REVIEW ARTICLE Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 1 of 21 A review of oil and gas seepage in the Nuussuaq Basin, West Greenland – implications for petroleum exploration Flemming G. Christiansen*1 , Jørgen A. Bojesen-Koefoed1 , Gregers Dam1 , Troels Laier2, Sara Salehi1 1Geological Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark, 2Geological Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark (Emeritus) Abstract The Nuussuaq Basin in West Greenland has an obvious exploration poten- tial. Most of the critical elements are well documented, including structures that could form traps, reservoir rocks, seals and oil and gas seepage that documents petroleum generation. And yet, we still lack a full understanding of the petroleum systems, especially the distribution of mature source rocks in the subsurface and the vertical and lateral migration of petroleum into traps. A recently proposed anticlinal structural model could be very interest- ing for exploration if evidence of source rocks and migration pathways can be found. In this paper, we review all existing, mostly unpublished, data on gas observations from Nuussuaq. Furthermore, we present new oil and gas seepage data from the vicinity of the anticline. Occurrence of gas within a few kilometres on both sides of the mapped anticline has a strong thermogenic fingerprint, suggesting an origin from oil-prone source rocks with a relatively low thermal maturity. Petroleum was extracted from an oil-stained hyaloclas- tite sample collected in the Aaffarsuaq valley in 2019, close to the anticline. Biomarker analyses revealed the oil to be a variety of the previously charac- terised “Niaqornaarsuk type,” reported to be formed from Campanian-age source rocks. Our new analysis places the “Niaqornaarsuk type” 10 km from previously documented occurrences and further supports the existence of Campanian age deposits developed in source rock facies in the region. 1 Introduction The exploration potential for petroleum in the Nuussuaq Basin in West Greenland (Figs 1 and 2) was first realised in the early 1990s, based on the observations of oil seepage followed by core drilling and conventional explo- ration drilling (Christiansen 1993, 2011; Christiansen et al. 1994a, 1994b, 1995b, 1996a, 1996b, 1997a). However, we currently lack a full understanding of the petroleum systems of the area. Although oil seeps have been widely recognised on many coastal localities and classified in detail analytically (Bojesen-Koefoed et al. 1999, 2007; Christiansen et al. 1996c), we still do not know the areal distribution of mature petroleum source rocks in the subsur- face and the vertical and lateral migration of oil and gas into possible traps or to the surface. Most recently, Sørensen et al. (2017) proposed a new play concept based on the photogrammetric mapping of inversion structures. A newly mapped large structural anticline on central Nuussuaq (Fig. 2) with expected good *Correspondence: fgc@geus.dk Received: 24 Mar 2020 Accepted: 08 July 2020 Published: 04 Dec 2020 Keywords: Nuussuaq Basin, West Greenland, gas observations, oil and gas geochemistry, anticline petroleum exploration model Abbreviations: DGU: Geological Survey of Denmark GGU: Geological Survey of Greenland GEUS: Geological Survey of Denmark and Greenland GC–MS: gas chromatography–mass spectrometry GCFID: gas chromatography–flame ionization detection MPLC: medium-pressure liquid chromatography GC–MSSIM: selective ion monitoring GC–MS DInSAR: Differential Synthetic Aperture Radar Interferometry NDVI: Normalized Difference Vegetation Index GEUS Bulletin is an open access, peer- reviewed journal published by the Geological Survey of Denmark and Greenland (GEUS). This article is distributed under a CC-BY 4.0 licence, permitting free redistribution, and reproduction for any purpose, even commercial, provided proper citation of the original work. Author(s) retain copyright. Edited by: Catherine Jex (GEUS, Denmark) Reviewed by: Chris Parry (GER X AS, now University of Stavanger, Norway) and Sverre Ohm (University of Stavanger, Norway) Funding: See page 19 Competing interests: None declared Additional files: See page 19 https://doi.org/10.34194/geusb.v44.4567 https://orcid.org/0000-0001-6098-9402 https://orcid.org/0000-0001-5647-2769 https://orcid.org/0000-0002-2905-3136 https://orcid.org/0000-0002-8999-603X mailto:fgc@geus.dk Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 2 of 21 www.geusbul let in.org reservoirs and seals is an obvious exploration target if mature source rocks and migration pathways can be demonstrated. To understand this target and to provide the necessary input for a risk assessment, we need to further document oil and gas seepage in the inland areas, especially along and east of the Kuugan- nguaq–Qunnilik Fault zone in central Nuussuaq (Fig. 2). Compared to the numerous oil seeps along the coasts of Disko and Nuussuaq, only a few records have been obtained inland, where exploration logistics are more complicated and costs are higher. Also, freshly eroded rocks along the coast seem to better preserve oil than inland exposures, where volcanic rocks weather differ- ently due to frequent melting and freezing processes and often alter to rocks with a distinct smell of soil. Less attention has been paid to document the occur- rences of gas in the Nuussuaq Basin, although some preliminary data were obtained during systematic anal- yses of boreholes drilled by the Geological Survey of Greenland (GGU), which later merged with the Geolog- ical Survey of Denmark to form the Geological Survey of Denmark and Greenland (GEUS) and industry. Unfor- tunately, in a number of these records, gas was not sampled and documented properly or at all. This paper presents a systematic review of all gas observations and data in the Nuussuaq Basin in order to understand the petroleum systems and aid future exploration. Here, we (1) summarise existing data for gas accumulations, much of which were, until now, only available in unpub- lished GGU and GEUS reports and (2) present new criti- cal data based on samples collected in 2019. These new data are important to characterise oil and gas seepage near to the Kuugannguaq–Qunnillik Fault zone, where future drilling is being considered. Fig. 1 Simplified geological map of the Nuussuaq Basin, West Greenland, showing the position of the outcrop- ping sediments on Disko, Nuussuaq and Svartenhuk Halvø. EBF: Eastern Bound- ary Fault. Location of Umiivik-1 core is indicated. For the purpose of this paper, Nuussuaq Basin refers to the area shown in this figure. nN Nuussuaq Umiivik-1 71°N 72°N 72°N 51°W53°W 71°N 70°N 69°N 55°W 51°W Svartenhuk Halvø Ubekendt Ejland Greenland ice sheet Uummannaq Innerit Hareøen Fig. 2 Iti lli Fa ul t Vaigat Disko Disko Bugt Ilulissat Qeqertarsuaq Aasiaat EBF EBF 50 km GREENLAND Neogene sediment cover offshore Saqqaata Qaqqaa central complex Paleocene picrites (Vaigat Formation) Undifferentiated basalts offshore Naqerloq Formation Svartenhuk Formation Maligât Formation Maastrichtian– Paleocene sediments Albian–Campanian sediments Extensional fault Precambrian basement Fault with lateral or alternating displacements https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 3 of 21 www.geusbul let in.org 2 Geological setting and exploration models of the Nuussuaq Basin The Nuussuaq Basin is a rift basin that developed during Cretaceous – Paleocene due to extension between Canada and Greenland. The basin is charac- terised by outcropping sediments on Disko, Nuussuaq and Svartenhuk Halvø. The southern limit is located around Qeqertarsuaq, Disko (Fig. 1), but the northern and western limits are less well defined. For the pur- poses of this paper, Nuussuaq Basin corresponds to the area shown in Fig. 1. The sediments of the Nuus- suaq Basin and the overlying volcanic rocks are well exposed throughout the Disko–Nuussuaq–Svartenhuk Halvø region and are important to understand the sed- imentology, stratigraphy, depositional and subsidence history of the sedimentary basins in West Greenland. The Nuussuaq Basin has been intensively studied as an analogue for offshore basins. Most of these studies are based on large field campaigns in 1991–1997 and 2004, combined with many shorter field trips (Christian- sen 1993; Christiansen & Pulvertaft 1994; Christiansen et al. 1992, 1995a, 1996a, 1997a, 1998). For an overview of previous research and exploration history, see Dam et al. (2009) and Christiansen (2011). The present paper focuses on the parts of the Nuus- suaq Basin on western and central Nuussuaq between the Itilli and the Kuugannguaq–Qunnilik Fault zones (Fig. 2). In this part of the Nuussuaq Basin, the sedimen- tary succession is covered by a few kilometres of vol- canics of the Vaigat and Maligât Formations (Figs 1–3; Pedersen et al. 2017, 2018). The underlying sediments were mainly characterised by drilling or from field work on exposures in the Itilli Valley, along the Itilli Fault zone (Figs 1 and 2). The known sedimentary succession is dominated by marine sediments of mid-Cretaceous to Palaeogene age. A general facies change occurs from deltaic and slope sediments close to the Kuugannguaq–Qunnilik Fault zone to deeper marine turbidites in and around the Itilli Fault zone (Dam et al. 2009). Many mudstone intervals occur in the Itilli and Kangilia Formations (Dam et al. 2009); some of these may represent possible source rocks and many are likely to have good sealing capacities (Fig. 3). The most likely reservoir intervals are turbidite sandstones in the Itilli Formation and incised valley sandstones of the Quikavsak and Agatdal Forma- tions and their equivalents (Dam & Sønderholm 1994, 1998; Dam et al. 2009; Hjuler et al. 2017; Kierkegaard Fig. 2 Simplified geological map of north- ern Disko and western Nuussuaq in the Nuussuaq Basin. Location of wells and cores with oil and gas, major and minor oils seeps, localities with various types of gas observations and the approximate position of the anticline from Sørensen et al. (2017; red-dashed line) are marked. 