西藏阿里孔雀河晚更新世以来的阶地发育特征  

The evolution of Kongque River terraces since the Late Pleistocene in Ali, Tibet

作　　者：杨玮琳 刘擎 郭浩 刘耕年[1] YANG Weilin;LIU Qing;GUO Hao;LIU Gengnian(College of Urban and Environmental Sciences,Peking University,Beijing 100871)

机构地区：[1]北京大学城市与环境学院,北京100871

出　　处：《第四纪研究》2023年第5期1199-1210,共12页Quaternary Sciences

基　　金：科技部第二次青藏高原综合科学考察研究项目(批准号:2019QZKK0205);国家自然科学基金项目(批准号:41771005)共同资助。

摘　　要：一直以来,喜马拉雅山河流阶地发育的控制因素广受讨论。本研究选取了喜马拉雅山北坡的孔雀河作为分析对象,通过详细的野外考察和精确定年,探究了气候变化和构造运动对阶地发育的影响。结果表明孔雀河共发育了5级河流阶地,且均为基座阶地。阶地面砾石的10Be暴露测年揭示了T5~T1阶地分别形成于88.8±5.8 ka、约18.7~16.8 ka、 14.5±1.3 ka、 11.9±1.2~11.2±1.1 ka和1.9±0.5 ka;对比青藏高原气候变化资料以及恒河、印度河上游阶地研究成果,表明轨道尺度的气候变化或千年尺度的快速气候变化导致河流堆积下切过程快速转换,形成多级河流阶地。在降水较少的冷期,河道水动力条件减弱,河道堆积;在印度季风增强的暖期,侵蚀能力增强,河道快速下切。研究区晚更新世至末次冰盛期(LGM)期间的河流下切过程稳定,下切速率约为0.5 mm/a;LGM以来,孔雀河下切速率加快,约为1.0~1.8 mm/a。The fluvial terrace evolution and its driven mechanism across the Himalayas have been widely discussed over a century.However,previous studies mainly paid attention on the southern Himalayan,leaving a research gap on the northern Himalayan.In order to fill in this blank,we selected the Kongque River as the study area.The Kongque River is one of the tributaries of the upper Ganges River,located on the northern slopes of the Himalayas.Geomorphological mapping was delineated with the help of Google Earth remote sensing image,Global Position System(GPS),and altimetric survey technology.Detailed field observations and in-situ cosmogenic radionuclide 10Be exposure dating were conducted to determine the surface-exposure ages of the preserved terraces.By comparing the dating results with climatic proxies,the evolution patterns of the Kongque River terraces were discussed.Two sample sites were selected in Kongque River in this study.The sample site one(30.54°N,81.02°E)is located at the upper Kongque River,and the sample site two(30.49°N,81.07°E)is located at the middle Kongque River.Five fluvial terraces were identified at sample site two,orderly named from T5(old)to T1(young).The terrace surfaces are about 67.3 m,25.3 m,21.3 m,18.3 m,and 4 m higher than the nearest riverbed.The fluvial facies are composed of poorly sorted and moderately rounded gravels,with thick of 7 m,2 m,2 m,2.2 m,and 2 m for T5~T1,respectively.Three fluvial terraces(T5,T3,and T2)were detected at sample site one.The terrace surfaces are about 67.1 m,22.1 m,and 19 m higher than the nearest riverbed.The fluvial gravel layer thickness of each terrace is around 7 m,1.2 m,and 2.7 m,respectively.All fluvial terraces are strath terraces.The pebble samples collected from terrace surfaces(T5,T3,and T2 at sample site one;T2 and T1 at sample site two)were used for 10Be surface exposure dating.Note that the age of T4 has not been directly measured for the sampling restrictions.Instead,we estimated it based on the river's average incision rate.The 10Be exposur

关 键 词：河流阶地 下切速率 气候变化 构造运动 孔雀河 

分 类 号：P546[天文地球—构造地质学] P931.1[天文地球—地质学]