C13C12 abundances in components of carbonaceous chondrites and terrestrial samples

The C13C12 compositions of components from nine carbonaceous chondrites were measured mass spectrometrically. Direct and indirect measurements revealed that the carbon. ates are significantly enriched in C13 with δC13 usually ranging from +40 to +60%. PDB. In contrast, the residue from acid treatment was considerably lighter, as low as −27%. The bulk isotopic composition of specimens from any one meteorite varied considerably, dependent upon the relative concentrations of carbonate and organic matter. Of the extractable organic matter in Orgueil, the saponifiable fraction had a δC13 value of −25%., while the non-saponifiable was significantly heavier (−13%. PDB). A number of terrestrial samples were also examined in order to 1. (1) provide checks on the experimental procedures and 2. (2) help to interpret the meteoritic data. Although similar fracfcionation patterns can be found in terrestrial materials, the C13C12 variations are smaller by a factor of 3 than the equivalent ones in meteorites. Possible mechanisms for the meteoritic trends are discussed.