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Geological development of the Northeast Greenland Shelf N. E. HAMANN,1 R. C. WHITTAKER2 and L. STEMMERIK3 1 Nunaoil A/S, DK-3900 Nuuk, Greenland (Present address: DONG, Agern Alle 24-26, DK-2970 Hørsholm, Denmark; e-mail: NEH@ dong.dk) 2 Geoarctic Ltd., 600 8th Avenue NW, Calgary, Alberta T2P 3P2, Canada 3 Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark Abstract: Seismic data from the East Greenland shelf show that the northern part of the shelf, north of 758N, can be subdivided into ﬁve, roughly northeast-trending, major tectonic elements. From west to east they are: the Koldewey Platform, the Danmarkshavn Basin, the Danmarkshavn Ridge, the Thetis Basin and the Marginal High. A sixth tectonic element, the Shannon High, has been deﬁned in the southern part of this area. The offshore areas between 728300 N and 758N are dominated by Tertiary plateau basalts, which obscure the acoustic signals from the deeper sedimentary succession. Seismic data from the area north of 758N indicate the presence of a fairly complete succession of ? Devonian to Neogene age, exceeding the recorded interval (8 sec TWT – 13 km) in thickness in the deeper parts of the Danmarkshavn Basin. The succession has been subdivided into 15 seismic mega-sequences. In absence of well control, they have been dated by comparison to the onshore successions of East Greenland and eastern North Greenland, and the offshore successions in the southern Barents Sea and on the mid-Norwegian shelf. The Upper Palaeozoic succession is broadly similar to that of the southern Barents Sea, i.e. marine-dominated, with thick Upper Carboniferous – Lower Permian halite deposits in the northern Danmarkshavn Basin. The Mesozoic succession seems to show greater similarities to the onshore basins of East Greenland: rifting started during the mid-Jurassic and peaked near the Jurassic–Cretaceous boundary. The post-volcanic succession reﬂects deposition on a passive margin subjected to temporary uplift during the early Miocene and the latest Miocene to earliest Pliocene. Keywords: Northeast Greenland Shelf, tectonic evolution, Carboniferous –Permian, Mesozoic, Cenozoic The vast shelf areas offshore East Greenland form one of the few Greenland.) Marine Seismic (KANUMAS) Project. The KANU- remaining ‘white spots’ in the geological understanding of the MAS Project was initiated in 1991 to allow the ﬁrst comprehensive post-Caledonian evolution of the Norwegian – Greenland Sea area. seismic reconnaissance survey of the frontier basins offshore The more than 1200 km long and 200– 600 km wide shelf from northern Greenland. The project has been carried out by six major Scoresby Sund in the south to the continental margin in the north oil companies (BP, Exxon, Japan National Oil Company, Shell, forms the conjugate margin to the well known shelf areas west of Statoil, Texaco and Nunaoil) with Nunaoil A/S, a joint Green- Norway (Fig. 1). Also, the onshore areas of East Greenland and land – Denmark state-owned company, as operator. Nunaoil eastern North Greenland are geologically well known, since the acquired a total of 6839 km of multichannel seismic data and sedimentary succession in these areas form classical analogues to gravity data offshore East Greenland in four surveys between 1991 the Mesozoic rift succession offshore Mid-Norway and the late and 1995 (Fig. 1). Due to the pack-ice and icebergs offshore East ˚ Palaeozoic succession of the Barents Sea (e.g. Hakansson & Greenland the data form a very open grid with line spacing Stemmerik 1989; Surlyk 1990, 2003; Stemmerik et al. 1993). between 50 – 80 km in the area between 728N and 798N. This paper The most comprehensive overview of the structure of the East is based on the interpretation of these data supplemented with Greenland shelf is given by Larsen (1990) based on aeromagnetic 5000 km of seismic data acquired by the Geological Survey of data, supported by scattered seismic and marine gravity data from Greenland in 1981 and 1982 (NAD Project) in the area south of the area south of 748N. The data base for that overview included 728N. The relatively small amount of seismic data provides only a the ﬁrst multichannel reﬂection seismic surveys on the East very open grid, and gravity data compiled from various sources ¨ Greenland shelf in the late 1970s (Hinz & Schluter 1980; Hinz have proved useful for mapping the trend of major structures in the et al. 1987), reﬂection seismic and marine gravity data from the subsurface. Fourteen seismic horizons have been interpreted, but North Atlantic D (NAD) Project 1983–1989 (Larsen 1984), and data from a regional aeromagnetic survey (Larsen & Thorning due to lack of deep wells on the Northeast Greenland Shelf only 1980). Thus, at that stage, the understanding of the stratigraphy one of these has been properly dated based on a tie to ODP Site and basin structure of the shelf north of 748N was based entirely on 987. All other seismic horizons are tentatively dated using a aeromagnetic data (Larsen 1990). Since then, additional infor- variety of methods: (1) knowledge on the timing of regional mation has been obtained from reﬂection seismic data acquired in tectonic events and eustatic sea level changes from the onshore the outer shelf areas between 798 and 808300 N (Hinz et al. 1991). areas in East Greenland and the Norwegian offshore areas has In this paper we describe the major structures of the East been used to determine major seismic sequence boundaries; Greenland Shelf and the discuss the Late Palaeozoic – Neogene (2) lithological marker horizons like the top of the Paleocene evolution based on proprietary regional seismic data acquired as volcanics and the top of the salt have been dated based on part of the Kalaallit Nunaat (The Greenlandic name for correlation to East Greenland and the Barents Sea, respectively; HAMANN , N. E., WHITTAKER , R. C. & STEMMERIK , L. 2005. Geological development of the Northeast Greenland Shelf. In: DORE , A. G. & VINING , B. A. (eds) ´ Petroleum Geology: North-West Europe and Global Perspectives—Proceedings of the 6th Petroleum Geology Conference, 887 –902. q Petroleum Geology Conferences Ltd. Published by the Geological Society, London. 888 N. E. HAMANN ET AL. Fig. 1. Simpliﬁed geology of North-East Greenland and the broad outline of the offshore areas covered by the KANUMAS project. KANUMAS seismic lines acquired during the 1991, 1992, 1994 and 1995 surveys are shown in red. Onshore localities mentioned in the text are shown. and (3) magnetic anomalies have been used to give a maximum (Figs 1 and 3). It is only 60 km wide at the southern tip of age of the overlying sediments (Fig. 2). Liverpool Land (708N) where the glacially deepened Scoresby Sund fjord reaches the shelf edge, and a thick sediment wedge extends over the continental margin to locally widen the shelf. Study area Sea-ice and icebergs in the study area offshore East Greenland The Northeast Greenland Shelf from 758N and northwards covers set major limitations on seismic acquisition, and would present an an area approximately 200 km wide and 600 km long. Water even greater challenge to exploration drilling and production. The depths are generally between 100– 300 m, ranging from less than entire shelf is ice-covered most of the year by pack-ice carried 20 m over shallow shoals to the west to more than 500 m along the down from the Arctic Ocean by the East Greenland Polar Current. shelf edge. The shelf narrows to around 120 km between Traill Ø The ice starts to melt in the Danmark Strait in April and May, and and Shannon (72– 758N) and becomes even narrower southwards usually the areas around Jameson Land are ice-free in August and NE GREENLAND SHELF DEVELOPMENT 889 Fig. 2. The timing of major tectonic