Establishment of the stable isotopic stratigraphy of Banded Iron Formations

带状铁地层（BIFs）、层状锰矿床和二氧化硅烧结矿是具有清晰带状结构的化学沉积物的典型例子。这些沉积岩是随着溶液中二氧化硅、铁和锰的溶解度降低而从海水或热液溶液中沉淀到海底或陆上的。测定了这些带状化学沉积岩中氧、碳、硫稳定同位素组成的变化，以阐明其成因。将新开发的co_2激光微探针氟化技术应用于西澳大利亚Hamersley盆地Brockman铁组，研究了石英在燧石和氧化铁介带中的亚毫米尺度氧同位素组成。结果表明，bif的δ ^<18>O值在16.0 ~ 23.0*之间变化，与前人研究的bif同位素均质相反。δ ^<18> 0的大变化可能表明热液活动是导致Hamersley bfs形成的原因。测定了西澳大利亚马拉曼巴铁组页岩大带中有机碳和碳酸盐碳的同位素值。极低的有机C δ ^<13>C值（-41.0—37.1*）表明海洋中存在变暖生物和变养生物的活动。根据碳酸盐碳同位素组成估算海水中溶解碳酸氢盐的δ ^<13>C为δ ^<13>C=—12*。与现代海洋HCO_3^-（—1.0*）相比，这一低值也被解释为受甲烷菌和甲烷氧化菌活动影响的碳循环系统的结果。测定了北野五金矿石英烧结矿中石英的δ ^<18>O值和野田多川矿变质层状锰矿中硅酸锰矿物的δ ^<18>O值。讨论了水热溶液的来源。

Banded iron formations (BIFs), bedded manganese deposits, and silica sinters are the typical examples of chemical sediments that possess clear banding texture. These sedimentary rocks have precipitated on seafloor or subaerial surface, from seawater or hydrothermal solutions with the decrease of solubilities of silica, iron, and manganese in solutions. Variation of stable isotopic compositions of oxygen, carbon, and sulfur in these banded chemical sedimentary rocks have been measured to clarify their genesis.1.Newly developed CO_2-laser microprobe fluorination technique was applied to the Brockman Iron Formation, Hamersley basin, Western Australia, to investigate submillimeter scale oxygen isotopic compositions of quartz both hosted in chert and iron-oxide mesobands. Our data show that delta^<18>O values of BIFs vary between 16.0 and 23.0*, on the contrary to the previous studies that BIFs are isotopically homogeneous. The wide variation of delta^<18>O probably suggests that hydrothermal activities have been responsible for the formation of Hamersley BIFs.2.Isotopic values of organic and carbonate carbon in shale macrobands of the Marra Mamba Iron Formation, Western Australia were measured. The very low delta^<13>C values of organic C,-41.0--37.1*, suggest the activity of the metanogens and metanotrophs in the ocean. The delta^<13>C of dissolved bicarbonate in seawater estimated from carbon isotopic compositions of carbonate was delta^<13>C=--12*. This low value, compared to that of the modern marine HCO_3^- (--1.0*), was also explained as the results of a carbon-cycle system affected by the activities of metanogens and methanotrophs.3.The delta^<18>O values of quartz in silica sinter from the Kitano-oh gold deposits, and those of manganese silicate minerals from the metamorphosed bedded manganese deposits of the Noda-Tamagawa mine were measured. The origin of hydrothermal solutions is discussed.