U同位素在重建古海洋氧化还原环境中的应用  

Application of U Isotope Fractionation Effect in the Analysis of Paleooceans Redox Environments

作　　者：朱紫光 侯佳凯 朱光有 李茜 厉梦琪 Zhu Ziguang;Hou Jiakai;Zhu Guangyou;Li Xi;Li Mengqi(PetroChina Research Institute of Petroleum Exploration and Development,Beijing 100083,China;School of Geosciences,Yangtze University,Wuhan 430100,China)

机构地区：[1]中国石油勘探开发研究院,北京100083 [2]长江大学地球科学学院,湖北武汉430100

出　　处：《地球科学》2025年第3期1250-1262,共13页Earth Science

基　　金：国家自然科学基金面上项目(No.42073068).

摘　　要：U同位素载体在沉积和成岩过程中均会发生显著的分馏,导致人们对古海洋氧化还原环境的误判.本文系统梳理了U同位素的分馏机制,逐一阐述了其在碳酸盐岩、黑色页岩和铁锰结壳的沉积和成岩过程中的分馏行为,并提出了理想载体的特征及消除沉积成岩效应的技术手段.总体而言,U同位素分馏机制丰富多样,分馏程度受反应速率、电子通量和环境离子强度等多种因素影响.碳酸盐岩和黑色页岩的沉积与成岩作用通常导致同位素组成偏重,而铁锰结壳则会出现相反方向的分馏,分馏程度受沉积环境和岩性组成的控制.实际应用中应选择成岩程度较低、以文石为主的海相碳酸盐岩,并采用离子交换色谱等技术手段,精确表征古海洋氧化还原环境.U isotope carriers undergo significant fractionation during sedimentation and diagenesis,often leading to misinterpretations of paleoocean redox conditions.This study systematically reviews the fractionation mechanisms of U isotopes,detailing their behavior during the sedimentation and diagenesis of carbonates,black shales,and ferromanganese crusts.It also proposes characteristics of ideal carriers and techniques to mitigate diagenetic effects.Overall,U isotope fractionation mechanisms are diverse,influenced by factors such as reaction rates,electron flux,and ionic strength.Sedimentation and diagenesis in carbonates and black shales typically result in heavier isotope compositions,while ferromanganese crusts exhibit fractionation in the opposite direction.The extent of fractionation is controlled by depositional environments and lithological composition.In practical applications,marine carbonates with low diagenetic alteration and primarily aragonitic mineralogy are recommended.Advanced techniques,such as ion-exchange chromatography,should be employed to accurately reconstruct the redox conditions of paleooceans.

关 键 词：U同位素 分馏效应 分馏机理 古海洋 氧化还原环境 沉积学 地球化学 

分 类 号：P597[天文地球—地球化学]