铀同位素反演古海洋环境的研究进展  

Research advance for uranium isotope as a quantitative proxy for paleo-oceans anoxic or oxic environment

作　　者：罗劬侃 曹建华[2,3] 钟亮[2,3] 白冰 王奇岗 廖红为[2,3,5] 宗克清 覃汉莲 LUO Qukan;CAO Jianhua;ZHONG Liang;BAI Bing;WANG Qigang;LIAO Hongwei;ZONG Keqing;QIN Hanlian(School of Earth Sciences,China University of Geosciences,Wuhan,Hubei 430078,China;Institute of Karst Geology,CAGS/Key Laboratory of Karst Dynamics,MNR&GZAR/International Research Center on Karst under the Auspices of UNESCO,Guilin,Guangxi 541004,China;Pingguo Guangxi,Karst Ecosystem,National Observation and Research Station,Pingguo,Guangxi 531406,China;School of Environmental Studies,China University of Geosciences,Wuhan,Hubei 430078,China;Key Laboratory of Geological Survey and Evaluation of Ministry of Education,China University of Geosciences,Wuhan,Hubei 430078,China)

机构地区：[1]中国地质大学地球科学学院,湖北武汉430078 [2]中国地质科学院岩溶地质研究所/自然资源部、广西岩溶动力学重点实验室/联合国教科文组织国际岩溶研究中心,广西桂林541004 [3]广西平果喀斯特生态系统国家野外科学观测研究站,广西平果531406 [4]中国地质大学环境学院,湖北武汉430078 [5]中国地质大学地质探测与评估教育部重点实验室,湖北武汉430078

出　　处：《中国岩溶》2024年第4期957-968,共12页Carsologica Sinica

基　　金：广西自然科学基金项目“238U/235U对泥盆纪-石炭纪古海洋环境转型的指示意义——以桂林南边村全球辅助层型剖面为例”(2022GXNSFBA035593)。

摘　　要：铀同位素因可定量反演全球尺度古海洋缺氧洋底分布面积占比(%)而被广泛应用在埃迪卡拉纪末期以来的重要大洋缺氧或生物事件中。通过对国内外相关文献进行综述,系统总结了利用铀同位素开展定量反演的原理、方法与成果,初步构建了铀同位素定量反演的还原性海洋洋底面积占比(%)与大气氧气浓度、大洋缺氧或生物事件的耦合关系,发现:(1)铀同位素反演结果与各缺氧或生物事件吻合度较高,表明铀同位素确实为有效的全球尺度深时尺度定量反演指标;(2)还原性海洋洋底扩张与大气氧气浓度变化之间普遍存在滞后性,推测与海平面、海洋生产力、海洋内部环流变化及底层水氧化还原反应的滞后性相关。指出铀同位素反演受样品后期成岩、风化蚀变作用的影响,可能存在解译误差;铀同位素单指标解译结果存在精准度偏低的缺点,需采用多指标综合反演的方法提升反演精度。Compared with other elements that are sensitive to redox environments(U,Mo,V,S,Fe,Cu,Zn,Ni),uranium isotopes have the advantage to quantitatively reflect long-term and global-scale paleoredox of oceans,due to its uniform composition in the oceans globally,and quantitative relationship with the proportion of the anoxic seafloor areas in ancient oceans.Therefore,uranium isotopes are widely used in the events such as the Late Ediacaran,Early Cambrian,Ordovician/Silurian,Late Devonian,Devonian/Carboniferous,Permian/Triassic,Triassic/Jurassic,and OAE 2(Oceanic Anoxic Event 2).Through a review of previous papers,the author has systematically summarized the principles,methods,and results of using uranium isotopes for quantitative analysis of paleoredox.It has found that the core of current uranium isotopes quantitative method is the mass balance box model of seawater uranium(mass balance box model)and its isotopes and the related variants.By simplifying the uranium mass balance box model based on the proportion and fractionation coefficient of different types of uranium sinks,the redox environment and duration of ancient oceans can be quantitatively reflected.However,there may be ambiguity in the interpretation regarding whether the marine environment contains sulfur or not.In addition,by reviewing previous papers,the author has set up a preliminary coupling relationship among the proportion of anoxic seafloor area(%)reflected from uranium isotopes,atmospheric oxygen concentration,and oceanic anoxic or biological events.It has found that:(1)the uranium isotope analysis results were highly consistent with the occurrence time and extent of various anoxic or biological events,especially being coincident with the events that occurred in the Late Ediacaran,Late Ordovician,Late Devonian Frasnian-Famennian,Devonian/Carboniferous,Permian/Triassic,and Triassic/Jurassic periods,indicating that uranium isotopes are indeed an effective global scale and deep-time scale proxy for quantitative analysis on paleoredox of oceans.(2)The t

关 键 词：铀同位素 定量反演 铀同位素模型 大洋缺氧 生物事件 

分 类 号：P736[天文地球—海洋地质]