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...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。展开更多
In this study, we analyzed stable calcium isotope results of authigenic carbonates from two cold seep areas of the Dongsha area and the Baiyun Sag in the northern South China Sea. The stable isotopes of carbon and oxy...In this study, we analyzed stable calcium isotope results of authigenic carbonates from two cold seep areas of the Dongsha area and the Baiyun Sag in the northern South China Sea. The stable isotopes of carbon and oxygen as well as the mineral composition of authigenic carbonates were used to investigate control calcium isotope fractionation. The δ44/40Ca ratios of the southwestern Dongsha area samples ranged from 1.21‰ to 1.52‰ and the ratio of the Baiyun Sag sample was 1.55‰ of the SRM915a isotope standard. X-ray diffraction analysis showed that the carbonate samples consisted of dolomite, calcite and aragonite, with small amounts of high-Mg calcite and siderite. The δ13C values of the carbonates of the southwestern Dongsha area varied between δ49.21‰ and δ16.86‰ of the Vienna PeeDee Belemnite (VPDB) standard and the δ18O values ranged from 2.25‰ to 3.72‰ VPDB. The δ13C value of the Baiyun Sag sample was 2.36‰ VPDB and the δ18O value was 0.44‰ VPDB. The δ13C values of the carbonates of the southwestern Dongsha area revealed there is methane seeping into this area, with a variable contribution of methane-derived carbon. The sampled carbonates covered a range of δ13C values suggesting a dominant methane carbon source for the light samples and mixtures of δ13C values for the heavier samples, with possibly an organic or seawater carbon source. The δ18O values indicated that there is enrichment in 18O, which is related to the larger oxygen isotope fractionation in dolomite compared to calcite. The results of the Baiyun Sag sample exhibited normal seawater carbon and oxygen isotopic values, indicating that this sample is not related to methane seepage but instead to precipitation from seawater. The relatively high δ44/40Ca values indicated either precipitation at comparatively high rates in pore-water regimes with high alkalinity, or precipitation from an evolved heavy fluid with high degrees of Ca consumption (Raleigh type fractionation). The dolomite samples from the Dongsha area revea展开更多
文摘前人对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。
基金supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-YW-GJ03-01)the National Natural Science Foundation of China (40706022, U0733003 and 41176052)+1 种基金the National Basic Research Program of China (2009CB219502-4)the Knowledge Innovation Program of South China Sea Institute of Oceanology, Chinese Academy of Sciences (LYQY200806)
文摘In this study, we analyzed stable calcium isotope results of authigenic carbonates from two cold seep areas of the Dongsha area and the Baiyun Sag in the northern South China Sea. The stable isotopes of carbon and oxygen as well as the mineral composition of authigenic carbonates were used to investigate control calcium isotope fractionation. The δ44/40Ca ratios of the southwestern Dongsha area samples ranged from 1.21‰ to 1.52‰ and the ratio of the Baiyun Sag sample was 1.55‰ of the SRM915a isotope standard. X-ray diffraction analysis showed that the carbonate samples consisted of dolomite, calcite and aragonite, with small amounts of high-Mg calcite and siderite. The δ13C values of the carbonates of the southwestern Dongsha area varied between δ49.21‰ and δ16.86‰ of the Vienna PeeDee Belemnite (VPDB) standard and the δ18O values ranged from 2.25‰ to 3.72‰ VPDB. The δ13C value of the Baiyun Sag sample was 2.36‰ VPDB and the δ18O value was 0.44‰ VPDB. The δ13C values of the carbonates of the southwestern Dongsha area revealed there is methane seeping into this area, with a variable contribution of methane-derived carbon. The sampled carbonates covered a range of δ13C values suggesting a dominant methane carbon source for the light samples and mixtures of δ13C values for the heavier samples, with possibly an organic or seawater carbon source. The δ18O values indicated that there is enrichment in 18O, which is related to the larger oxygen isotope fractionation in dolomite compared to calcite. The results of the Baiyun Sag sample exhibited normal seawater carbon and oxygen isotopic values, indicating that this sample is not related to methane seepage but instead to precipitation from seawater. The relatively high δ44/40Ca values indicated either precipitation at comparatively high rates in pore-water regimes with high alkalinity, or precipitation from an evolved heavy fluid with high degrees of Ca consumption (Raleigh type fractionation). The dolomite samples from the Dongsha area revea
