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Organic geochemical screening and biological marker analysis was carried out on a total of 45 Albian-Cenomanian sandstone and mudstone samples collected from a landslide block on thenorth coast of Disko island, central West Greenland. The landslide block covers an area of severalsquare kilometres, and originated approximately 400 m up-section from where it moved to itspresent position after the last glaciation. The mudstones are generally rich in organic carbon butshow no potential for petroleum generation. However, biodegraded oil stains were found in thepoorly lithified sandstones. Staining by undegraded or only slightly degraded oil in volcanic rocks iscommon in this region, but the occurrence described here is the only known outcrop where staining occurs in siliciclastic sediments, and also the only one known in which the oil is severely biodegraded. The oil stains appear to represent a biodegraded variety of the Cretaceous marine shale derived Itilli oil type which is known from many locations in the Disko-Nussusaq-Svartenhuk Halvø region. The oils entered the sandstones before the landslide event, probably during or beforethe extrusion of the volcanic succession in the Paleogene. This is the first time that a petroleum seepage has been found to the east of the Kuugannguaq-Qunnillik fault zone, which is located approximately 30 km west of Asuk. The presence of stainingby marine oil at Asuk demonstrates that marine petroleum source rocks were deposited muchfurther eastwards than was previously thought, thus expanding the area of potential explorationsignificantly. The presence of marine source rocks to the east of the Kuugannguaq-Qunnillik faultzone may explain the frequent observation of Direct Hydrocarbon Indicators in seismic datacollected in the Vaigat Sound. [ABSTRACT FROM AUTHOR]

Coals and coaly mudstones of the Cretaceous Atane Formation are exposed along the north coast of the island of Disko and the south coast of Nuussuaq peninsula, West Greenland. Numerous oil seepages have been found in the region, but the so-called Kuugannguaq oil type only occurs at the north coast of Disko. The oil is presumed to have been generated from coaly (Type III) source rocks in the Vaigat strait where the Atane Formation is thermally mature due to deep burial. The exposed coals and coaly mudstones may thus be thermally immature equivalents of the active source rocks. The exposed section at Qullissat on the island of Disko is composed of four sedimentary facies associations: delta plain, distributary channel, delta front, and transgressive sand sheet. Samples of coals and coaly mudstones from the delta plain association were analysed for their total organic carbon (wt % TOC) and total sulphur (wt % TS) contents, and their source rock potential was determined by Rock-Eval pyrolysis. The organic matter composition was analysed by reflected light microscopy and the thermal maturity was established by vitrinite reflectance measurements. The Qullissat samples were supplemented with source rock screening data from coals and coaly mudstones from the Atane Formation at Paatuut on the south coast of Nuussuaq. The coals and coaly mudstones from Qullissat are dominated by huminite, but several samples have a considerable content of inertinite. The mineral content is high in some samples. Inundations of the peat-mires may have been quite frequent resulting in the formation of the coaly mudstones. TS contents (0.13–8.97 wt %) and the presence of framboidal pyrite suggest that the precursor peats were influenced by seawater, and that peat formation probably occurred during rises in relative sea-level. The organic matter is thermally immature, and a constructed vitrinite reflectance gradient for the region suggests that the Qullissat section prior to exhumation was buried to 1,500–1,600 m depth. Hydrogen Index (HI) values from both Qullissat and Paatuut are generally low; estimated maximum HI values for three Qullissat coals yield values of 140–190 mg HC/g TOC. The coals are gas-prone and only marginally oil-prone, and may in addition possess a limited oil expulsion efficiency. The effective oil window extends from approximately 1.0–1.6%Ro and the start of the effective oil window is located at about 3,000 m depth. Very thick sedimentary successions in the Vaigat strait indicate that such burial depths have been reached for the Atane Formation offshore, and up-dip migration of hydrocarbons from these source rocks may have generated the Kuugannguaq oil seepage. [ABSTRACT FROM AUTHOR]