Re-Os isotope system in organic-rich samples for dating and tracing: Methodology, principle, and application

Abstract

In the last three decades, significant progress has been made in the investigation of rhenium‑osmium (Re-Os) isotopic system in organic-rich samples. The Re-Os geochronometer can provide precise absolute depositional ages of organic-rich sediments (ORS) and information on the age of the generation, migration, and charge of crude oil. Thus, this dating tool is widely used to establish the time scale of some important geological events, such as glaciations, evolutionary events, mass extinctions, and atmosphere/ocean oxygenation. In addition, the initial Os isotope ratio obtained from Re-Os isochrons of ORS can provide vital insights into the Os isotopic fluctuations of ancient seawater, which could be used to track some geological events (e.g., bolide impacts, changes to continental weathering, and large igneous provinces), and that obtained from oil samples can fingerprint crude oil to their source. Overall, the Re-Os geochronometer exhibits a promising prospect for stratigraphy, marine geology, and petroleum geology. Several studies have not only highlighted the significance of the Re-Os geochronometer but also revealed the characteristic distribution of Re-Os in organic-rich samples as well as its complex behavior in the sedimentary environment. organic-rich samples as well as its complex behavior in the sedimentary environment. This makes the analytical methodology for organic-rich samples different from that traditionally used for sulfides and meteorites, and the mechanisms of data interpretation may vary in the different sedimentary environments. Therefore, this article reviewed the history of the development of analytical methodologies for Re-Os isotope application in organic-rich samples, highlighting the principal challenges associated with each technique and facilitating the selection of the analytical method best adapted to various organic-rich samples. We also introduced the necessary context of the geochemical behavior of Re-Os during sedimentary geological processes and discussed the possible mechanism of Re-Os geochronometer formation and disturbances to the closure of the Re-Os isotope system by citing examples of published cases and associated application-based controversies.