塔里木盆地西缘新生代风成沉积记录及其古气候意义研究

The Cenozoic aridification in the Asian interior is closely linked to the retreat of the Tethyan Realm, the uplift of the Tibet Plateau, and the North Hemesphere glaciation. The onset of deposition of aeolian sediments in the central Loess Plateau was dated at 7-8 Ma, aeolian accumulation in the western part was suggested to commence as early as 22-25 Ma, whereas, the aeolian records from the Northern Pacific illustrated that the aeolian deposits has existed over the Cenozoic, with a stepwise intensified trend in mass accumulation rate. Previous studies raised a series of questions: How old is the Asian aridification? What is the aridification history of the source regions? What is the forcing mechanism of Asian drying?. The western Tarim Basin is located in arid central Asia, northern areas of the Tibetan Plateau, which is directly affected by the retreat of the Tethyan Realm and the uplift of the Tibetan Plateau. The complete Cenozoic sequence here records a continous environmental change from a shallow marine basin to an arid high altitude inter-mountain basin. Our initial investigations suggested that aeolian deposits privailed in the Cenozoic sequence. In this project, 5 complete Cenozoic sections were selected to develop chronological, sedimentological and palaeoenvironmental work. We attempt to reconstruct the Cenozoic aeolian history of the western Tarim Basin under a rough chronological frame, and to provide direct and complete records from the source region for understanding the Cenozoic aeolian history and the possible forcing mechanism of Asian aridification.

新生代亚洲内陆干旱化与特提斯海消亡、青藏高原隆升、全球冰量变化相关。研究表明，黄土高原主体风成沉积出现于7-8 Ma，黄土高原西部的风成沉积可追溯到22-25 Ma，而北太平洋的记录显示新生代风成沉积普遍存在，只是沉积通量存在变化。所以，中国风成沉积到底有多老？风尘源区的干旱历史如何？新生代干旱化的驱动因素是什么？等问题，可能是目前风尘沉积研究的关键科学问题。塔里木盆地西缘位于青藏高原北侧的亚洲内陆干旱中心，同时受特提斯海退缩和青藏高原隆升的直接影响，完整的新生代沉积序列记录了该地区由特提斯海演变为干旱的高海拔环境的历史。我们在前期工作中发现，新生代地层中普遍存在风成砂和粉尘沉积。本项目拟在该地区选择5条新生代剖面，开展系统的年代学、沉积相、古环境和风成沉积的鉴定和估算研究，建立具有粗年代框架的新生代风成沉积演化序列，为认识中国风成沉积在整个新生代的变化和内陆干旱化机制提供源区的完整记录。

新生代亚洲内陆干旱化与青藏高原隆升、特提斯海的退缩和全球降温等构造/地质事件密切相关，关键区域新生代地层中风成沉积记录的研究是恢复亚洲内陆干旱化历史的关键。本项目选择了位于亚洲内陆干旱核心区的塔里木盆地为主要的研究区域，对出露较好的五个中-新生代剖面开展了系统的沉积相、年代学和古环境的研究。结合多种沉积学手段和数学方法，建立了识别和提取复杂沉积环境下风成沉积的半定量方法。在磁性地层、生物地层和绝对测年手段的约束下，恢复了塔里木盆地白垩纪以来的风成沉积演化序列。结果表明塔里木盆地风成沉积的历史可以追溯至白垩纪。新生代时，塔里木盆地风成沉积在~34 Ma、~23 Ma、~16 Ma、~8 Ma、~5.3 Ma和~3.6 Ma时显著增加，说明新生代时亚洲内陆干旱化发生了阶段性增强。这一认识进一步得到了其它气候代用指标证据的支持。对于盆地干旱化的驱动因素在白垩纪和新生代早期主要归因于副特提斯海的退缩，上新世后干旱化主要受控于青藏高原得显著隆升。这些结果为进一步认识特提斯海退出塔里木盆地的时间、亚洲内陆干旱化演化的重要时间界限以及与高原隆升、副特提斯海演化和全球冰量变化之间的动力联系等重大科学问题提供了可信的沉积学和年代学证据。依托项目支持发表SCI论文6篇，中文核心论文1篇，培养博士生3名，硕士生3名，并与国外内同行开展了深入的交流。