释为沉积在一个高海拔的淡水湖泊系统中。该项目最初将更好地估计羊口组的年龄，这一点很重要，因为在该地区很少有地层记录能捕捉到这个时间间隔。对羊山口形成年代的更好估计可能有助于开发古近纪期间快速气候变化的新记录，古近纪是地球历史上最温暖的时期之一，以许多快速、短期的变暖事件为标志，这些事件被称为超热事件。我们还希望改进对岩石形成时该地区海拔高度的估计。最后，这个项目将提供关于这些岩石如何在今天的湖泊中形成以及在形成后如何改变的新信息，这将改进研究人员如何从其他类似的岩石中解释古代气候。这个项目是及时的，符合国家利益，因为我们需要更好地了解美国西部，其中大部分是高海拔地区，将如何应对未来的环境变化。例如，这个项目可以帮助我们更好地了解美国西部供水面临的威胁，以及估计这些地区相对于全球估计的温度变化程度的潜力。此外，羊关组含有一些石油。这个项目将更好地了解这些岩石形成后的历史，这将为我们提供更多关于可能允许石油迁移到岩石中的变化的信息，让我们更深入地了解类似类型岩石中的潜在石油资源。大多数现代高海拔地区的变暖速度比相似纬度的低海拔地区快，这反过来影响了这些地区的水资源和生态系统。然而，导致气温升高的机制尚不清楚。积雪反照率反馈通常被认为是造成这种效应的主要因素，但这种机制不适用于过去在两极或高海拔地区几乎没有冰的“温室”时期，例如白垩纪和古近纪。对温室气候下高海拔地区的研究可以帮助我们了解其对全球变暖气候的敏感性，并有助于阐明驱动这一现象的基本机制。此外，山间盆地产生了迄今为止大多数温室气候和热活动的陆地记录（如古新世-始新世热最大值- petm）。因此，更好地了解这些地区对变暖的反应将改善陆地古气候记录与海洋记录的比较，并有助于解决它们之间差异的来源。本项目以内华达州中部晚白垩世-中始新世羊口组（SPF）为研究对象，该组沉积时高度至少为2 km。SPF保存了适合稳定同位素分析的厚层湖相微生物岩碳酸盐序列，SPF的年龄表明它可能保存了K-Pg边界、PETM和其他早始新世的快速变暖事件。然而，由于年龄限制有限，因此我们正在利用磁地层学和方解石U/Pb年代学来改进年代地层格架。此外，我们还描述了微生物岩沉积学特征，并生成了一套全面的传统和“块状”稳定同位素值，分辨率高于0.5微米。为了更好地了解微生物在湖相碳酸盐沉淀和蚀变中的作用，我们在北美的三个碱性湖泊中采样了现代微生物岩，这些湖泊跨越了不同的环境和气候。我们正在开发沉积物和孔隙水的传统和块状同位素数据集；详细的沉积微相描述；湖泊水和孔隙水碳酸盐化学数据集；地表和浅层亚地表微生物群落16S rRNA基因扩增子测序。我们将把这些数据集结合到湖泊微生物岩的解释框架中，我们将应用于SPF来评估高海拔环境对全球变暖条件的反应。该项目通过对本科生、研究生和一名博士后研究员的培训和指导，促进对科学的发现和理解。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。

This project will reconstruct a high elevation environment during the globally warm period between ~70 and 50 million years ago. Researchers have little information about high elevation sites during past periods of increased global temperature, although modern high elevation settings appear to be highly sensitive to rapid changes in climate. We are focusing our research on the Sheep Pass Formation, which is interpreted to have been deposited in a high elevation, fresh water lake system. The project will initially provide a better estimate of the age of the Sheep Pass Formation, which is important since there are few stratigraphic records that capture this time interval in this region. A better estimate of the age of the Sheep Pass Formation may enable development of new records of rapid climate change during the Paleogene, which was one of the warmest times in Earth's history and was marked by numerous rapid, short-term warming events known as hyperthermals. We also expect to improve estimates of the elevation of this region at the time of creation of the rocks. Finally, this project will provide new information about how these rocks form in lakes today and are altered after creation, which will improve how researchers interpret ancient climate from other rocks like these. This project is timely and serves the national interest because we need to better understand how the western US, much of which is at higher elevations, will respond to future environmental change. For example, this project may help us better understand threats to the water supply in the western US, as well as potential for estimating how much temperatures may change in these regions relative to global estimates. In addition, the Sheep Pass Formation contains some oil. This project will produce better understanding of the history of these rocks after they were created, which will give us more information on the changes that may have allowed oil to migrate into the rocks, giving us more insight into potential oil resources in similar types of rocks.Most modern high elevation regions are warming faster than lower elevation regions at similar latitudes, which in turn affects water resources and ecosystems in those regions. However, the mechanisms driving this increase in temperature are unclear. The snow-albedo feedback is often invoked as a major contribution to this effect, but this mechanism would not apply during 'greenhouse' times in the past with little to no ice at the poles or high elevations, such as the Cretaceous and Paleogene. Study of high elevation regions during greenhouse climates may provide insight into their sensitivity to globally warm climate, and help elucidate the fundamental mechanism(s) driving the phenomenon. Additionally, intermontane basins have yielded most of the existing terrestrial records of greenhouse climate and hyperthermals to-date (e.g. the Paleocene-Eocene Thermal Maximum-PETM). Thus, better knowledge of how these regions respond to warming will improve comparisons of terrestrial paleoclimate records to marine records and help resolve sources of discrepancy between them. This project focuses on the Late Cretaceous-middle Eocene Sheep Pass Formation (SPF) in central Nevada, which was at least 2 km high at the time of deposition. The SPF preserves a thick succession of lacustrine microbialite carbonate suitable for stable isotope analysis, and the age of the SPF suggests that it may preserve the K-Pg boundary, the PETM, and other Early Eocene rapid warming events. However, age constraint is limited, so we are using magnetostratigraphy and calcite U/Pb geochronology to improve the chronostratigraphic framework. In addition, we are characterizing the microbialite sedimentology and generating a comprehensive suite of traditional and 'clumped' stable isotope values at better than 0.5 m.y resolution. To better understand the role of microbes in lacustrine carbonate precipitation and alteration, we are sampling modern microbialites in three alkaline lakes in North America that span diverse environments and climates. We are developing traditional and clumped isotope datasets of sediments and porewaters; detailed sediment microfacies descriptions; lake water and porewater carbonate chemistry datasets; and 16S rRNA gene amplicon sequencing of surface and shallow subsurface microbial communities. We will combine these datasets into an interpretive framework for lacustrine microbialites that we will apply to the SPF to assess how high elevation environments responded to globally warm conditions. This project is advancing discovery and understanding of science through the training and mentoring of undergraduate and graduate students and a postdoctoral researcher.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.