IMPACT OF MAGMATISM ON PETROLEUM SYSTEMS IN THE SVERDRUP BASIN, CANADIAN ARCTIC ISLANDS, NUNAVUT: A NUMERICAL MODELLING STUDY

237Journal of Petroleum Geology, Vol. 30(3), July 2007, pp 237-256

© 2007 The Authors. Journal compilation © 2007 Scientific Press Ltd

IMPACT OF MAGMATISM ON PETROLEUMSYSTEMS IN THE SVERDRUP BASIN,CANADIAN ARCTIC ISLANDS, NUNAVUT:A NUMERICAL MODELLING STUDY

S.F. Jones1*, H. Wielens2, M-C. Williamson2 and M. Zentilli3

Numerical modelling is used to investigate for the first time the interactions between a petroleumsystem and sill intrusion in the NE Sverdrup Basin, Canadian Arctic Archipelago. Although hydrocarbonexploration has been successful in the western Sverdrup Basin, the results in the NE part of thebasin have been disappointing, despite the presence of suitable Mesozoic source rocks, migrationpaths and structural/stratigraphic traps, many involving evaporites. This was explained by (i) theformation of structural traps during basin inversion in the Eocene, after the main phase ofhydrocarbon generation, and/or (ii) the presence of evaporite diapirs locally modifying the geothermalgradient, leading to thermal overmaturity of hydrocarbons. This study is the first attempt at modellingthe intrusion of Cretaceous sills in the east-central Sverdrup Basin, and to investigate how theymay have affected the petroleum system.

A one-dimensional numerical model, constructed using PetroMod9.0®, investigates the effectsof rifting and magmatic events on the thermal history and on petroleum generation at the DepotPoint L-24 well, eastern Axel Heiberg Island (79o23’40”N, 85o44’22”W). The thermal history isconstrained by vitrinite reflectance and fission-track data, and by the tectonic history. The simulationidentifies the time intervals during which hydrocarbons were generated, and illustrates the interplaybetween hydrocarbon production and igneous activity at the time of sill intrusion during the EarlyCretaceous. The comparison of the petroleum and magmatic systems in the context of previouslyproposed models of basin evolution and renewed tectonism was an essential step in the interpretationof the results from the Depot Point L-24 well.

The model results show that an episode of minor renewed rifting and widespread sill intrusionin the Early Cretaceous occurred after hydrocarbon generation ceased at about 220 Ma in theHare Fiord and Van Hauen Formations. We conclude that the generation potential of these deeperformations in the eastern Sverdrup Basin was not likely to have been affected by the intrusion ofmafic sills during the Early Cretaceous. However, the model suggests that in shallower sourcerocks such as the Blaa Mountain Formation, rapid generation of natural gas occurred at 125 Ma,contemporaneous with tectonic rejuvenation and sill intrusion in the east-central Sverdrup Basin.A sensitivity study shows that the emplacement of sills increased the hydrocarbon generation ratesin the Blaa Mountain Formation, and facilitated the production of gas rather than oil.

1 Department of Geology and Geophysics, University ofCalgary, 2500 University Drive NW, Calgary, Alberta,T2N 1N4, Canada.

2 Geological Survey of Canada (Atlantic), PO Box 1006,Dartmouth, NS, B2Y 4A2, Canada.

3 Department of Earth Sciences, Dalhousie University,Halifax, NS, Canada.

* author for correspondence, email: [email protected]

INTRODUCTION

Exploration geologists commonly develop numericalmodels based on source-rock properties such asthickness, thermal conductivity, porosity, permeability,

Key words: 1D modelling, Axel Heiberg Island, maficsills, hydrocarbon generation, petroleum system,Sverdrup Basin, source rock, thermal history, CanadianArctic Islands, Arctic magmatism.

238 Magmatism and petroleum systems in the Sverdrup Basin

total organic carbon (TOC), geochemical maturationparameters, vitrinite reflectance, palaeo-temperatures,and heat flow to simulate hydrocarbon generation andmigration. The potential impact of volcanic processeson the hydrocarbon potential of offshore rift basinshas been recognized (e.g. Symonds et al., 1998;Svensen et al., 2004). However, quantitative hydrocarbonsystems models applied to continental rift basins rarelyinclude the effects of igneous intrusions.

The focus of this study is the Depot Point L-24well drilled by Panarctic from 1972-1973 in theSverdrup Basin in an area located on eastern AxelHeiberg Island, Nunavut, a well we considerrepresentative of the NE Sverdrup Basin in terms ofcomplexity and reliable documentation (Fig.1). TheSverdrup Basin, a large sedimentary basin with provenhydrocarbon resources (Chen et al., 2000), contains

a thickness of over 10 km of Mesozoic sedimentaryrocks, and locally abundant volcanic and intrusiverocks. In this paper, we present a numerical model todetermine the effects of sill emplacement onhydrocarbon systems in this basin.

The following scientific questions are addressed:(1) How can key observations on the hydrocarbon andmagmatic systems in the Sverdrup Basin be integrated?(2) How and where in the evolution of the SverdrupBasin did sill emplacement affect the hydrocarbonsystem? (3) How do the results obtained in thenumerical model vary when sills are not introducedin the stratigraphic column, or when the age of sillemplacement varies? (4) Can the modelling of theeffects of igneous activity on the hydrocarbon systembe extrapolated to other parts of Axel Heiberg Island,the Sverdrup Basin, or other Arctic basins?

