(Appendix) Chemical composition of bottom sediments at DSDP Leg 72 Holes

The distributions of calcium carbonate, of amorphous silica, and of 21 chemical compounds and elements in sediments of Holes 515A, 515B, 516, 516F, 517, and 518 are highly nonuniform; they change depending on the sediment types, grain size, and mineral composition. The main source of the lithogenous elements (K, Li, Rb, Fe, Ti, Zr, Ni, Cr, Sn) is terrigenous matter of South America. These elements correlate well or at least satisfactorily with each other and with the sum of clay minerals. CaCO3, amorphous SiO2 and organic C form a second group, the main source of which is biota of the ocean. Zn, Cu, Ba, Mo, (V, Na) are a third group, which is supplied by both terrigenous and biogenic matter. Judging by the distribution of chemical elements and components in sediments of Site 515, this area of the Brazil Basin is characterized by the rather constant conditions of pelagic terrigenous sedimentation from upper Eocene till Holocene. Small changes in chemical composition of sediments throughout the section are linked mainly to the evolution of subaerial source provinces, changes in hydrodynamic regime, and fluctuations of the ocean level. The chemical composition of sediments from the Rio Grande Rise sites suggests the existence of three main stages of sedimentation in this area. The first stage is the initial period of sediment accumulation on basalts at the beginning of the Late Cretaceous. Then followed sedimentary conditions notable for their sharp changes in chemical composition and type. Beginning in the middle Eocene and persisting into the Holocene, stable conditions of sedimentation characterize a third stage, represented by the formation of approximately 700 m of nannofossil oozes of rather monotonous chemical composition.515A、515B、516、516F、517及518号钻孔（Holes）沉积物中，碳酸钙（calcium carbonate）、无定形二氧化硅（amorphous silica）以及21种化合物与元素的分布极不均匀，其分布特征随沉积物类型、粒度及矿物组成的变化而改变。 岩源元素（lithogenous elements）（K、Li、Rb、Fe、Ti、Zr、Ni、Cr、Sn）的主要来源为南美洲陆源物质（terrigenous matter）。这些元素彼此之间以及与黏土矿物（clay minerals）总含量之间均呈现显著相关性，或至少具有较好的相关性。碳酸钙（calcium carbonate）、无定形二氧化硅（amorphous silica）与有机碳（organic C）构成第二组组分，其主要来源为海洋生物（biota）。Zn、Cu、Ba、Mo、（V、Na）则为第三组组分，其物质供给同时涵盖陆源与生物成因（biogenic）两类物质。 基于515钻探站位（Site 515）沉积物中化学元素与组分的分布特征可知，巴西盆地该区域自始新世晚期（upper Eocene）至全新世（Holocene），始终处于较为稳定的远洋陆源沉积环境。剖面内沉积物化学成分的小幅变化，主要与陆上物源区（subaerial source provinces）演化、水动力条件（hydrodynamic regime）改变以及海平面波动相关。 里奥格兰德海隆（Rio Grande Rise）各钻探站位沉积物的化学成分特征表明，该区域的沉积作用可划分为三个主要阶段。第一阶段为白垩纪晚期（Late Cretaceous）初期玄武岩基底上的初始沉积堆积期。随后进入第二阶段，该阶段以沉积物化学成分与沉积类型的剧烈变化为典型特征。自始新世中期（middle Eocene）直至全新世（Holocene），为第三阶段，该阶段以稳定的沉积环境为特征，形成了总厚度约700米、化学成分较为均一的超微化石软泥（nannofossil oozes）。