阿拉善高原苏宏图盆地粘土沙丘形成演变过程及其古环境意义研究

Clay dunes, characterized by a higher content of silt and clay commonly occurred on the lee side margin of closed-basin lake in arid and semi-arid areas, are important component of aeolian landform and extensively identified in most of continents on the Earth. Study on its formation mechanism, development and evolution process and geomorphological Significance are of great significance not only for enriching the knowledge of diversity of aeolian landforms landscape and strengthening the understanding the process of aeolian geomorphology, but also helping us to better reconstruct the regional paleoclimate and paleoenvironment. As a special kind of aeolian dunes, clay dune have been extensively identified in most of continents of the Earth, however, little is studied in Asian as to date. We firstly identified the occurrence of clay dunes, with shapes of asymmetric barchans and liner or seif dunes, in the Suhongtu Basin of Alashan Plateau,north China, and selected the clay dune as study subject. A multi-disciplinary approach, including research methods in geomorphology, sedimentology, Quaternary geology, geochronology, Paleoclimatology will be applied in the project to systemically study their distribution, morphology, structure, and reveals the influence factor of clay dunes formation and development , and dynamic mechanism; Using OSL Dating techniques, establishing chronology of typical clay dunes sedimentary sequence, reveals the development and evolution process of the clay dunes in Suhongtu Basin, and Significance of Paleoenvironment, then, combined with the analysis of paleoclimatic and environmental proxies, to reconstruct the evolution history of regional climate and environment since the late Pleistocene.

粘土沙丘是一种主要分布在盆地盐湖边缘等地区的特殊风成地貌景观，探究其形成发育机理、演变过程和古环境意义，不仅有助于丰富对风沙地貌景观多样性的认识，增强对风沙地貌过程的了解，还有助于更好的重建区域古气候环境变化。作为一种特殊的风成沙丘，粘土沙丘在许多大洲均有分布，然而，在亚洲一直没有发现并报道过这一风成地貌类型。申请者等人第一次在阿拉善高原苏宏图盆地发现了粘土沙丘，拟以此为研究对象，综合运用地貌学、沉积学、第四纪地质学、古气候学等方法，通过对苏宏图盆地粘土沙丘内部构造、沉积物组成及区域风况等的研究，揭示粘土沙丘形成发育的影响因素及其动力机制，进而丰富和完善粘土沙丘形成发育理论；通过OSL测年，建立典型粘土沙丘沉积年代序列，揭示苏宏图盆地粘土沙丘形成发育与演变过程，明确粘土沙丘沉积古环境意义，结合古气候环境代用指标分析，进而重建晚更新世以来区域环境演变历史，探讨区域气候变化对全球变化的响应。

粘土沙丘作为一种特殊的风成地貌景观，具有独特的沉积构造、形态特征、形成发育机理和地貌意义。然而，和近20年来对砂质沙丘形成发育机理、演变过程及其对全球变化的响应所取得的巨大成就相比，对粘土沙丘的研究在我国几乎很少涉及，因而对其研究具有重要的科学价。项目以阿拉善高原苏宏图盆地粘土沙丘作为研究对象，利用遥感、地貌学、地球化学和粒度分析，结合野外考察和年代学分析等手段，对苏宏图盆地粘土沙丘分布、形态、沉积构造沙、移动速率，粘土沙丘沙物质来源，沙丘形成原因、演变过程及其古环境意义等进行了详细研究。结果显示：(1)苏宏图盆地粘土沙丘是以土壤团聚体和砂颗粒混合的形式被风搬运、堆积形成的，耙状粘土沙丘是东西走向遵循不稳定床型发育模式的新月形沙丘叠加上东南延伸遵循延伸模式的次生臂膀而成；(2)苏宏图盆地粘土沙丘形态多样、移动速率快、倾斜层理和交错层理发育明显，与美国和澳大利亚粘土沙丘具有显著差异，这可能与苏宏图盆地粘土沙丘粘土含量相对较低、砂含量相对较高，以及物源相对丰富、气候更加干旱有关；(3)苏宏图盆地在距今7.8~6.3ka期间气候较为湿润，可能发育了较大范围的湖泊，而在此之后，随着降雨减少，湖泊逐渐干涸，导致大面积的湖湘沉积物出露地表，为粘土沙丘的形成发育提供了充足的物质来源；(4)宏图盆地现代粘土沙丘景观的形成不晚于1.34ka，最近500a以来，粘土沙丘普遍发育，指示了苏宏图盆地风沙活动强烈，气候较为干旱。项目的执行丰富了我们对风沙地貌景观多样性的认识，增强我们对风沙地貌形成发育与演变过程和地貌环境意义的理解。