Osmium concentrations and ¹⁸⁷Os/¹⁸⁸Os ratios of three sediment reference materials

抄録

¹⁸⁷Os/¹⁸⁸Os ratios and osmium concentrations were analyzed in sedimentary reference materials JSd-3, JMS-1, and JMS-2, issued by the Geological Survey of Japan, using the isotope dilution method with negative thermal ionization mass spectrometry (ID-N-TIMS). The chemical procedures used in this study are based on Carius tube digestion combined with carbon tetrachloride extraction to separate Os. The obtained ¹⁸⁷Os/¹⁸⁸Os ratios of JSd-3, JMS-1, and JMS-2 were 0.941-1.149, 0.3894-0.465, and 0.747-0.848, respectively, and their Os abundances were 27.07-39.32 ppt, 80.8-106.6 ppt, and 281-317.2 ppt, respectively. Variations among the samples presumably reflect differences in sources and depositional environments. The Os isotopic ratios and abundances were variable within individual samples. The relative 95% confidence intervals of Os concentrations and isotopic ratios were respectively 13% and 6.2% for JSd-3, 15% and 9.8% for JMS-1, and 4.3% and 4.2% for JMS-2. These variations probably reflect the heterogeneity of the original rock of each reference material. Low concentration and high isotope ratio of JSd-3 probably results from the derivation of the original rocks from continental components with low Os abundance and elevated ¹⁸⁷Os/¹⁸⁸Os. Inputs of anthropogenic Os were inferred in JMS-1, a nearshore sediment from an urbanized locality, which had high Os contents and relatively low Os isotopic ratios. Greatly elevated Os concentrations and high ¹⁸⁷Os/¹⁸⁸Os in JMS-2, a pelagic clay, may reflect the scavenging of Os in seawater into Mn-Fe oxyhydroxides deposited on the seafloor.