The Re-Os geochronometer can be used to date sedimentary successions lacking suitable horizons for traditional geochronology techniques such as Ar-Ar or U-Pb zircon geochronology.
For example, the boundaries of many Phanerozoic systems, epochs, and stages are marked by the deposition of black shale units, several of which are coincident with mass extinction events.
When oil is formed from a source rock, a proportion of the Re and Os from the source rock is transferred to the oil, thus one can date the formation process using the Re - Os geochronometer.
Furthermore, as Re and Os have been inherited from the source rocks, Os isotopes can be employed to correlate an oil with its source.
Rhenium-Osmium dating is carried out by the isochron dating method.
This causes high ratios of Re/Os in oceanic crust (which is derived from partial melting of mantle) and low ratios of Re/Os in the lower mantle.The Rhenium-Osmium (Re-Os) geochronometer is a novel tool for dating ancient sedimentary successions.