Characterization of Upper Palaeozoic organic-rich units in Svalbard: implications for the petroleum systems of the Norwegian Barents shelf

Recent discoveries of hydrocarbons along the western margin of the Norwegian Barents Shelf have emphasised the need for a better understanding of the source rock potential of the Upper Palaeozoic succession. In this study, a comprehensive set of organic geochemical data have been collected from the Carboniferous – Permian interval outcropping on Svalbard in order to re-assess the offshore potential. Four stratigraphic levels with organic-rich facies have been identified: (i) Lower Carboniferous (Mississippian) fluvio-lacustrine intervals with TOC between 1 and 75 wt.% and a cumulative organic-rich section more than 100 m thick; (ii) Upper Carboniferous (Pennsylvanian) evaporite-associated marine shales and organic-rich carbonates with TOC up to 20 wt.%; (iii) a widespread lowermost Permian organic-rich carbonate unit, 2–10 m thick, with 1–10 wt. % TOC; and (iv) Lower Permian organic-rich marine shales with an average TOC content of 10 wt.%. Petroleum can potentially be tied to organic-rich facies at formation level based on the gammacerane index, δ ¹³C of the aromatic fraction and/or the Pr/Ph ratio. Relatively heavy δ ¹³C values, a low gammacerane index and high Pr/Ph ratios characterize Lower Carboniferous non-marine sediments, whereas evaporite-associated facies have lighter δ ¹³C, a higher gammacerane index and lower Pr/Ph ratios.