Radiogenic Isotopes

The Rhenium-Osmium Geochronometer

Rhenium-osmium (Re-Os) geochronology exploits the β decay of ¹⁸⁷Re to ¹⁸⁷Os (with a half-life of ~42.5 billion years). The decay of ¹⁸⁷Re to ¹⁸⁷Os provides a useful chronometer and tracer tool, as both elements are organophilic and are thus highly enriched in organic-rich sedimentary units relative to upper continental crust.

Application

At Origin Analytical our focus is on utilising the Re-Os isotope system to enhance our understanding of subsurface petroleum systems. This can yield valuable information regarding both the hydrocarbon-generating source rock and the associated hydrocarbons. Through use of this technique we are able to constrain: 1. The absolute timing of source rock deposition; 2. The timing of oil generation; and 3. Oil and source rock relationships, through oil-source correlation.

Analytical Technique

Isotopic analyses of organic-rich rocks and oils are conducted on a Negative Thermal Ionisation Mass Spectrometer (NTIMS). Following powdering (organic-rich sediments) and asphaltene separation (oils), the samples are prepared for analysis by Carius tube digestion, prior to solvent extraction of Os and purification of Re via ion exchange chromatography.