藏东南帕隆藏布流域冰川地貌光释光测年研究

Quaternary glacial history and mechanisms of glacier fluctuation in the Qinghai-Tibetan Plateau are still highly debated, mostly due to insufficient chronological works. As one of the few dating techniques which can be applied to directly date glacial landforms, optically stimulated luminescence (OSL) has wide foregrounds in Quaternary Glaciology research. However, it was found in recent research practices that dating glacial sediment was more complicated and more problematic than dating other kinds of sediment when using OSL methods. Precisely and accurately dating is the future direction of international Quaternary Glaciology research. To match the demands of future development of Quaternary Glaciology research in the Qinghai-Tibetan Plateau, more investigations and case studies of OSL dating on glacial sediments are required. The Palongzangbu Valley is located in the southeastern Tibet. Plenty of distinct and complete glacial landform series were well preserved in this valley. Therefore, it is an ideal area both to test OSL dating on glacial sediments and reconstruct Quaternary glacial history. The paths of OSL dating applications in Quaternary Glaciology research in the Qinghai-Tibetan Plateau are going to be explored through various methods. Firstly, samples from different sedimentary facies and different geomorphological positions of modern glacial sediments and ancient glacial landforms will be collected. Secondly, different OSL methods will be applied to determine equivalent dose (De) and internal check will carry out. Thirdly, cross-check between OSL ages and other dating methods will be provided. Reliable ages can be obtained based on these methods. Detailed chronological sequence of Quaternary glacier fluctuations in Palongzangbu will be established. In addition, Quaternary glacial history is going to be compared with paleo-climatic records, to investigate mechanisms of glacier fluctuation in this area.

对青藏高原第四纪冰川历史及冰川进退规律的认识仍存不少争议，最重要的原因是年代学工作的不足。作为为数不多的能用于冰川地貌直接定年的测年技术之一，OSL在第四纪冰川研究上的应用前景很广。但近年的研究实践发现，冰川沉积OSL测年比其它沉积类型复杂，问题也更多。高精准度测年是国际第四纪冰川研究的未来方向。冰川沉积OSL测年仍需进行更多探索和实证研究，以适应我国青藏高原第四纪冰川研究发展的需要。藏东南帕隆藏布流域冰川地貌保存完整清晰，且序列很多，是进行冰川沉积OSL测年试验和古冰川历史重建的理想地点。拟通过对该区现代冰川沉积和古冰川地貌的不同沉积相和地貌部位采样、对比运用不同OSL方法测试等效剂量、辅以其它测年技术交叉对比等手段，摸索OSL技术在青藏高原第四纪冰川研究的应用之路。在此基础上，获取可信的OSL年代，建立帕隆藏布详尽的第四纪冰川年代序列，并与周边古气候记录对比，揭示研究区冰川进退的规律。

青藏高原第四纪冰川发育的时间及其气候响应仍是个有争议的问题。最关键的原因是当前冰川地貌测年仍有较大的不确定性。光释光（OSL）是为数不多的可应用于第四纪冰川研究的测年技术之一，近年在青藏高原的应用中也发现了少问题。本项目选择深受印度季风影响的藏东南帕隆藏布流域作为研究区域，在若干典型冰川谷地进行冰川地貌调查、采样和年代测定等工作。目的是：1）摸索冰川沉积OSL测年的可行办法；2）建立帕隆藏布流域较为可信的第四纪冰川年代框架，恢复冰川波动历史，探讨冰川波动的气候响应机制。.在本项目及相关项目的支持下，课题组成员对帕隆藏布流域进行了3次野外考察和采样。对该区域帕隆藏布达巴沟、栋曲沟、波堆藏布主谷、波堆藏布白玉沟、亚隆藏布松龙沟、曲宗藏布茶绕沟、德普沟、星木沟等谷地共采集近百个OSL、宇生核素（TCN）、电子自旋共振（ESR）和14C等测年样品并进行了测试。.研究的主要进展和成果：.1）详细调查了帕隆藏布流域不同时代冰川地貌的分布和发育特征。发现了该区域最老的冰川作用证据，比之前确认的最老冰期——古乡冰期冰碛（MIS-6）的位置更高，初步确定为MIS-12阶段，与中梁赣冰期对应。.2）对年轻冰川沉积、有独立年代的冰川地貌进行OSL测年及可靠性检验。对不同沉积部位进行采样，尝试了多种OSL方法，包括石英OSL大测片、小测片、单颗粒技术，石英Post-IR OSL，多矿物IRSL等。其中单颗粒技术的系统应用在青藏高原第四纪冰川研究中尚属首次。探索了适合冰川沉积OSL测年的野外采样和实验测试方法，对第四纪冰川测年具有参考意义。.3）在多个冰川谷地对冰川地貌序列进行OSL及其它测年，建立了帕隆藏布流域较为详实的第四纪冰川年代序列。研究表明该区域至少经历了MIS-12、MIS-6、MIS-4、MIS-2、新冰期和小冰期等几次冰进。.4）即使在印度季风控制的藏东南地区，冰川波动主要受控于气温变化。