Indication of migrated hydrocarbons in Tertiary vo1canic rocks from western Nugssuaq, central West Greenland

The Marrait kitdlit area has been mapped in some detail (Henderson, 1975) and is well known for its few metres thick calcareous fossiliferous conglomerates (Hansen, 1970; Rosenkrantz, 1970; Jiirgensen & Mikkelsen, 1974), and for its hydrothermal veins (KarupMøller , 1969; Binzer & Karup-Møller, 1974). A sequence of hyaloclastites and minor fossiliferous conglomerates is overlain by picritic and olivine-poor basaltic lava flows, all belonging to the early Tertiary Vaigat Formation. Later faulting has cut the volcanic pile into blocks which are downthrown by about 0.5 to 1 km compared to a stable plateau 5 km to the east. Scattered exposures of Cretaceous to early Tertiary marine mudstone with intercalated sandstone occur in the Itivdle valley and represent the pre-volcanic substratum (Henderson et al., 1976). West of the Itivdle valley a sequence of basalts at least 3 km thick from the Maligåt Formation, which overlies the Vaigat Formation, is exposed (Hald, 1976) suggesting that the investigated locality at Marrait kitdlit was once covered by several kilometres of volcanic rocks. A major NE-SW striking fault zone extends from the southern tip of Hareøen through the Itivdle valley to Umanak Fjord over a distance of at least 60 km (fig. 1). Associated with this fault zone is the largest known palaeo-hydrothermal high-temperature area in the Tertiary volcanic province of West Greenland. The high-temperature hydrothermal zone is observed on the southern part of Hareøen as local fossil hot spring areas where basaltic lavas and tufts are altered to crumbling white and grey masses, and in Itivdle as areas of hydrothermally metamorphosed lavas and hyaloclastites which may locally contain epidote. The degree of metamorphism in these areas exceeds by far the regional non-penetrative low zeolite facies metamorphism which characterizes the volcanic lithologies elsewhere in the Disko-Nugssuaq region.


Indication of migrated hydrocarbons in Tertiary vo1canic rocks from western Nugssuaq, central West Greenland
A. K. Pedersen During the field season of 1985 the author briefly visited Marrait kitdlit at the southern part of the entrance to the Itivdle valley on Nugssuaq ( fig. 1). This paper briefly describes the occurrence of possibly migrated organic material in a vein in Tertiary basalt and presents it in a regional context.

Regional geology
The Marrait kitdlit area has been mapped in some detail (Henderson, 1975) and is well known for its few metres thick calcareous fossiliferous conglomerates (Hansen, 1970;Rosenkrantz, 1970;Jiirgensen & Mikkelsen, 1974), and for its hydrothermal veins (Karup-Møller , 1969;Binzer & Karup-Møller, 1974). A sequence of hyaloclastites and minor fossiliferous conglomerates is overlain by picritic and olivine-poor basaltic lava flows, all belonging to the early Tertiary Vaigat Formation. Later faulting has cut the volcanic pile into blocks which are downthrown by about 0.5 to 1 km compared to a stable plateau 5 km to the east. Scattered exposures of Cretaceous to early Tertiary marine mudstone with intercalated sandstone occur in the Itivdle valley and represent the pre-volcanic substratum (Henderson et al., 1976). West of the Itivdle valley a sequence of basalts at least 3 km thick from the Maligåt Formation, which overlies the Vaigat Formation, is exposed (Hald, 1976) suggesting that the investigated locality at Marrait kitdlit was once covered by several kilometres of volcanic rocks. A major NE-SW striking fault zone extends from the southern tip of Hareøen through the Itivdle valley to Umanak Fjord over a distance of at least 60 km ( fig. 1). Associated with this fault zone is the largest known palaeo-hydrothermal high-temperature area in the Tertiary volcanic province of West Greenland. The high-temperature hydrothermal zone is observed on the southern part of Hareøen as local fossil hot spring areas where basaltic lavas and tufts are altered to crumbling white and grey masses, and in Itivdle as areas of hydrothermally metamorphosed lavas and hyaloclastites which may locally contain epidote. The degree of metamorphism in these areas exceeds by far the regional non-penetrative low zeolite facies metamorphism which characterizes the volcanic lithologies elsewhere in the Disko-Nugssuaq region.

Hydrothermal vein
A hydrothermal vein is exposed over a distance of a few metres in the Marrait kitdlit area on the southern flank of a NW-SE trending ridge just west of Tufdalen about 50 m southwest of the main fossiliferous conglomerate at Tufdalen (loc. 2 in Binzer & Karup-Møller, 1974). The vein, which cuts through olivine-poor subaerial basalt lava flows, is about 10 cm thick and consists of aggregates of centimetre-sized carbonate crystals. In the inner part of the vein are cavities which are partly filled by a loose black granular powder ( fig. 2). The 'powder' consists of from < 0.2 to l mm grains of clay coated by a black substance which also coats parts of the carbonalc crystals of tlle cavity walls.
A cursory exarnination of cleavage fragments of the carbonate has revealcd the presence uf aqueuus liquid-vapour indusions (degree of filling about 0.95) with saiinities around two equivalenl weight % NaCL No hydrocarbon-bearing inclusions were found (J. Konncrup-Madsen, personal comlllunication, 1985).
A sample of the clay granules (GGU 279075) has been analyzcd for total carbon (Te) and 'total organic carbon' (TOC) and a Rock Eval analysis has been carried out by thc source rock laboratory of DGU and GGU. The sample contains 1.30 wt.% TC and 1.18 wt. % TOC and the hydrocarbons are cornplerely degraded, probably by (hermaj alteration. The 'or-4cm >-------<1. ganic carbon' presumably accurs as the thio black coating which must have precipitated from a nuid phasc.
The present exmnple shows that hydrocarbolls have migrated vertically at least 500 m IIpwards in to Yaigat Formation volcanic rocks wilhin the ltivdle-HareØen fault zone. A former high-temperature hydrothermal zone extends for at leas t 8 km aeross the fault system and it is Iikcly that at Ieast several hundred square kilometres (and probably much more) within the Jtivdle-Hareøen fault system have been affecled by the hot hydrothermal solutions. Con· sequently. organic matter in Cl cOl1siderable volume af shale, both om,hore and offshore in the area. could have genera ted hydroearbons.
Aeknowledgements. The author wishes to acknowledge field support from the Arctic Station, Godhavn, and from Greenex AJS. The source rock laboratory of DGU and GGU provided analyticai data. The work was supported by the Danish Natural Science Research Counci!.