黄河源玛曲段末次冰消期以来古洪水事件与冻融褶皱现象研究  

PALAEOFIOOD EVENTS AND PERIGLACIAL INVOLUTIONS DURING THE LAST DEGLACIATION IN THE MAQU REACH IN THE YELLOW RIVER SOURCE AREA

作　　者：肖奇立 陈豆 张玉柱 王宁练[1,2] 黄春长 王浩宇 贾雅娜 潘昭烨 XIAO Qili;CHEN Dou;ZHANG Yuzhu;WANG Ninglian;HUANG Chunchang;WANG Haoyu;JIA Yana;PAN Zhaoye(Shaanxi Key Laboratory of Earth Surface System and Environmental Carrying Capacity,Xi'an 710127,Shaanxi;College of Urban and Environmental Sciences,Northwest University,Xi'an 710127,Shaanxi;School of Geography and Tourism,Shaanxi Normal University,Xi'an 710062,Shaanxi;State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,Xi'an 710061,Shaanxi)

机构地区：[1]陕西省地表系统与环境承载力重点实验室,陕西西安710127 [2]西北大学城市与环境学院,陕西西安710127 [3]陕西师范大学地理科学与旅游学院,陕西西安710062 [4]中国科学院地球环境研究所,黄土与第四纪地质国家重点实验室,陕西西安710061

出　　处：《第四纪研究》2022年第4期1010-1026,共17页Quaternary Sciences

基　　金：国家自然科学基金项目(批准号:41801060、41971116和41971088);中国科学院(A类)战略性先导科技专项项目(批准号:XDA20060201)和中国科学院地球环境研究所黄土与第四纪地质国家重点实验室开放基金专项项目(批准号:SKLLQG2107)共同资助。

摘　　要：通过对黄河源玛曲段开展广泛细致的野外考察,在黄河左岸第二级阶地前缘达尔琼东(DEQ-E)地点发现了两组漫滩相古洪水泛滥沉积层(OFD1和OFD2)。剖面厚448.5 cm,层次分明,未经人为扰动,沉积学特征显著。结合野外宏观特征与室内磁化率和粒度指标分析结果,确定这两组OFD(245.0~448.5 cm)为典型的黄河大洪水溢出河槽形成的泛滥沉积物,共记录了两期11次古洪水事件。基于光释光(OSL)测年数据,确定了这些古洪水事件的发生时段以及OFD1上部(270.0~330.5 cm)冻融褶皱现象的发育年代。这两期古洪水事件分别发生在14900±1010~12800±1130 a和11060±880~9820±390 a,在时间坐标上分别对应于末次冰消期中的B?lling-Aller?d暖期和早全新世气候逐渐转暖阶段。由于青藏高原冰川对气温变化响应敏感,在B?lling-Aller?d暖期和早全新世气候逐渐转暖的大背景下,此时黄河源区发育的大规模冰川积雪会加速消融,抑或叠加区域暴雨的影响,进而导致了该河段大洪水事件的频发。另外,根据沉积地层的先后顺序及其发育特征,确定OFD1上部冻融褶皱发育年代为12500~11500 a,在时间坐标上与末次冰消期中的新仙女木寒冷事件(YD)对应。由于此时青藏高原整体以急剧降温为特征,使得该研究河段的沉积地层受到显著的冻融作用,进而形成了典型的冻融褶皱/冻融泥流等冰缘地貌类型。该研究成果有助于深入理解黄河源流域水文系统和地貌发育过程对全球气候变化的响应规律。Palaeoflood hydrological studies were carried out in the Maqu Reach in the Yellow River source area,two units of overbank flood deposits(OFD) was found at the DEQ-E site(34°00’13″N,101°54’04″E;3430 m a.s.l.).The DEQ-E profile is 448.5 cm thick,with complete outcropping,clear layers and remarkable sedimentological features.The pedostratigraphy of the DEQ-E profile from the top to the bottom is listed as modern soil(MS,0.0~60.0 cm)→mid-Holocene paleosol (S0,60.0~180.0 cm)→Early Holocene transitional loess (Lt,180.0~245.0 cm)→overbank flood deposits (OFD,245.0~448.5 cm).In total,94 samples were collected for sedimentary analysis and 8 samples were obtained from the DEQ-E profile to determine the chronology.The low magnetic susceptibility(χ) values in the DEQ-E profile vary from 10.4×10to 96.6×10m~3/kg,and lowerχlf values(10.4×10-8~24.1×10m~3/kg) were found in the OFD units.This implies that the OFD were not affected by weathering pedogenesis after deposition.The grain-size distribution curves in the profile show that the OFD units are dominated by sand (>63μm).The loess-soil deposits (modern soil,transitional loess and palaeosol) at the DEQ-E site are dominated by silt (2~63μm).In addition,grain-size indices in the profile,such as skewness(Sk),kurtosis(K),and sorting coefficients (S) also differentiate the OFD and aeolian loess-soil deposits well.According to the optically stimulated luminescence(OSL) dating method,the first episode of overbank flooding was dated to 14900±1010~12800±1130 a and correlated with the B?lling-Aller?d warm interval of the last deglaciation.The second episode occurred occurred at 11060±880~9820±390 a,that is,the Early Holocene.As for the mountain glaciers are sensitive to temperature and precipitation.Under the warm and humid climate during the B?lling-Aller?d warm interval and the Early Holocene,and thus the mountain glaciers in the Yellow River source area melted more quickly.The accelerated melting of glacier snow,or the superimposition of regional torrential

关 键 词：古洪水事件 冻融褶皱 光释光测年 末次冰消期 黄河源 

分 类 号：P534.632[天文地球—第四纪地质学] P941.78[天文地球—古生物学与地层学]