ABSTRACT

-The carbon and oxygen isotopic abundances were determined for calcites and dolomites filling gaps in the Ogi basalt. The isotopic ratios of the carbonates are in the range from -24 to -32 ‰ in δ¹³C_PDB and from 31 to 36 ‰ in δ¹⁸O_SMOW. They were too low in δ¹³C and too high in δ¹⁸O to understand that they were derived from carbonatite. The δ¹⁸O values are also too high to interpret that they were derived from basaltic magma. The isotopic data suggest that they were precipitated probably from lagoonal sea water under anaerobic conditions.