54°30´ GANE#1 GANW#1 GANK#1 GANT#1 GRO#3 55° 55°30´ 55°30´ 54°30´ 54°30´55° 70°30´ 70°30´ 70°15´ 70°15´ 70°45´ 54° 54° Max o ccurence of A naanaa M b Iti lli F au lt zo ne G as sø F au lt zo ne Annertuneq core with gas hydrates Pingo 132 with gas Visman boreholes with gas Aaffarsuaq Valley Serfat cores with gas K uu ga nn gu aq –Q un ni lik F au lt zo ne V A I G A T M A L I G Â T Fault zone Lake, pingo with gas Major oil seep Minor oil seep Outcrop of basement Outcrop of volcanic rocks Outcrop of Cretaceous-Paleocene sediments Covered Core hole with gas Core hole with oil Core hole with oil and gas Deep well with oil and gas Sikillinge Asuk 10 km Marraat-1 New Pingo Gassø Lake Gassø Lake Tr ac e of a nt ic lin e 574305 A gatdalen Iti lli Va lle y https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 4 of 21 www.geusbul let in.org Fig. 3 Simplified sedimentary and volcanic stratigraphy of the Nuussuaq Basin on Disko, Nuussuaq and Svartenhuk Halvø. The rela- tionship between petroleum seeps and stains and main petroleum systems elements is shown. Possible ages for source rocks of the following oil types are shown: M: Marraat type; N: Niaqornaarsuk type; I: Itilli type; K: Kuugannguaq type. The Eqalulik type source rock is not known, but it is assumed to be early Cretaceous. Many of the petroleum stains in the Vaigat Formation are associated with later Eocene dykes. Vaigat Formation includes the following: An: Anaanaa Member; Na: Naujánguit Member; Or: Ordlingassoq Member. Note that the Eocene volcanic units are rather thin and not regionally distributed. Hareøen Formation is only found on Hareøen, Erqua Formation only on Ubekendt Ejland and Naqerloq Formation only on Hareøen and westernmost parts of Nuussuaq, Ubekendt Ejland and Svartenhuk Halvø. Based on Sørensen et al. (2017), Dam et al. (2009) and Pedersen et al. (2017, 2018). Upper Cretaceous Paleocene Eocene Oligocene Miocene Pliocene Quaternary Lower Cretaceous 0 Ma 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 Aptian Albian Cenomanian Turonian Coniacian Santonian Campanian Maastrichtian Danian Selandian Thanetian Ypresian Lutetian Bartonian Priabonian Rupelian Chattian Aquitanian Burdigalian Langhian Serravallian Tortonian Mainly continental deposits Mainly marine or deltaic sandy/silty deposits, locally mudstones Mainly marine mudstones, locally sandy/silty Messinian Zanclean Piacenzian P al eo ce ne E oc en e 61 –6 0 60 –5 8 56 –5 4 54 –5 3 39 –3 8 62 –6 1 M al ig aâ t Fm S va rt en hu k Fm N aq er lo q F m E rq ua Fm H ar eø en Fm Va ig at F m Ma Volcanic stratigraphy Chronostratigraphy Sedimentary stratigraphy NW SE NW SE Source rock Unconformity (Hareøen) (Hareøen) Kangilia Fm Itilli Fm Itilli Fm Atane Fm Agatdal Fm Eqalulik Fm M N K I Quikavsak Fm Lake, pingo with gas Core hole with gas Core hole with oil Core hole with oil and gas Major oil seep Minor oil stain An Or Na https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 5 of 21 www.geusbul let in.org 1998). The most likely traps are extensional-rotated fault blocks formed in the Cretaceous or Palaeogene, or late Paleocene inversion structures such as the anticline mapped by Sørensen et al. (2017). Nuussuaq experienced a short, but very intensive, exploration phase in 1994–1998, driven largely by new, and at that time unpublished, data on oil seepage. The small Canadian company grønArctic Energy Inc. man- aged to drill four fully cored stratigraphic boreholes (GANW#1, GANE#1, GANK#1, and GANT#1) and one deep wildcat well (GRO#3) in 1994–1996. But, despite many encouraging oil shows and documentation of good reservoirs and seals in the Upper Cretaceous and Palaeogene succession, the company was unable to raise funding for further drilling and they eventually relinquished their licences in May 1998. 3 Existing data from oil seeps and bore holes in the Nuussuaq Basin The first oil-seeps on Nuussuaq were discovered in the Marraat area in 1992 (Christiansen 1993). Since then, significant time and resources have been invested to find additional localities, especially along the coast, with evidence of either visible oil seepage or micro-seepage in mineralised veins. Oil seepage is very common in an area on western Nuussuaq (Christiansen et al. 1996c). Following the years of systematic field work, evidence of oil has also been found in many other localities, includ- ing Disko, Hareøen, Ubekendt Ejland and Svartenhuk Halvø (Figs 1 and 2). Several hundred samples of oil seeps or oil-impreg- nated cores on Nuussuaq were analysed in detail by Bojesen-Koefoed et al. (1997a, 1999), and supplemented more recently by Bojesen-Koefoed et al. (2007). They described the characteristics of the oil samples from the region and grouped them into five distinct oil types. These types are adopted here, but for a complete over- view of the oil-type classification, we refer the reader to Bojesen-Koefoed et al. (1999, 2007). The main models of source rock distribution, depositional environment and generative history of the source rocks are based on state-of-the-art analyses and are documented in detail (Bojesen-Koefoed et al. 1999, 2004, 2007; Christiansen et al. 1996c). Some of the oils have a unique composition of biological markers, containing organic compounds such as lupanes and a series of norhopanes that were only rarely documented at the time of analyses (Nytoft et al. 2000, 2002). Understanding the distribution and concentration of different oil types is important for petroleum explora- tion on Nuussuaq. Previous studies demonstrated work- ing petroleum systems and first indications of where the source rocks could be expected in the subsurface, where and when they have generated oil and how migration, and in some cases degradation, took place. The oils so far recorded in the Nuussuaq Basin occur in two main settings: 1. In oil-impregnated porous lavas and hyaloclastites that may have formed exhumed continuous reser- voirs in the deeper part of the volcanic succession, especially within the Anaanaa Member of the Vaigat Formation (Pedersen et al. 1998) or just below, in the uppermost part of the sedimentary successions (Fig. 3). Oil-impregnated rocks hold large volumes of hydrocarbons, which were generated, and probably migrated vertically, from an underlying source rock such as oil of the “Marraat deltaic type” or the lesser known “Eqalulik type” or “Niaqornaarsuk type” (as defined by Bojesen-Koefoed et al. 1999). This migra- tion likely occurred during and shortly after the main phase of volcanism in the region (62–60 Ma) with rapid subsidence and possibly increased heat flow. Such oils occur over large parts of western Nuussuaq, especially in the area from Marraat-1–GANE#1– Sikillinge (Fig. 2), where several billion barrels of more or less degraded oil may fill out most available poros- ity in the volcanics (Christiansen et al. 2006; see Supplementary File S6). 