Fig. 1. Map of Circum-Arctic landmasses showing the location of the Canadian Arctic Islands in northernNunavut. The outline of the Sverdrup Basin is shown by a dotted line. Volcanic and intrusive rocks ofCretaceous age belonging to the High Arctic Large Igneous Province are shown in red (HALIP; see text forexplanation). Igneous rocks of Tertiary age are shown in black. Major structures in the Arctic Ocean are alsoshown: full line, active ridge; dashed line, aseismic ridge (modified from Srivastava, 1985).

239S. Jones et al.

We conclude that in the Sverdrup Basin and otherCircum-Arctic volcanic basins, hydrocarbon systemsmodelling must, in future exploration strategies, takeinto account the role and impact of magmatism onthe petroleum system at all stages of the basin history.

THE SVERDRUP BASIN

The Canadian Arctic Islands contain severalgeological provinces that exhibit a general northwarddecreasing age. Archean to Lower Proterozoicbasement rocks and Cambrian to Devonian rocks ofthe Interior Platform underlie Palaeozoic rocks of theFranklinian Mobile Belt. The Sverdrup Basin is anintra-continental basin that originated during a LateCarboniferous-Early Permian rifting eventaccompanied by minor basaltic volcanic activity(Esayoo Formation). It consists of an elongatedstructural depression that measures 1,300 km by 400km, overlies deformed Paleozoic strata, and is shapedby the surrounding fold belt (Davies and Nassichuk,1991; Trettin, 1989). To the north, the Sverdrup Basinis bordered by the uplifted Sverdrup Rim (Meneleyet al., 1975), Arctic continental margin and CanadaBasin. The depositional and structural history of theSverdrup Basin lasted for 250 million years, and endedwith the onset of the Eurekan orogen, a LateCretaceous to Paleocene compressional event thatincluded basin inversion, exhumation and erosion(Harrison, 2005). The Sverdrup Basin also hostsmajor evaporite deposits that formed canopies during

the Early Cretaceous by the coalescence and mergingof various evaporite sheets stemming from diapirs(Jackson and Harrison, 2006).

Our current understanding of basin history is basedon two tectonic models. Sweeney (1977) recognizedthree depositional stages corresponding to (i) theinitial rifting event (330-230 Ma), and renewed basintectonism and foundering in (ii) the early Mesozoic(225-124 Ma) and (iii) the late Mesozoic (124-74 Ma).In contrast, the subsidence model of Stephenson etal. (1987) invoked a single rifting event during theCarboniferous-Early Permian to account for the pre-Valanginian fill of the Sverdrup Basin. Anextrapolation of the model to include Cretaceousstratigraphy suggests that thermal subsidence andsediment compaction can account for Valanginian-Campanian sedimentation throughout the basin exceptin the vicinity of Axel Heiberg Island and westernEllesmere Island. The authors envisaged a second,relatively minor rifting event during the EarlyCretaceous (or earliest Late Cretaceous) restricted tothe eastern part of the Sverdrup Basin. This model isconsistent with the style and age of emplacement ofthe Sverdrup Basin Magmatic Province (Williamson,1988; Villeneuve and Williamson, 2006).

The study area is located in the east-central partof the Sverdrup Basin, on Axel Heiberg Island (Fig.2). Fig. 3 shows that the Palaeozoic and Mesozoicsuccessions reach a maximum thickness of 13 km(Embry, 1991; Chen et al., 2000). These strata weredeposited during transgressive-regressive cycles

Fig. 2. Map of the Canadian Arctic Archipelago showing the outline of the Sverdrup Basin and the regionalextent of intrusive rocks in the Sverdrup Basin Magmatic Province (dashed line). Both volcanic rocks andassociated dykes and sills (dotted line) crop out in the east-central part of the Sverdrup Basin. The solid circleshows the location of the L-24 Depot Point well at 79o23’40”N, 85o44’22”W, eastern Axel Heiberg Island(from Villeneuve and Williamson, 2006).

96°

ARCTIC OCEAN

Banks I.

76° 80°112°72°

72°128°

144°

144°76° 80° 80°96°112°126°

80°

Bathurst I.

Cornwall I.

Melville I.

Mackenzie King I.

Ellef Ringnes I.Prince Patrick I.

Devon I.

Axel Heiberg I.

Ellesmere I.

AmundRingnes

I.

200 km

GSC

Intrusive Rocks

Volcanic and Intrusive Rocks

L-24 Depot Point well

Sverdrup Basin Magmatic Province

Location Buchanan Lake (Fig. 5)

N


triggered by episodic variations in the rate ofsubsidence, eustatic sea level fluctuations, andsediment supply (Embry and Johannessen, 1993). Mostof the strata are of clastic origin with subordinatecarbonate rocks. However, the Mesozoic successionis intruded by evaporite diapirs that originated in theUpper Mississippian to Middle Pennsylvanian OttoFiord Formation (Davies and Nassichuk, 1991). Thesediapiric structures and the Permian volcanicsuccessions of the Esayoo Formation associated withthe initial rifting event are not illustrated on Fig. 3.

