新疆天山地区不同海拔黄土记录的末次冰消期以来的环境演变

Environmental changes since last deglaciation recorded in loess at different altitude in Tianshan Mountains,Xinjiang

新疆天山地区是中亚干旱区的重要组成部分,在研究全球环境变化和区域气候方面具有重要意义。选取天山地区不同海拔的3个黄土剖面,结合磁学参数、粒度、碳酸盐、总有机碳含量,探讨该区域地形对粉尘堆积和气候环境的影响以及末次冰消期以来的环境演变。结果表明:1)在天山北麓,磁化率、粒度和总有机碳含量变化指示海拔相对较高的黄土沉积对湿润气候环境更加敏感;2)伊犁盆地由于相对湿润的气候环境,其黄土沉积磁化率高于天山北麓,体现了地形因素的重要作用;3)新疆天山地区海拔较高的黄土沉积响应轨道和亚轨道尺度气候变化,各指标均指示末次冰消期以来气候环境由干冷向暖湿转变;在亚轨道尺度上尤其是中晚全新世,湿度逐渐增加。

Located in the eastern part of arid Central Asia,Tianshan regions,Xinjiang have played great significance on global and regional environmental change.In this study,we selected three loess sections at LJW10(43°58'29″N,85°20'10″E;1462 m a.s.l.),BYH10(44°02'26.7″N,87°48'54.0″E;622 m a.s.l.)and KS16(43°25'56.4″N,83°56'35.5″E;1314 m a.s.l.),which located at northern slope of Tianshan Mountains and Yili Basin,respectively.These sections all deposited at least from last deglaciation.Climatic proxies including magnetic parameters(χlf,χfd),particle size(<10μm grain size fraction,Md),carbonate content(CaCO3)and total organic carbon(TOC)are compared within the three loess sections at different altitudes.In addition,we collected and sorted out the publishedχlf spanning the whole Holocene,in northern slope of Tianshan Mountains and Yili Basin at different altitudes.Our results show that:(1)At the northern slope of Tianshan Mountains,theχlf,χfd,<10μm grain size fraction and TOC content in LJW10 section are higher than that in the BYH10 section,and the coarser particle is evidenced by the Md in BYH10 section,which indicates the loess sections at relatively high altitude are more sensitive to moisture variation.(2)Due to the relatively humid climate environment,the magnetic susceptibility of loess deposits in Yili Basin is higher than that in the northern slope of Tianshan Mountains,which reflects the importance of the topographic factor.(3)Theχfd and<10μm grain size fraction presents lower values from last glaciation to Holocene and increase gradually during Holocene especially Middle-Late Holocene.Compared with surrounding records,it can be found that the loess sections at relatively high latitude record the climate change at orbital and sub-orbital scale,which presents an environment changes from cold/dry to warm/moist since last deglaciation.At sub-orbital scale,the moisture revealed from the climatic proxies increased gradually during Middle-Late Holocene.