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TitleThe origin and biodegradation of surface and subsurface hydrocarbon seeps on Melville Island, Canadian Arctic Archipelago
AuthorFowler, M; Obermajer, M; Brent, T; Dewing, K; Mort, A
Source27th International Meeting on Organic Geochemistry, IMOG 2015 Prague, book of abstracts; by IMOG Organizing Committee; 2015 p. 531-532
Alt SeriesEarth Sciences Sector, Contribution Series 20140513
MeetingInternational Meeting on Organic Geochemistry; Prague; CZ; September 13-18, 2015
Mediapaper; on-line; digital
File formatpdf
ProvinceNunavut; Western offshore region; Northwest Territories
NTS78G; 79B; 88H; 89A
AreaMelville Island; Cape Grassy; Sabine Penisnsula
Lat/Long WENS-116.0000 -108.0000 77.0000 75.0000
Subjectsfossil fuels; stratigraphy; oil seeps; Upper Triassic; Lower Triassic; biodegradation; bitumen; gas; Sverdrup Basin; Bjorne Formation; Isachsen Formation; Schei Point Group; Roche Point Formation; Canyon Fiord Formation; Cape Phillips Formation; Carboniferous; Triassic
ProgramWestern Arctic Sverdrup Basin, GEM2: Geo-mapping for Energy and Minerals
LinksOnline - En ligne (PDF, 100 MB)
AbstractThe Sverdrup Basin is a large Mesozoic basin in the Canadian Arctic Archipelago where a number of petroleum fields were discovered between 1965 and 1985. These were mostly in the Melville to Ellef Ringnes islands area, in Upper Triassic to Lower Jurassic reservoirs although minor shows occur throughout the Mesozoic. It is generally accepted that Middle Triassic Schei Point shales are the source of most of the oils (e.g. Brooks et al, 1992). However, the source of the gas, including that in the two largest conventional gas fields (Drake and Hecla) in the Canadian Arctic at the north end of the Sabine Peninsula on Melville Island (Fig. 1), is still uncertain.
The Lower Triassic Bjorne Formation 'tar sands' in the Marie Bay area of north-west Melville Island occur over a 70 by 20 km area and are Canada's second largest oil sand deposit after the Alberta Oil Sands (Fig. 1). While suspected to be sourced from the Schei Point Group, no definitive data has been published to support this. Other lesser known seeps have also been reported on Melville Island including in the Lower Cretaceous Isachsen Formation at Cape Grassy to the north of the Bjorne Formation occurrences, and another over a hundred kilometres further east at the south end of the Sabine Peninsula within the Upper Carboniferous Canyon Fiord Formation (Fig. 1). Samples were collected from these bitumen deposits and analyzed using standard organic geochemistry techniques. Staining has also been reported in some wells drilled on or in close proximity to Melville Island. Wherever possible, these samples were also collected and analyzed.
Despite the severe surface climate (mean average ground temperatures ~ minus 16.5°C), the Bjorne Formation bitumen samples collected from the Marie Bay deposit were all severely biodegraded with large UCM humps in the saturate fraction gas chromatograms. The effects of biodegradation on the biomarker range distributions vary, especially with regard to the 17?(H)-hopanes. In some samples the distributions of these compounds seem to be little affected, while in others all the 17-alpha-(H)-hopanes have been removed and only 25-norhopanes are present. Steranes appear to be less affected by biodegradation than the hopanes and are only slightly altered, even in those samples containing only 25-norhopanes and no 17-alpha-(H)-hopanes. C26-C28 Triaromatic steranes are undegraded in all samples although C20 and C21 members have been removed. The distributions of these compounds suggest a correlation to Schei Point extracts and most Sverdrup Basin oils. Oil staining was observed at a depth of 1095 m in the Triassic Roche Point Formation in the West Hecla P-62 well drilled in Hecla and Griper Bay between the Sabine Peninsula and Marie Bay (Fig. 1). These hydrocarbons are also biodegraded with n-alkanes missing but less than the surface samples as acyclic isoprenoids are present and biomarkers seem unaffected. The Cretaceous hosted surface samples also show a range in biodegradation as evident by differences in their biomarker distributions. One interesting difference from the Triassic outcrop samples was that steranes were more affected than hopanes with the ??? 20R isomers removed and the decreased amounts of C27 and C28 relative to the C29 steranes. The 17?(H)-hopanes appear to be little affected. These bitumens can also correlated to a Triassic source. Regional maturity maps for the Schei Point Group uggest there must have been long distant migration for all these hydrocarbons (Dewing and Obermajer, 2011).
The Carboniferous surface seep hydrocarbons are also biodegraded but there is little effect on biomarker distributions except for the lack of C20 and C21 triaromatic steranes. These bitumens clearly have a different source from the other seep samples. For example, they lack the C30 4-desmethylsteranes observed in the Mesozoic samples. Biomarker characteristics suggest a Paleozoic carbonate source rock. Comparison with source rock extracts suggest that the very organic-rich Upper Ordovician to Upper Silurian Cape Phillips Formation is the most likely candidate. This unit has also been suggested as a source for the Bent Horn light oils found in Middle Devonian carbonates on Cameron Island (Obermajer et al., 2010). The presence of Cape Phillips sourced hydrocarbons on Melville Island has major implications for finding petroleum in pre-Mesozoic
Franklinian Basin strata, that were mostly overlooked in the previous exploration cycle.
Summary(Plain Language Summary, not published)
Triassic Schei Point shales are the source of most oils in the Canadian Arctic but the source of gas is still uncertain. The Triassic Bjorne Formation tar sands on Melville Island are Canada's second largest oil sand deposit. While considered to be Schei Point sourced, no definitive data has been published to support this. Bitumen samples were collected from these deposits and other seeps including in the Cretaceous at Cape Grassy and in the Carboniferous at the Sabine Peninsula, and from wells drilled in close proximity where staining was discovered. All samples were analyzed using standard organic geochemistry techniques to determine the origin of hydrocarbons. While most bitumen samples correlate to the Mesozoic Schei Point source rocks, the Carboniferous seeps were probably sourced in the Paleozoic, most likely the Cape Phillips strata. The presence of Paleozoic sourced hydrocarbons on Melville Island would have major implications for finding petroleum in pre-Mesozoic Franklinian Basin strata, mostly overlooked in the previous exploration cycle.