THE SVERDRUP BASINMAGMATIC PROVINCE

The Sverdrup Basin Magmatic Province (SBMP; Fig2) was emplaced episodically from the EarlyCretaceous to the Paleogene as hypabyssal intrusivesheets and dykes, flood basalts and central volcanoes(Balkwill and Fox, 1982; Ricketts et al., 1985; Embryand Osadetz, 1988; Williamson, 1988; MacRae et al.,1996). The occurrence of igneous rocks in evaporitedomes (Davies and Nassichuk, 1991) and theidentification of dyke swarms from aeromagnetic datain the western Sverdrup Basin (Miles, 2002) suggestthat intrusive rocks occur throughout the archipelago,while volcanic successions are restricted to the easternpart of the Basin (Fig.2).

The SBMP displays all the characteristics of alarge igneous province, and is often grouped withother Circum-Arctic igneous provinces of similar age(High Arctic Large Igneous Province; Tarduno, 1998;Buchan and Ernst, 2006; Drachev and Saunders,2006). Volcanic rocks of tholeiitic, ferrobasaltic, andalkaline character were emplaced episodically overa period of 40 Ma and are associated, spatially andat each time interval, with sills and dykes of the samecomposition (Williamson, 1988; 1998). Theemplacement of flood basalts in the eastern SverdrupBasin during the Early Cretaceous is consistent withthe subsidence model of Stephenson et al. (1987). Atwo-layer lithospheric stretching model, such as theone proposed by Keen et al. (1994) and Williamsonet al. (1995) for the Labrador margin, could accountfor the volume and shift in compositional characterof intrusive rocks associated with minor rifting latein the basin history. However, a link with hot spotactivity in the adjacent Arctic Ocean cannot beprecluded. Villeneuve and Williamson (2006)demonstrated in a 40Ar-39Ar study of mafic igneous rocksfrom the eastern Sverdrup Basin that magmatism peakedduring two time intervals (127-129 Ma and 92-98 Ma),the second of which was coeval with the developmentof the proto-Arctic Ocean and volcanism at the site ofthe Alpha Ridge (Van Wagoner et al., 1986; Embry andOsadetz, 1988; Williamson, 1988; Vogt et al., 2006).

Fig. 3. Schematic stratigraphic cross-section of the Sverdrup Basin, illustrating the Mesozoic succession closeto the depocentre, Axel Heiberg Island. Salt intrusions and dykes are not illustrated. (Modified from Embry,1991, with data of Harrison and Jackson, 2007).

241S. Jones et al.

Fig. 3 is a schematic stratigraphic cross-section ofthe Sverdrup Basin. Flood basalts and sills on AxelHeiberg Island are well exposed in the PrincessMargaret Range, which stretches north-south acrossthe length of the island. Basaltic lava flows occur inthe Isachsen and Strand Fiord Formations. Sills intrudethe entire Mesozoic succession and are particularlyabundant in shales of the Blaa Mountain Formation;they are rare in sedimentary units within and overlyingthe Christopher Formation. In outcrop, the sillsaverage 10-50 m in thickness and display white-coloured contact zones of hornfels in shales andsiltstones (Fig. 4), and quartzite in sandstones. Thedense spacing of the sills in the Triassic succession isillustrated on a map of Buchanan Lake, eastern AxelHeiberg Island (Fig. 5). Buchanan Lake is locatedsome 37.5 km NW of the study area. Work in progressby Dewing et al. (pers. comm., 2006) on thedistribution of igneous rocks in Arctic wells showsthat igneous rock units occur in all the wells drilledin the Eureka Sound area.

THE PETROLEUM SYSTEM

Nineteen hydrocarbon discoveries have been madein the western Sverdrup Basin with 119 wells drilled

in Mesozoic plays (Chen et al., 2000), a success rateof almost 16%. Approximately 75% of thehydrocarbon pools host natural gas. Mesozoic rockson Melville Island, King Christian Island and westernEllef Ringnes Island in the south-central to SWSverdrup Basin host 25 gas and eight oil pools (Chenet al., 2002). Many wells targeted the Late Palaeozoicand Mesozoic units (Balkwill, 1978); most of thediscoveries are in a Late Triassic to Early Jurassic,thick, widespread sandstone unit, the Heibergsandstone (Chen et al., 2002). Plays and discoveriesare in structural traps, mainly salt-cored, lowamplitude folds (Chen et al., 2002).

Strata within the Blaa Mountain, Ringnes, andAwingak Formations have good source rock potentialwith TOC values of 4.0-6.0% and hydrogen indices(HI) of 100-400 mgHC/gTOC. Strata within the HareFiord, Van Hauen, Jameson Bay, Deer Bay andChristopher Formations have lower source rockpotential with TOC = 0.5-2.5% and HI = 50-300mgHC/gTOC (Gentzis and Goodarzi, 1993a; 1993b;1991). The key lithologic units are the Blaa MountainFormation (Mid–Late Triassic; Anisian – mid Norianbasinal calcareous shales), the Blind Fiord Formation(Early Triassic; Indusian – Oienekian sands andsiltstones), the Van Hauen Formation (Roadian silty

Fig. 4. Buchanan Lake, located approximately 38 km NW of the Depot Point L-24 drill site. The photographshows massive sills with columnar jointing and light-coloured margins intruding poorly-consolidated Triassicshale beds of the Blaa Mountain Formation (up to 50 m in thickness) along the north shore of the lake.Contact planes are offset along regularly-spaced faults. (Photo by M.-C. Williamson).


shales), and the Hare Fiord Formation (Moscovian –Roadian basinal shales) (data compiled from: Embry,1991; Trettin, 1989; Balkwill et al., 1983; Gentzis andGoodarzi, 1991).