events to have affected the North Atlantic region. Also shown the interpreted mega-sequences from the KANUMAS surveys. Please note the coloured boundaries between the mega-sequences. These are used in the seismic sections in this paper. Chronostratigraphic scale based on Harland et al. (1989). The relative sea level rise is taken from Vail et al. (1978). September. Further to the north, iceberg and pack-ice can be deepening to 4000– 5000 m north of 788N, where a thick Upper encountered anywhere on the shelf in all seasons of the year. Palaeozoic succession seems to be present in the inner part of the shelf (Fig. 4A). The onshore areas to the west, between 76 – 808N, consist mainly of crystalline basement with very scattered outliers Tectonic elements of Jurassic and Upper Carboniferous sediments (Stemmerik & The East Greenland Shelf consists of three broad regions with their Piasecki 1990; Piasecki et al. 1994). Between 80– 818N, up to own distinctive geological and tectonic style: (1) the North-East 1000 m of Upper Carboniferous – Permian carbonates, locally Greenland Shelf; (2) East Greenland volcanic province; and (3) the underlain by more than 1000 m of Lower Carboniferous Liverpool Land –Blosville Kyst Shelf (Fig. 3). This subdivision siliciclastics are exposed on Holm Land and Amdrup Land corresponds roughly to that of Larsen (1990) and Hinz et al. (Stemmerik et al. 2000). The carbonate succession extends (1993). offshore as evidenced by outcrops on the islands of Henrik Krøyer Holme at 808450 N, to cover the northern part of the platform. The onshore succession is dissected by a series of Northeast Greenland Shelf WNW-trending faults, which controlled sedimentation during the The Northeast Greenland Shelf includes the areas north of the Late Palaeozoic and was re-activated during the Mesozoic island of Shannon at approximately 758N (Fig. 3). It is more than ˚ (Stemmerik & Hakansson 1991; Stemmerik et al. 2000). Seismic 400 km long and 150–300 km wide. The southern boundary is here data indicate that similarly trending structures are prominent in the deﬁned by the northern margin of thickly developed Tertiary northern part of the platform area and most likely related to strike- volcanics of the East Greenland volcanic province and the northern slip faulting along the Greenland Fracture Zone. limit is the present-day shelf break. The Northeast Greenland shelf The eastern margin of the platform is formed by a series of is characterized by a number of northeast-trending structural highs north– south-trending, en echelon faults separating the platform ﬁrst inferred from aeromagnetic data (Larsen 1984, 1990). Based from the deep Danmarkshavn Basin to the east (Fig. 4a). The fault on the KANUMAS seismic data it is possible to subdivide the system seems to have been active from the Late Carboniferous and shelf into six major tectonic elements, described in detail below onward, and evidence for late reactivation of faults and minor (Figs 3 and 4). inversion is present in the southern part of the platform. This part of the platform is characterized by a stratigraphic punctuated Koldewey Platform. The Koldewey Platform is a 30 – 70 km succession of Upper Jurassic and Lower Cretaceous sediments that wide structural high stretching from the island of Store Koldewey overstep basement and/or thin down-faulted remnants of older, and northwards to at least 808N based on seismic and gravity data most likely Carboniferous strata. The seismic data indicate a thin (Fig. 5). It forms the western, landward portion of the shelf and is succession punctuated by many unconformities just east of Store characterized by relatively shallow basement depths, generally Koldewey island, and the studies of the outcrops on the island between 2000– 3000 m in the southern part of the platform conﬁrm this interpretation (e.g. Stemmerik & Piasecki 1990). 890 N. E. HAMANN ET AL. Fig. 3. Tectonic elements of the East Greenland shelf. The gross outline of the offshore tectonic elements is based on interpretation of the KANUMAS seismic data. Oceanic magnetic anomalies and the onshore geology are from Escher & Pulvertaft (1995). The main structural elements: The Koldewey Platform, Danmarkshavn Basin, Danmarkshavn Ridge, Thetis Basin and Marginal High are described in the text, and generalized cross sections of the shelf are shown in Figure 4. Note the salt basin in the northern axis of the Danmarkshavn Basin. NE GREENLAND SHELF DEVELOPMENT 891 Fig. 4. Geoseismic cross sections of (a) the Northeast Greenland Shelf (north of 758N) and (b) the Jameson Land Basin – Liverpool Land Shelf (c. 718N). The northern section is based on KANUMAS seismic data and illustrates the very different development of the inner and the outer shelf. Note the similarities between the Jameson Land Basin and the Danmarkshavn Basin, including huge thicknesses of post-Caledonian sediments and an almost complete stratigraphic succession. The seismic mega-sequences are described in the text. Shannon High. The Shannon High is a relatively small feature, immediately to the east of Store Koldewey island (Larsen 1990). only 100 km long and 20 km wide, located between 758N and 768N Seismic and gravity data show that basin extends northwards to at (Fig. 3). The high was ﬁrst identiﬁed onshore Shannon and its least 788N and more likely 808N, being at least 400 km long. It offshore extension was suggested on basis of magnetic data widens from less than 50 km in the south to more than 100 km in (Larsen 1990). The Shannon High is a steep-sided basement horst the north (Figs 3 and 5). The Koldewey Platform deﬁnes the delineated by north– south-oriented normal faults that were active western margin of the basin, and the eastern margin is a series of during the Mesozoic, and most probably forms a northeastward northeast-trending structural highs, collectively referred to as the extension of the well-described system of rotated fault-blocks at Danmarkshavn Ridge. The basin is deep, more than 13 km in the Wollaston Forland (e.g. Surlyk 1978, 2003). The northern limit of south where the top basement reﬂector is below the recorded the high seems to be controlled by a major fault zone that links a seismic data (8 s TWT) (Fig. 4a). Northwards the basin becomes transfer zone at the continental margin to a long-lived lineament in shallower, judging from the limited data set. The basin includes a the Bessel Fjord area, and is marked by a local Tertiary fairly complete sedimentary succession of ?Devonian to Recent depositional basin. age. Numerous unconformities along the basin margins indicate In the offshore areas north of Shannon, the high is overlain by a repeated tectonic activity throughout the basin history. thin succession of Tertiary sediments, whereas Tertiary volcanics The central part of the basin is characterized by major salt are seen to lie directly on basement on Shannon island. It is diapirism from 808N southwards to at least 778N (Figs 3 and 10). therefore likely that the high extends southwards below the The salt is limited to the basinal areas and is seen to pass into time basaltic cover into the East Greenland volcanic province (Fig. 3). equivalent carbonates deposited on the tectonically more stable Koldewey Platform. By comparison to the Nordkapp Basin in the Danmarkshavn Basin. The Danmarkshavn Basin is a large, very Norwegian Barents Sea, the salt is inferred to be of Late deep sedimentary basin, characterized by salt tectonics in the Carboniferous – earliest Permian age, and thus age equivalent to centre (Figs 3 and 4a). It was originally deﬁned as a narrow basin the lower part of the carbonate succession in North Greenland 892 N. E. HAMANN ET AL. Fig. 5. Gravity anomaly map (contour interval 10 mgal): Bouguer (land), free air (sea). Processed by the Danish National Survey and Cadastre, Copenhagen. The names of the main structural elements are superimposed. The main structural elements, especially the Danmarkshavn Basin and the Shannon High, are clearly seen as gravimetric anomalies. (e.g. Stemmerik 2000). Transition from carbonate-dominated with the main fault escarpment to the east, towards the Thetis successions, over structural highs and stable platforms, to salt in Basin (Figs 3,4a). The ridge trends northeast – southwest; it is a more rapidly subsiding basins has been described from the Late well deﬁned basement high in the southwest, but north of 778N it Palaeozoic of both the southern Barents Sea and the Sverdrup Basin becomes a less well deﬁned platform area. Gravity and magnetic of Arctic Canada (e.g. Larssen et al. 2002), and by analogy the data indicate that the ridge continues north of the seismic coverage Danmarkshavn Basin is likely to represent the late Palaeozoic rift to 788N and southwards beneath the Tertiary basalts for at least axis between Norway and Greenland (e.g. Gudlaugsson et al. 1998). 