Developing a Record of Quaternary Climatic Oscillation for the Eastern Sahara through Analysis of Fossil-spring Tufas and Lacustrine Deposits, Western Desert, Egypt

这项资助发展了东撒哈拉第四纪的气候年代学，并通过对目前极度干旱的埃及西部沙漠的化石泉和湖泊沉积物的调查、测绘和分析，限制了撒哈拉湿相环境的条件。春天的碳酸盐，或称凝灰岩，可以通过铀系列和电子自旋共振技术测定年代，并直接记录北非降水增加的时间。通过凝灰岩、湖相碳酸盐、腹足壳文石等稳定同位素地球化学指标重建了这些湿润期的环境条件。利用湖泊沉积物调查和地球化学分析数据，建立了湖泊水化学演化的水文和同位素平衡模型。这些模式产生了洪积期湖泊生命周期内气候变化的定量估计。由此获得的数据被用来检验这样一种假设，即撒哈拉雨期比间冰期的极大期发生得更频繁，这是对基于轨道岁差和倾角的非洲季风波动的反应。建立一个精确、详细的东撒哈拉气候年表，可以与区域气候记录（地中海和大西洋核心，东非裂谷湖泊核心）进行详细的比较，这有助于将气候联系拼凑起来。u系列日期的预估精度还允许直接与轨道参数进行比较，以便测试基于日照的机制，以在北非产生降雨，或确定该区域的非轨道气候波动。该研究获得的气候历史还可以用来检验关于第四纪期间北非大陆在全球碳和甲烷收支中所起作用的假设。像撒哈拉沙漠这样大片地区的“绿化”，以及整个撒哈拉沙漠广泛湖泊的形成，将对气候系统产生重要的反馈。最后，更好地了解北非雨期的频率和强度将有助于重新评估撒哈拉在第四纪期间作为现代人类从非洲扩散的障碍的程度，这是人类起源研究中的一个重要问题。拟议工作的更广泛影响包括通过在达赫勒绿洲举办关于第四纪地质和地貌学实地技术的短期课程，促进与埃及科学家的合作与协作。这项工作构成了一个PI博士学位的基础。S女研究生。气候年表保存在基于网络的世界古气候学数据中心数据库中，允许广泛使用。在野外工作中收集的样品成为古环境重建课程的一部分。

This grant develops a climate chronology for the Quaternary of the Eastern Sahara and to constrain the conditions of humid-phase environments in the Sahara via survey, mapping, and analysis of fossil-spring and lacustrine deposits in the currently hyperarid Western Desert of Egypt. The spring carbonates, or tufas, are datable by Uranium-series and Electron Spin Resonance techniques, and directly record times of increased precipitation in North Africa. The environmental conditions of these humid phases are reconstructed via the stable-isotope geochemistry of tufas, lacustrine carbonates, and gastropod-shell aragonite, among other proxies. Data from survey and geochemical analyses of lacustrine sediments are used to build hydrologic- and isotopic- balance models of lacustrine hydrochemical evolution. These models generate quantitative estimates of climatic variability during the lifespan of the pluvial -phase lakes. Data thus obtained is used to test the hypothesis that Saharan pluvial phases have occurred more frequently than interglacial maxima, as a response to orbital precession- and obliquity-based fluctuations in the African Monsoon.The establishment of a precise, detailed climate chronology for the Eastern Sahara allows for detailed comparison with regional climate records (Mediterranean and Atlantic cores, East African Rift Valley lake cores), which aids in piecing together climate linkages. The projected precision of the U-series dates also permits direct comparison with orbital parameters, in order to test insolation-based mechanisms for generating rainfall in North Africa, or to identify non-orbital climatic fluctuations in the region. The climatic history obtained by the research could additionally be used to test hypotheses regarding the role of the North African landmass in global carbon and methane budgets over the course of the Quaternary. The 'greening' of such a substantial area as the Sahara, as well as the formation of extensive lakes throughout the Sahara would generate significant feedbacks to the climate system. Finally, a better understanding of the frequency and intensity of North African pluvial phases would allow for a re-evaluation of the extent to which the Sahara acted as a barrier to the dispersal of modern humans out of Africa during the Quaternary Period, an important concern in human origins research.Broader impacts of the proposed work include the fostering of cooperation and collaboration with Egyptian scientists through the hosting of a short course on field techniques in Quaternary geology and geomorphology in Dakhleh Oasis. This work forms the basis of a Ph. D. for one of the PI.s female graduate students. The climate chronology is deposited with the web-based World Data Center for Paleoclimatology database, allowing widespread use. Samples collected during field work become part of a course on paleoenvironmental reconstruction.