2. In migration conduits, especially along faults, dykes, fractures or as fluid inclusions in thin mineralised veins in many different volcanic units (Fig. 3). Oils also occur in some sands in the Asuk area on Disko (Fig. 2). Such oils are generally low in volume and concentration, but are known from large areas on Disko, Nuussuaq, Ubekendt Ejland and Svartenhuk Halvø, where they often belong to the “Itilli type,” pre- sumed to be generated from a marine mid-Creta- ceous source rock (Fig. 3; Bojesen-Koefoed et al. 1999, 2007). The first setting offers some possibilities for local exploration, especially in incised valley deposits of the Lower Paleocene Quikavsak and Agatdal formations on western Nuussuaq. The area of exploration interest is, however, rather small with complex structural features that are not likely to define large targets. The second setting suggests good exploration opportunities over much larger areas in the deeper part of the Cretaceous succession and supports the anticlinal model suggested by Sørensen et al. (2017). The main area of known oil seeps and stains was sig- nificantly enlarged after numerous field seasons. It is likely that the area containing oil of the “Marraat type” can be further extended inland towards the north and northeast. The easternmost record of the “Marraat type” is the GANK#1 borehole. It is unclear whether this oil https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 6 of 21 www.geusbul let in.org type can be traced further into the Kuugannguaq–Qun- nillik Fault zone (Fig. 2). The main challenge for future oil seep studies is to find more examples from the second setting, especially along a possible fairway from north- ern Nuussuaq along the anticline to central and south- ern Nuussuaq. The major fault zones in the region are also interesting targets for future studies, as they may have been important migration pathways. 4 Existing records of gas in the Nuussuaq Basin Well-documented analytical records of gas observa- tions in the Nuussuaq Basin are relatively few. There are some historical observations of gas leakages from lakes or pingos, but they have not been analysed with modern analytical methods. More recent records were obtained during drilling campaigns, which revealed a high like- lihood of widely distributed gas under pressure in the subsurface of the Nuussuaq Basin, either below a per- mafrost seal or deeper in the sedimentary succession. Since 1992, improved sampling techniques were devel- oped for drilling and field work by the GGU and later by GEUS, which ensured a better understanding of gas dis- tribution in the subsurface. Here, we review all known records of gas observations in chronological order and describe the various sampling techniques used, their limitations, to provide key results and make preliminary interpretations. 4.1 Numerous GGU boreholes, drilled in 1992 Numerous cores were drilled at Agatdalen (Fig. 2), Anner- tuneq (Fig. 2) and Svartenhuk Halvø (same location as Umiivik-1; Fig. 1) in 1992. These shallow fully cored bore- holes were drilled to depths between 45 and 95 m by GGU using a custom-made light-weight rig that could be mobilised using small helicopters. The main goal was to document the presence of oil-prone source rocks within the marine Cretaceous succession (Fig. 3; Christiansen 1993; Christiansen et al. 1994c). Core samples for gas analysis were taken in metal tubes. Results were reported by Laier (1994) in an unpublished institutional report, which is provided here as Supplementary File S1. Gas amounts were relatively low, which precluded stable isotopic analysis. Methane concentrations were low relative to ethane, propane and butane, which suggest preferential leakage of lighter molecules. For this reason, cans were used in subse- quent studies, replacing the tubes. During the drilling at Annertuneq (core number 400407), white to bluish gas hydrates were observed at a depth of c. 7 m (Fig. 4). At the time of drilling, it was not realised that the material was gas hydrates and samples evaporated before they could be properly described and secured for analysis. 4.2 Marraat-1 core, drilled in 1993 Marraat-1 (408001) core (location Fig. 2; sample num- bers 408011 and 408020 in Table 1) was drilled by the Canadian company Falconbridge Ltd. for GGU in August 1993. It terminated at a depth of 448 m. The well was subsequently logged in October–November 1993 and some additional fluid samples of formation water were taken. The main goal was to clarify if the solid bitumen found at the surface was an indication of undegraded oil in the subsurface (Christiansen et al. 1994a; Dam & Christiansen 1994). The subsequent analytical programme focused on the oil composition that suggested new models for age and depositional environment of the source rock (Bojesen-Koefoed et al. 1999; Christiansen et al. 1994b, 1996c). Some core pieces were sealed in cans for sub- sequent gas and formation fluid analyses. These data were reported by Laier (1994; see Supplementary File S1) and Christiansen et al. (1995b) and are summarised in Table 1. Two samples of a rather dry gas had a suffi- cient concentration of methane to allow analysis of sta- ble carbon isotopes. Values of δ 13C (13C/12C) and wetness indicate a mixed thermogenic biogenic origin (Table 1; Fig. 5). 4.3 Falconbridge mineral exploration cores, drilled in 1994 During their mineral exploration programme for nickel sulphides in 1994, Falconbridge Ltd. observed gas bub- bles and froth on core surfaces. They penetrated a zone of pressured gas at c. 290 m depth in one of the bore- holes in the Serfat area (core number FP94-11-04; Fig. 2). The gas was found in Cretaceous sediments below thick sills on the north coast of Nuussuaq (Dam & Nøhr-Han- sen 1995). Five samples of gas were obtained from the cores and stored in plastic containers. Data were provided Fig. 4 Bluish gas hydrates at c. 7 m depth in core 400407 at Annertuneq on the north coast of Nuussuaq (location in Fig. 2). Core diameter is 3.0 cm. Photo taken on 1 August 1992. https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 7 of 21 www.geusbul let in.org Ta bl e 1  G as c om po si tio ns fo r se ve n co re s in th e N uu ss ua q Ba si n, W es t G re en la nd Co re (c or e nu m be r) Sa m pl e nu m be r or c or e pi ec e D ep th (m ) CH 4 (p pm ) C 2H 6 (p pm ) C 3H 8 (p pm ) iC 4H 10 (p pm ) nC 4H 10 (p pm ) iC 5H 12 (p pm ) nC 5H 12 (p pm ) δ13 C 1 (‰ ) δ13 C 2 (‰ ) δ13 C 3 (‰ ) δD C 1 (‰ ) W et ne ss G as o ri gi n D at a so ur ce s M ar ra at -1 (4 08 00 1) 40 80 11 1 41 .0 28 .9 0. 08 −5 3. 4 36 1 Th La ie r 19 94 ; s up pl em en ta ry fi le S 1 (a ls o in cl ud e ad di tio na l a na ly se s) 40 80 20 1 82 .0 37 .1 0. 10 −5 3. 4 37 1 Th Se rf at (F P9 4- 11 -0 4) 38 00 02 2 29 0. 0 10 42 36 1 13 6 3. 1 8. 8 0. 5 0. 5 −1 1. 2 −2 0. 3 −2 0. 9 2. 1 Th H M La ie r un pu bl is he d da ta O ct ob er an d D ec em be r 19 94 38 00 03 29 0. 2 22 52 51 6 13 1 3. 1 10 .2 1. 0 1. 8 3. 5 Su pp le m en ta ry fi le s S2 a nd S 3 38 00 04 29 0. 4 27 65 49 3 13 5 3. 4 10 .4 0. 8 1. 4 4. 4 38 00 05 29 0. 6 23 06 54 1 16 8 4. 7 14 .0 1. 0 1. 5 3. 6 38 00 06 2 29 0. 8 20 06 48 1 15 5 4. 8 13 .0 0. 9 1. 5 −2 2. 2 −2 3. 7 −2 1. 9 3. 1 Th H M G AN W #1 (3 80 10 1) 38 01 05 3 72 1. 0 83 2 00 0 61 0 00 13 0 00 15 00 10 00 −4 3. 3 −2 8. 1 −2 7. 1 −1 99 .0 11 2 Th L M Ch ri st ia ns en e t a l. 19 95 b G AN E# 1 (4 39 00 1) 43 90 07 3 63 1. 0 82 3 00 0 28 8 −4 5. 4 22 0 00 Th L M Ch ri st ia ns en e t a l. 19 96 b (a ls o in cl ud e ad di tio na l a na ly se s) 43 90 01 -3 68 63 3. 7 44 4 00 33 3 33 0 67 .3 14 4 28 18 −4 5. 1 67 Th L M 43 90 01 -5 30 68 9. 8 91 00 4 −4 0. 9 22 60 Th M M G AN K# 1 (4 39 20 1) 43 92 01 -0 54 19 4. 5 46 7 00 21 10 38 4 54 30 .8 10 .4 3. 5 −4 9. 5 18 .7 Th L M Ch ri st ia ns en e t a l. 19 96 b (a ls o in cl ud e ad di tio na l a na ly se s) 43 92 01 -1 13 36 5. 9 23 0 00 0 53 00 19 20 12 2 15 2 11 7 −4 6. 9 −3 2. 3 31 .9 Th L M 43 92 01 -1 18 37 9. 7 13 3 00 0 46 30 15 40 14 0 12 2 24 8 −4 1. 9 21 .6 Th L M G AN T# 1 (4 39 10 1) 43 91 07 3 24 7. 2 76 00 −6 5. 4 0 Bi og en ic Ch ri st ia ns en e t a l. 19 96 b 43 91 11 3 60 8. 8 26 9 00 24 0 30 −3 4. 8 10 0 Th H M 43 91 12 3 60 8. 8 64 2 00 0 41 0 −3 5. 0 15 66 Th H M 43 91 16 60 8. 8 37 2 00 36 16 .3 1. 2 3. 9 0. 5 1 −3 7. 0 71 1 Th H M 43 91 01 -4 20 64 9. 4 18 8 90 0 33 50 56 2 68 19 2 30 18 −4 6. 0 −3 0. 4 48 .2 Th L M 43 91 01 -4 47 73 7. 0 82 0 00 25 6 40 .2   −4 0. 1 27 7 Th M M 43 91 01 -4 49 74 3. 7 26 4 00 0 39 0 16 00 86 24 2 28 39 −4 0. 4 13 3 Th M M 43 91 01 -4 57 2 76 9. 3 23 0 00 15 60 27 8 8. 8 21 .7 1. 9 2. 6 −3 6. 8 12 .5 Th H M 43 91 01 -4 58 77 4. 0 10 7 00 0 19 10 34 9 3 7 n. a. n. a. −3 9. 7 47 .1 Th M M 43 91 01 -4 65 79 4. 0 43 2 00 63 2 10 1 4. 1 10 .9 0. 9 1. 3 −3 9. 1 58 .9 Th M M 43 91 01 -4 72 2 81 6. 2 38 8 00 19 3 82 5. 7 10 .3 0. 9 1. 3 −2 0. 8 14 1 Th H M 43 91 28 3 90 1. 3 33 9 00 −6 8. 0 0 Bi og en ic Co nt in ue d https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 8 of 21 www.geusbul let in.org Ta bl e 1  G as c om po si tio ns fo r se ve n co re s in th e N uu ss ua q Ba si n, W es t G re en la nd (C on tin ue d) Co re (c or e nu m be r) Sa m pl e nu m be r or c or e pi ec e D ep th (m ) CH 4 C 2H 6 C 3H 8 iC 4H 10 nC 4H 10 iC 5H 12 nC 5H 12 δ13 C 1 (‰ ) δ13 C 2 (‰ ) δ13 C 3 (‰ ) δD C 1 (‰ ) W et ne ss G as o ri gi n D at a so ur ce s U m iiv ik -1 (4 39 30 1) 10 4. 7 33 1 00 0 72 8 79 7 22 3 15 1 −5 1. 2 21 7 Th L M Ch ri st ia ns en e t a l. 19 97 b (a ll an al ys es ) 15 1. 3 44 9 00 26 50 78 2 21 5 84 34 .7 −2 1. 1 13 .1 Th L M 19 9. 7 20 1 40 0 20 20 46 4 tr tr −4 3. 7 81 .1 Th L M 25 0. 7 39 4 80 17 50 59 9 39 .5 56 .7 −2 0. 6 16 .8 Th L M D am e t a l. 19 98 (a dd iti on al in te rp re ta tio n) 30 7. 