80 km (Figs 3 and 5). The eastern, faulted boundary has in places a In the northern part of the basin many salt diapirs have penetrated heave of over 10 km at basement level with a throw of more than nearly to the seaﬂoor, possibly reﬂecting increased Cenozoic uplift 7000 m. The faulting represents a major amount of extension of this part of the shelf as also indicated by a general thinning of the during several tectonic episodes but most intensely during the Tertiary sedimentary succession in this direction (Figs 4a and 10). latest Jurassic – earliest Cretaceous and in the Early Tertiary. Faulting has controlled salt tectonism along the basin axis, Footwall uplift and erosion is estimated to have removed at least producing NNE-trending salt walls. The salt movements took 2000– 3000 m of Upper Palaeozoic and Mesozoic sediments from place during several distinct phases, which correlate to tectonic the top of the ridge, and Tertiary sediments overlie unconformably events or pulses affecting the evolution of the basin (Fig. 2). Broad older sediments (Figs 4a and 7). The depth to basement on the anticlines along the margins in the Danmarkshavn Basin are related ridge varies considerably along-strike; it is generally shallow in the to Tertiary structural inversion, with a component of salt tectonism. south and increases northwards and westwards where up to 4000 m A seismic line acquired by BGR in 1988 at 798 300 N clearly shows of Mesozoic and older sediments are preserved. one of these broad anticlines (Hinz et al. 1991). Tertiary sills and basalts become increasingly common south of Thetis Basin. The Thetis Basin, situated east of the 778N and their cross-cutting relationship make interpretation more Danmarkshavn Ridge, is a relatively young basin probably difﬁcult in this area. The southern limit of the Danmarkshavn dominated by a thick Cretaceous and Tertiary succession (Figs 3 Basin is therefore obscured by thick Tertiary volcanics (Fig. 3). and 4a). The basin trends NNE, roughly parallel with the continental margin, and is approximately 200 km long and up to Danmarkshavn Ridge. The Danmarkshavn Ridge consists of a 60 km wide from 758300 N to 788N. To the east it is limited by the series of westerly dipping tilted fault blocks, 10 – 60 km wide, Marginal High. The presence of this deep ‘Cretaceous’ basin, which form a platform area to the east of the Danmarkshavn Basin equivalent to the Cretaceous Vøring Basin off Norway, on the NE GREENLAND SHELF DEVELOPMENT 893 outer part of the Northeast Greenland Shelf, was ﬁrst predicted by 1991, 1993; Seidler et al. 2004). Later, Mesozoic rift phases are Hinz et al. (1993) based on the BGR seismic proﬁles and mostly known from the northern part of the region, north of Kong aeromagnetic data. Oscar Fjord (728N) (e.g. Surlyk 1978, 1990; Surlyk & Noe- The Cretaceous forms the acoustic basement in the basin but Nygaard 2001); Devonian sediments are also best known from comparison of mapped depths to the base of the Cretaceous with this area. The thickness of the Devonian –Jurassic succession is depths to magnetic basement in Haimilia et al. (1990), suggests estimated to exceed 17 km (9 km Devonian) in the Jameson Land that there is an older sedimentary succession beneath the basin in the south, thinning northwards. North of Kong Oscar Cretaceous. The presence of this deep basin has been conﬁrmed Fjord, the cumulative thickness of the Devonian – Cretaceous by gravity modelling (unpublished KANUMAS data). sediments is 14 – 15 km (8 km Devonian) but nowhere is the entire succession preserved. The thickness of the Jameson Land Marginal High. A marginal high relief area forms the edge of the succession is thus comparable to that of the Danmarkshavn continental shelf in Northeast Greenland (Fig. 3). It is only crossed Basin where the thickness of the sedimentary succession exceeds by KANUMAS lines in the southern part and is not illustrated in the recorded interval (8 seconds TWT – approximately 13 km) this paper. The top of the volcanic succession forms a strong, high- (Figs 4a, 4b and 7). However, the depositional successions in the amplitude reﬂector, which obscures any acoustic signal from the two basins are not directly comparable since thick salt deposits, deeper part. The top of the basalts is subaerially eroded, suggesting like those seen in the Danmarkshavn Basin, are not present in the that the top of the high was above sea level during the Palaeogene, Jameson Land basin. ﬁnally being covered by a Neogene sedimentary wedge during The onshore areas between 75 – 778N have a fragmentary record post-rift thermal subsidence. The eastern margin of the high is of Jurassic and Cretaceous sediments, and between 77 – 808N, post- characterized by seaward-dipping reﬂectors and pseudo- Caledonian sediments are only known from small, isolated escarpments, and a single submarine volcano. The Marginal outcrops. North of 808N, along the east coast of Greenland, High can be compared to the high-relief Vøring Plateau on the onshore basins started to form during the Early Carboniferous and Norwegian margin (Eldholm et al. 1990), which would suggest subsidence continued into the Triassic. Following a prolonged that it owes its origin to the extrusion of Tertiary basalts during the uplift, deposition resumed during the late Jurassic; Mesozoic opening of the Atlantic in the Early Eocene. deposition occurred in localized pull-apart basins related to stike- ˚ slip movements in the Harder Fjord Fault Zone (Hakansson & Stemmerik 1989). The onshore geology thus indicates signiﬁcant East Greenland volcanic province changes in both structural style, depositional evolution and uplift The East Greenland volcanic province is deﬁned as the offshore history of the exposed basins from south to north (Fig. 8). area from approximately 728300 N to 758N dominated by Tertiary Stratigraphic and lithological data therefore have to be evaluated plateau basalts (Fig. 3). The southern limit of the volcanic rocks is carefully before being applied to the offshore areas, and evidently close to the Jan Mayen Fracture Zone and the northern limit is many of the offshore basins have no onshore counterpart. The close to the Bivrost Fracture Zone. In the offshore areas, volcanic stratigraphy and evolution of these offshore basins are more rocks obscure any acoustic signal from the deeper parts of the similar to the deep basins at the western margin of the Norwegian basin; the volcanic rocks extend westwards and form the top of the shelf. outcrops between 73 – 758N. In this part of East Greenland, deep Interpretation of the proprietary data set allows 15 seismic Early Carboniferous – Cretaceous, N – S rift basins occur below