In the eastern part of the Sverdrup Basin, many ofthe wells were drilled on salt-cored anticlines and theexploration results were disappointing, despite thepresence of adequate source rocks and structures.Explanations proposed include the timing ofaccumulation and migration in the hydrocarbonsystem, the thermal focussing effects of diapirs (Arneet al., 2002; Zentilli et al., 2005) and the additional,undocumented thermal effects of sill intrusion. Forexample, the total thickness of igneous units in twowells drilled in the Eureka Sound area is approximately500 m (20 units, 529 m total thickness of igneous rockat Mokka A-02, eastern Axel Heiberg Island, 79o31’12”N, 87o01’14”W; and 17 units, 466 m total thicknessof igneous rock at Fosheim N-27, western EllesmereIsland, 79o36’54”N, 84o43’19”W (Dewing, unpubl.data). The Depot Point L-24 well was chosen for thisstudy because the small number of igneous unitsintruding the succession (n = 6) allowed a simplifiedand first-order evaluation of the thermal effects ofmagmatism on the petroleum system.

Three processes have affected the eastern andcentral regions of the Sverdrup Basin: deep burial,mafic magmatism and exhumation (Balkwill, 1978).Hydrocarbon generation predictions in the SverdrupBasin require the geological characteristics ofvolcanic and hydrocarbon systems to be integratedand their interactions explored. Sill emplacementcauses heating, pore fluid expulsion and metamorphicreactions which affect basin evolution (Malthe-Sørenssen et al., 2004). As a result, the heat thatigneous intrusions introduce in the basin successionscan lead to hydrocarbon over-maturation (Archer etal., 2005).

BASIN MODELLING

PetroModA classical approach to basin modelling can bemerged with data on volcanic systems using variouscomputer software programmes. In this study,PetroMod9.0® (Integrated Exploration Systems,Germany) was chosen for model construction andsimulation. One-dimensional thermal andsedimentation modelling has been successfullyapplied elsewhere to simulate hydrocarbon generation

Fig. 5. Geological map of the Buchanan Lake area showing the density of sill spacing on the south shore. Theformations in this area are intersected by the Depot Point L-24 well and two other wells in Eureka Sound areathat record sills with a total thickness of 500 m. Units strike NNW and dip 20o W. Note that the sillthicknesses are not expressed to scale. (Modified from Williamson, 1988).

243S. Jones et al.

and maturity levels (e.g. Waples, 1998). High-qualitymodel results require measured physical properties asinput parameters to keep the model as realistic aspossible (Waples, 1998). We used well log data fromthe Depot Point L-24 well as a framework, augmentedby other measured data and inferred values as discussedbelow.

The stratigraphic succession drilled in the DepotPoint L-24 well (Fig. 2) is shown on a digital log (Fig.6). The well intersects six igneous units with a totalthickness of 158 m, making it a good candidate for anumerical simulation to test the effects of intrusions onpetroleum systems based on well log data and

petrography. The units consist of coarse-grainedgabbros and diorites that vary in thickness between9 and 68 m. The units intrude sandstones, siltstonesand shale in concordant fashion. The uppermost sillshows a single contact aureole. However, this unitis assumed to be a sill, because the contactmetamorphic zone is almost half of the sillthickness, and other sills intrude the same BlindFiord Formation. The aureoles formed in responseto the increased temperature from the intrusion,which allows crystallization and the formation ofnew minerals, especially in clay-rich deposits. Thecontact-metamorphic rocks consist of very fine-

Fig. 6. Depot Point L-24 well log showing the lithologies with their grain sizes intersected by the well. Theformation names and depths are listed alongside the well. Basaltic sills are in red and the bordering contact-metamorphic zones in violet.


grained quartzite, meta-siltstone and hornfels. Someof the contact zones show fracturing, chloritizationand/or silicic and dolomitic cement.

Model construction and input dataTo explore the thermal impact of sill emplacement onpetroleum systems, a computer model integrating allavailable data for the simulation of hydrocarbongeneration and for palaeo-temperature profiling in thelithologic column within a 1D section was constructed.The 1D model process focuses on the generation ofoil and gas. Modelling of migration pathways andhydrocarbon traps would require 2D and 3D data, bothof which were beyond the scope of this study.

