黄土记录的新疆地区全新世有效湿度变化历史研究

Climate changes are poorly documented and understood in Xinjiang. The recovered paleoclimate evolution patterns remains controversy. Therefore, the much broader records need to investigate. Loess deposit is one of main investigation object in paleoclimate research and widely distributed in study area, however, which is observed less attention in Xinjiang paleoclimate research. In this project, two or three loess-paleosol sequences will be collected from each loess sedimentary area according to altitude, including: Junggar Basin, Ili river valley, and Tarim Basin, to investigate that:.First, the chronological sequence of each section was established by Optical Stimulated Luminescence dating technology due to lack of organic materials for reliable 14C dating. Although, quartz grains have shown several problems when apply OSL dating in Xinjiang loess, Potassium feldspar (K-feldspar) is an alternative choice. The Infrared Stimulated Luminescence (IRSL) signal observed at an elevated temperature following a prior infrared (IR) stimulation at 50℃ is more stable and has a much lower fading rate which can lead to more accurate dating data. .Second, surface sample will be collected in each loess sedimentary area according to altitude. Comparing the correlation between their magnetic characteristics and local moisture index, the ideal proxy will be selected. .Third, basing on chronology and proxy data, Holocene effective moisture evolution history being recorded by each section will be recovered. The spatial and temporal disparities of Holocene effective moisture evolution in Xinjiang will be investigated by contrasting recording in different altitude and among each loess sedimentary area..Fourth, combining the previous researches, we try to reconstruct effective moisture evolution pattern during Holocene. .This work will provide more thorough and better comprehensive understanding about Holocene effective moisture dynamics in Xinjiang.

新疆全新世古气候研究薄弱，恢复的气候演化模式存在明显争议。较广泛分布的黄土沉积为古气候研究提供了良好记录。本研究拟分别于准噶尔盆地、伊犁河谷、塔里木盆地边缘沿海拔高度采集黄土剖面进行古气候研究：通过红外释光pIRIR技术获取的钾长石释光年代，辅以AMS 14C技术获取的碳屑年代，建立可靠的全新世黄土年代序列；在各山脉沿海拔高度采集现代黄土样品，通过其环境磁学参数与现代气候记录对比提取与当地有效湿度关系最为密切的磁学指标，并参考有机质含量、色度、粒度等参数重建各剖面记录的有效湿度变化历史；通过对比各沉积区之间和各沉积区内不同海拔高度黄土剖面的古气候记录，分析新疆地区全新世有效湿度的时空分布及其变化规律；结合前人工作，进一步讨论新疆地区全新世有效湿度变化框架。

本研究首先对天山黄土进行环境磁学调查，指标分析结果显示：天山黄土的物质来源复杂，沉积物中原生磁性矿物的输入并不稳定；地层磁化率变化受原生磁性矿物输入和次生磁性矿物形成共同控制。相比较而言，频率磁化率和非磁滞剩磁与饱和等温剩磁的比值等反应超细颗粒磁性矿物浓度的参数可用于准确指示地层生物化学风化历史，进而反演该地区湿度演化历史。其次，本研究本研究对比了沉积物的石英和长石的释光行为，其中粗颗粒石英使用单颗粒再生法（SAR）和长石使用两步法（pIRIR）技术可以提取误差较小的沉积年代。基于释光年代和碳十四年代结果，建立了各研究剖面地层年代序列。最后，结合地层年代序列和代用指标，本研究重建了天山地区不同海拔黄土沉积记录的全新世湿度演化历史。结果显示：该区域古土壤发育开始时间约为6ka前后，且湿度逐渐增加至晚全新世，不同海拔黄土记录的气候演化模态基本一致。该气候演化模态与湖泊反演的湿度演化历史相似，并且在更早的间冰期也曾出现。本研究结果表明在万年时间尺度上，干旱区山盆系统气候因子分异对湿度演化的影响十分有限；支持中亚干旱区的间冰期气候演化模态区别于季风区，其湿度演化具有明显的区域特征，似乎呈现“暖干—冷湿”的水热组合。