Geochemistry of pore water and sediments from ODP Leg 136 sites

During Leg 136 drilling was conducted at two sites in pelagic sediments of the north central Pacific Ocean. In this report, pore-water analyses for major seawater constituents, alkalinity, ammonia, nitrate, phosphate, silica, Ba, Fe, Li, Mn, and Sr are presented. Although concentration gradients are generally weak, resulting from slow sedimentation and concomitant diffusive communication with overlying water, there is evidence of sediment/pore-water interactions, associated sediment diagenesis, and formation of authigenic minerals. Bulk major and trace element compositions of the sediments are consistent with reactions inferred to occur within the sediments and with the lithology and mineralogy. Elemental compositions of the sediments are not strongly affected by diagenesis and are primarily related to the dominant mineralogy. Sediments are typical of deep ocean pelagic settings with a significant contribution from the alteration of volcanic ash and the formation of zeolites. Sedimentary rare earth element patterns also provide evidence of active scavenging processes by Mn and Fe oxide phases in the deeper sediments at Site 842.

第136航次（Leg 136）在中北太平洋远洋沉积物（pelagic sediments）的两个站位开展了钻探作业。本报告呈现了该作业的孔隙水分析（pore-water analyses）结果，涵盖主要海水组分、碱度（alkalinity）、氨（ammonia）、硝酸盐（nitrate）、磷酸盐（phosphate）、二氧化硅（silica）、钡（Ba）、铁（Fe）、锂（Li）、锰（Mn）及锶（Sr）。尽管受缓慢沉积作用（slow sedimentation）及伴随的与上覆水体（overlying water）的扩散交换影响，浓度梯度（concentration gradients）普遍较弱，但仍存在沉积物-孔隙水相互作用（sediment/pore-water interactions）、相关沉积物成岩作用（sediment diagenesis）以及自生矿物（authigenic minerals）形成的相关证据。沉积物的整体常量与微量元素组成（bulk major and trace element compositions）与沉积物内部推断发生的反应、岩性（lithology）及矿物学（mineralogy）特征相吻合。沉积物的元素组成受成岩作用影响微弱，主要受控于优势矿物组合（dominant mineralogy）。该沉积物属于典型的深海远洋沉积环境（deep ocean pelagic settings）产物，其中火山灰蚀变（alteration of volcanic ash）与沸石（zeolites）形成过程贡献显著。沉积物的稀土元素配分模式（rare earth element patterns）同样证实，842站位（Site 842）深层沉积物中的锰铁氧化物相（Mn and Fe oxide phases）介导了活跃的清除作用过程（scavenging processes）。