Deciphering climate information from authigenic mineral transformations in the Chew Bahir sediment cores: Towards a continuous half-million year climate record from the Southern Ethiopian Rift

周巴希尔钻探项目(CBDP)从埃塞俄比亚南部的周巴希尔盆地采集了重复的沉积物记录，以通过阐明关键时期的气候背景，检验目前关于解剖学上的现代人及其迁出非洲期间人与气候相互作用的假说。然而，由于气候参数和沉积物组成的复杂和特定地点的关系，从湖泊沉积物中破译古气候是具有挑战性的。确定和分析保存在整个核心的适当气候指标，对于建立关于气候变化的高分辨率、连续记录至关重要。这里提议的项目旨在破译Chew Burir沉积物岩心中自生矿物转化的古环境信息，以便提供有意义的数据，这些数据可能是从埃塞俄比亚南部裂谷获得可靠和连续的50万年气候记录的关键。在水文受限的环境中，如Chew Babir，自生粘土矿物和沸石的组成强烈地受到古湖水化学的控制，这对降水/蒸发比的波动做出了反应。在一项初步研究中，Chew Burir矿物组合，特别是丰富的粘土矿物，已被证明通过精细调整其晶体组成，对古盐度和碱度的变化做出敏感的反应。由于~290m长的复合岩心主要由高活性粘土组成，因此该物质有可能通过矿物学和地球化学分析提供连续的古水化学和古气候信息。这一潜在的数据集可能对项目的成功至关重要，因为其他一些替代物(例如花粉和硅藻)只能断断续续地保存。在项目的头两年，我们建议(1a)确定整个长岩心湿、干和极度干旱阶段的特征矿物组合；(1b)确定得出古水文数据所需的粘土矿物和沸石的自生蚀变的精确程度；(2a)将矿物学(X射线衍射学)与地球化学(µXRF)联系起来，以显示水文气候控制与Chew Burir代用矿物的形成和保存之间的联系；(2b)从先前定义的沉积条件和阈值破译从轨道到十年的气候变化；(3)评估不同类型的气候变化(持续时间、突发性、内部变异性和幅度)对早期人类栖息地和生活条件的影响。总之，拟议项目的结果将对理解复杂的气候替代物的形成作出重要贡献，使人们能够从周伯海尔沉积岩芯中破译连续的古气候信息，并提供可能对检验气候变化对人类进化和迁移性影响的假设至关重要的数据。

The Chew Bahir Drilling Project (CBDP) has cored duplicate sediment records from the Chew Bahir basin in southern Ethiopia to test current hypotheses on human-climate interaction during the development of anatomically modern humans and their migrations out of Africa by elucidating the climatic context of critical time periods. However, deciphering paleoclimate from lake sediments is challenging due to the complex and site-specific relationships of climate parameters and sediment composition. Determining and analysing suitable climate proxies that are preserved throughout the core is essential to establishing a high resolution, continuous record on climate change. The project proposed here aims to decipher paleoenvironmental information from authigenic mineral transformations in the Chew Bahir sediment cores in order to contribute meaningful data that could be key to developing a reliable and continuous half million-year climate record from the Southern Ethiopian Rift. In a hydrologically restricted setting, such as Chew Bahir, the composition of authigenic clay minerals and zeolites are strongly controlled by the hydrochemistry of the paleolake, which responds to fluctuations in the precipitation/evaporation ratio. In a pilot study, the Chew Bahir mineral assemblages, especially the abundant clay minerals, have been shown to react sensitively to variations in paleosalinity and alkalinity by finely adjusting their crystallographic composition. Since the ~290-m-long composite core is dominantly comprised of those highly reactive clays, the material has the potential to provide continuous paleohydrochemical and paleoclimatic information through mineralogical and geochemical analyses. This potential dataset could be critical to the success of the project as some other proxies (e.g. pollen and diatoms) are only preserved intermittently. In the first two years of the project, we propose to (1a) identify characteristic mineral assemblages for wet, dry and hyper-arid phases throughout the long core; (1b) determine the precise degree of authigenic alteration in clay minerals and zeolites necessary to derive paleohydrologic data; (2a) link mineralogy (XRD) with geochemistry (µXRF) to show the links between hydroclimatic control, and the formation and preservation of the Chew Bahir proxies; (2b) decipher climatic change on orbital to decadal timescales from previously defined depositional conditions and thresholds; (3) evaluate the impact of different types of climatic change (duration, abruptness, internal variability and magnitude) on the habitat and living conditions of early humans. In summary, the results of the proposed project will form an important contribution to the understanding of complex climate proxy formation, enable continuous paleoclimate information to be deciphered from the Chew Bahir sediment cores, and contribute data that may be essential for testing hypotheses of the impact of climatic change on human evolution and mobility.