若尔盖盆地黄河牛轭湖古河道沉积物磁学特征及其古环境意义  

Magnetic characteristics of paleochannel sediments of the Yellow River in the Zoige basin and their paleoenvironmental significance

作　　者：赵嘉雯 王龙升 张玉柱 陈莹璐 胡守云[4] 张桂叶 孟丽卫 战超[1] 王庆[1] ZHAO Jiawen;WANG Longsheng;ZHANG Yuzhu;CHEN Yinglu;HU Shouyun;ZHANG Guiye;MENG Liwei;ZHAN Chao;WANG Qing(Institute of Coastal Research,Ludong University,Yantai 264025,Shandong,China;Shaanxi Provincial Key Laboratory of Earth Surface System and Environmental Carrying Capacity,College of Urban and Environmental Sciences,Northwest University,Xi'an 710127,China;State Key Laboratory of Estuarine and Coastal Research,East China Normal University,Shanghai 200241,China;State Key Laboratory of Lake Science and Environment,Nanjing Institute of Geography&Limnology,CAS,Nanjing 210008,China;State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,CAS,Xi'an 710061,China)

机构地区：[1]鲁东大学海岸研究所,烟台264025 [2]西北大学城市与环境学院陕西省地表系统与环境承载力重点实验室,西安710127 [3]华东师范大学河口海岸学国家重点实验室,上海200062 [4]中国科学院南京地理与湖泊研究所,湖泊与环境国家重点实验室,南京210008 [5]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,西安710061

出　　处：《地理学报》2025年第1期167-182,共16页Acta Geographica Sinica

基　　金：国家自然科学基金项目(42377207,42277449,42330406);黄土与第四纪地质国家重点实验室开放基金项目(SKLLQG2024);山东省高等学校青创团队人才引育计划。

摘　　要：青藏高原东北部若尔盖盆地古河道沉积物特征提供了丰富的区域环境演变信息。本文选择具有代表性的黄河牛轭湖古河道沉积剖面(NYQ-B)进行系统环境磁学分析,并结合光释光测年数据,对黄河牛轭湖古河道沉积剖面记录的环境演变信息进行研究。结果表明:该剖面中沉积物磁性矿物主要以PSD和MD磁铁矿为主,风化、成壤和早期成岩等作用是影响磁性矿物的主要因素。其中,磁性矿物含量最低值出现在古洪水泛滥沉积层和古河床沉积层,最高值在现代土壤层。古牛轭湖相A层沉积于(3.24±0.26)—(2.96±0.24) ka,该时期气候条件温暖湿润,较高的χ、SIRM值和χARM/χ、χARM/SIRM值,反映了沉积物中含有丰富的因经历强风化作用而形成的细颗粒物质。古牛轭湖相B层磁学性质指示了(2.87±0.27)—(1.84±0.20) ka趋于干冷的气候特征。NYQ-B剖面记录的两期古洪水事件分别发生在(2.96±0.24)—(2.87±0.27) ka和(1.84±0.20)—(1.70±0.16) ka,分别对应全新世大暖期向晚期干旱时期转折阶段和黑暗时代冷期。这两个时段气候相对寒冷干燥,青藏高原山地冰川普遍推进,冰雪融水的贡献相对有限,而气候转折和突变时期大气环流异常停滞、中低纬系统之间相互作用引发的暴雨是导致古洪水事件的主要原因。研究结果丰富了环境磁学在古河道沉积序列研究中的应用,有助于理解黄河源水文特征及其对全球气候变化的响应规律。The characteristics of paleochannel sediments in the Zoige basin of the northeastern Tibetan Plateau offer rich information regarding regional environmental evolution.This paper examined the representative paleochannel profile of the Yellow River Oxbow lake(NYQ-B)using systematic environmental magnetic analyses,and integrated with optical luminescence dating data to investigate the environmental evolution recorded in the paleochannel sedimentary profile.The primary magnetic minerals identified in the sediments of the profile NYQ-B were pseudo-single domain(PSD)and multi-domain(MD)magnetite.Magnetic minerals in the sediments of the profile NYQ-B were mainly influenced by weathering mechanisms,pedogenesis,and early diagenesis.The lowest concentrations occurred in the paleoflood and paleochannel deposits and the highest concentrations were found in the modern soil layer.The paleo-oxbow lake(A)deposits were formed from(3.24±0.26)to(2.96±0.24)ka,characterized by warm and humid climatic conditions.The higherχand SIRM values andχARM/χandχARM/SIRM values of these sediments indicate that they contain abundant fine sediment formed by strong weathering.The magnetic characteristics of the paleo-oxbow lake(B)deposits indicated that the period from(2.87±0.27)to(1.84±0.20)ka had dry and cold climatic features.The two paleoflood events recorded in the profile NYQ-B occurred at(2.96±0.24)to(2.87±0.27)ka and(1.84±0.20)to(1.70±0.16)ka,which correspond to the Holocene Climatic Optimum during the late dry period and Dark Age Cold Period,respectively.During these two periods,the climate was relatively cold and dry,leading to the general advancement of mountain glaciers on the Tibetan Plateau.We concluded that the contribution of ice and snow meltwater was relatively limited,while major flood events primarily resulted from heavy rainfall triggered by atmospheric circulation anomalies and interactions between middle-and low-latitude systems during climatic transition and abrupt change.These results enrich the application of

关 键 词：环境磁学 古河道 牛轭湖 若尔盖盆地 环境演变 

分 类 号：P512.2[天文地球—地质学] P532