Age of oils in West Greenland: was there a Mesozoic seaway between Greenland and Canada?

Abstract

For many years the existence of an oil-prone source rock off West Greenland was challenged by industry. But since 1992 when active oil seeps were found onshore West Greenland on the Nuussuaq peninsula (Fig. 1; Christiansen et al. 1996; Bojesen-Koefoed et al. 1999), the question has changed focus to the age, distribution and potential of the source rock. Five different oils – each with their own characteristics – have been reported by the Geological Survey of Denmark and Greenland (GEUS). One of these, a typical marine shalederived oil with a possible regional distribution, is known as the Itilli oil. Geochemical analysis suggests that it may have been generated from Cenomanian–Turonian age marine shales, equivalent to prolific source rocks known from Ellesmere Island, Nunavut, Canada. Three of the other oils were generated from deltaic source rocks of Albian, Campanian and Paleocene ages, while one is of unknown origin (Bojesen-Koefoed et al. 1999). The presence of a regional marine source rock is important to petroleum exploration; GEUS has therefore investigated the possible existence of Mesozoic, in particular Cenomanian–Turonian, petroleum source rocks in West Greenland offshore areas. Since sediments older than the Santonian are not known from any of the six wells drilled offshore West Greenland (Fig. 1), assessment of oil-prone source rocks in older sedimentary successions must rely on circumstantial evidence offered by oil chemistry data and analogy studies. Petroleum in quantities amenable to chemical analysis has so far not been recovered from offshore. However, oilbearing fluid inclusions are known from the Ikermiut-1 well (unpublished data 2001, Phillips Petroleum and GEUS), a gas-kick was recorded during drilling of the Kangâmiut-1 well (Bate 1997), and seismic data indicate hydrocarbons in many areas (cross-cutting reflectors, bright spots, smearing of seismic). Petroleum exploration offshore West Greenland suffered for many years under the misconception that oceanic crust covered vast areas, rendering the region unattractive. However, the presence of thick sedimentary successions and rotated fault blocks in Cretaceous basins have been demonstrated to be present in areas previously believed to be underlain by Cretaceous–Tertiary oceanic crust (cf. Chalmers & Pulvertaft 2001). New high-quality seismic data, acquired by the seismic company TGS-NOPEC over recent years, combined with gravimetric data, have further demonstrated the presence of deep basins containing thick sedimentary successions in other areas (e.g. Christiansen et al. 2002). Despite the progress made over the past few years, the geological evolution of the Davis Strait region in general remains poorly understood, but new data on oil chemistry may shed some light on the history of this region.