7 14 8 00 0 20 17 66 0 tr tr −3 8. 9 55 .3 Th L M 40 3. 6 77 5 00 25 70 58 0 40 92 −2 4. 6 24 .6 Th H M 45 0. 5 68 5 00 37 00 50 0 78 82 −2 1. 9 16 .3 Th P M 75 2. 5 40 4 20 0 17 6 00 19 40 15 5 17 5 −3 1. 8 20 .7 Th P M 79 4. 0 43 9 20 64 00 12 80 16 7 12 4 −2 7. 6 5. 7 Th P M 91 0. 4 41 0 96 0 51 0 80 65 40 59 0 29 3 29 .6 −3 2. 6 −2 7. 9 −2 4. 4 7. 1 Th P M 10 65 .6 49 9 40 55 40 92 5 10 0 10 0 −2 0. 1 7. 7 Th P M 11 51 .4 42 5 00 0 77 1 20 12 9 30 24 70 14 90 65 8 18 4 −3 5. 1 −2 7. 6 −2 3. 6 4. 7 Th P M 11 63 .6 34 8 00 0 79 5 00 17 4 60 40 00 21 60 87 2 21 9 −3 4. 6 −2 7. 8 −2 4. 6 3. 6 Th P M 11 71 .9 41 0 00 0 46 8 00 93 40 20 00 14 00 62 2 20 0 −3 2. 9 −2 7. 6 −2 3. 5 7. 3 Th P M 11 82 .6 38 9 60 92 10 29 10 69 0 57 0 25 0 92 −1 1. 4 −2 0. 7 −2 1. 5 3. 2 Th P M 11 97 .9 31 3 00 0 21 00 12 70 27 0 25 8 95 41 .5 −3 7. 8 −2 2. 2 −2 4. 2 92 .8 Th P M 1 Co nt ai ne d hi gh n itr og en . 2 D iff er en tia l l ea ka ge o f C 1 a nd li gh t i so to pe s. 3 S te el c yl in de r. tr : t ra ce a m ou nt s. B la nk c el ls in di ca te th at th e co m po un d is no t p re se nt (b el ow d et ec tio n lim it) o r t ha t i so to pe s w er e no t a na ly se d. C H 4 (C 1): m et ha ne ; C 2H 6 (C 2): et ha ne ; C 3H 8 (C 3): pr op an e; iC 4H 10 : i so bu ta ne ; n C 4H 10 : n -b ut an e; iC 5H 12 : i so pe nt an e; n C 5H 12 : n -p en ta ne ; w et ne ss : C 1/( C 2 + C 3); Th : t he rm og en ic ; L M : l ow -t he rm al m at ur ity w ith re sp ec t t o oi l g en er ati on ; M M : m ed iu m - th er m al m at ur ity w ith re sp ec t t o oi l g en er ati on ; P M : p os tm at ur e w ith re sp ec t t o oi l g en er ati on ; n .a .: no t a na ly se d. https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 9 of 21 www.geusbul let in.org by Laier in October and December 1994 as unpub- lished data (see Supplementary Files S2 and S3, respectively) and are summarised in Table 1. The samples contained significant volumes of gas with relatively high concentrations (up to 3000 ppm) of wet gases. C-isotope composition of methane (δ13C1), ethane (δ13C2) and propane (δ13C3) suggested a ther- mogenic origin from a source rock with a relatively high thermal maturity. The data suggested a loss of lighter isotopes by diffusion from the plastic contain- ers (Table 1). This was tested by experiments of the containers (Laier, unpublished data, December 1994; Supplementary File S3). 4.4 GANW#1, drilled in 1994 GANW#1 (core 380101, Fig. 2) was drilled by grønArc- tic Energy, Calgary, Canada in September–October 1994 as a follow-up to the Marraat-1 borehole (Christiansen et al. 1995a). The main goal was to penetrate the base of the volcanic succession and to document further oil impregnation at depth. One gas sample (380105) from a depth of 721 m was sampled from the wellhead in a steel cylinder, and a full suite of gas analyses was carried out. The data were reported by Christiansen et al. (1995b) and are presented in Table 1. The gas had a moderate wetness (Table 1; Fig. 5). δ13C1 versus δD of methane (δDC1) sug- gests a thermogenic origin from a source rock and an association with oil (Fig. 6), while δ13C1 versus δ13C2 sug- gests a low thermal maturity dominated by type III kero- gen (Fig. 7; Christiansen et al. 1995b). 4.5 GANE#1, GANK#1 and GANT#1, drilled in 1995 Three fully cored boreholes GANE#1 (core 439001), GANK#1 (core 439201) and GANT#1 (core 439101) and one sidetrack (GANE#1A; data not shown here) were drilled by grønArctic Energy in the summer of 1995 to depths of between 398 and 901 m as part of their explo- ration and production license on western Nuussuaq (locations in Fig. 2). The main goal was to characterise the sedimentary succession below the volcanic suc- cession and to demonstrate an active petroleum sys- tem. All boreholes revealed oil and gas within volcanic or sedimentary rocks. Detailed sedimentological and stratigraphical studies and comprehensive geochemi- cal analyses of organic compounds were carried out by GGU for grønArctic Energy (Christiansen et al. 1996b). Some of these data are presented in Table 1. Some gases sampled in steel cylinders together with gas from core-pieces sealed in cans were analysed. Gas was commonly observed in many intervals in GANT#1 Fig. 5 Wetness (C1/C2+C3) versus δ13C of methane (δ13C1) for Marraat-1, GANW#1, Umiivik-1 and Pingo 132. C1: methane; C2: ethane; C3: propane. Compositional fields indicate biogenic or thermogenic origin. Modified from Schoell (1984). 10000 1000 100 10 1 C 1/ (C 2 + C 3) –40 –60 –80 Bacterial Thermogenic GANW#1 Umiivik-1 Pingo 132Marraat-1 δ13C1 Fig. 6 δ13C of methane (δ13C1) versus δD of methane (δDC1) for GANW#1 and Pingo 132. Plotted compositional fields (blue lines) are from Jenden and Kaplan (1989). –300 –200 –100 δDC1 –20 –30 –40 –50 –60 –70 Microbial gas Mixed gas Oil-associated gas Condensate- associated gas δ1 3 C 1 GANW#1 Pingo 132 https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 10 of 21 www.geusbul let in.org and GANE#1, indicated by bubbles in the drilling fluids. Most notable was the gas flaring of GANE#1 at a depth of c. 660 m (see fig. 4 in Christiansen et al. 1996a). Corre- sponding cores from this drilling depth show oil impreg- nation with the relatively rare “Eqalulik type” that cannot be correlated to any known source rock (Bojesen-Koe- foed et al. 1997a, 1999). In GANE#1 (and GANE#1A), gas was commonly observed in several sandstone intervals (631–641, 684– 689 and 696–702 m). In GANT#1, gas was commonly observed in many sandstone intervals between 575 and 775 m. Most of these gases are thermogenic in origin. But their variable composition suggests the presence of both low maturity gases from the penetrated succession and high maturity gases that may have migrated from deeper in the subsurface (Table 1). 4.6 Umiivik-1, drilled in 1995 Umiivik-1 (core 439301) was drilled as a 1200 m deep stratigraphic well by grønArctic Energy for GGU in August to September 1995. The main goal was to test and document a Cenomanian–Turonian source rock (Bate & Christiansen 1996; Dam et al. 1998). In the deeper part of the well, gas was heard to be escaping the core. Some intervals revealed a white froth on the core surface when it was removed from the core barrel (Bate & Christiansen 1996). Twenty-seven core pieces were sealed in cans and analysed for their gas composition (Christiansen et al. 1997b; Dam et al. 1998). Sixteen of these are presented in Table 1 – the remaining nine samples had no detect- able amounts of gas. Gas concentrations of the 16 sam- ples were high, with significant amounts of wet gases such as propane, butane and pentane (Table 1). In some deeper parts of the well, concentrations were so high that the sampling cans deformed. Compositions in the deeper part are typical of thermogenic gas associated with oil (Table 1; Figs 5 and 7). Unfortunately, the iso- topic composition trend suggests some diffusion after sampling as suggested by Christiansen et al. (1997b). The presence of a postmature oil-prone source rock in the deeper part (below 1100 m) of Umiivik-1 was docu- mented in more detail by Drits et al. (2007). 4.7 GRO#3, drilled in 1996 GRO#3 was drilled by grønArctic Energy in the summer of 1996, following promising results from previous drill- ing and seep studies (Christiansen et al. 1997a, 1998). Cores or sidewall cores were not included in the drill- ing programme, and the organic geochemical results are based on analysis of cuttings only (Bojesen-Koefoed et al. 1997b; Christiansen et al. 1998). Eight sandstone intervals were drillstem tested to obtain fluid samples, but results were inconclusive. Later, log interpretation Fig. 7 δ13C of methane (δ13C1) versus δ13C of ethane (δ13C2) for GANW#1, Umiivik-1 and Pingo 132. Maturity lines are calcu- lated from Faber (1987) for type II kero- gen. Ro: vitrinite reflectance. –40 –35 –30 –25 –20 –50 –45 –40 –35 –30 δ1 3 C M et ha ne 0.5 %Ro 0.7 %Ro 0.9 %Ro 1.1 %Ro 1.3 %Ro 1.5 %Ro 1.8 %Ro 2.0 %Ro 2.5 %Ro 3.0 %RoMix, different thermogenic gases or microbial methane oxydation Mix, microbial methane GANW-1 Umiivik-1 Pingo 132 δ13C Ethane + + + + + + + + + + https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 11 of 21 www.geusbul let in.org indicated many intervals with high gas concentrations (Kristensen & Dam 1997). These petrophysical data are not presented in this review. 4.8 Vismann mineral exploration, drilled in 2007 The company Vismann Exploration Inc. drilled two mineral exploration boreholes in the Aaffarsuaq val- ley, in 2007, based on previously observed geophysical anomalies in the area (Fig. 2). The logistical operation was complex and required construction of a new road into the Aaffarsuaq valley. Both of the wells were sus- pended due to gas under pressure at depths of 154 and 133 m. Neither of the holes reached bedrock and they only penetrated the Quaternary overburden (glacial tills). Unfortunately, no gas was sampled. 