Data used are: geological formations, lithologies,formation thicknesses, formation ages (Table 1),erosion rates, and age of sill emplacement. Toconstrain the model, well data such as vitrinitereflectance, sea level, heat flow, and porosity areincluded. In addition, fission-track data are used toconstrain the time of basin inversion. The bestconstrained parameters are the lithologies,thicknesses, and sill characteristics previously definedfrom well studies and field work. The reliability ofthe heat flow data is more difficult to establish.Present-day heat flow values are highly variable onregional and local scales. The software provides

default settings for physical parameters such asconductivity, compaction with depth, and source rockkinetics; the programme is used for both modelconstruction and simulation. The programme thenintegrates these processes and characteristics with oneanother, and simulates their behaviour to yield aprediction that includes hydrocarbon generation,migration, accumulation and loss over time. It alsosimulates processes such as compaction of thesediments over time, and the related porosityreduction. Migration and accumulation are notsimulated by the one-dimensional model.

Formations that have been eroded from the siteand units below the penetration depth of the well wereinferred from the general stratigraphy, neighbouringwells, generalised cross sections, and lithology-isopach maps from Embry (1991), Trettin (1989),Balkwill et al. (1983), and Gentzis and Goodarzi(1991). In this paper, the units intersected by the wellare referred to as the Depot Point L-24 well; and theentire modelled column (intersected and inferred) asthe Depot Point L-24 column.

No Rock-Eval data are available from the well;therefore source rock properties had to be inferredfrom the literature which documents total organiccarbon (TOC) and hydrogen index (HI) values for theMesozoic Ringnes, Awingak, and Blaa Mountain

Formation Name Dominant Lithology Thickness (metres)

Depositional Environment Age

Expedition Fm Sandstone 500 delta front Late Cretaceous; Campanian - Maastrichtian

Kanguk Fm Silty shale 150 offshore shelf Late Cretaceous; mid Cenomanian - Santonian

Strand Fiord Fm Basalt 300 N/A Early Cretaceous; late Albian - mid Cenomanian

Bastion Ridge Fm Silty shale 50 offshore marine Early Cretaceous; late Albian

Hassel Fm Sandstone 150 delta front Early Cretaceous; mid Albian

Christopher Fm Sandy shale 600 offshore, then shelf Early - Late Cretaceous; late Aptian - mid Albian

Isachsen Fm Sandstone 200 nearshore shelf Early Triassic; Valanginian - late Aptian

Deer Bay Fm Shale & siltstone 100 outer shelf Late Jurassic - Early Cretaceous; mid Tithonian - Berriasian

Awingak Fm Sandstone 250 shallow shelf Late Jurassic; mid Oxfordian - Tithonian

Ringnes Fm Shale & siltstone 100 basinal Mid - Late Jurassic; Bajocian - Oxfordian

Jameson Bay Fm Sandy siltstone 50 offshore shelf Early - Mid Jurassic; Toarcian - Aalenain

Heiberg Fm Sandstone 2000 delta front to nearshore shelf

Late Triassic - Early Jurassic; mid Norian - Pliensbachian

Blaa Mountain Fm Calcareous shale 1000 basinal Mid - Late Triassic; Anisian - mid Norian

Blind Fiord Fm Siltstone and shale 2926 slope Early Triassic; Indusian - Oienekian

Van Hauen Fm Silty shale 587 slope Roadian

Hare Fiord Fm Shale 303 basinal Moscovian - Roadian

Otto Fiord Fm Halite 200 evaporite deposits Upper Carboniferous

Basement Basement N/A N/A N/A

Table 1. Lithologies intersected by the Depot Point L-24 well (shaded rows) and inferred units used for theconstruction of the one-dimensional model framework. The depositional ages and environment for eachformation were used to create the model and construct a sea level curve. The data were compiled fromEmbry (1991), Trettin (1989), Balkwill et al. (1983), and Gentzis and Goodarzi (1991).

245S. Jones et al.

Formations in the western Sverdrup Basin (e.g.Gentzis and Goodarzi, 1993a; Gentzis and Goodarzi,1993b; Gentzis and Goodarzi, 1991). TOC and HIvalues used in the model are listed in Table 2. Themodel requires kinetic data which dictate the rates ofgeneration and the types of hydrocarbons produced.The data are not available for potential source rockson Axel Heiberg Island; therefore Burnham Type IIkinetic data (Burnham and Sweeney, 1989) waschosen as “best fit”.

Although vitrinite reflectance measurements areavailable from the Depot Point L-24 well (Arne etal., 2002) their quality only allowed the thermal historyto be constrained in a general sense. The high vitrinitereflectance values (2-4%) near the base of the wellreflect the deep burial of the Permian formations andthe intrusion of igneous rocks (Arne et al., 2002).

Heat FlowReconstruction of the thermal history for part of thebasin requires knowledge of present-day and palaeo-heat flows, i.e. the flux of heat from higher to lowertemperature areas. Present-day heat flow values weredetermined from bottom-hole temperature (BHT) data

(Jones et al., 1989), drill stem tests, or can be measuredwith probes; palaeo-heat flow and palaeo-gradientvalues can be estimated from vitrinite reflectanceprofiles, coalification parameters (Majorowicz andEmbry, 1998) and fission track data.

Present-day heat flow, thermal conductivity andgeothermal gradient values for the Depot Point L-24well are 42 mW/m2, 1.9 W/m/K, and 22 mK/m,respectively (Jones et al., 1989). Majorowicz andEmbry (1998) reported a much higher heat flow of 68mW/m2. This discrepancy is probably due to variationin measurement techniques and interpretation. Overthe entire Sverdrup Basin, present-day heat flow valuesrange from 40-90 mW/m2 (Majorowicz and Embry,1998). The large range of heat flow values is due to thelarge area, variations in crustal type and thickness, saltdiapirs and possible measurement errors.

