CHARACTERIZATION OF UPPER PALAEOZOIC ORGANIC-RICH UNITS IN SVALBARD: IMPLICATIONS FOR THE PETROLEUM SYSTEMS OF THE NORWEGIAN BARENTS SHELF

J. B. Nicolaisen^a,e,*, G. Elvebakk^b, J. Ahokas^c, J. A. Bojesen-Koefoed^d, S. Olaussen^e, J. Rinna^c, J. E. Skeie^c and L. Stemmerik^a,e

^a Natural History Museum of Denmark, University of Copenhagen, Denmark.

^b Geo-Moski AS, Norway

^c Aker BP, Norway.

^d GEUS, Geological Survey of Denmark and Greenland, Denmark.

^e UNIS, University Centre in Svalbard, Norway.

^* Corresponding author, email: jakob.kristensen@snm.ku.dk

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, δ¹³C of the aromatic fraction and/or the Pr/Ph ratio. Relatively heavy δ¹³C values, a low gammacerane index and high Pr/Ph ratios characterize Lower Carboniferous non-marine sediments, whereas evaporite-associated facies have lighter δ¹³C, a higher gammacerane index and lower Pr/Ph ratios.

Key words: Norway, Barents Sea, Svalbard, Spitsbergen, Upper Palaeozoic, source rocks, petroleum, geochemistry, gammacerane index, biomarkers, isotope ratios.

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