Stable isotope ratios and geochemical composition of authigenic carbonates from ODP Sites 186-1150 and 186-1151

Several carbonaceous layers or fragments were recovered from sediments of Sites 1150 and 1151 on the deep-sea terrace of the Japan Trench during Leg 186. The X-ray diffraction analysis (XRD) data indicate that these are predominantly dolomitic. In this study, carbon and oxygen isotopes of these carbonates recovered at Sites 1150 and 1151 are presented. The oxygen isotope ratios of the dolomites analyzed range from +0.4 per mil to +4.1 per mil vs. Peedee formation belemnite (PDB) and those of calcites from +0.6 per mil to +2.8 per mil PDB. The isotopic composition of carbon varies from -7.0 per mil to +12.3 per mil PDB in dolomite and from -13.4 per mil to -24.1 per mil PDB in calcite. The wide range of carbon isotopic compositions indicates that the carbonate samples were formed by the decomposition of organic matter through reactions such as oxidation, sulfate reduction, and methane formation during diagenesis.

在第186航次（Leg 186）期间，科研人员从日本海沟深海阶地的1150和1151站位沉积物中回收得到多套含碳地层或碳质碎屑。X射线衍射分析（X-ray diffraction, XRD）结果显示，此类含碳物质主要以白云石质组分为主。本研究报道了从1150和1151站位回收的上述碳酸盐样品的碳、氧同位素测试数据。经测试的白云石氧同位素比值相对于佩迪组箭石（Peedee formation belemnite, PDB）标准介于+0.4‰至+4.1‰之间，方解石的氧同位素比值则介于+0.6‰至+2.8‰（相对于PDB）。白云石的碳同位素组成介于-7.0‰至+12.3‰（相对于PDB），方解石的碳同位素组成则介于-13.4‰至-24.1‰（相对于PDB）。碳同位素组成的宽泛分布区间表明，本次研究的碳酸盐样品是在成岩作用阶段，经由氧化作用、硫酸盐还原作用以及甲烷生成等反应，由有机质分解形成的。