Radiometric Dating of Source Rocks Using Rhenium and Osmium Isotopes

Shawn C. Wright
University of Houston

Recent advances in analytical techniques and mass spectrometry have opened new opportunities for the direct dating of source rocks using the ¹⁸⁷Re - ¹⁸⁷Os isotope chronometer. Re and Os are present in ORMs in parts-per-billion and parts-per-trillion quantities, respectively. ORMs are enriched in these elements by orders of magnitude when compared to other crustal lithologies. With careful sample selection and preparation, and digestion using Jones Reagent, age uncertainties of ~1% (2σ) are achievable. All Re-Os ages to date are based on whole-rock aliquots, with no clear understanding of where the Re and Os are hosted between the various fractions. Knowing the location, abundance, and isotopic concentration of Re and Os in the various fractions (sulphides, oxides, bitumen, and kerogen) will provide a thorough understanding of the Re-Os system during ORM deposition and burial. This will significantly improve validity and reliability of whole-rock isochrons.

This project aims to investigate the Re and Os concentrations and isotopic concentrations of the different fractions of ORMs, as well as oil (SARA) in order to identify the primary sinks for these elements during sequestration, as well as the sources of Re and Os during hydrocarbon generation. This study will focus on well-studied, natural laboratories which will allow for the validation of the depositional age of source rocks, as well as be single, associated source basins that will provide minimal migration and mingling of hydrocarbons generated from multiple source-rocks. The results of this work will enhance petroleum systems analysis and in turn the success of petroleum exploration.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013