黄、东海陆架泥质区自生黄铁矿成因及其控制因素

Formation Mechanism and Controlling Factors of Authigenic Pyrite in Mud Sediments on the Shelf of the Yellow Sea and the East China Sea

海洋自生黄铁矿的形成过程与有机质矿化过程密切相关,是构成全球C-S-Fe生物地球化学循环的重要一环。黄、东海陆架在全新世高水位期以来,广泛发育泥质沉积区,其中赋存大量自生黄铁矿,为研究其成因及其控制因素提供了契机。平面上,黄铁矿的分布与细粒泥质沉积伴生,因为细粒沉积物相对富集有机质且沉积环境稳定,有利于微生物硫酸盐还原的进行。黄、东海沉积动力、有机质来源和海洋生产力的区别导致黄铁矿生成与埋藏的差异,进而引起相关指标(例如C/S值)的不同。垂向上,黄铁矿的含量一般随着深度的增加而升高,说明随着埋深的增大,孔隙水中溶解氧耗尽后有利于硫酸盐还原的进行;黄铁矿硫同位素随着深度的增加而加重(富集^(34)S),这可能与成岩系统的封闭性有关,也可能与甲烷厌氧氧化驱动的硫酸盐还原有关。另外,沉积速率通过影响有机质的埋藏、孔隙水和海水的联通效率以及硫酸盐—甲烷转换带的位置进而控制黄铁矿的含量及同位素组成。黄、东海陆架泥质区在沉积动力和沉积过程方面积累了大量优秀研究成果,可在此基础上,结合多硫同位素、原位微区测试等先进实验方法,发掘自生黄铁矿在探讨现代海洋C-S-Fe循环及深时海洋化学演化等重大科学问题的潜在价值。

The formation process of marine authigenic pyrite(FeS2)is closely related to the organic mineralization process,representing an important part of the global C-S-Fe biogeochemical cycle.Since the Holocene highstand of sea level,the shelves of the Yellow Sea and the East China Sea have developed mud deposits extensively,in which a large number of authigenic pyrites are present,which provides an opportunity to study their genesis and controlling factors.In terms of spatial distribution,the distribution of pyrite is accompanied by fine-grained mud sediments,because fine-grained sediments are relatively rich in organic matter,and the relatively stable depositional environment is conducive to the progress of microbial sulfate reduction.The differences in sedimentary dynamics,organic matter sources and marine productivity in the Yellow Sea and the East China Sea lead to differences in the formation and burial of pyrite,which in turn cause differences in related indicators(such as the C/S ratio).In the vertical direction,the content of pyrite generally increases with the increase of depth,indicating that as the depth of burial increases,the dissolved oxygen in the pore water is depleted,which is beneficial to the sulfate reduction;the sulfur isotope of pyrite becomes isotopically heavy with the depth(enrichment of ^(34)S),which may be related to the openness of the diagenetic system,or the sulfate reduction driven by anaerobic oxidation of methane.In addition,the sedimentation rate controls the content and isotopic composition of pyrite via affecting the burial of organic matter,the efficiency of communication between pore water and seawater,and the location of the sulfate-methane transition zone.The mud areas of the shelves of the Yellow Sea and the East China Sea have accumulated a large number of excellent research results in sedimentary dynamics and sedimentary processes.On this basis,combined with advanced analyzing methods such as multi-sulfur isotopes,in-situ elemental on single pyrite crystal,the potential value of pyrite could be excavated to deal with major scientific issues such as the modern ocean C-S-Fe cycle and deeptime ocean chemical evolution.