冲绳海槽沉积物孔隙水地球化学特征及其指示意义

Geochemical characteristics and indicative significance of pore water in the sediments of Okinawa Trough

通过对东海外陆坡–冲绳海槽GSW1孔沉积物孔隙水δ^(13)C、δ^(18)O、δ^(11)B、δ^(37)Cl同位素和Cl^(-)、SO_(4)^(2-)、K^(+)、Na^(+)等离子指标的分析,探讨了沉积物早期成岩作用、流体来源、迁移和氧化环境的变化。研究发现,GSW1孔孔隙水溶解无机碳主要来自海水和有机质,SO_(4)^(2-)浓度随深度下降比较平缓,Cl^(-)浓度远低于海水,该孔表层沉积物中硫酸盐消耗主要由有机质硫酸盐还原作用(OSR)所控制,甲烷厌氧氧化作用(AOM)发生在4 m以下更深的层位。OSR产生的H_(2)S向上扩散富集并被氧化,是导致GSW1孔110~360 cm处SO_(4)^(2-)浓度未明显下降的主要因素。孔隙水SO_(4)^(2-)浓度整体随着深度增加呈减小的趋势,表明GSW1孔沉积环境由氧化、次氧化环境逐渐转变为还原环境。δ^(11)B、δ^(37)Cl值垂向变化波动较大,一方面受到早期成岩阶段有机质降解的影响,也可能与孔隙流体扩散以及沉积物/孔隙水相互作用有关。

Through the analysis of the δ^(13)C,δ^(18)O,δ^(11)B,δ^(37)Cl isotopes and Cl^(-),SO_(4)^(2-),K^(+),and Na^(+)ion index in the sediment pore water of the core GSW1 in the East China Sea outer Slope-Okinawa Trough,the changes of early diagenesis,fluid sources,migration and oxidation environment of sediments were discussed.The results show that the pore water dissolved inorganic carbon of the core GSW1 mainly comes from sea water and organic matter,the concentration of SO_(4)^(2-)decreases more gently with depth,and the concentration of Cl^(-)is much lower than seawater.The sulfate consumption in the surface sediments of this pore is mainly caused by organoclastic sulfate reduction(OSR)controlled,anaerobic oxidation of methane(AOM)occurs in deeper layers below 4 m.The H2S produced by OSR diffuses upwards and is enriched and oxidized,which is the main factor that causes the 110-360 cm SO_(4)^(2-)content to not significantly decrease.The overall trend of pore water SO_(4)^(2-)concentration decreases with depth,indicating that the deposition environment of core GSW1 has gradually changed from an oxidizing and sub-oxidizing environment to a reducing environment.The vertical changes of δ^(11)B and δ^(37)Cl fluctuate greatly.On the one hand,they are affected by the degradation of organic matter in the early diagenesis stage,and they may also be related to the diffusion of pore fluid and sediment/pore water interaction.