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Calcium-aluminium-rich inclusions (CAIs), most commonly observed in carbonaceous chondrite groups (CV, CO, and CM chondrites), have anomalous oxygen isotopic compositions, with Δ[sup.17]O and Δ[sup.18]O values down to ~-40 per mil [...], 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 ([sup.16]O) excesses, similar to those in spine[ grains in calcium-aluminium-rich inclusions in Allende and other carbonaceous chondrites. The existence of [sup.16]O-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 [sup.16]O-rich carrier of presolar origin.

Focuses on excesses in olivine-rich inclusions in Yamato-86009 and Murchison chondrites. Their relation to calcium-aluminium-rich inclusions, most commonly observed in carbonaceous chondrite groups; Details of results of situ ion microprobe analyses of oxygen isotopes; Conclusion 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.