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近年来,钼(Mo)元素有关的地球化学指标在刻画古海洋化学环境上发挥越来越重要的作用.本文系统介绍了Mo在海洋地球化学循环过程中的富集和同位素分馏基本原理及其在古海洋化学重建中的具体应用.综述表明:铁锰氧化物/氢氧化物的吸附和H2S的硫代作用是Mo在沉积物中富集的主要途径.因此,缺氧沉积物中Mo的富集通常反映了水柱和/或沉积物孔隙水中H2S的出现.硫化沉积物中Mo富集程度除与水柱或孔隙水中硫化程度有关外,还与海洋Mo库的大小有关.基于上述原理,对海洋硫化沉积物中Mo及Mo/TOC的地史演化重建表明:海洋Mo库演化与大气和海洋的演化历程具有很好的对应关系,表现出与地球两次大气-海洋氧化事件对应的阶段性演化特征.Mo同位素分馏原理及应用表明:强硫化沉积物可以有效记录沉积时海水的Mo同位素组成,而其他过程,包括锰铁氧化物/氢氧化物的吸附作用、低浓度H2S作用等均会导致沉积物不同程度富集轻Mo同位素.成岩作用可能会导致上述Mo富集和同位素分馏过程复杂化.在对沉积时海水的Mo同位素组成和不同水体环境下输出的Mo同位素组成进行必要约束的前提下,应用Mo同位素质量平衡模型可以对地质历史时期海洋总体的氧化还原状态进行定量重建.综上,Mo对局部和全球海洋的氧化还原状态变化敏感,可以有效应用于古海洋不同尺度的水体化学重建;但由于海洋化学过程的复杂性,在应用Mo地球化学指标进行古海洋化学重建时需要注意可能的多地球化学过程叠加的干扰.
In recent years, geochemical indicators related to molybdenum (Mo) have played more and more important roles in depicting paleoceanochemical environments.In this paper, the basic principles of enrichment and isotopic fractionation of Mo in marine geochemical cycles It is shown that the adsorption of Fe-Mn oxides / hydroxides and the thio-reaction of H2S are the main ways for the enrichment of Mo in sediments. Therefore, the contents of Mo in the anoxic sediments Enrichment generally reflects the presence of H 2 S in pore water of sediments and / or sediments, and the degree of enrichment of Mo in sulphide sediments is related to the size of marine Mo reservoirs, in addition to the degree of sulphurization in the water column or pore water.Based on the above principle, The historical reconstruction of Mo and Mo / TOC in marine sulfide deposits shows that the evolution of marine Mo reservoirs has a good correspondence with the evolution of the atmosphere and oceans, and shows the stage corresponding to the two atmospheric-oceanic oxidation events of the Earth The evolution of Mo isotope fractionation theory and application shows that the strongly sulphide sediments can effectively record the Mo isotopic composition of seawater during sedimentation, while the other processes, including the adsorption of ferromanganese oxide / hydroxide The use of low concentrations of H2S and other effects will lead to different degrees of enrichment of sediments of light Mo isotopes.Diolite may lead to the complexity of the Mo enrichment and isotopic fractionation process.In the deposition of seawater Mo isotope composition and water environment Output of Mo isotope composition under the premise of the necessary constraints, the application of Mo isotope mass balance model can be geological history of the redo state of the ocean quantitative reconstruction. In summary, Mo local and global ocean redox state changes sensitive to However, due to the complexity of ocean chemistry processes, it is necessary to pay attention to the superimposition of possible multi-geochemical processes in the application of Mo geochemical indicators for paleoceanochemical reconstruction.