4.9 Lakes and pingos The best opportunity to observe gas seepage in land terrains, like the Nuussuaq Basin, is from lakes, pin- gos, below newly formed ice or on partly wet mud flats. Pingos are conspicuous mound-like landforms that are common in regions with continuous permafrost. They may have craters resembling those of mud volcanoes (Pissart 1988). Active pingos are formed by periglacial processes, have an ice core of frozen water and often grow over time. Some eventually collapse. Pingos are common in many valleys on Disko, Nuussuaq and Svartenhuk Halvø. Expedition anecdotes of bubbling lakes suggested the presence of gas seepage as early as the 1930s. Early analyses of both gas and water col- lected in the 1930s and 1940s were first presented in the context of petroleum exploration by Henderson (1969). These early analyses document a significant content of methane and alkaline water associated with gas seep- age. Many of the pingos in the region were more sys- tematically studied in the 1990s – most of them were dry. Some occasionally show crater lakes or outlets of spring water under artesian pressure. Sampling of these waters may give information on the composition of water and gases below the permafrost. Pingo 132 (Fig. 2) north of the Aaffarsuaq river seems to have been rather active and wet over many decades. Note that Henderson (1969) uses the term Qapiortoq kit- dleq for the same pingo. Pingo 132 was visited and sam- pled on several occasions in 1991 and 1992. Snow fans were observed to disappear from Pingo 132 later than on any other southward facing slopes in this part of the Aaffarsuaq valley. On one occasion, a fountain of water under pressure was observed (Fig. 8A). A similar feature was documented in a photo taken on 25 August 1939 by B. Thomsen (see fig. 6 in Henderson 1969). Looking downstream from the snow fan, which covers part of the pingo, the valley floor is described as being overgrown with algae and other vegetation, suggesting that the outlet has been active over long periods of the year and that the water is rich in nutrients. This remark- able colouration may be a good proxy for remote-sens- ing studies of other similar outlets in the region. Elsewhere, gas seepage from the hinterland of Mar- raat is indicated by the so-called Gassø lake (Fig. 2), depicted in the 1:100 000 geological map of the area (Rosenkrantz et al. 1974) and the official Geodætisk Institut 1:250 000 topographical map from 1980. The lake was visited by Flemming G. Christiansen and Inger Salomonsen on 28 July 1994. The lake surface showed clear evidence of seepage as intense bubbling (Fig. 8B). Analyses of lake water (sampled in cans) indicated a complete dominance of nitrogen (Laier, unpublished data, October 1994; Supplementary File S2), suggesting either long-distance migration of gases that are ther- mally very mature, or more likely that oxygen had been lost by bacteria in an anoxic environment. A third and more recent example is from the Marraat area, where a new pingo seems to be actively forming (Figs 2 and 8C). The normally flat riverbed surface is doming with new fractures in the peaty soil. The under- lying ice-core is beginning to be exposed and large bub- bles of gas are visible in small ponds nearby, beneath recently formed ice (Fig. 8D). Such features with frac- tures opening to permafrost below – and possibly with degrading permafrost – may become more common on Nuussuaq in the years to come, especially in areas with active movements. 4.10 Marine records Geophysical data, including conventional seismic data and high-resolution shallow seismic data, indicate that gas could be very common in the sedimentary suc- cession below the seabed of Vaigat (location in Fig. 2). Examples of so-called direct hydrocarbon indicators have been observed offshore in Vaigat, particularly as flat spots but also as gas cloud features (Bojesen-Koe- foed et al. 2007). Geochemistry data of pore waters from gravity cores indicate that gas hydrates may also be present at sev- eral places offshore in Disko Bugt and Vaigat (Mikkelsen et al. 2012; Nielsen et al. 2014). This is supported by numerous observations of pockmarks, seabed mud diapirs and change in reflection patterns on geophysi- cal data in the area. Kuijpers et al. (2001) also observed intense degassing from two cores south of Disko. To the best of our knowledge, no gas samples have been analysed. 4.11 Summary: existing gas observations Historical observations of gas seepage in the Nuussuaq Basin are to some degree supported by modern analyt- ical data. Large parts of the Nuussuaq Basin are clearly https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 12 of 21 www.geusbul let in.org B C D A Fig. 8 Features of Pingo 132 in Aaffarsuaq Valley, Gassø lake, and a new pingo near Marraat-1 core. A: Water fountain indicating water with a high gas content under artesian pressure below the permafrost, 17 August 1991. B: Surface of Gassø lake with clear indications of gas seepage, 28 July 1994. C: Doming, soil fracturing and possible formation of a new pingo near Marraat-1, 27 July 2006 (photo: Roy Fitzsimmons). D: Gas trapped under ice in a small pool near Marraat-1, 27 July 2006. https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 13 of 21 www.geusbul let in.org underlain by a sedimentary succession that contains high concentrations of gas. Although dominated by bio- genic gas, gases from surface lakes and pingos show a distinct thermogenic component. The gases from bore- holes are mainly thermogenic in origin, and in some cases, their composition suggests an association with oil. These oil-associated gases have a rather low thermal maturity corresponding to the thermal maturity of the sediments penetrated by drilling. In several cases, examples of thermally high- maturity gases have been recorded. These gases may have migrated from the deeper part of the sedimentary suc- cession or were generated in the vicinity of dykes and sills. Clearly, better systematic sampling techniques, proper handling and storage, and most importantly, rapid analyses using modern instrumentation could provide much more valuable information. GANT#1, Pingo 132 and the Vismann mineral explo- ration holes are all in close proximity to the anticline, suggested by Sørensen et al. (2017) to be a large poten- tial target for future exploration. It is therefore partic- ularly important to get more data on oil and gas seeps from this area. 5 2019 reconnaissance to sample oil and gas seepage 5.1 Biomarkers in oil seepage near the Kuugannguaq–Qunnilik Fault zone On 26 July 2019, we visited a number of planned drill sites next to the Kuugannguaq–Qunnilik Fault zone in the Aaffarsuaq valley to check for oil seepage (Fig. 2). Hyaloclastites from the deep part of the Vaigat Forma- tion were examined for signs of petroleum staining. The hyaloclastites are from unit 409 of the Nuusap Qaqqar- sua Member within the Naujánguit Member of the Vaigat Formation (Fig. 3; see details in Pedersen et al. 2002, 2017). We sampled the hyaloclastites, located c. 340 m.a.s.l., close to the outlet of the Qunnillik canyon (sam- ple site 574305 in Fig. 2), a few hundred metres west of the expected trace of the Kuugannguaq– Qunnillik Fault zone. We picked out small pieces of a hard, fresh rock with thin carbonate veins and a distinct petroliferous odour for organic geochemical analyses using standard meth- ods (Bojesen-Koefoed et al. 2018). A sample of rock pieces was lightly crushed and extracted for 4 h (1 h immersed in boiling solvent followed by 3 h of rinsing) using a Soxhtec™ instrument and a 93+7 vol./vol. dichloromethane + methanol mix- ture as solvent. The extract was recovered by evapora- tion over N2 and weighed. A 238 g sample was extracted to obtain a total yield of 6.2 mg extract, corresponding to c. 26 ppm. Asphaltenes were precipitated by the addition of 40-fold excess n-pentane. Asphaltenes were recovered by centrifugation and rinsed through several stages with n-pentane. Asphaltenes account for 27.4% by weight of the total. Maltene (i.e. asphaltene-free) fractions were separated in saturated hydrocarbons, aromatic hydrocarbons and polar fractions by medi- um-pressure liquid chromatography using a procedure modified from Radke et al. (1980). The maltene fraction is dominated by polar NSO compounds (Table 2). The saturated hydrocarbon fraction was analysed by gas chromatography–flame ionization detection (GCFID) using a Shimadzu gas chromatograph, furnished with a 30-m WCOT ZB-1 capillary column. Biomarker analysis was carried out by gas chromatography–mass spec- trometry (GC–MS) using an Agilent 6890N gas chro- matograph, fitted with a 30 m WCOT ZB-5 capillary column, coupled to a Waters (Micromass) Quattro Micro GC tandem quadrupole–hexapole–quadrupole MS. The instrument was run in both Selective Ion Monitor- ing mode (GC–MSSIM) and GC–MS–MS parent–daughter mode. The  sample was run several times using meth- ods designed to optimise the representation of different compounds. Gas chromatographic data on the saturated hydro- carbon fraction show a strongly front-end evaporated distribution of n-alkanes, a high proportion of long- chain components (Fig. 9A) and no unresolved complex mixture, suggesting limited biodegradation (Fig. 9A). Front-end losses of short-chain components make cal- culation of standard ratios futile, including the pristane/ phytane ratio. The concentrations of tricylic terpanes (Fig. 9B) are relatively low, and their distribution partially obscured by the presence of abundant unknown components in the same range, probably various other tri- and tetracy- clic components. Pentacyclic triterpanes show a series of hopanes ranging from C27 to C35, including notable proportions of 28.30-bisnorhopane (H28, Fig. 9C) and oleanane (O, Fig. 9C), plus trace amounts of bicadinanes and taraxastane (not shown). Extended 28-bisnorho- panes are absent, as are nor/bisnorlupanes. The bisho- mohopane isomerisation ratio has reached equilibrium Table 2 Maltene fraction extracted from oil-stained hyaloclastics (sample site 574305, Fig. 2) in the Affarsuaq valley, Nuussuaq Basin Sample Saturated hydrocarbons (wt.