Average Re (108 ng/g) and Os (0.52 ng/g) concentrations for the Matewan coal samples are of the same order in magnitude as those observed for Phanerozoic black shale (Table 3). Re and Os preserved in black shale are often found to be marine in origin. Comparable Re and Os concentration levels in the Matewan coal and the black shale (Table 3) hint at a similar source and/or paleo-environment; that is, some or all of the Re and Os may be of marine origin. In order to evaluate this, the contributions of seawater to the Re (Resw) and Os (Ossw) contents of the coal samples are estimated. For this calculation, it Trichostatin A is assumed that Re and Os in the Matewan coal samples are mainly derived from terrestrial and marine sources. The available data for terrestrial coal samples constrains the Re/TOC (∼18×10−10∼18×10−10) and Os/TOC (∼0.52×10−10∼0.52×10−10) ratios for terrestrial sources (Table 3; Baioumy et al., 2011). These ratios for terrestrial coals, excluding an outlier sample with an order of magnitude higher Re concentration, are comparable to those for terrestrial plant leaves (Table 3). The Resw and Ossw for the Matewan coal samples can be calculated using Re/TOC and 188Os/TOC ratios of non-marine coals (Table 3), and the following equations. For Ossw estimation, TOC-normalized ratio of 188Os (instead of total Os) is used to avoid effect of radiogenic 187Os on total Os.equation(1)Resw=Resample−[(ReTOC)terrestrial×TOCsample]equation(2)Ossw=Ossample188−[(Os188TOC)terrestrial×TOCsample]
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