the megasequences, of proposed Devonian to Pleistocene age, to be volcanic rocks (e.g. Surlyk 1978, 1990; Stemmerik et al. 1991, identiﬁed on the Northeast Greenland Shelf (Fig. 6). They will not 1993), and it is therefore likely that similar age rift basins occur in be described in detail in this overview paper where focus rather the offshore areas beneath the thick basalt succession. will be on the gross stratigraphic development of the offshore basins. Liverpool Land –Blosville Kyst Shelf Devonian –mid-Carboniferous The region south of the Jan Mayen Fracture Zone (Fig. 3) has a markedly different structural style to the areas to the north. It is The oldest part of the offshore succession is included in Mega- characterized by few but large faults blocks, rather than the much sequences DCI and DCII, most likely of Devonian – mid- narrower fault spacing to the north in the East Greenland Basin. Carboniferous age (Fig. 2). The succession is believed to rest The amount of extension, however, appears to be similar in the two on basement, but seismic resolution of this part of the succession areas. Further to the south, the offshore area is divided into the is poor. The clearest evidence for the presence of Devonian – Liverpool Land Shelf and the Blosville Kyst Shelf (Larsen 1990). mid-Carboniferous deposits is on the northern part of the Tertiary plateau basalts cover a large proportion of these areas, and Danmarkshavn Ridge, where these strata are relatively shallow. at the outer part of the shelf oceanic crust occurs beneath a thick It has not been possible to map the distribution and thickness Tertiary wedge. In this area, the location of the ocean – continent variations of the succession. The Devonian– mid-Carboniferous transition zone is marked by a series of pseudo-escarpments and succession is characterized by chaotic and wedge shaped reﬂec- seaward-dipping reﬂectors (Larsen 1990). tion patterns. The seismic character indicates large lateral variations in the rate of deposition, which is characteristic for non-marine high- energy environments and deposition in half-grabens, and mega- Geological Development sequences DCI and DCII are suggested to represent an offshore Onshore East Greenland, the post-Caledonian basins started to equivalent to the Devonian and Lower Carboniferous non-marine subside during the mid-Devonian, and a stratigraphically almost sediments onshore East Greenland (Figs 6 and 8) (Olsen 1993; complete succession of mid-Devonian to Cretaceous sediments is Vigran et al. 1999). In the onshore area, deposition took place in a preserved between Scoresby Sund and Kuhn Ø (70 – 758N) N– S-trending series of basins from Jameson Land in the south to (Fig. 6). Deposition took place during a prolonged period of Hudson Land in the north (71– 748300 N). There is no evidence rifting, which started near the Devonian – Carboniferous boundary of Devonian and Carboniferous basins north of 748300 N in and continued into the Cretaceous. Initial, Early and Late East Greenland, and possibly the locus of subsidence was Carboniferous, and latest Permian – Early Triassic rifting occurred shifted to the offshore Danmarkshavn Basin along a linieament along almost the entire length of the outcrop area from Jameson conjugate to the Bivrost Fracture Zone/Lineament off Norway Land in the south to Clavering Ø in the north (e.g. Stemmerik et al. (Tsikalas et al. 2002). 894 N. E. HAMANN ET AL. Fig. 6. Correlation of major lithological units in the onshore sedimentary basin in eastern Greenland from 708N to 818N. For location of the basins see Figure 1. Note the very different development of the Upper Carboniferous–Lower Permian succession between the Wandel Sea Basin in the north and the Jameson Land Basin in the south and the stratigraphically more punctuated Mesozoic succession in the East Greenland basin. Chronostratigraphic scale based on Harland et al. (1989). Late Carboniferous – Early Permian Barents Sea and on Svalbard (e.g. Steel & Worsley 1984; Larssen et al. 2002). By analogy to the onshore areas, mega-sequence CPI Sediments of Late Carboniferous – Early Permian age have been is most likely composed of non-marine to marginal marine interpreted on the Koldewey Platform, the Danmarkshavn Ridge sediments (Fig. 8). The high-amplitude, relatively high-continuity and in Danmarkshavn Basin (see Figs 7, 8 and 9). On the west reﬂectors of mega-sequence CPII are interpreted as interbedded ﬂank of Danmarkhavn Ridge, the succession reaches a thickness of carbonates and evaporites of Late Carboniferous – Early Permian 2 seconds (TWT; approximately 5000 m) (Figs 4a and 7); it thins age (Figs 8 and 9). They reﬂect deposition on shallow-water rapidly away from the central part of the basin. The seismic platforms along the margins of the Danmarkshavn Basin. The resolution of this part of the section is generally poor. It has only lateral transition between the platform facies and the time- been possible to analyse it in some details close to the Koldewey equivalent basinal halite deposits in the northern Danmarkshavn Platform and in shallowest part of the Danmarkshavn Ridge, where Basin is not clearly deﬁned in the seismic data, but the outline of it is possible to identify two mega-sequences, CPI and CPII (Figs 7 the salt basin roughly corresponds to the area of active salt and 8). In these areas, mega-sequence CPI is characterized by movement (Fig. 3). variable amplitude, low-continuity reﬂectors, with rapid variation The seismic facies analysis of the CPII mega-sequence thus in thickness, and CPII forms a relatively continuous package of indicates that the marine Late Carboniferous – mid-Permian high-amplitude reﬂectors with little variation in thickness (Fig. 7). depositional system known from the Barents Sea, Svalbard and The mobilized salt in the central parts of the northern North Greenland continued southward to include the northern parts Danmarkshavn Basin (Figs 3 and 10) is believed to be the basinal of the East Greenland Shelf (Stemmerik 2000). correlative of CPII (Figs 8 and 9). The change in seismic facies from wedge-shaped basin ﬁll (CPI) to a relatively continuous, high-amplitude package of uniform Mid-Permian –Triassic thickness (CPII) probably represents a transition from syn-rift The mid-Permian – Triassic succession is included in two sedimentation to deposition in a thermally subsiding basin. A mega-sequences, PTI and PTII, both present on the Koldewey similar change in depositional style is widely recognized in the Platform, the Danmarkshavn Ridge and in the Danmarkshavn NE GREENLAND SHELF DEVELOPMENT 895 Fig. 7. A W–E striking seismic section across the southern part Danmarkhavn Ridge and Thetis Basin. The colour code for the seismic horizons is explained in Figure 2, and the seismic mega -sequences are described in the text. Basin (Figs 4a, 7 and 8). It is 700– 800 ms (TWT) thick and the Danmarkshavn Ridge, the mega-sequence onlaps the underlying basal reﬂector marks locally an angular unconformity with erosion succession in a similar fashion as seen on the Loppa High in the of the underlying sediments (not present in Figs 7 and 9). A similar western Norwegian Barents Sea (e.g. van Veen et al. 1993). prominent unconformity is observed on the BGR seismic data on Throughout the region, the siliciclastic Upper Permian and Lower the northernmost part of the shelf, where the base of a unit roughly Triassic successions consist of deep marine shales, locally with corresponding to mega-sequence PTI is seen to onlap the source potential, and shallow to deep marine sandstones and underlying Carboniferous– Lower Permian sequence (Hinz et al. conglomerates (e.g. van Veen et al. 1993; Kreiner-Møller & 1991). The basal unconformity most likely correlates to an Stemmerik 2001; Bugge et