南海神狐海域Site 4B沉积物地球化学特征及其对甲烷渗漏的指示意义  

Geochemical Characteristics of Site-4B Sediments from the Shenhu Area of the South China Sea: Implications for methane seepage

作　　者：王竣雅 邬黛黛[2] 陈雪刚[1] WANG JunYa;WU DaiDai;CHEN XueGang(Ocean College,Zhejiang University,Zhoushan,Zhejiang 316021,China;Key Laboratory of Gas Hydrate,Guangzhou Institute of Energy Conversion,Chinese Academy of Sciences,Guangzhou 510640,China)

机构地区：[1]浙江大学海洋学院,浙江舟山316021 [2]中国科学院天然气水合物重点实验室,中国科学院广州能源研究所,广州510640

出　　处：《沉积学报》2019年第3期648-660,共13页Acta Sedimentologica Sinica

基　　金：中国石油—中科院科技合作项目(2015A-4813);国家自然科学基金项目(41273022);中国科学院青年创新促进会(2014321)~~

摘　　要：前人对Site 4B站位海底浅表层沉积物的研究显示该站位历史上可能存在甲烷渗漏事件。为研究该站位的甲烷渗漏历史,分析了Site 4B站位柱状沉积物的元素地球化学特征,及沉积物中Mg/Ca和Sr/Ca比随深度的变化规律以及自生碳酸盐矿物的分布特征。元素相关性分析表明:研究区Ca、Sr等碳酸盐相关的元素极有可能来自于与甲烷渗漏有关的自生碳酸盐。结合沉积物的粒度特征,认为Site 4B站位在15.78 ka B.P.之前泥火山活动造成甲烷渗漏,且甲烷渗漏速率具有增大—减小的周期性变化特点。研究站位在24.15 ka B.P.、27.47 ka B.P.、31.05 ka B.P.具有相对较高的甲烷渗漏速率,且在31.05 ka B.P.达到最大值。研究结果对探明南海北部的甲烷渗漏历史具有重要的意义。Previous studies on Site 4B suggested the presence of methane seepage in this area. In this study,we systematically analyzed the particle size distribution,minerals,and chemical compositions of the sediments at an interval of 15 cm. The particle size distribution varied significantly at a depth of 98 cm,which is ascribed to the changed hydrodynamic conditions. Significantly increased particle size was discovered at depths of 161 cm,186 cm,and 213 cm. According to the sedimentation rate,these abnormally increased particle sizes occurred 24.15 ka,27.47 ka,and 31.05 ka,which may be related to methane seeping events.The chemical compositions of the sediments changed with the particle size variation. At depths lower than 98 cm,the concentrations of CaO,Na2O,and Sr increased with depth,while that of SiO2,Al2O3,Fe2O3,Px dramatically decreased. At depths larger than 98 cm,on the contrary,these elements did not change significantly with depth. The positive correlations between CaO,Na2O,and Sr,as well as the negative correlations between these elements and SiO2 indicated that the carbonates (containing Ca and Sr) were affected by secondary processes,e.g.,the production of authigenic carbonate from methane seepage. The variation of the Mg/Ca and Sr/Ca ratios as a function of depth suggests that the sediment might be affected by mud volcanic activity before 15.78 ka. The mud volcanic activity arrived at a maximum at 35.96 ka,where the highest Mg/Ca and Sr/Ca ratios were measured. Furthermore,we calculated the relative contents of aragonite,high-Mg calcite,biogenic calcite,and detrital materials by using Bayon's model. The results indicate that the detrital materials likely originated from a stable source,while the calcite and aragonite were authigenic carbonates produced by microbial activities related to methane seepage. Combined with previous studies on pyrite and the particle characteristics of the sediments,we postulated that the methane seepage was related to the mud volcano activity before 15.78 ka. These periodic mud

关 键 词：甲烷渗漏 自生碳酸盐 Sr/Ca MG/CA 南海 天然气水合物 

分 类 号：P618.13[天文地球—矿床学] P744.4[天文地球—地质学]