Evaluating Re–Os systematics in organic-rich sedimentary rocks in response to petroleum generation using hydrous pyrolysis experiments

Re–Os age for the Lower–Middle Pennsylvanian Boundary and comparison with associated palynoflora

“…The y-intercept represents the initial osmium composition and MSWD = mean square weighted deviation, a measure of the line fit. control the binding and preservation of Re and Os into organic-rich sediments (Rooney et al, 2012;Selby et al, 2009); however, although while reduced sedimentation rate may correlate with elevated Re/Os, it is not the principal cause. Water column conditions, including pH and temperature (Georgiev et al, 2011) and salinity (Martin et al, 2001), have been proposed as influential in the regulation of uptake and fractionation of Re and Os; however, there are no proxy data available for these parameters within the Betsie Shale Member.…”

“…Water column conditions, including pH and temperature (Georgiev et al, 2011) and salinity (Martin et al, 2001), have been proposed as influential in the regulation of uptake and fractionation of Re and Os; however, there are no proxy data available for these parameters within the Betsie Shale Member. Rooney et al (2012) evaluated a similar type-III-kerogen-bearing shale, the Jurassic Staffin Bay Formation in Scotland. Although their study supported the finding that Re and Os are bound within the kerogen of an organic-rich shale, they did not observe the strong preferential inclusion of Re over Os seen in the Betsie Shale Member.…”

“…Finally, the conditions below the sediment-water interface may be critical controls on relative uptake of Re and Os may be conditions below the sediment-water interface. More strongly anoxic or euxinic conditions may exist in pore waters compared to the overlying water column, which may enhance higher uptake of Re provided that the pathway to the overlying water column remains open (Lewan and Maynard, 1982;Rooney et al, 2012). This effect could be enhanced if condensed sections promote diffusion rates from the water column to pore waters (Lewan and Maynard, 1982).…”

Behavior of Re and Os during contact between an aqueous solution and oil: Consequences for the application of the Re–Os geochronometer to petroleum

“…In this system, 187 Re decays to form 187 Os with a decay constant of about 1.666 Â 10 À11 yr À1 (Smoliar et al, 1996), equivalent to a half-life of about 43 billion years. The particular advantage of the Re-Os system is that, unlike the parent and daughter elements of most other radioisotope systems, Re and Os are strongly organophile elements Creaser, 2003, 2005a;Miller, 2004;Selby et al, 2005;Rooney et al, 2012). This characteristic has allowed the Re-Os system to be used quite successfully for the dating of organic-rich rocks such as black shales, which are highly enriched in Re and Os relative to most other crustal rocks (e.g.…”

“…Since the kerogen of potential source rocks is highly enriched in these elements, it seems reasonable to think that Re and Os in oil are derived from this kerogen during oil generation (Selby and Creaser, 2005a;Selby et al, 2005Selby et al, , 2007Finlay et al, 2010Finlay et al, , 2011. To verify this assumption, Rooney et al (2012) and later Cumming (2012) conducted hydrous pyrolysis experiments to determine how Re and Os are partitioned between the oil expelled from the source rock and the bitumen and kerogen that remain. These authors found that after heating, the generated bitumen and the residual kerogen have very similar 187 Os/ 188 Os ratios, but different Re/Os ratios.…”