al. 2002; Seidler et al. 2004). During unconformity at the base of the upper Artinskian succession in the mid-Triassic, sedimentation in the Jameson Land basin shifted North Greenland and on Spitsbergen, and the mid-Permian to dominantly continental mode, while the Middle and Upper unconformity in East Greenland (e.g. Surlyk et al. 1986; Triassic succession is fully marine in the southwestern Barents Stemmerik 2000) (Fig. 6). It apparently represents marginal uplift, Sea. It is therefore most likely that the Triassic succession consists since continuous sedimentation is known from the deep offshore of marine shales and sandstones (Fig. 8). basins in the Barents Sea. The lower, PTI mega-sequence is characterized by low-angle listric faults, which have broken the bedding into a series of small Jurassic fault blocks by quite brittle deformation and sole out in an The Jurassic succession in the shelf areas has been divided into evaporite layers near the base of the section (Fig. 9). The listric three seismic mega-sequences, JI, JII and JIII, roughly correspond- faults are interpreted to be early, as the sequences above are ing to the Lower, Middle and Upper Jurassic (Figs 7 and 8). All undisturbed. Faulting is probably related to dissolution of three mega-sequences are known from the Koldewey Platform, the evaporites, possibly thin gypsum or halite layers at the base of Danmarkshavn Ridge and the Danmarkshavn Basin (see Figs 4a, 7 sequence, during prolonged subaerial exposure at or near the and 10). Jurassic deposits could also be present int the deeper parts Permian –Triassic boundary. The seismic character of mega- of the Thetis Basin (Fig. 4a). The lower JI mega-sequence is sequence PTI, including the distinctive, small-scale faulting is 200– 300 ms (TWT) thick in most of the region but locally remarkably similar to that of the Permian seismic sequence thickens in the northern part of the Danmarkshavn Basin where onshore Jameson Land (Fig. 9), and provides a stratigraphic tie deposition took place in rim-synclines around growing salt pillows between the two basins. The top of the unit reﬂects a marked shift (Fig. 10). The base of Megasequence JI is a low-angle in seismic character from a succession characterized by high- unconformity marked by a strong, high-amplitude reﬂector along amplitude reﬂections to an overlying, well-bedded section the margins of the Danmarkshavn Basin (Fig. 7). Erosional characterized by lower-amplitude reﬂections (Fig. 9). There is truncation related to minor footwall uplift of the major fault blocks little evidence for erosional truncation at the surface, but it is is seen along the basin margin. Mega-sequence JI is generally interpreted to mark a major change in lithology from carbonates parallel-bedded and characterised by interbedded, high and low- and chert to sandstones and shales comparable to that described amplitude intervals with very high continuity. A minor angularity from the onshore areas (e.g. Surlyk et al. 1986; Stemmerik 2000). divides a lower interval dominated by relatively high-amplitude A similar transition is described from the Finnmark Platform in the reﬂectors from an upper interval with a much lower amplitude and Norwegian Barents Sea, where it is shown to be diachronous less reﬂection on the seismic data (Fig. 7). (Samuelsberg et al. 2003). The high-amplitude reﬂectors at the base of the mega-sequence The overlying mega-sequence PTII is characterized by parallel- JI suggest that it consists either of a shale-prone section or that coal bedded internal reﬂectors (Figs 7 and 9). It is relatively thin in the or evaporite layers are present (Fig. 7). The seismic character westernmost offshore part of the Koldewey Platform, indicating favours correlation with the lacustrine Kap Stewart Formation of either condensation or punctuated deposition in this area. On the ˚ Jameson Land (Fig. 6) or the marginal marineAre Formation of 896 N. E. HAMANN ET AL. Fig. 8. Chronostratigraphic cross section of the Northeast Greenland Shelf based on interpretation of KANUMAS seismic data. The lithology is based on a combination of seismic facies analysis and comparison to onshore geology. Comparison to Figure 6 shows that the Upper Carboniferous– Permian succession is broadly similar to that of the Wandel Sea Basin in eastern North Greenland, whereas the Mesozoic succession has more in common with that of the East Greenland and Jameson Land basins. offshore mid-Norway. The upper, low-amplitude and less The Upper Jurassic mega-sequence JIII forms a very high- reﬂective part of the mega-sequence can be correlated to the amplitude interval, particularly where it is thin over intrabasinal shallow marine, sand-prone Neill Klinter Group of Jameson Land highs. The thinning is gradual by convergence around the margins (Fig. 6) and the Tilje, Ile, Ror and Not formations of offshore mid- of the Danmarkshavn Basin and across the smaller fault blocks and Norway (e.g. Dam & Surlyk 1995). salt features, suggesting condensation of the sequence rather than The overlying mega-sequence JII shows highly variable onlap (see Fig. 10). JIII also thins towards the western part of thickness across the shelf and is missing over large areas along Koldewey Platform; there the thinning is accompanied by a change the margins of the Danmarkshavn Basin due to regional uplift and in amplitude from high to low. The thickness variations suggest erosion (Figs 7 and 8). The internal reﬂectors are generally low- that the tectonic activity continued into the Late Jurassic. In the amplitude, homogeneous with wavy discontinuous bedding, and northern Danmarkshavn Basin deposition took place in rim- the lack of distinct reﬂectors at the base of the mega-sequence synclines (Fig. 10). The high-amplitude sections of mega- suggests a seismically homogeneous section across the boundary sequence JIII are believed to represent the offshore continuation (Figs 7 and 10). The thickness variations across the Danmarkshavn of the Upper Jurassic oil-prone shales described from the onshore Basin and the associated basin margin uplift suggest deposition in basins in East Greenland (see Surlyk 2003). The amplitude shift at tectonically active setting. The base of the succession marks the the western Koldewey Platform suggests a change in facies from onset of mid-Jurassic rifting and can be correlated to the base of oil-prone shales to a more coarse-grained proximal section. A the Pelion Formation in East Greenland (Surlyk 2003). The likely equivalent to this succession is exposed further to the west succession is believed to be sand-prone, sourced from uplifted on the island of Store Koldewey (southern Koldewey Platform) fault blocks along the basin margins, and this mega-sequence, by from where Stemmerik & Piasecki (1990) reported approximately analogy to the Norwegian Shelf, is regarded as the primary 60 m of marine medium- to ﬁne-grained sandstones of Oxfordian– reservoir target on the Northeast Greenland Shelf. Kimmeridgian age to rest directly on basement. NE GREENLAND SHELF DEVELOPMENT 897 Fig. 9. Seismic section across the northern part of the Danmarkhavn Basin. The colour code for the seismic horizons is explained in Figure 2, and the seismic mega-sequences are described in the text. Latest Jurassic – Early Cretaceous reﬂector, which oversteps the Danmarkshavn Ridge from the west. The uppermost part of the succession oversteps the underlying Uppermost Jurassic– Lower Cretaceous deposits are present over units with a marked onlap onto the Danmarkshavn Ridge (Fig. 4a) most of the northern shelf except for the eastern part of the and more localized, erosional truncated intra-basinal highs, above Danmarkshavn Ridge (Figs 4, 8 and 10). The Uppermost Jurassic– salt pillows (Fig. 9). Lower Cretaceous deposits