Re-Os同位素在沉积地层精确定年及古环境反演中的应用进展

摘要

As Re and Os are organophilic and redox-sensitive, Re and Os are concentrated from seawater in organic-rich sediments. Re-Os geochronology of organic-rich sediments has the potential to provide direct depositional ages and vital information on the Os isotope. The successful application of Re-Os in organic-rich sedimentary rocks making it possible to obtain absolute ages for the deposition of sedimentary successions directly, and hence the age of some sedimentary deposits and glacial can be dated and constrained. From the Re-Os isotope characteristics obtained for organic-rich sediments, the Palaeoenvironment can be reconstructed, and this helps to know and understand the paleoenvironmental evolution and to date and trace the metallic deposits and oil/gas reservoir, thus playing an important role in studying numerous major issues, such as the mass extinction and the impact events. Based on the Re-Os isotope data available, the authors obtained Os isotope curve for seawater from 2.7 Ga to the present day. In addition, the variations in the Os isotope compositions of seawater since 2.7 Ga are helpful to the study of the paleoenvironmental evolution. In this paper, some factors affecting the precision of Re-Os isochron age for organic-rich sediments are investigated. The Re-Os isotope system will play a unique role in the dating of organic-rich sedimentary rocks and the reconstruction of palaeoenvironment.%Re-Os 同位素亲有机质的性质,使得富有机质沉积岩在沉积的过程中能够吸附富集海水中的 Re、Os,沉积岩的沉积压实过程也是其中 Re-Os 同位素体系封闭计时的过程,沉积岩 Re-Os 同位素等时线年龄代表地层沉积时代, Os同位素初始比值187Os/188Os反映沉积时海水的Os同位素比值。Re-Os同位素体系在富有机质沉积岩中的成功应用,能够直接确定地层沉积时代,从而对地层界线进行直接厘定,并且能够对一些沉积矿床形成时代、冰川事件发生时代进行厘定和限制。通过沉积岩 Re-Os 同位素特征,可以对古环境进行反演,有助于了解全球大气海洋的演化,气候的变化,对研究生物灭绝等重大地质事件发生的时限和机制以及金属矿床的成矿物质来源具有重要意义。文章阐述了Re-Os同位素在富有机质沉积岩中应用的原理,并列举了Re-Os同位素在沉积地层精确定年及古环境反演中应用实例,说明了富有机质沉积岩Re-Os同位素分析精度及其影响因素,以使 Re-Os 同位素体系作为一种强有力的工具,解决更多的沉积地层时代问题以及更好地对古环境进行反演。