古新世-始新世极热事件南阳盆地湖相沉积物的岩石磁学研究  

THE STUDY OF ROCK MAGNETISM IN LACUSTRINE SEDIMENTS FROM THE NANYANG BASIN DURING THE PALEOCENE-EOCENE THERMAL MAXIMUM

作　　者：梁耀 王学婷 陈祚伶[1] LIANG Yao;WANG Xueting;CHEN Zuoling(Key Laboratory of Cenozoic Geology and Environment,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029;University of Chinese Academy of Sciences,Beijing 100049)

机构地区：[1]中国科学院地质与地球物理研究所,中国科学院新生代地质与环境重点实验室,北京100029 [2]中国科学院大学,北京100049

出　　处：《第四纪研究》2024年第5期1215-1224,共10页Quaternary Sciences

基　　金：国家重点研发计划项目(批准号:2022YFF0800800)资助。

摘　　要：古新世-始新世极热事件(PETM)是发生在早新生代的一次历时短暂的快速增温事件,该事件的主要地质特征为大幅度碳同位素负漂(CIE),表明当时有巨量富12C的轻碳注入海气系统,其排放场景与当今人类碳排放非常相似,故对这类事件的研究有重要的现实意义。已有研究表明,磁性矿物的产生、保存与气候环境变化之间有密切关系,因此,通过对PETM时期沉积岩磁学参数的研究,可以揭示增温背景下古环境演化的时空特征。前人利用磁学方法研究海相沉积物时发现,PETM时期磁学信号出现显著响应,但不同研究区域的具体驱动机制有所差异。本研究对南阳盆地湖相PETM地层开展磁学分析,测量岩石磁学参数,发现PETM时期沉积岩磁性有所增强,磁铁矿含量增加,直到极热事件结束后才缓慢恢复到背景水平,说明事件发生前、发生期间和事件结束后的湖泊环境经历了氧化→弱还原→氧化这3个阶段,且陆相与海相沉积物对PETM具有相似的磁学响应机制。The Paleocene-Eocene Thermal Maximum(PETM)was a swift warming event that transpired during the early Cenozoic era.The prominent geological hallmark of the PETM was the significant negative carbon isotope excursion(CIE),signifying a substantial influx of 12C-enriched light carbon into the ocean-atmosphere system during that period.This emission scenario bears a striking resemblance to contemporary human carbon emissions.Therefore,the event has been considered as a geological analog for the ongoing and forthcoming anthropogenic warming and its associated environmental changes.Previous studies have demonstrated the close correlation between the formation and conservation of magnetic minerals and shifts in climate and environmental conditions.Thus,magnetic parameters of sediments spanning the PETM can unveil the temporal and spatial attributes of paleoenvironmental evolution within the context of global warming.Prior investigations applying magnetic methods on marine sediments have identified noteworthy magnetic responses to the PETM;however,the fundamental mechanisms behind these phenomena remain subjects of debate.In this paper,we conducted a magnetic study of the lacustrine sedimentary rocks,marl and limestone,of the 50-meter-thick strata corresponding to the PETM in the Nanyang Basin(32.65°N,111.46°E).This basin,situated in the eastern Qinling orogen,is an intermontane down-faulted basin emerged during the late Mesozoic as a result of the collision between the North China Block and Yangtze Block.Totally 21 samples from the intervals of pre-PETM,during-PETM and post-PETM were chosen for measurements of hysteresis loops,direct current demagnetization,isothermal remanent magnetization acquisition curves and first-order reversal curves,with the data processed by applications like HystLab,Max UnMix and FORCinel.The outcomes reveal that saturation magnetization exhibited enhancement,whereas bulk coercivity dropped during the PETM-Peak period;additionally,magnetite content experienced an upsurge while the hematite con

关 键 词：古新世-始新世极热事件(PETM) 南阳盆地 一阶反转曲线主成分分析 等温剩磁分解 氧化还原 

分 类 号：P534.612[天文地球—古生物学与地层学] P532[天文地球—地质学] P318.4