are probably also present in the Thetis Onshore East Greenland two different tectonic styles are Basin (Fig. 4a). The basal boundary is marked by one of the recognized to the north and south of the Kong Oscar Fjord– Jan highest amplitude and regionally most extensive horizons on the Northeast Greenland Shelf (see Figs 9 and 10). It marks an angular Mayen Fracture Zone (728N). The northern area was broken up unconformity over the Danmarkshavn Ridge and shows a into tilted fault blocks, which became progressively fragmented characteristic low-angle erosional truncation of the underlying and narrower with time (e.g. Surlyk 1978, 2003). The Jameson high-amplitude reﬂectors. The unconformity cuts deeper into the Land area to the south underwent only mild tilting, but enormous section southeast of the Danmarkshavn Ridge and on the eastern quantities of coarse sand of the Raukelv Formation were shed into ﬂank of the Danmarkshavn Ridge it is overstepped by a later the basin during this period (Surlyk & Noe-Nygaard 1991; Surlyk angular unconformity (Figs 4a and 7). The KI mega-sequence 2003). Coarse-grained Hauterivian –earliest Albian sediments are generally onlaps the reﬂector along the margins of the basin and known from an isolated structural high at Hold with Hope (748N) over intra-basinal highs. The thickness variations show that (Kelly et al. 1998; Larsen et al. 2001). They pass laterally into a accumulation took place in a number of major half-grabens. shale-dominated succession of Early Aptian– Early Albian age, Major NNE– SSW-oriented faults along the ﬂanks of the Shannon which eventually drowned the high. The succession is separated High, Koldewey Platform and the Danmarkshavn Ridge controlled from the overlying mid-Albian –Turonian shales by an angular deposition. In the northern part of the Danmarkshavn Basin, the unconformity, possibly reﬂecting a minor tectonic event during the tectonic activity triggered major salt movements and a number of early Albian. The mid-Albian – Cenomanian succession has a smaller fault blocks developed. highly diachronous base reﬂecting a continued onlap on the The seismic resolution is generally good in this interval, inherited Lower Cretaceous rift topography during overall sea- particularly in the Danmarkshavn Basin and along the Danmark- level rise (Nøhr-Hansen 1993; Whitham et al. 1999). shavn Ridge. The basal part of the succession is restricted to the The unconformity at the base of mega-sequence KI can Danmarkshavn Basin and the ﬂanks of the Danmarkshavn Ridge. be correlated to the mid-Volgian unconformity at the base The base of an overlying sequence is marked by a high-amplitude of the Wollaston Forland Group onshore East Greenland 898 N. E. HAMANN ET AL. Fig. 10. Comparison of seismic character between the Jurassic and older succession in the Jameson Land Basin, and the offshore Danmarkshavn Basin, East Greenland. The onshore seismic picks are well constrained by ties to surface outcrop and they correlate remarkably well with the offshore area, suggesting that the areas have a very similar geological history. Note the distinctive small-scale listric faulting in the Permian carbonates in both sections, and that the thickness of the Triassic to Jurassic succession is similar in both areas. The colour code for the seismic horizons is explained in Figure 2, and the seismic mega-sequences are described in the text. (see Surlyk 1978, 2003), and represents culmination of rifting Upper Cretaceous sediments are widespread on the northern (Figs 2 and 3). The divergent bedding and the thickness variations shelf, except at the Danmarkshavn Ridge (see Figs 4, 7, 8 and 11). suggest that the lower part of the mega-sequence is composed of The base of the succession is deﬁned by a high-amplitude reﬂector syn-rift deposits comparable to those described from the Wollaston with high continuity. There is little evidence for erosional Forland Group by Surlyk (1978). The overlying seismically truncation beneath the reﬂector, but there is well-developed homogeneous succession is believed to represent shale-dominated onlap or baselap just above, particularly along the margins of the units, most likely of Hauterivian – early Albian and mid-Albian – Danmarkshavn Basin and around salt domes in the northern part of Cenomanian age (Fig. 8). The uppermost Jurassic – Lower the basin. The transition from the underlying succession appears to Cretaceous succession thus records deposition during decreasing be conformable in the centre of the basin (Fig. 10). In the southern tectonic activity from onset of rifting in the latest Jurassic, very part of the Danmarkshavn Basin the unit has been preferentially similar to the events recorded onshore East Greenland and offshore intruded by Tertiary sills (Figs 4a and 11). The Upper Cretaceous Norway. Deposition in the Danmarkshavn Basin was controlled by mega-sequence KII is slightly asymmetric in the Danmarkshavn a few major faults similar to those at the margins of the Jameson Basin, being thickest in the west. It thins rapidly westwards on the Land Basin (Fig. 4), in contrast to the large number of smaller- Koldewey Platform due to erosional truncation of the top during a scale faults described in the northern part of onshore East later, Cenozoic uplift (Fig. 4a). The mega-sequence is absent over Greenland. most of the Danmarkshavn Ridge, apparently largely due to depositional thinning towards the western margin of the ridge (Fig. Late Cretaceous 4a). Parts of, or the whole, mega-sequence are also missing over several of the large salt structures on the northern part of the shelf During the Santonian, strike-slip faulting continued along the (Fig. 10). In the Thetis Basin sedimentation was controlled by a northern margin of Greenland whereas rifting and subsidence major fault zone composed of several probably listric faults along dominated in the areas to the south, until Maastrichian, where domal uplift related to the development of a hot spot mantle plume the western margin of the basin (Fig. 7), and the KII mega- started in the south. In East Greenland deposition is dominated by sequence thins towards the Marginal High and eastern part of the offshore mudstones; turbidites of ?Middle Coniacian and Santo- Thetis Basin (Fig. 4a). nian age most likely record minor rift events (Kelly et al. 1998; The KII mega-sequence has been divided into three seismic Surlyk & Noe-Nygaard 2001). The Late Cretaceous to the end of sequences, KIIa– KIIc in the Danmarkshavn Basin (not described the Paleocene marked a period of major uplift and erosion of the in detail in this paper). The KIIa sequence, the lower part of mega- Greenland craton, west of the sedimentary basins. Deep marine sequence KII, is seismically opaque and probably represents shales sandstones of the Lysing Formation, offshore Norway, seem to of Turonian–Coniacian age. The basal part may represent the have been sourced from East Greenland (Morton & Grant 1998). Turonian transgression, known from most of the North Atlantic NE GREENLAND SHELF DEVELOPMENT 899 Fig. 11 Paleocene deltaic sequence s in the southern part of the Danmarkshavn Basin, represented by prograding wedges. The delta is comparable in thickness to the Paleocene delta of the UK sector of the North Sea, although less extensive. The colour code for the seismic horizons is explained in Figure 2, and the seismic mega-sequences are described in the text. Region. It is followed by an interval of Santonian–Maastrichtian age The Paleocene mega-sequence TI has been subdivided into four characterized by fairly continuous reﬂectors with relatively high sequences of which the lower three form prograding wedges of amplitude (KIIb and KIIc), which are interpreted as evidence for a Paleocene deposits and the last, TId, represents