柴达木盆地东北缘怀头他拉剖面粘土矿物记录的亚洲内陆干旱化

The arid Asian interior is the key region of the Earth environment system. The history and forcing mechanisms of the Asian interior aridification have attracted considerable interests and extensively been studied. Due to the absence of paleoclimatic records directly obtained from the Asian inland, there still exist many unsolved problems related to the Asian aridification. The Qaidam Basin in the northeastern Tibetan Plateau is directly situated in the arid Asian inland with extremely thick Cenozoic strata, which provides an ideal place to investigate the history and forcing mechanisms of aridity in the Asian inland. However, the complex and changeable sedimentary facies, frequently embedded conglomerates and sandstones relating to intense tectonic uplift of the northern Tibetan Plateau in this long sedimentary sequences not only limit the precise dating of basin sediments, but also lead multiple interpretations of sedimentary environment proxies. The clay minerals of sediments mostly represent chemical alteration products of the source rocks in the drainage area, which are less affected by changes of sedimentary facies, and have been proven to be reliable proxies to reconstruct the long-scale paleoclimate change. In this proposal, the clay minerals collected from the Huaitoutala section (15.7-1.8 Ma) in the northeastern Qaidam Basin are employed. Firstly, the origin of the clay minerals can be determined by analyzing the polytypes and scanning electron microscopy. Then a high-resolution paleoclimatic record in the Qaidam Basin can be reconstructed from the clay assembles, which can reveal the arid events in the Asian inland since 15.7 Ma. Furthermore, by comparing the obtained clay-derived paleoclimate records with the global climate records and regional tectonic activities, it can reveal the major impact factors to the Late Cenozoic paleoclimate change in the northern Tibetan Plateau. This study will shed new lights on the initiation of aridification in the Asian interior and its further forcing mechanisms.

亚洲内陆干旱区是地球环境系统的关键地区之一。关于新生代亚洲内陆干旱化的起始时间、演化过程和驱动机制一直存在争议，重要原因在于缺少干旱区内部的直接地质记录。柴达木盆地独特的地理位置及巨厚的新生代地层使其成为研究内陆干旱化的理想场所。但高原北部强烈隆升导致的盆地沉积相变化、砂砾岩层频繁出现，不仅限制了盆地沉积物的精确定年，更使沉积环境指标常具多解性。沉积物中粘土矿物主要来自母岩风化，受沉积环境影响较小，是重建流域环境变化的理想指标。本项目拟以柴达木盆地东北部怀头他拉剖面（15.7-1.8 Ma）粘土矿物为研究对象，通过粘土矿物多型并结合扫描电镜分析确定粘土矿物成因；通过粘土矿物组合建立盆地15.7 Ma以来高分辨率气候变化记录，厘定内陆干旱区干旱事件；通过气候变化记录与全球气候变化及高原北部构造事件对比，探讨晚新生代高原北部气候变化的主控因素，为亚洲内陆干旱化的形成时间及驱动机制研究提供依据。

亚洲内陆干旱化形成演化及其驱动机制研究有助于我们理解新生代区域和全球古气候变化过程和机制。本项目针对新生代亚洲内陆干旱化演化过程和驱动机制存在争议问题，选择干旱区内部柴达木盆地东北缘的怀头他拉剖面（15.7-1.8 Ma）为研究对象。通过柴达木盆地怀头他拉剖面沉积物粘粒级（<2µm）组分中详细的粘土矿物及其组合特征来重建流域化学风化和古气候演化历史，并在此基础上讨论其控制因素，为深入探讨青藏高原隆升及其风化和气候变化效应提供依据。通过研究获得主要结论如下：.（1）通过怀头他拉剖面中粘土矿物半定量分析，获得了该剖面粘土矿物记录，结合伊利石、绿泥石及伊蒙混层比等变化特征，确定该剖面粘土矿物受成岩作用影响较小。.（2）通过性质稳定的微量元素比值结果表明中中新世以来怀头他拉剖面粘土矿物组合受物源影响较小，主要反映了流域化学风化过程；而~11-9.6 Ma期间，受物源影响较大。.（3）依据剖面粘土矿物变化记录，获得了柴北缘中中新世以来化学风化强度变化序列：即15.7-12.6 Ma 化学风化较强，12.6 Ma以来化学风化强度呈逐渐减弱趋势。结合生物化石和前人研究成果，认为柴达木盆地中中新世以来气候经历了由15.7-12.6 Ma相对湿润转变为12.6-5.6 Ma半干旱-半湿润、以及5.6 Ma以来显著干旱的阶段性演化过程。.（4）通过粘土矿物及其组合记录与全球气候变化记录及高原北部构造事件的对比研究，揭示中中新世以来柴北缘古气候变化主要受全球气候变化的影响；其次，晚新生代高原北部强烈构造隆升及东亚季风对区域气候变化也有影响。. 上述研究为亚洲内陆干旱化的形成时间及驱动机制研究提供了重要依据。