综合大洋钻探计划311航次沉积物中自生碳酸盐岩碳、氧稳定同位素特征

为了探索水合物背景下沉积物中自生矿物响应,对采自综合大洋钻探计划(IODP)311航次沉积物中自生碳酸盐岩颗粒进行了矿物组成、形貌特征和碳、氧稳定同位素特征等研究。X光粉晶衍射(XRD)和扫描电镜(SEM)结果显示碳酸盐岩颗粒的主要矿物成分是铁白云石和方解石,呈多孔状结核和不规则状集合体产出。碳酸盐岩颗粒的碳稳定同位素δ13CPDB低至-41.50‰,证实其碳源源自甲烷,其成因与甲烷厌氧氧化过程有关,印证了研究区存在海底甲烷渗漏现象,是甲烷水合物赋存区重要的识别标志之一。碳酸盐岩颗粒的氧稳定同位素δ18OPDB总体上随着沉积物深度增加而减小,可能指示沉积物的背景温度由下而上(从早到晚)逐渐降低。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碳酸盐岩的碳、氧稳定同位素记录,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类似的甲烷事件记录具有重要的理论和实践指导意义。

Stable Carbon and Oxygen Isotopes Characteristics of the Authigenic Carbonates in Recovered Sediments during IODP 311 Expedition

To understand better the responses of authigenic minerals in sediments of the gas hydrate geo-system,some authigenic carbonates in sediments from IODP 311 Expedition were analyzed for the purposes of studying their mineral components,textures,and stable carbon and oxygen isotopes.XRD and SEM results show that Fe-dolomites and calcites are the dominant minerals in the authigenic carbonates,which occurred mainly in pore-rich spheroids and un-regular aggregations.The δ13 CPDB of collected authigenic carbonates recorded the typical extreme negative values is low to-41.50‰,indicating the involvement of methane in the anaerobic oxidation of methane(AOM)under the methane seepage in gas hydrate geo-system.The δ18OPDB of the authigenic carbonates generally decreased with depth,possibly implying a decreasing environment temperature during carbonate precipitation from lower(old) to upper(new) part of sediment column.This study thus has a significant meaning in exploring the potential marine gas hydrate in China and in deciphering the ancient methane hydrate-associated sedimentary records in the Earth history.