the plateau basalts. more variable lithology of interbedded sandstone and shale. The The internal reﬂection pattern can best be observed in the southern Danmarkshavn Ridge appears to have acted as a local sediment part of the Danmarkshavn Basin where most of the mega-sequence source area at this time, indicating a considerable amount of footwall has been preserved (see Fig. 11). In this area, up to 500 m of uplift and erosion of the underlying section (Figs 4a and 7). In the sediments are recorded. Sequences TIa– TIc consist of prograding, northern part of the Danmarkshavn Basin, the tectonic pulse sigmoidal reﬂectors with classic ofﬂap of the topset beds, and triggered salt diapirism and the rim-synclines ﬁlled rapidly with downlap of the bottomset beds (see Tsikalas et al. 2004). The sediments as the salt structures collapsed over what had previously succession generally progrades from the western margin of the been pillow or domal features. The sediments were sourced locally, Koldewey Platform and eastwards to form a depositional wedge in probably from the eroded crests of salt structures. The overlying the Danmarkshavn Basin (Fig. 11). In the Thetis Basin the interval Maastrichtian–Danian succession is of relatively uniform thickness has a homogeneous internal character and is generally reﬂection and appears to be shale-prone (Fig. 8). free, suggesting a much lower energy, shale-dominated section (Figs 7 and 11). The Danmarkshavn Ridge apparently formed an intrabasinal high at this time and acted as a barrier to siliciclastic Paleocene input into the outer basin. In areas south of Shannon island where Onshore Greenland the Early Tertiary was mainly a period of thick basalt successions are present, only intra-volcanic reﬂectors extension in the southern part of the region (East Greenland), are seen, and it is not possible to detect the base of the volcanics. where the base is marked by an unconformity. In the northern Outside the volcanic area, mainly north of Shannon island, the parts, in the Wandel Sea Basin area, the stress-regime changed lateral equivalent to the base of the lavas appears to be from extension to a period of compression along the major dextral conformable with the underlying succession. strike-slip fault zone (Fig. 2). This compressional phase is believed to have occurred close to the Cretaceous – Tertiary boundary ˚ Post-volcanics (Eocene –Quaternary) (Hakansson & Stemmerik 1989). In East Greenland, the volcanics are often underlain by ﬂuvial conglomerates and there is evidence Magnetic data have shown that the opening of the northern part of of a marked Danian uplift of the onshore areas (e.g. Larsen et al. the North Atlantic Ocean was initiated in the Early Eocene (Fig. 1999). The Early Tertiary volcanics were extruded during three 2). Subsequent tectonism in the area is generally considered to be discrete events (Tegner et al. 1998). The main volcanic phase is related to the two-stage opening of the ocean. The ﬁrst stage the Blosseville – Scoresby Sund plateau basalts (55– 56 Ma), which involved the separation of Norway from the eastern margin of the correlates to the time of continental break-up. Lavas of this age are Jan Mayen Ridge micro-continent, which was at that time attached known from 648N to Shannon Ø (Shannon Island) at 758N, a to Greenland south of the Jan Mayen Fracture Zone (Larsen 1990). distance of approximately 1200 km. North of the volcanic The second stage is related to the transfer of the ocean spreading province, age equivalent sediments were deposited, derived from centre to its present position off East Greenland, and which led to the uplifted basin margins. the ﬁnal separation of the Jan Mayen Ridge from Greenland in the The base of the Paleocene succession is deﬁned by a marked Late Oligocene. Passive margin subsidence during the drift phase reﬂector, which forms a distinctive, continuous but slightly uneven has been interrupted by regional basin margin uplift and inversion erosional horizon in the Danmarkshavn Basin. In the central parts in the Miocene. The ﬁnal North Atlantic plate readjustment of the basin it is a non-depositional hiatus with no evidence of occurred during magnetic anomalies 5 and 6 (Middle – Late erosional truncation (Fig. 7). There it is downlapped from the west Miocene) when movement along the Spitsbergen Fracture Zone (Fig. 11). There is a marked, apparent increase in interval velocity began between Greenland and Svalbard. During this period, above the horizon, which suggests changes in facies. The basal Eurasia continued to move slightly obliquely northwest relative to unconformity becomes less distinct into the Thetis Basin (Figs 7 Greenland (Ziegler 1988). Inversion structures of Late Miocene and 11). The basal horizon probably correlates to the Danian age have been recognized in the Vøring Basin; they are most likely erosional event in the onshore areas. ´ related to ridge-push (Dore & Lundin 1996). The post-volcanic 900 N. E. HAMANN ET AL. succession has been divided into three mega-sequences: TII-TIV, section generally die out at the sequence boundary (Fig. 11). of Eocene – Late Oligocene, early Miocene – Late Miocene and Erosional truncation of the underlying sequences increases Early Pliocene– Holocene age (Figs 4a and 8). towards the western margin of the Thetis Basin and across the Mega-sequence TII has a fairly uniform thickness of 500– Danmarkshavn Ridge (Figs 7 and 11). Structural tilting and 1200 m throughout the shelf although it locally thins over intense erosion occurred prior to deposition of the mega- structural highs and is missing due to later erosion particularly sequence. The removed section increases in age down to Lower towards the west and north, on the Koldeway Platform and in the Cretaceous along the western margin of the Koldewey Platform western part of Danmarkshavn Basin (see Figs 4a, 7 and 11). The (Figs 4a and 7), and deep erosion is demonstrated between 748 base is deﬁned by the top volcanics horizon, which forms a strong and 768 N. The prominent and extensive unconformity is reﬂector at the base of the overlying siliciclastic sequence. To the interpreted to be of Early Pliocene age and has previously been north the base is represented by a volcaniclastic bed similar to (and described from the Northeast Greenland Shelf margin (Hinz approximately the of same age as) the Balder Formation tuffs in et al. 1993). Mega-sequence TIV is over 1500 m thick in the the North Sea. This horizon can be easily identiﬁed (see Fig. 7). central parts of the Thetis Basin and is thin just east of the The mega-sequence is characterized by continuous even-bedded, Danmarkshavn Ridge; further towards west it disappears (Figs 4a high-amplitude reﬂectors, which are parallel to sub-parallel. It and 7). The mega-sequence can be subdivided into a number of onlaps the eastern and western margins of the Danmarkshavn sequences with a predominantly prograding depositional pattern. Basin at a low angle and thins over the Danmarkshavn Ridge. In It is characterized by channel ﬁll deposits to the north and west of the Thetis Basin there is a steeply onlapping surface onto the the Thetis Basin, suggesting periods of non-deposition and Danmarkshavn Ridge (Figs 7 and 11), and apparent distal downlap erosion of the inner parts of the shelf. against the outer ridge in the east. In the upper part, low-angle prograding beds indicate a possible increase in depositional energy towards the top of the section, possible caused by a relatively Hydrocarbon potential minor tectonic pulse (Fig. 7). The mega-sequence is also present The presence of an active hydrocarbon system in the area is along the continental margin onlapping the eastern edge of the demonstrated by many direct hydrocarbon indicators (ﬂatspots, Marginal