F.G. Christiansen (editor) 1989:
Petroleum geology of North Greenland
Bulletin Grønlands Geologiske Undersøgelse 158, 92 pp.
Lower Palaeozoic sediments of the Franklinian basin are well exposed in a broad zone across North Greenland. The region was characterized by major generally east-west trending facies belts throughout the depositional period. In the southern shelf areas predominantly carbonate sedimentation took place, bordered to the north by outer shelf and slope mudstones. In the north mainly siliciclasitic deep-water sedimentation prevailed in the trough.
All shale and dark carbonate units were studied and extensively sampled, followed by shallow core drilling of the most interesting intervals. The analytical programme included LECO/Rock Eval, palynological, petrographic, reflectance and fluorescence, gas chromatography, mass spectrometry, carbon isotope and X-ray diffraction studies of source rocks and migrated bitumens, porosity and permeability measurements of potential reservoir rocks, and fluid inclusion and fission track studies to reveal the thermal history.
Two major organic rich units of potential source quality occur in the region: the Lower to Middle Cambrian Henson Gletscher Formation and lateral equivalents, and the Lower Silurian shales, of which especially the interval of late Llandovery age seems promising. Both units have moderate to high contents of organic carbon, typically between 3 and 6%, and a good to excellent generative potential of immature samples. The organic matter in the Henson Gletscher Formation is dominated by amorphous kerogen, whereas the Silurian shales also contain minor contents of graptolites, chitinozoans and scolecodonts.
Geochemically, the kerogen in both source rocks is of Type II. The extractable organic mater is rather similar in gross composition. The Cambrian extracts have lighter carbon isotope composition and lower pristane/phytane ratios when compared to those of the Silurian, and a different distribution of hopane and sterane biomarkers.
The thermal maturity of the source rocks ranges from immature or early mature in the southernmost areas to postmature or low metamorphic in the northernmost areas, with only a narrow mature transition zone. This simple and consistent maturity pattern, with the exception of a few anomalies caused by intrusion or tectonism, has been mapped across most of North Greenland.
Evidence of hydrocarbon generation and migration is widespread in the region, observed as oil-stained carbonates or sandstones, as solid bitumen or as seeping asphalt. Most of the examples are closely associated with nearby source rocks, but numerous bitumens in the southernmost area without any known source rock point towards important long-distance migration of oil. The chemical composition of these bitumens is in accordance with a Cambrian source rock.
The similarity between the thermal maturity pattern and ten tectono-metamorphic zones, fission track data, and abrupt changes in thermal maturity between Lower Palaeozoic and Upper Palaeozoic or Mesozoic sediments all suggest that the maturation and most of the petroleum generation took place before or during the Ellesmerian orogeny in Late Devonian or Early Carboniferous time.
Large amount of hydrocarbons were generated; estimates of the total generative potential base on most likely values of depositional area, thickness of source rocks and geochemical data suggest values in the range of 25-100 x 10exp9 m3 of petroleum. More than 90% of this amount was probably generated and even prospects with low migration efficiencies could contain significant accumulations. The two most obvious play types, the Silurian carbonate reef and the sandstones in the Henson Gletscher Formation, seem disappointing due to high thermal maturity and deep erosional level. The best prospectable play type is accumulations in the southern part of the region as a result of long distance migration.
Contents of volume:
Review of the Lower Palaeozoic basin in North Greenland with special emphasis on petroleum geology
Analytical programme and applied methods
Palynological studies of the organic matter
Composition of organic matter in source rocks
Timing of thermal episodes
Quantitative aspects and economic implications
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