A long duration of the 16 O-rich reservoir in the solar nebula, as recorded in fine-grained refractory inclusions from the least metamorphosed carbonaceous chondrites.

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In situ ion microprobe analyses of oxygen isotopes in Yamato-86009 and Murchison chondrites show that they contain abundant olivine-rich inclusions that have large oxygen-16 (16O) excesses, similar to those in spinel grains in calcium-aluminium-rich inclusions in Allende and other carbonaceous chondrites. The existence of 16O-enriched olivine-rich inclusions suggests that oxygen isotopic anomalies were more extensive in the early solar system than was previously thought and that their origin may be attributed to a nebular chemical process rather than to an unidentified 16O-rich carrier of presolar origin.

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