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

Chew Bahir钻探项目（CBDP）从埃塞俄比亚南部的Chew Bahir盆地提取了重复的沉积物记录，通过阐明关键时期的气候背景，来验证目前关于解剖学上现代人类发展过程中人类与气候相互作用的假设。然而，由于气候参数与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。确定和分析在整个地核中保存的合适的气候代用物对于建立高分辨率、连续的气候变化记录至关重要。这里提出的项目旨在从Chew Bahir沉积物岩心的自生矿物转化中破译古环境信息，以提供有意义的数据，这些数据可能是开发埃塞俄比亚南部裂谷50万年来可靠和连续的气候记录的关键。在水文条件受限的环境中，如Chew Bahir，自生粘土矿物和沸石的组成受到古湖泊水化学的强烈控制，这对降水/蒸发比的波动作出反应。在一项初步研究中，研究表明，Chew Bahir矿物组合，特别是丰富的粘土矿物，通过精细调整其晶体组成，对古盐度和碱度的变化反应敏感。由于~290 m的复合岩心主要由这些高活性粘土组成，该材料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。这个潜在的数据集可能对项目的成功至关重要，因为其他一些代用品（如花粉和硅藻）只是间歇性地保存下来。在项目的前两年，我们建议（1a）在整个长岩心中确定湿、干和超干旱阶段的特征矿物组合；（1b）确定获得古水文资料所必需的粘土矿物和沸石自生蚀变的精确程度；（2a）将矿物学（XRD）和地球化学（µXRF）联系起来，显示水文气候控制与Chew Bahir代用物的形成和保存之间的联系；（2b）根据先前确定的沉积条件和阈值，在轨道到年代际尺度上破译气候变化；(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。综上所述，本项目的研究结果将为理解复杂的气候代理形成机制做出重要贡献，使人们能够从Chew Bahir沉积物岩心中破译连续的古气候信息，并为检验气候变化对人类进化和迁移影响的假设提供必要的数据。

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.