High and truncated against the apparent escarpment bright spots, gas chimneys, etc.), seen on the seismic data. A formed by the oceanic basalts (see Tsikalas et al. 2004). number of favourable geological factors also point to the oil Mega-sequence TIII is separated from the underlying deposits potential of the area. The East Greenland Shelf is almost certainly by a distinct erosional unconformity ﬁrst reported by Hinz et al. underlain by the same proliﬁc Upper Jurassic source rock that has (1993). This unconformity is locally seen to be directly on oceanic sourced most of the major oil ﬁelds in the North Atlantic region, basement on the outer continental slope, but in most of this area and by comparison with the onshore succession it is likely that there is a thin layer of sediments below the unconformity. The several deeper source intervals are likely to be present (e.g. overlying, TIII mega-sequence shows apparent onlap towards the Christiansen et al. 1992). The tectonic development of the shelf (Fig. 4a). The unconformity has also been identiﬁed on the Danmarkshavn Basin indicates that the Upper Jurassic source Liverpool Land Shelf. It is most likely of earliest Miocene age and rocks have been buried deeply enough to generate hydrocarbons, related to basin margin uplift during the separation of the Jan and most likely these have migrated towards the eastern margin of Mayen Ridge in the latest Oligocene – earliest Miocene (Hinz et al. the basin and the Danmarkshavn Ridge. Potential trapping 1993). In the Thetis Basin the mega-sequence shows downlap onto structures include large-scale fault blocks similar to those of the the basal horizon, towards the shelf edge (Fig. 7). Slumping occurs major North Sea ﬁelds. Regionally extensive, excellent quality along the western margin of the Thetis Basin and a distinct, deeply reservoir intervals are likely to be present in the Middle to Upper incised erosional surface has been observed along the edge of the Jurassic succession, and additional reservoir potential exists Danmarkshavn Ridge (Fig. 7). The horizon cuts up to 150–200 m throughout the Devonian–Paleocene syn-rift succession. The into the underlying parallel laminated sequence, forming a very most prospective area for the Jurassic play is on the margins of irregular surface, overlain by a chaotic or steeply downlapping the Danmarkshavn Basin and along the Danmarkshavn Ridge. sequence (Fig. 4a). The unconformity runs approximately N – S Further potential may exist in the central and southern parts of along the edge of the Danmarkshavn Ridge, and is interpreted to the shelf, but the geological understanding of these areas is have formed a sharp palaeo-shelf edge. West of the palaeo-shelf complicated by the thick Tertiary volcanics. The post-rift Tertiary edge, the horizon gently onlaps across the Danmarkshavn Ridge section may also have some potential in the outer parts of the shelf, and into the Danmarkshavn Basin, where it is truncated by particularly in the northern part of the Blosseville Kyst Shelf. Megasequence TIV (Figs 4a and 7). Mega-sequence TIII reaches a The KANUMAS seismic data have established the East thickness of over 2000 m along the axis of the Thetis Basin, but Greenland Shelf as a potential major hydrocarbon province. thins eastward over the marginal high, and across the continent – Large areas of the East Greenland shelf appear to be oil-prone and ocean boundary. The megasequence shows rapid depositional include several potentially giant structures. Tertiary volcanism and thinning west of the Thetis Basin, before it is erosionally truncated the later Cenozoic regional uplift events are unlikely to have by the overlying sequence (Figs 4a and 7). The thickness and severely reduced the prospectivity of the region. volume of Late Oligocene – Miocene deposits in the Thetis Basin shows that a period of major uplift and erosion took place at the time. The upper part of the succession displays low-amplitude Summary and conclusions folds and faults. The faults occur throughout the shelf area, in NE trending zones about 10 – 20 km wide, and are separated by wide The more than 1200 km long and 200– 600 km wide shelf east of areas of generally undisturbed sediments. The faults are steeply Greenland forms the conjugate margin to the shelf areas west of dipping and convergent and show evidence of drag and reversal, Norway. The East Greenland Shelf can be divided into three broad with throws of up to about 200 m along the eastern margin of the regions based on interpretation of c. 6800 km of multichannel Danmarkshavn Basin. This type of faulting is characteristic of seismic data from the area between 728N and 798N and additional strike-slip movement, and the inversion structures probably 5000 km of seismic data offshore Liverpool Land. The very open formed during a period of compression during the Late Miocene. seismic grid allows us to recognize ﬁve major, roughly northeast- Mega Sequence TIV is characterized by a strong, high- trending structural elements on the Northeast Greenland Shelf, amplitude basal reﬂector in the outer parts of the shelf, and a north of 758N (Fig. 3). The structures most probably extend south marked decrease in interval velocity. The horizon has not been of 758N for some distance, but the presence of a thick volcanic affected by tectonism, and faults and folds seen in the underlying succession obscure the seismic signal on this part of the shelf. NE GREENLAND SHELF DEVELOPMENT 901 The most prominent feature on the Northeast Greenland shelf is Hinz, K., Meyer, H. & Miller, H. 1991. North-East Greenland shelf north of the 50 – 100 km wide and more than 400 km long Danmarkshavn 798N: results of a reﬂection seismic experiment in sea ice. Marine and Basin (Fig. 3). It contains a more than 13 km (8 s TWT) thick Petroleum Geology, 8, 461 –467. sedimentary succession of proposed Devonian to Palaeogene age Hinz, K., Endholm, O., Block, M. & Skoseid, J. 1993. Evolution of North (Figs 4 and 8). The basin resembles the onshore Jameson Land Atlantic volcanic continental margins. Petroleum Geology of North- Basin both in structural style and in having very thick, .13 km, west Europe. In: Parker, J. R. (ed.) Proceedings of the Fourth and stratigraphically almost complete post-Caledonian succes- Conference. Geological Society, London, 901–913. ˚ Hakansson, E. & Stemmerik, L. 1989. Wandel Sea basin – A new synthesis sions. However, the depositional evolution of the two basins is of the late Paleozoic to Tertiary accumulation in North Greenland. believed to be very different, particularly during Late Carbonifer- Geology, 17, 683–686. ous – Triassic times (see Figs 6 and 8). Kelly, S. R. A., Whitham, A. G., Koraini, A. M. & Price, S. M. 1998. The Devonian – Triassic development of the Northeast Green- Lithostratigraphy of the Cretaceous (Barremian –Santonian) Hold land Shelf resembles that of the Norwegian Barents Sea, and the with Hope Group, NE Greenland. Journal of the Geological Society, Danmarkshavn Basin is a likely southern continuation of the London, 155, 993–1008. Nordkapp Basin rift (Gudlaugsson et al. 1998). The post-Triassic Kreiner-Møller, M. & Stemmerik, L. 2001. Upper Permian lowstand fans of evolution of the Greenland Shelf seems to be broadly similar to the Bredehorn Member, Schuchert Dal Formation, East Greenland. In: that of the shelf areas west of Norway. Main rifting took place Martinsen, O. J. Dreyer, T. (eds) Sedimentary Environments Offshore during the mid- and late Jurassic, and during the Cretaceous new Norway – Palaeozoic to Recent. NPF Special Publication, 10, 51 –65. deep basins started to form on the more distant part of the shelf. Larsen, H. C. 1984. Geology of the East Greenland shelf. 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