沉积岩汞同位素的古环境指示意义  

Mercury isotopes in sedimentary rocks as a paleoenvironmental proxy

作　　者：郑旺 周岸文 孙若愚 陈玖斌 Wang Zheng;Anwen Zhou;Ruoyu Sun;Jiubin Chen(Institute of Surface-Earth System Science,School of Earth System Science,Tianjin University,Tianjin 300072,China)

机构地区：[1]天津大学地球系统科学学院,表层地球系统科学研究院,天津300072

出　　处：《科学通报》2023年第6期628-643,共16页Chinese Science Bulletin

基　　金：国家自然科学基金(41973009,41625012,41830647,41961144028)资助。

摘　　要：环境与生命的协同演化是地球科学的核心问题之一,而古环境的精确重建对于认识生命演化规律、机制以及预测地球宜居性的未来发展方向具有至关重要的意义.近年来,沉积岩中的汞及其同位素组成在重建地球古环境演化方面展现出巨大的潜力,获得了广泛的关注和应用,已发展成一个新的研究方向.其主要原因是汞及其同位素组成在记录古代火山活动和海洋氧化还原状态方面具有不可替代的优势,能为研究上述过程与重大环境和生命演化事件的关系提供新的证据.本文系统分析了古代沉积岩的汞同位素数据及其意义,总结了大型火山活动和海洋氧化还原状态改变引起汞同位素变化的特征与机制,深入探讨了火山类型及释放汞的方式、大气和海洋汞循环过程、沉积环境、岩性、成岩作用、汞赋存形态等因素对沉积岩汞同位素组成的影响,并对该领域当前存在的问题和发展前景作出了评述和展望.总体而言,这一研究领域仍处于起步阶段,对古环境演化事件中汞同位素组成的变化规律和分馏机理还缺乏系统和定量的认识,亟须深入研究.未来需要揭示古环境汞循环过程中的同位素分馏机理,进一步明确汞同位素指示古环境演化的原理和影响因素,拓展其在环境和生命协同演化领域的应用.The co-evolution of Earth’s environment and life is one of the most fundamental questions in Earth science.Precise paleoenvironmental reconstruction is the key to understanding the evolution of life,which help predict the future prospect of Earth’s habitability.In recent years,mercury(Hg)and its stable isotopes in ancient sedimentary rocks have emerged as irreplaceable tools to reconstruct Earth’s paleoenvironment,opening a new frontier in Earth science.This study summaries the current state of Hg isotope geochemistry in paleoenvironmental research,and reviews the status and prospects of this promising research field.Mercury and its stable isotopes have been primarily applied as proxies for large-scale volcanic activities(e.g.,large igneous provinces,LIPs),terrestrial soil erosion,and oceanic redox conditions,facilitating the evaluation of the roles of these processes in critical environmental and biotic crises,such as mass extinctions.For example,LIPs are able to emit large quantities of Hg that are readily dispersed globally through the atmosphere,leading to widespread Hg enrichment in marine and terrestrial sediments.Mercury isotopes can distinguish between volcanic and non-volcanic Hg sources,owing to the unique mass-independent fractionation(MIF,represented by Δ^(199)Hg)that this element undergoes.During LIP events,the Δ^(199)Hg value can display either positive or negative shifts relative to the pre-volcanic values,or shifts towards the MIF value of direct volcanic emission(Δ^(199)Hg≈0).A positive shift is typically observed in sections where Hg emitted by volcanism has undergone long-distance transport before deposition,because the photochemical transformations during atmospheric dispersion typically result in positive Δ^(199)Hg in oxidized Hg species that deposit more easily to ocean.A negative shift is typically explained as the result of enhanced inputs of terrestrial Hg associated with soils and plants,which are characterized by negativeΔ^(199)Hg in modern environments.For example,most mar

关 键 词：汞同位素 古环境 生物大灭绝 火山 海洋氧化还原状态 地球宜居性 

分 类 号：P588.2[天文地球—岩石学] P597[天文地球—地质学]