班戈错盐湖古湖岸堤石英光释光年代学及其古环境指示意义研究

古湖岸堤是湖泊湖面变化的地貌学证据,通过古湖岸堤沉积年代学研究可重建地质时期湖泊演化历史。青藏高原内陆湖泊众多,保存了大量的第四纪时期古湖岸堤,是研究过去湖泊演化和气候变化信息的重要载体。对青藏高原班戈错盐湖北岸和东岸的低位连续古湖岸堤开展了地貌调查和光释光年代学研究。结果表明班戈错自末次冰消期(13. 5±1. 2 ka BP)以来,湖面整体呈波动下降过程,期间出现了4期湖面稳定阶段,分别在末次冰消期(13. 5±1. 2～11. 2±1. 0 ka BP)、全新世早中期(10. 1±0. 8～6. 5±0. 5 ka BP)、全新世后期(4. 2±0. 4～3. 1±0. 2 ka BP)以及全新世晚期(1. 7±0. 1～1. 2±0. 1 ka BP)。全新世晚期约1. 7 ka BP以后湖面迅速退缩,湖泊蒸发浓缩进入盐湖阶段。在末次冰消期班戈错高湖面形成主要与北半球太阳辐射强度增加引起气温升高,导致区域冰雪融水量增加相关,而在全新世湖面变化主要受印度季风强度变化控制。

Optically Stimulated Luminescence Dating of Paleo-shorelines of Bange Co, Qinghai-Tibetan Plateau and Its Implications for Palaeo-environment

Paleo-shorelines are geomorphologic evidence of past lake level changes, the fluctuation history of lake level can be reconstructed through chronology of paleo-shorelines. There are many enclosed lakes in Qinghai-Tibetan Plateau, which preserved numerous paleo-shorelines during Quaternary, these paleo-shorelines are ideal archives for study the evolution of lakes and climate change. Bange Co is surrounded by conspicuous regressive shorelines attesting to high-water levels in the past. In the present work, we carried out geomorphologic investigation and optically stimulated luminescence (OSL) dating for the paleo-shoreline sediments distributed in northern and eastern Bange Co. The result reveals four stages of relatively stable and high lake level, which happened during last deglacial (13.5±1.2~11.2±1.0 ka BP), early to middle Holocene (10.1±0.8~6.5±0.5 ka BP), late Holocene (4.2±0.4~3.1±0.2 ka BP)and(1.7±0.1~1.2±0.1 ka BP).After 1.7 ka BP, the lake level was dropped swiftly and the lake evolved into saline lake. The deglacial lake level transgression is likely due to increase of north hemisphere insolation and corresponding glacial melt waters.While fluctuations of lake level during Holocene were mainly controlled by variation of Indian Summer Monsoon.