%) Aromatic hydrocarbons (wt.%) Polar compounds (wt.%) 574305 10.0 2.5 87.5 NSO: nitrogen, sulphur, oxygen. https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 14 of 21 www.geusbul let in.org at 0.61 (H32 S/(S+R), Table 3, Fig. 9C). The sample shows high concentrations of aromatic diterpanes which are a common feature of terrestrial oils found on Nuussuaq, moderate concentrations of phenanthrene and methyl- phenanthrene (not shown), and the presence of di- and triaromatic oleanane. The sterane distribution is strongly dominated by C29 moieties and shows very high propor- tions of diasteranes (Fig.  9D). C30 desmethyl steranes are absent, but C26-steranes are relatively prominent and allow calculation of a nordiacholestane ratio of 0.37 (Holba et al. 1998). C29-sterane 20S/(20S+20R) and αββ/ (ααα+αββ) isomerisation ratios are both below equilib- rium at 0.43 and 0.42, respectively (Table 3, Fig. 9D). Sample 574305 can be classified as a “Niaqornarsuk type” oil with some notable deviations, according to its biological-marker characteristics as first defined by Bojesen-Koefoed et al. (1999; Table 4). A few parameters fall outside the established range for this oil type, nota- bly the relative abundance of diasteranes and 28,30-bis- norhopane. However, the following diagnostic criteria are fulfilled: 1. Appreciable concentrations of 28,30-bisnorhopane and absence of extended 28-norhopanes (Table 4). 2. Presence of oleanane (perhaps coeluting with small amounts of lupane, see Nytoft et al. [2020]), with no or negligible concentrations of nor/bisnorlupanes (Table 4, Fig. 9C). 3. Strong predominance of C29-steranes and absence of C30 desmethyl steranes (Table 4, Fig. 9D). The aromatic fingerprint, in particular the moderate concentrations of phenanthrene and methylphenan- threne, further supports the identification of sample 574305 as “Niaqornarsuk type” oil. The characteristic features of the “Niaqornarsuk type” oil were originally defined using only GC–MS(SIM) data, which are inferior to modern GC–MS–MS. Sterane data based on GC–MS(SIM) suffer from coelution prob- lems, which often cause misleadingly low ratios of dias- teranes to regular steranes. The Niaqornaarsuk oil type has been linked to Cam- panian-age source rocks, based on the geochemical correlation to Campanian-age shales of the GANT#1 borehole (Bojesen-Koefoed et al. 1999), which are per- fectly conformable with a nordiacholestane ratio of 0.37 (Holba et al. 1998). The sample was collected at least 10 km from any other known occurrence of surface seep- age near the Kuugannguaq–Qunnillik Fault zone, which is encouraging for future exploration. The presence of a Niaqornaarsuk oil type at a considerable distance from the only hitherto known occurrences of this oil type fur- ther supports the presumed existence of Campanian age deposits developed in source-rock facies in the region. GCFID GC-MSSIM m/z 191 GC-MS-MS Pentacyclics Sum of 9 transitions GC-MS-MS Steranes Sum of 5 transitions P ris ta ne P hy ta ne nC 20 nC 25 nC 30 nC 35 H 30 H 29 H 28 O + L Tm Ts 29 Ts M 29 M 30 H 31 (S + R ) H 32 (S + R ) H 33 (S + R ) S29 αα αS αα αR αβ βS αβ βRD 27 D 27 D 27D 27 A B C D Fig. 9 GCFID and GC–MS–MS data (time vs. signal) for a sample of oil-stained hyaloclastics (sample site 574305; Fig. 2), Aaffarsuaq Val- ley, Nuussuaq Basin. A: GCFID data. B: GC–MSSIM for m/z 191. C: GC– MS–MS of pentacyclics. Sum of nine transitions. D: GC–MS–MS of steranes. Sum of five transitions. Symbols are as follows: nCx: nor- mal alkanes (x = carbon number); pristane: C19 acyclic isoprenoid; phytane: C20 acyclic isoprenoid; Ts: 18α-trisnorneohopane; Tm: 17α-trisnorhopane; H28: 28,30-bisnorhopane; H29: norhopane; 29ts: C29 neohopane; M29: normoretane; O+L: coelution of ole- anane + lupane; H30: hopane; M30: moretane; HXX (S+R): homo- hopanes, doublets 22S and 22R isomers; XX = carbon number; D27: C27 diasteranes; S29: C29 regular steranes; αααS: regular sterane ααα 20S isomer; αββS: regular sterane αββ 20S isomer; αββR: regu- lar sterane αββ 20R isomer; αααR: regular sterane ααα 20R isomer. https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 15 of 21 www.geusbul let in.org 5.2 Gas seepage in Aaffarsuaq Valley 5.2.1 Remote-sensing analysis of Pingo 132 On 26 July 2019, Pingo 132 in the Aaffarsuaq valley, cen- tral Nuussuaq, was visited to check for mud extrusion and gas seepage (Fig. 2). Although Pingo 132 is perigla- cial in origin, it resembles typical mud volcanos from classical petroliferous basins or geothermal fields with mud overflow (see Etiope 2015; Mazzini & Etiope 2017; Mazzini et al. 2011). Today, there is evidence of recent mud extrusion in the area. The mud cropping out is pale in colour, has rather steep sides and many irregular fractures and erosional features that are not likely to survive more than a few winters. There is little to no vegetation on the extruded mudstone, which is in contrast to the older parts of the pingo and surrounding valley floor. The actual mudstone contains numerous clasts of rounded basements boulders, some Cretaceous Atane Formation sandstone lithologies and a few volcanic rock types – all typical of the Quaternary tills in the Aaffarsuaq valley (Fig. 10). High-resolution satellite images provide good pos- sibilities for detecting surface movements of the pingo and measuring slow displacement rates of centimetres to metres per year. Using Differential Synthetic Aperture Radar (SAR) interferometry (DInSAR; Rosen et al. 2000) to plot the phase differences between two or more sat- ellite SAR images allows us to detect movement in the direction of line-of-sight of a few millimetres and helps characterise the dynamics of terrain uplift. Combining the two complementary techniques overcomes the lim- itations of using just one of these methods. To visually identify the changes in the shape of Pingo 132 and outcropping mud over time, we used optical four-band PlanetScope time-series with 5 m spatial resolution between 2017 and 2019 (Fig. 11A). The Nor- malized Difference Vegetation Index (NDVI) is calcu- lated from the same dataset (Fig. 11B) to enhance the Table 3 Key geochemistry parameters for sample 574305 Sample C19–26 Tricyclics/ hopane C23 Tricyclic/ hopane C25/C26 Tricyclics C24 Tetracylic/ hopane H32 S/(S+R) Ts/(Ts+Tm) S29 S/(S+R) S29 αββ/ (ααα+αββ) 574305 0.09 0.01 0.83 0.01 0.61 0.41 0.43 0.42 H32 S/(S+R): bishomohopane isomerisation ratio; Ts/(Ts + Tm): 18α-trisnorneohopane/(18α-trisnorheohopane + 17α-trisnorhopane); S29 S/(S+R): C29 sterane 20S/(20S+20R) isomerisation ratio; S29 αββ/(ααα+αββ): C29 sterane αββ/(ααα+αββ) isomerisation ratio. Table 4 Comparison of sample 574305 with the Niaqornaarsuk oil type (Bojesen-Koefoed et al. 1999) Sample H28/H29 H29/H30 O/(O + H30) D27/RS27 RS27/RS29 S27% S28% S29% 574305 0.31 1.14 0.18 4.0 0.32 19 21 60 Niaqornaarsuk oil type Mean 0.17 0.92 0.06 0.87 0.32 20 14 65 Minimum 0.13 0.81 0.04 0.73 0.20 15 12 57 Maximum 0.23 1.02 0.10 1.19 0.47 27 17 73 H28/H29: 28,30-bisnorhopane to norhopane ratio; H29/H30: norhopane to hopane ratio; O/(O+H30): oleanane to oleanane + hopane ratio D27/ RS27: C27 diasterane to C27 regular sterane ratio; RS27/RS29: C27 to C29 ratio of regular steranes; S27%, S28%, S29%: relative distribution of regular steranes. Fig. 10 Extruding muds from the side of Pingo 132. Note the many rounded basements boulders in the mud. Height of sec- tion c. 3 m. Photo taken on 26 July 2019. https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 16 of 21 www.geusbul let in.org 200 m A B C July 2017 July 2018 July 2019 August 