Collaborative Research: ACACIA: Ancient Climate and the Authigenic Clay Index of Aridity

技术摘要：Acacia解决了第四纪地质学、古气候学和湖泊地质学面临的几个关键问题。该项目的假设包括：1)湖泊沉积物的全岩地球化学受自生粘土的组成和丰度的影响；2)东非湖泊流域干旱的开始反映为八面体镁含量和氧同位素组成的富集度；3)八面体铝丰度反映了与干旱阶段结束有关的淡水分水岭冲刷；以及4)环境波动反映了当时被认为占主导地位的进动(Olduvai)和偏心(Olorgesailie)轨道影响。Acacia将从Olduvai(坦桑尼亚)和Olorgesailie(肯尼亚)盆地的具有良好特征的地层剖面中采样和分析亚微米自生粘土矿物和相关材料。为了开展这项工作，我们将与领先的国际现场团队合作--Olduvai Gorge的Proyecto Olduvai(由马德里大学领导)和Olorgesailie的Olorgesailie钻井项目(由Smithsonian Institution和肯尼亚国家博物馆领导)。Acacia调动了一支在东非拥有丰富现场经验的团队，并拥有沉积学、X射线衍射和荧光、高分辨率透射电子显微镜和硅酸盐稳定同位素地球化学方面的分析专业知识。这些努力将提高我们对全球气候系统、热带环境对全球气候变化的反应、脊椎动物和无脊椎动物生态系统结构的变化以及人类谱系进化的理解。Acacia将支持本科生研究，加强国际合作，并与坦桑尼亚Olduvai Gorge附近地区唯一的一所小学合作，为1000多名坦桑尼亚K-8学生提供教育推广和支持。非技术摘要：Acacia将利用现代分析方法来研究湖泊沉积物如何记录过去的环境变化。尽管科学家之前曾使用工具重建过去的环境变化，如研究化石花粉或浮游生物，但许多湖泊的沉积物堆积不包含任何化石或其他材料来重建古代环境。对于这些情况，Acacia将开展粘土矿物的研究，其中许多粘土矿物直接从湖水中化学沉淀出来。我们将从坦桑尼亚的奥杜瓦伊峡谷和肯尼亚的奥洛格塞利盆地的露头和岩心中取样，这些地方有很久的火山灰，所以我们知道年代。我们将从这些湖泊沉积物样本中分离出小于千分之一毫米的颗粒，分析它们的化学成分，并使用电子显微镜拍摄和分析它们。基于这些分析，我们将能够推断这些古老的湖泊何时含有淡水和咸水，这是东非气候何时潮湿和干旱的一个强有力的指标。结合东非环境变化的其他知识，这将为我们提供重要线索，了解热带环境如何响应全球气候变化，非洲生态系统在过去数百万年里如何变化，以及早期人类进化的环境如何随时间变化。这也将使我们深入了解微观粘土颗粒如何与湖水进行化学作用，这对世界各地的湖泊环境都很重要。Acacia将支持几名本科生和研究生，与加拿大、西班牙、坦桑尼亚和肯尼亚的机构建立国际合作，并向坦桑尼亚一所学生超过1000人、资源稀少的小学开展外联活动。

Technical Abstract:ACACIA addresses several key issues facing Quaternary geology, paleoclimatology, and limnogeology. The project hypotheses include 1) that whole-rock geochemistry of lake sediments is influenced by the composition and abundance of authigenic clays; 2) that the onset of aridity in East African lacustrine watersheds is reflected by enrichment in octahedral Mg content and oxygen isotopic compositions; 3) that octahedral Al enrichment reflects freshwater watershed flushing associated with the termination of arid phases; and 4) that environmental fluctuations reflect precession (Olduvai) and eccentricity (Olorgesailie) orbital influences thought to dominate at those times. ACACIA will sample and analyze sub-micrometer authigenic clay minerals and associated materials from well characterized stratigraphic sections in the Olduvai (Tanzania) and Olorgesailie (Kenya) Basins. To carry out this work we will partner with leading international field teams - Proyecto Olduvai at Olduvai Gorge (led by Universidad Complutense de Madrid), and the Olorgesailie Drilling Project at Olorgesailie (led by the Smithsonian Institution and the National Museums of Kenya). ACACIA mobilizes a team with extensive field experience in East Africa, along with analytical expertise in sedimentology, X-ray diffraction and fluorescence, high-resolution transmission electron microscopy, and silicate stable isotope geochemistry. These efforts will improve our understanding of the global climate system, tropical environmental responses to global climate change, changes in vertebrate and invertebrate ecosystem structure, and the evolution of the human lineage. ACACIA will support undergraduate research, enhance international collaborations, and partner with the only elementary school in the region near Olduvai Gorge, Tanzania, providing educational outreach and support to over 1000 Tanzanian K-8 students.Non-Technical Abstract:ACACIA will bring modern analytical approaches to bear on the question of how lake sediments record environmental changes in the past. Although scientists have previously used tools to reconstruct past environmental change such as the study of fossil pollen or plankton, many lakes have sediment accumulations that contain no fossils or other materials for reconstructing the ancient environment. For those cases in particular, ACACIA will develop the study of clay minerals, many of which chemically precipitate directly from lake water. We will sample from outcrops and cores in the Olduvai Gorge, Tanzania, and the Olorgesailie Basin, Kenya, which have well-dated volcanic ashes so we know the ages. From these lake sediment samples we will separate out particles that are smaller than 1/1000th of a millimeter, analyze their chemistry, and use electron microscopes to take pictures and analyze them. Based on those analyses, we will be able to infer when these ancient lakes contained fresh versus saline water, which is a strong indicator of when climate was humid versus arid in East Africa. Combined with other knowledge of environmental change in East Africa, this will give us important clues as to how tropical environments respond to global climate change, how African ecosystems have changed over the past few million years, and how the environments of early human evolution changed through time. This will also give us great insight into how microscopic clay particles interact chemically with lake water, which is important to the environments of lakes worldwide. ACACIA will support several undergraduate and graduate students, build international collaborations with Canadian, Spanish, Tanzanian, and Kenyan institutions, and conduct outreach to a Tanzanian elementary school with over 1000 students and few resources.