HYDROGEN AND OXYGEN ISOTOPE COMPOSITIONS IN KEROGEN FROM THE ORGUEIL METEORITE - CLUES TO A SOLAR ORIGIN

Hydrogen and oxygen isotope contamination of acid-demineralised residues of the Orgueil carbonaceous meteorite has been accurately determined by an original method involving isotopically labeled reagents. Results are consistent with contamination occurring by addition and by isotopic exchange of a fraction of the indigenous reservoir with the reagents. The isotopic compositions of the uncontaminated non-exchangeable fraction of the acid residues are: δD = + 1360%., δ17O = +3.3%., δ18O = +6.0%.. They are ascribed to the mean insoluble meteoritic organic matter. It is unlikely that the number of isotopic reservoirs in the acid residues exceed 2. These results imply that, if organic oxygen and hydrogen acquired their isotopic compositions in the same environment, the process yielding the large deuterium enrichment of the insoluble kerogen has occurred within the solar gas, i.e., within the dense molecular cloud that gave birth to the solar nebula. In the course of this study, isotopically light carbon (δ13C ≤ -48%.) has been detected in the stepwise pyrolysis of Orgueil acid residues. © 1990.