2019August 2018August 2017 18 August 2017 14 August 2019 10–22 August 2019 5 August 201813 July 2017 12 July 2019 5–17 July 2019 11–23 June 2019 200 m 200 m -3 -2 -1 -1 1 0 1 2 3 Fig. 11 Remote-sensing images and analysis of Pingo 132, Affarsuaqq valley. Red-dashed lines indicate the location of Pingo 132. A: Optical four-band PlanetScope data with 5 m spatial resolution for July and August 2017–2019. B: Normalized Vegetation Index (NDVI) for July and August 2017 and 2019. Negative values of NDVI correspond to water. Values close to zero (–0.1 to 0.1) generally correspond to barren areas of rock, sand or snow. Low positive values (0.2–0.4) represent shrubs, while high values (approaching 1) indicate green vegetation. C:Close-up of Pingo 132. Selected differential interferograms (wrapped interferometric phase) from track 175. Upper row: 10 August 2019–22 August 2019 (temporal baseline: 12 days; normal baseline: –0.06 m). Lower row: 5 July 2019–17 July 2019 (temporal baseline: 6 days; normal baseline: 15.68 m) and 11 June 2019–23 June 2019 (temporal baseline: 6 days; normal baseline: 5.46 m). https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 17 of 21 www.geusbul let in.org interpretation of the identified patterns and to measure the concentration of green vegetation. Two Sentinel-1 tracks (i.e. 171 descending and track 90 ascending) cover the same area. Differential SAR Interferometry was car- ried out for the descending track between 11 June and 3 September 2019 using the Arctic digital elevation model (Porter et al. 2018). The interferograms were unwrapped, and the deformational rates are reported as the satellite line-of-sight rates projected onto the steepest slope. The results indicate significant vertical movements in both summer and winter, suggesting “uplift” rates of c. 1 cm every 12 days, probably related to mud accumu- lation (Fig. 11C). Furthermore, seasonal variation in the uplift rate seen in the DInSAR data matches the seasonal pattern observed in the optical data. It seems that most of the observed mud extrusion took place in the sum- mer of 2017. 5.2.2 Geochemistry of gas seepage The present water outlet is on the lower, south side of the pingo. It is associated with fractures in the soil and peat and small ponds with bubbling gas (see videos in Supplementary Files S4 and S5). Some of the partly dry mudflats show gas-escape vents (Fig. 12A). The sandier material displays a crater-like feature, a few centimetres in size (Fig. 12B). A gas sample was taken in a plastic bottle where gas displaced the outlet water, kept cool and analysed within a week for CH4 and C2H6 by standard gas chromatogra- phy (Christiansen et al. 1997b). The sample was stored and later analysed for stable carbon and hydrogen iso- topes by Martin Krüger at Bundesanstalt für Geowis- senschaften und Rohstoffe in Hannover (for methods, see Blumenberg et al. 2016). The seeping gas is mainly composed of methane with a small amount of ethane (Table 5). The carbon isotope composition of methane and ethane using standard classification plots suggests a thermogenic origin with a relatively low thermal matu- rity (Figs 5–7). 5.2.3 Geochemistry of water associated with gas accumulation or seepage Geochemistry of formation water associated with oil and gas accumulations or related to oil and gas seepage may provide important additional information on the migration and degradation history. Water under pres- sure has been recorded in a few places on Nuussuaq, both in the Marraat-1 and GANK#1 wells and in some pingos. Some historical data were published by Hen- derson (1969), and additional data from the early nine- ties were compiled and reported by Christiansen et al. (1995b). These are presented in Table 5 along with new data for Pingo 132. The formation fluids from Marraat-1 have a higher salinity than seawater and a very high Ca/Mg ratio sug- gesting a deep brine origin (Table 6). There is some variation between different levels, suggesting that the Fig. 12 Gas seepage from Pingo 132. A: Gas escape structures on recently dried-out mud flat on the southern side of Pingo 132, 26 July 2019. Size is c. 20 × 30 cm. B: Centimetre-scale mounds formed by gas seepage at Pingo 132, 26 July 2019. Hammerhead for scale. Table 5 Geochemistry of gas escaping from Pingo 132 sampled in 1991, 1992 and 2019 Sample number Date CH4 (C1) (ppm) C2H6 (C2) (ppm) δ13C1 (‰) δ13C2 (‰) δDC1 (‰) Wetness Data sources 358472 17 August 1991 723 000 530 −45.8 n.a. n.a. 1364 Laier 1994 400843 14 July 1992 468 000 n.d. −40.4 n.a. n.a. n.d. Laier 1994 400844 14 July 1992 81 800 790 −38.1 n.a. n.a. 1035 Laier 1994 400894 14 August 1992 355 000 175 −43.4 n.a. n.a. 2028 Laier 1994 547303 26 July 2019 239 000 164 −43.2 −34.5 −233 1460 This study n.a.: not analysed; n.d.: not determined. Wetness: C1/(C2 + C3). C3 not present in any samples. https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 18 of 21 www.geusbul let in.org different volcanic lithologies and their content of zeo- lites could affect composition. Pingo 132 is less saline than Marraat-1 (Table 6). It should be noted that in Pingo 132, there is an increased salinity compared to river water, and with high Na/K ratios, low Ca/Mg ratios and low Cl/SO4 ratios (Table 6). The 1991 and 1992 samples (fountain water only) have a rather consistent composition through time and a slightly enriched pH between 8.78 and 8.97 (average: 8.89) compared to the river, sea and formation waters and a high alkalinity (Table 6). The 2019 sample was col- lected in a small pool and seems to be dominated by surface water from melting snow. 6 Implications for exploration and recommendation for future studies The 2019 and previously documented gas data and 2019 oil seep data from Nuussuaq support an exploration model for the anticlinal structures mapped by Sørensen et al. (2017). Petroleum extracted from an oil-stained hyaloclastite sample, collected in the Aaffarsuaq valley, in 2019 represents a facies variety of the “Niaqornaar- suk type” sensu Bojesen-Koefoed et al. (1999). The pres- ence of a “Niaqornaarsuk type” oil 10 km from other known occurrences of this oil type further supports the presumed existence of Campanian age deposits devel- oped in source-rock facies in the region. Importantly, we observed no sign of mixing with the “Marraat type,” suggesting that the Marraat source rock disappears somewhere between GANK#1 and the Kuugannguaq– Qunnilik Fault zone, or that the source rock, if present, is thermally immature. Furthermore, numerous examples of gas occur within a few kilometres on either side of the mapped anticline and along possible migration path- ways. These gases have a thermogenic fingerprint and suggest a possible origin from oil-prone source rocks with a relatively low thermal maturity. Further geological and structural mapping using 3D photogrammetry combined with geophysical data would be an ideal approach to develop the exploration model in the region. Moreover, future studies should Table 6 Geochemistry of water samples from Pingo 132 and nearby formation water, seawater and river water Sample Location Type pH Alk Cl (mg/l) SO4 (mg/l) Na (mg/l) K (mg/l) Ca (mg/l) Mg Cl/SO4 Na/K Ca/Mg Data sources 358472 Pingo 132 Fountain water 8.78 46.6 256 200 1135 9.48 3.68 86 1.28 119..7 0.04 Laier 1994; Christiansen et al. 1995b 400843 Pingo 132 Fountain water 8.97 42.6 248 178 1110 9.74 1.68 68.5 1.39 114.0 0.02 Laier 1994; Christiansen et al. 1995b 400844 Pingo 132 Fountain water 8.97 29.7 53.1 177 750 6.72 2.46 54.5 0.30 111.6 0.05 Laier 1994; Christiansen et al. 1995b 400894 Pingo 132 Fountain water 8.78 44.8 258 180 1140 9.28 2.63 76.5 1.43 122.8 0.03 Laier 1994; Christiansen et al. 1995b 547303 Pingo 132 Fountain water 7.87 3.17 19.9 2.16 69.6 1.52 4.30 5.71 9.2 45.7 0.75 This study 408011 Marraat-1 Formation water (41 m depth) 7.42 0.92 29 200 1484 9650 188 6740 790 19.68 51.3 8.53 Laier 1994; Christiansen et al. 1995b 408021 Marraat-1 Formation water (82 m depth) 7.41 0.58 29 600 1252 8180 126 8560 630 23.64 64.9 13.59 Laier 1994; Christiansen et al. 1995b 408035 Marraat-1 Water under pressure (346 m depth) 7.15 0.43 26 500 1276 6780 167 8160 630 20.77 40.6 12.95 Laier 1994; Christiansen et al. 1995b 408036 Vaigat, Maraat-1 Sea water 7.94 2.10 19 500 2340 10 500 402 430 1230 8.33 25.2 0.36 Laier 1994; Christiansen et al. 1995b 380132 Vaigat, GANW#1 Sea water 7.94 2.20 18 930 2033 8797 403 412 1217 9.31 21.8 0.34 Laier 1994; Christiansen et al. 1995b 380133 GANW#1 River water 8.20 3.20 13 11 20.7 0.29 32.4 17.5 1.18 71.4 1.85 Laier 1994; Christiansen et al. 1995b Alk: alkalinity. https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 19 of 21 www.geusbul let in.org systematically sample oil traces along faults and frac- tures and focus on rock types with carbonate-filled veins that often host fluid inclusions, to elucidate the vertical and lateral