In this model, heat flow during the onset ofCretaceous rifting (125 Ma) was estimated to be 90mW/m2, a value that is commonly used for rift basins;there are no published values for the heat flow duringrifting on Axel Heiberg Island. The subsequent heatflow values (Fig. 7) were calculated with a Mackenzie-type heat-flow decay formula (Turcotte and Schubert,

Formation TOC (wt. %) HI (mg HC/TOC)

Hare Fiord 1 50Van Hauen 1 50

Blaa Mountain 5 400Jameson Bay 0.5 150

Ringnes 6 400Awingak 4 100Deer Bay 2.5 50

Christopher 2.5 300

Table 2. Source rock properties (Total Organic Carbon, TOC, and Hydrogen Index, HI) assigned to eachlithology included in the numerical model. Values were available directly from the Depot Point L-24 well.Average values were inferred from other locations in the Sverdrup Basin. Values not reported in theliterature were calculated from the trends by Gentzis and Goodarzi (1993a, 1993b, 1991).

Fig. 7. The model refers to the following three data sets as boundary conditions over time as they define thedepositional environment: (a) a sea level curve in blue, (b) the sediment-water interface temperature ingreen, and (c) the heat flow values in red.


2002) and result in a present-day heat flow of 39 mW/m2, which is comparable to the value reported by Joneset al. (1989). The assumption that the increase in heatflow associated with rifting is instantaneous ingeological time (less than 1 Ma) is consistent with modelsof lithospheric stretching and magmatism at riftedmargins (Keen et al., 1994; Williamson et al., 1995).

Fission-track Data and Erosion RatesThrust fault timing, correlated with exhumation ofstrata and subsequent erosion in the Sverdrup Basin,is identifiable through the use of fission-track agedates. Fission-track data from the Depot Point L-24well yield a nearly constant age, ranging from 51 to59 Ma, for the top 1.5 km of strata. This indicatesrapid cooling and exhumation during the EarlyTertiary (Arne et al., 2002). Estimating from thelithologic column, approximately 5100 m of stratahave been eroded from the Depot Point L-24 column.Most of it was removed between 60 and 40 Ma duringthe period of most rapid erosion. Less than 1000 m ofrock was eroded thereafter, as basin inversion slowed.In the model, each period of erosion assumes a constanterosion rate. This is a highly simplified summary of theactual erosional history in the study area.

Sea LevelA palaeo- sea-level curve allows the weight of thewater column and the presence of water within thesediments to be considered in simulated processessuch as compaction. The sea-level data used are largelyqualitative and were compiled from Balkwill et al.(1983) and Embry (1991). The lithologies intersectedby the Depot Point L-24 well, and the eroded unitsprojected from nearby outcrop and well locations,provide clues about the depositional and erosionalenvironments as well as changing heat flow regime;thus they provide information about the local relativesea level. Balkwill et al. (1983) constructed a sea-level curve based on interpreted transgressive andregressive cycles in the Canadian Arctic Islands. Thisqualitative curve and the lithologies intersected by thewell were used to construct a general sea-level curvefor this part of Axel Heiberg Island (blue line, Fig. 7).Water depths were estimated to be fairly shallow dueto the nature of the basin, i.e. an intra-continental sea(e.g. Balkwill et al., 1983; Trettin, 1989). These inputparameters represent a highly simplified sea-levelmodel and due to the programme interface, singlenumerical values of 500 m, 250 m, 100 m and 0 mwere entered for basinal, slope, shelf and continentalenvironments, respectively.

Sediment-Water Interface TemperatureSimple data were used to derive the variations ofsediment-water interface temperature (SWIT) over

geological time. The results are illustrated in Fig. 7(green line). A present-day SWIT of 4°C is commonlyassumed at the bottom of northern oceans. Fossilforests on Axel Heiberg and Ellesmere Islands (Kuagaiet al., 1995; Greenwood and Basinger, 1994) andvertebrate fossils on Axel Heiberg Island (Tarduno etal., 1998) indicate an Eocene thermal high. SWITvalues of 20°C during the Eocene and 15°C duringthe Jurassic were used to reflect these generalizedclimate trends (Fig. 7). The actual surface temperaturenow is below 4°C, but that is far beyond the time rangerelevant to the topic of this paper.

