晚中新世以来黄土高原中部风成沉积的伊利石风化与东亚季风演变

As a well material for studying the evolution of East Asian Monsoon and environmental changes, the continuous aeolian sediments of red clay-loess-paleosol sequences are always one of the hot topics of environmental changes in Asia and the past global changes. Although many previous studies have made on conventional climatic substitute proxies, there are few studies on clay minerals especially illite weathering indexes, which are sensitive to environmental changes. This project is to take the red clay-loess-paleosol aeolian sediments sequences as the research carrier in the central Chinese Loess Plateau (CLP). The clay minerals are extracted and analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), geochemical elements and color proxies. The illite weathering proxies are extracted and the weathering characteristics and controlling factors of the aeolian sedimentary sequences are systematically analyzed and studied. Based on the existing record of chronology, compared with sedimentology, environmental magnetism, other regional records and simulation results, we will also discuss the coupling relations between illite weathering intensity and East Asian monsoon changes. It is great significant to study the mineralogy of continental sediments and further reveal the paleoclimate and environmental significance of the aeolian sediments in the CLP.

作为晚新生代东亚季风演变与环境变化的良好载体，黄土高原连续的红粘土-黄土-古土壤风成沉积序列一直是亚洲环境变迁与过去全球变化的研究热点。尽管前人对常规代用指标做了大量的研究工作，但作为对环境变化敏感的粘土矿物研究不多，尤其是对伊利石风化指标的研究鲜见，其古气候意义仍不明晰。本项目拟以黄土高原中部红粘土-黄土-古土壤风尘堆积序列为研究载体，提取粘土矿物，开展以X射线衍射为主，微形态、地球化学元素和色度为辅的分析测试研究，提取伊利石风化指标，系统地分析和研究这套风成沉积序列伊利石风化特征及控制因素。在已有的年代学基础上，将其与剖面沉积学和环境磁学记录对比，结合区域其它记录和模拟结果，探究伊利石风化与东亚季风演变之间的关系，对开展陆相沉积矿物学研究和进一步揭示黄土高原风成沉积蕴含的古气候与环境意义具有重要科学价值。

黄土高原连续的红粘土-黄土-古土壤风成沉积序列是晚新生代古环境变化的重要载体。粘土矿物是风成沉积中重要的组成矿物，其矿物成分及其相关指标的变化尤其是伊利石风化可以很好地记录和保存了风成沉积序列的古气候环境信息。本项目利用X射线衍射、X射线荧光光谱、颜色测试和扫描电子显微镜等技术手段，以伊利石风化、色度、地球化学元素和粘土矿物微形态为代用指标，开展了晚中新世以来黄土高原中部风成沉积剖面的粘土矿物学研究，结果表明：（1）确定了风成沉积不同阶段粘土矿物的组成。朝那和灵台红粘土和第四纪黄土-古土壤中粘土矿物组成基本一致，以伊利石为主，绿泥石、蒙脱石和高岭石次之，另有少量的混层矿物。（2）建立了伊利石风化强度指标。沉积剖面中伊利石结晶度值在黄土中高于临近的古土壤层和下伏红粘土层，而高岭石/（伊利石+绿泥石）比值则是黄土层中低于古土壤和红粘土层，说明了晚中新世以来红粘土-黄土-古土壤风成沉积序列中水热条件的变化引起伊利石风化程度有很大的差异，随着水热条件变弱，伊利石风化强度也在降低。可见，伊利石结晶度和高岭石/（伊利石+绿泥石）比值可以很好地反映伊利石风化强度。（3）明晰了伊利石风化点强度与东亚季风演化之间的关系。伊利石结晶度和高岭石/（伊利石+绿泥石）比值在冰期-间冰期旋回上的变化特征与东亚夏季风的变化基本一致，说明其可以很好地作为夏季风演化的替代性指标。同时伊利石风化程度的不断降低，可能与晚新生代持续的全球变冷有关。