distribution of the active petroleum systems in the Nuussuaq Basin. In some ways, this compares to the practice of traditional onshore exploration in areas like California and Texas more than a hundred years ago, where targets were often defined by a combination of surface structures and seeps. This rule of thumb is still valid in many onshore areas around the world, but knowledge of the distinct oil types can guide exploration even more efficiently. Systematic mapping, sampling and characterisation of gas seepage from pingos, lakes and thawing perma- frost could be similarly important in the future. Profes- sional sampling tools for both onshore and offshore activities, including transport and storage of samples under cool conditions, are important, and samples should be analysed as soon as possible to reduce con- tamination and diffusion. Modern isotope techniques with better resolution and low detection limits are likely to provide more details compared to the preliminary work of the 1990s. With degrading permafrost and some specific pingos experiencing rapid change, many more sampling sites are likely to be identified. Based on Pingo 132, it is obvious that satellite data providing both optimal images and interferograms can systematically identify areas of degrading permafrost. This would allow us to identify suitable sites to collect samples of gas and water that originate from below the permafrost seal. Furthermore, satellite data can be used for preliminary dating of mud extrusions. Finally, it must be emphasised that the changes observed over the last decades and years point towards a dynamic situation caused by climate change. This may potentially lead to much more frequent mud diapirism and emissions of gas in large parts of the Nuussuaq Basin when more permafrost degrades in the future. There is a strong need for many of the localities to be documented and monitored in detail. This has implica- tions not only for petroleum exploration but also from a viewpoint of nature preservation as many new local ecosystems are likely to develop and change over time in the coming decades. Acknowledgements Analytical data are from many different field projects by GGU/GEUS with additional funding from Danish and Greenlandic authorities. Con- tributions came especially from the former Danish Ministry of Energy Research Program (EFP), the previous Mineral Resources Adminis- tration for Greenland in Copenhagen, the previous Bureau of Miner- als and Petroleum in Nuuk and recently from the present Ministry of Industry, Energy, Research and Labour, Nuuk, Greenland. Close collab- oration with industry over the years, especially grønArctic Energy Inc. and its enthusiastic manager Cam Hanna has been very useful. Practi- cal help over many years and analytical support by John Boserup, Ditte Kiel-Duhring, H. P. Nytoft and Christina Rosenberg Lynge are highly appreciated. Martin Krüger at Bundesanstalt für Geowissenschaften und Rohstoffe in Hannover is gratefully acknowledged for performing isotopic analyses of the pingo gas samples collected in 2019. We would like to thank Dietmar Backes from the University of Luxembourg for giv- ing us access to PlanetScope imagery provided via the Planet’s Education and Research program that has been used for generation of NDVI maps. Comments on the paper by the reviewers Chris Parry and Sverre E. Ohm were welcome. Additional information Funding statement Samples from 2019 were collected on a field trip financed by Ministry of Industry, Energy, Research and Labour, Nuuk, Greenland. Other costs were paid by the Geological Survey of Denmark and Greenland. Author contribution FGC: writing the original draft (lead). JABK: analyses, presentation and discussion of oil geochemistry data. GD: contribution to historical data and petroleum exploration model. TL: analyses, presentation and discussion of water and gas geochemistry data. SS: analyses, presentation and discussion of satellite data. Additional files Six additional files are available online: https://doi.org/10.22008/FK2/ SO5VLD. References Bate, K.J. & Christiansen, F.G. 1996: The drilling of the stratigraphic borehole Umiviik #1, Svartenhuk Halvø, West Greenland. Grønlands Geologiske Undersøgelse Bulletin 172, 22–27. Blumenberg, M. et al. 2016: Hydrocarbons from near-surface sediments of the Barents Sea north of Svalbard – indication of subsurface hydro- carbon generation? Marine and Petroleum Geology 76, 432–443. https://doi.org/10.1016/j.marpetgeo.2016.05.031 Bojesen-Koefoed, J.A. et al. 1997a: Seep data from onshore West Green- land. Danmarks og Grønlands Geologiske Undersøgelse Rapport 1997/34, 7 pp. Unpublished report. Geological Survey of Denmark and Greenland, Denmark. Bojesen-Koefoed, J.A. et al. 1997b: Organic geochemistry and thermal maturity of sediments in the GRO#3 well, Nuussuaq, West Greenland. Danmarks og Grønlands Geologiske Undersøgelse Rapport 1997/143, 18 pp. Unpublished report. Geological Survey of Denmark and Green- land, Denmark. Bojesen-Koefoed, J.A. et al. 1999: Oil seepage onshore West Green- land: evidence of multiple source rocks and oil mixing. In: Fleet, A.J. & Boldy, S.A.R. (eds): Petroleum geology of Northwest Europe: Pro- ceeding of the 5th conference on the Petroleum Geology of North- west Europe, Geological Society, London, UK, 305–314. https://doi. org/10.1144/0050305 Bojesen-Koefoed, J.A., Nytoft, H.P. & Christiansen, F.G. 2004: Age of oils in West Greenland: was there a Mesozoic seaway between Greenland and Canada. Geological Survey of Denmark and Greenland Bulletin 4, 49–52. https://doi.org/10.34194/geusb.v4.4783 Bojesen-Koefoed, J.A. et al. 2007: Petroleum seepages at Asuk, Disko, West Greenland: implications for regional petroleum explo- ration. Journal of Petroleum Geology 30, 219–236. https://doi. org/10.1111/j.1747-5457.2007.00219.x Bojesen-Koefoed, J.A. et al. 2018: Petroleum potential of the Upper Jurassic Hareelv Formation, Jameson Land, East Greenland. Geologi- cal Survey of Denmark and Greenland Bulletin 42, 85–113. https://doi. org/10.34194/geusb.v42.4314 Christiansen, F.G. 1993: Disko Bugt Project 1992, West Greenland. Grøn- lands Geologiske Undersøgelse Rapport 159, 47–52. Christiansen, F.G. 2011: Greenland petroleum exploration: history, breakthroughs in understanding and future challenges. In: Spencer, A. et al. (eds): Arctic petroleum geology. Geological Society (London) Memoir 35, 647–661. https://doi.org/10.1144/M35.42 Table 6 Geochemistry of water samples from Pingo 132 and nearby formation water, seawater and river water Sample Location Type pH Alk Cl (mg/l) SO4 (mg/l) Na (mg/l) K (mg/l) Ca (mg/l) Mg Cl/SO4 Na/K Ca/Mg Data sources 358472 Pingo 132 Fountain water 8.78 46.6 256 200 1135 9.48 3.68 86 1.28 119..7 0.04 Laier 1994; Christiansen et al. 1995b 400843 Pingo 132 Fountain water 8.97 42.6 248 178 1110 9.74 1.68 68.5 1.39 114.0 0.02 Laier 1994; Christiansen et al. 1995b 400844 Pingo 132 Fountain water 8.97 29.7 53.1 177 750 6.72 2.46 54.5 0.30 111.6 0.05 Laier 1994; Christiansen et al. 1995b 400894 Pingo 132 Fountain water 8.78 44.8 258 180 1140 9.28 2.63 76.5 1.43 122.8 0.03 Laier 1994; Christiansen et al. 1995b 547303 Pingo 132 Fountain water 7.87 3.17 19.9 2.16 69.6 1.52 4.30 5.71 9.2 45.7 0.75 This study 408011 Marraat-1 Formation water (41 m depth) 7.42 0.92 29 200 1484 9650 188 6740 790 19.68 51.3 8.53 Laier 1994; Christiansen et al. 1995b 408021 Marraat-1 Formation water (82 m depth) 7.41 0.58 29 600 1252 8180 126 8560 630 23.64 64.9 13.59 Laier 1994; Christiansen et al. 1995b 408035 Marraat-1 Water under pressure (346 m depth) 7.15 0.43 26 500 1276 6780 167 8160 630 20.77 40.6 12.95 Laier 1994; Christiansen et al. 1995b 408036 Vaigat, Maraat-1 Sea water 7.94 2.10 19 500 2340 10 500 402 430 1230 8.33 25.2 0.36 Laier 1994; Christiansen et al. 1995b 380132 Vaigat, GANW#1 Sea water 7.94 2.20 18 930 2033 8797 403 412 1217 9.31 21.8 0.34 Laier 1994; Christiansen et al. 1995b 380133 GANW#1 River water 8.20 3.20 13 11 20.7 0.29 32.4 17.5 1.18 71.4 1.85 Laier 1994; Christiansen et al. 1995b Alk: alkalinity. https://doi.org/10.34194/geusb.v44.4567 http://www.geusbulletin.org https://doi.org/10.22008/FK2/SO5VLD� https://doi.org/10.22008/FK2/SO5VLD� https://doi.org/10.1016/j.marpetgeo.2016.05.031 https://doi.org/10.1144/0050305 https://doi.org/10.1144/0050305 https://doi.org/10.34194/geusb.v4.4783 https://doi.org/10.1111/j.1747-5457.2007.00219.x https://doi.org/10.1111/j.1747-5457.2007.00219.x https://doi.org/10.34194/geusb.v42.4314 https://doi.org/10.34194/geusb.v42.4314 https://doi.org/10.1144/M35.42 Christiansen et al. 2020: GEUS Bulletin 44. 4567. https://doi.org/10.34194/geusb.v44.4567 20 of 21 www.geusbul let in.org Christiansen, F.G. & Pulvertaft, T.C.R. 1994: Petroleum-geological activ- ities in 1993: oil source rocks the dominant theme of the season’s field programme. 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