Magmatic rocksSix sills based on the Depot Point L-24 stratigraphiclog (Fig. 6) were assumed to have been emplacedduring a single instantaneous event because no agedates were available. The age of intrusive rocks onAxel Heiberg Island is consistent with a widespreadAptian-Barremian event (128-132 Ma) alsodocumented in other areas of the Arctic. The age of125 Ma selected in this paper for the 1D numericalmodel is based on the ages of emplacement reportedby Villeneuve and Williamson (2006) for sills in theBuchanan Lake area (Figs 4, 5) and a dyke swarm onnorthern Axel Heiberg Island. It is possible that sillsintruded and lavas were emplaced in some of theeroded Mesozoic formations, but this cannot beestablished. Stratigraphic information summarized inFig. 3 shows that sills were preferentially intruded inshale-dominant lithologies, with some exception inthe sand-dominant Heiberg Formation. Finally, in allsimulations, we assumed that the magma temperaturecorresponds to the lower limit of basaltic melts uponextrusion (1000°C; Winter, 2001). Emplacementtemperatures for Antarctic sills of similar compositionhave been estimated to be 1100°C (Curtis and Riley,2003); therefore future revision of the model couldinclude modification to this parameter. It is expectedthat this type of modification would cause a slightincrease in the heat pulse due to sill emplacement;however, it would not change the overall modelresults.

ONE-DIMENSIONAL MODEL RESULTS

The simulation results for the Depot Point L-24column are presented here as plots and images of theburial history, thermal history and hydrocarbongeneration potential.

Burial HistoryThe burial history for the Depot Point L-24 column isillustrated in Fig. 8. Maximum burial occurred in theearly Tertiary and was followed by basin inversiondue to the Eurekan orogeny. The youngest strata were

247S. Jones et al.

eroded rapidly between 60 and 40 Ma; the Depot PointL-24 column is represented at the 0 Ma point by theunit thicknesses. The age of sill emplacement at 125Ma is marked with a black dashed line and the sillsare traced in bright red.

Thermal ProfileA temperature overlay in the top part of Fig. 9 showsthe thermal history of the lithological column at thesite of the Depot Point L-24 well. There is a markedtemperature increase at 125 Ma which represents thecombined effects of rifting and sill intrusion. Thegeothermal gradient changes at 125 Ma and heats thebasal strata, the Otto Fiord and Hare Fiord Formations,to near 500°C from previous temperatures of 175 to200°C. The bands of geothermal iso-temperature thensubside to deeper levels after the rifting and intrusion,and reach equilibrium by 0 Ma; this means that thetemperature pulses from rifting and sill emplacementhave dissipated.

The geologically instantaneous intrusion,combined with the rifting, presents a complex pictureat a small time scale. This is of course a simplification;however, a series of consecutive pulses within a brieftime interval would have a similar effect. The inset inthe top part of Fig. 9 (left) zooms in to the area out-lined by the white box to show the intrusion of severalsills as well as the temperature spike. The blue-greenarea shows the slower increase in temperature due tothe onset of rifting just prior to 125 Ma and sill

intrusion. The thin, vertical white line shows theexceeding of the maximum model-range temperatureof 500oC (in very close proximity to the intruding1000°C magma and off the scale) due to the sillintrusion, and in the red, orange and yellow coloursthe rapid decay of the increased temperature. Thiscooling period is indicated by the black arrow andthe increasingly lighter yellow zones. The sills have amagenta colour. The time axis on the inset covers onlyabout 5 million years. The black dashed box on themain image indicates where the rifting and intrusionshave an effect; the same area is shown in the lowerpart of Fig. 9 (A-D) with different scenarios asdiscussed below.

Upon rifting and sill emplacement, the BlaaMountain Formation, the best potential source rock,reached temperatures of 150-300°C, with the highertemperatures in rocks closer to the sills that intrudethe underlying Blind Fiord Formation. Prior to riftingand sill emplacement, the Blaa Mountain Formationwas at temperatures around 75-100°C. The sill contactzones were heated to significantly highertemperatures.

Hydrocarbon PotentialThe model results demonstrate that rifting and sillemplacement have profound effects on the thermalhistory of the Depot Point L-24 lithological columnand that oil and gas generation could have occurredin the strata intersected by the well. Fig. 10 shows a

Fig. 8. Burial history diagram for the Depot Point L-24 location includes Carboniferous to Cretaceousdeposition, sill emplacement and Tertiary basin inversion. The figure shows depth (vertical) versus geologicalhistory (horizontal) for the sediment column from circa 300 Ma until the present-day at the location of DepotPoint L-24 column. More rapid sedimentation shows as steeper sags and erosion as uplift; at 0 Ma the present-day sedimentary column is shown. The time scale is linear and ages are according to Harland et al. (1989)(small differences with more recent time scales are not relevant for this model). The vertical black dashedline shows the time of sill intrusion (125 Ma) and the sills themselves are traced in bright red.See Fig. 6 and Table 1 for a detailed description of the lithologies in the Depot Point L-24 well.


maturity-zone overlay onto the burial history plot. Theblue, green, red and yellow areas represent thermallyimmature, oil window, gas window, and over-maturezones, respectively. The oil and gas windows areinfluenced by the kinetic parameters and heat flowused. The temperature ranges for the oil and the gaswindows in the model are approximately 75-125°C and125-150°C, respectively. The temperature range givenfor the gas window is the optimal generation range; gasmay still be produced at temperatures above 150°C.

