Deuterium/hydrogen ratios in unequilibrated ordinary chondrites

The discovery1 of oxygen of anomalous isotopic composition in the Allende meteorite during the early 1970s led to the detailed investigation of primitive materials for unusual isotopic signatures. One element studied was hydrogen; major enrichments in deuterium relative to terrestrial and proposed nebula compositions have been discerned by close examination of specific phases within various meteorite samples. Here we report high and variable deuterium enrichments in two of the most unequilibrated (unmetamorphosed) type LL3 ordinary chondrites, Bishunpur and Semarkona. Water released from bulk unseparated material by pyrolysis has δD values up to ∼3,000‰) (SMOW) or in absolute terms a D/H ratio of ∼6×10−4. Thus, one of the highest deuterium contents yet encountered for a Solar System species has been observed without considering a specific fraction of a sample. Either these meteorites contain a greater proportion of the D-rich phase first recognized in meteorite separates, or a small fraction having an even more extreme deuterium content resides within them.