Sulfur and oxygen isotopic study of barite concretions from banks in the Japan Sea off the Northeast Honshu, Japan

Barite concretions from the Shinguri and other banks of the Japan Sea off the Northeast Honshu have sulfate extremely enriched in heavy sulfur and oxygen isotopes; the δ34S value relative to Canõn Diablo troilite ranges from +47.5 to +86.7‰ and the δ18O value relative to SMOW from +24 to +29‰. When δ34S values are plotted against δ18O values, most data closely fit a line having a slope of 4 (Fig.3). Although other possibilities can not be excluded, the isotopic and other geologic features strongly suggest that most plausible environments of their formation were isolated “sea water lakes” which possibly formed on the tops of these banks during the Quaternary glacier ages and where extensive bacterial reduction of sulfate took place. The barite concretions from New Zealand studied by RAFTER and MIZUTANI (1967) and a barite concretion from a bank off Baja, California are isotopically similar to those of the present study.