综合大洋钻探计划311航次沉积物中自生黄铁矿及其硫稳定同位素研究

Study on the Authigenic Pyrites and Their Sulfur Stable Isotopes in Recovered Sediments during IODP 311 Expedition

对综合大洋钻探计划(IODP)311航次652个岩心沉积物样品进行了自生黄铁矿颗粒筛选、显微形貌特征及其硫稳定同位素组成等初步研究。扫描电镜(SEM)照片显示黄铁矿以微球粒状和立方体状形貌产出,其成因与微生物作用和无机作用有关。黄铁矿的δ34SCDT值变化范围较大,从-35.4‰到+53.6‰,其成因与甲烷厌氧氧化作用(AOM)的关系密切。海水源为主的硫酸盐参与了沉积物上部的AOM过程,黄铁矿硫稳定同位素正偏的原因可能与较强的AOM作用和较多的残余硫酸盐参与有关。冷泉背景站位中黄铁矿的δ34SCDT值随着深度增加而增加,从浅表层的-35.83‰增加到深处的32.49‰,反映深处沉积物内黄铁矿形成过程中曾有过较多的残余硫酸盐参与还原,暗示其背景曾经是更高的甲烷通量和更强的AOM作用。研究结果提供了现代海洋天然气水合物背景下沉积物中自生黄铁矿及其硫稳定同位素特征记录,对于寻找我国海域天然气水合物资源,探索地史时期古海洋沉积物中甲烷事件记录具有重要的意义。

To understand better the response of authigenic minerals in sediments of the gas hydrate system, total 652 sediment samples recovered from IODP 311 Expedition were washed and all authigenic pyrites were picked up. SEM photographs show that pyrites occurred in forms of both micro-spheroids and cubic crystal aggregations, caused by microbial fossilization and inorganic processes, respectively. The stable sulfur isotopic compositions seem to have a wide range of δ^34SCDT values from - 35.4‰ to ＋ 53.6‰ for the processes of anaerobic oxidation of methane（AOM）. Sea salt sulfate in the upper part of sediment column was dominantly reduced by AOM, and the remained sulfate involving reduction would probably cause positive sulfur isotopic excursion of pyrites. In the cold vent the δ^34SCDT values increase gradually with depth from -35.83‰ near the top sediment to 32. 49‰ in deep, indicating that more remained sulfates once involved in reduction under higher methane flux and more intensive AOM. This study will have important impact on exploring the potential marine gas hy-drate in China and on deciphering the ancient methane derived sedimentary records in the Earth history.