New evidence for possible generation of oil off south-western Greenland

In 2011, traces of bitumen in the 1160 Ma old Ilímaussaq intrusion in South Greenland have been examined in order to determine their origin. The investigation was prompted by the recent interest in hydrocarbon exploration off western Greenland, an interest expressed in the form of four new licences in the region (Christiansen 2011). The hydrocarbon potential in the region was realised after reinterpretation of seismic profiles across the Labrador Sea, and this indicates the presence of a sedimentary basin off south-western Greenland (Fig. 1; Chalmers & Pulvertaft 2001). However, the main problem in petroleum exploration off south-western Greenland is that no prolific marine source rocks have been demonstrated (Christiansen 2011). Therefore, any trace of hydrocarbons, however small that may help demonstrate the occurrence of source rocks in the region, deserves careful examination. Recently, bitumen biomarkers have been used to question the presumed abiogenic origin of hydrocarbons in crystalline rocks of the Ilímaussaq intrusion (Laier & Nytoft 2012). In this paper, we focus on the origin of the bitumen and compare it with previous finds in central West Greenland. The presence of hydrocarbons in the Ilímaussaq intrusion has been known since 1970 (Petersilie & Sørensen 1970) but unlike the discovery of oil seeps in the Nuussuaq region in central West Greenland twenty years later, which had a positive impact on petroleum exploration (Christiansen 2011), the hydrocarbons in the Ilímaussaq intrusion were largely ignored in the context of offshore exploration. The reason for this is twofold: (1) hydrocarbons in the Ilímaussaq intrusion are much more difficult to recognise than on Nuussuaq, and (2) analytical results are confusing with respect to the origin of the hydrocarbons. Discrete millimetre-size hydrocarbon accumulations have only been observed twice, and samples of this material were unfortunately not available for analysis in the present investigation. The material, which is a waxy paraffinic hydrocarbon of C28H56, was located in vugs of pegmatite veins and labelled as an evenkitelike mineral by Konnerup-Madsen et al. (1979). Otherwise hydrocarbons in the Ilímaussaq intrusion only exist in fluid inclusions, mainly as C1–C5, and as dispersed bitumen invisible to the naked eye. The stable carbon isotopic ratio of methane (δ13C = –7‰) released from the inclusions by crushing (Petersilie & Sørensen 1970) differed from that of associated methane in most oil and gas reservoirs, which has δ13C values of –30 to –50‰. The ratio was closer to the isotopic ratio of primodial carbon of the Earth’s mantle, which has δ13C values around –5‰. The paraffinic hydrocarbons of ‘evenkite’ on the other hand had a δ13C value of –29‰, which is within the expected range for hydrocarbons generated by thermal maturation of organic matter (Konnerup-Madsen et al. 1988).