The striking feature in the maturity zone overlayis the jump of the maturity zones at the time of riftingand sill intrusion. The changes in temperature, and

thus the geothermal gradient, allow rock that wouldotherwise be immature, in particular the BlaaMountain Formation, to pass through the liquid-andgas-generating maturity zones and to producehydrocarbons. The deeper source rocks, the Hare Fiordand Van Hauen Formations, crossed the oil and gaswindows and went into over-mature zones at about220 Ma, prior to rifting and sill intrusion. We interpretthe results as indicating that the rifting and sillintrusion did not induce significant hydrocarbongeneration in the deepest source rocks. Shallow sourcerocks, for example the Awingak and RingnesFormations, are not heated highly enough for

Fig. 9. Temperature overlain on the burial history plot shown in Fig. 7. Main image shows there is a prominenttemperature spike at 125 Ma, the time of rifting and sill emplacement. The basal strata reach temperaturesaround 500°C. After rifting and sill intrusion, the spiked profile decays. The sills are the bold magenta lines.The white box outlines the area of the inset; the black dashed box traces changes in the temperature profiledue to the onset of rifting and is the area shown in (A)-(D) for various different scenarios. Insert: The greenand blue colours show the increase in temperature due to rifting. The very thin, white vertical line showswhere the rocks around the intruding sills were heated above 500ºC, and red to yellow colours show the rapidcooling thereafter.A. Rifting without sill intrusion: the temperature spike is wider and more subdued than in the original modelabove. The subsequent cooling trend is more gradual.B. Sill intrusion without rifting: the temperature spike is very sharp and decays rapidly.C. Rifting with sill emplacement at 110 Ma: this results in two temperature spikes -- the rounded rifting peakstarting at about 125 Ma, and the sharp sill intrusion spike at 110 Ma.D. Rifting with sill emplacement at 90 Ma: the sill intrusion produces a larger spike because the area hadcooled down more than in scenario (C).

249S. Jones et al.

hydrocarbon production; they remain thermallyimmature.

The model indicates that in the Hare FiordFormation, approximately 0.3 million tons of oil weregenerated between 245-220 Ma (Fig. 11, box A). Thegeneration of 0.6 million tons of gas is coeval with oilgeneration (not shown on Fig. 11). Rifting and sillemplacement occurred much later at 125 Ma; thus theydo not affect this hydrocarbon generation within theHare Fiord Formation. These quantities ofhydrocarbons produced directly reflect the model inputparameters. Therefore, the relative magnitudes of oiland gas for different formations should be comparedwith one another only to determine the most and leastproductive source rocks, and the numbers as suchshould not be quoted out of context. Hydrocarbongeneration in the younger Van Hauen Formation isvery similar to that in the Hare Fiord Formation.Approximately 0.3 million tons of oil and 0.6 milliontons of gas were generated between 240 and 210 Ma.

The Blaa Mountain Formation is at shallowerdepths than the Hare Fiord and Van Hauen Formations.Consequently, it remained at lower temperatures untilrifting and sill emplacement. Prior to 125 Ma, lessthan 0.8 million tons of oil (Fig 11, box A) and 0.2million tons of gas (Fig. 11, box B) were produced bythe Blaa Mountain Formation. Approximately 40million tons of oil were generated very rapidly at 125Ma (not shown on Fig. 11), and converted almostinstantaneously into 9 million tons of gas as a resultof rifting and sill emplacement. The white band on

Fig. 11 shows that the quantities are out of the legend(not computation) range; hence legend C and band Cwere inserted there to show this very rapid conversioninto gas. Oil generation ceased at about 124 Ma andgas generation does not occur after 123 Ma. The BlaaMountain Formation produced over one hundredtimes more oil and almost ten times more gas thanthe Hare Fiord and Van Hauen Formations.

SENSITIVITY STUDY

A single model has set ages for the intrusion. Toinvestigate the sensitivity of the petroleum generationto these ages, we explored the results of varying theparameters used in the modelling, in particular: sillintrusion, with or without the associated rifting event;magmatic versus amagmatic petroleum systems; andage of rifting event and sill emplacement. All theresults are illustrated on Figs 9 (A-D) and 10 (insetsA and B).

Rifting without sill intrusionWhen sills are omitted from the model, the thermalhistory changed significantly as shown in Fig. 9A.The temperature spike only represents rifting. Thegeometry of the temperature spike is rounded due tothe more gradual temperature effect of rifting. Thecooling and subsidence of geothermal isolines afterthe onset of rifting is more gradual than the rapiddecay after sill intrusion in the original model in theupper part of the figure. The temperatures reached

Fig. 10. Maturity overlain on the burial history (Fig. 7). The model shows thermally immature rocks in blueand over-mature rocks in yellow. The oil and gas windows are green and red, respectively.Main figure: a significant feature is the large, rapid jump in the position of the mature rock region due torifting and sill intrusion both at 125 Ma, as shown by the vertical dashed black line which qualitatively showsthe rate at which the Blaa Mountain Formation passes through the oil and gas windows. The sills aremagenta.Inset (A). Rifting at 125 Ma and sill intrusion at 122 Ma. The Blaa Mountain Formation is within the oilwindow for a short period of time. Intrusion of the sills initiates rapid gas generation. The slope of thedashed line is decreased.Inset (B). Rifting at 125 Ma with no intrusion of sills. The Blaa Mountain Formation resides within the oilwindow for about 5 Ma before entering the gas window. The slope of the dashed line is very gentle.


by the Blaa Mountain Formation are in the range 200-225°C, significantly lower values than the maximumtemperatures of 300oC in the model with the sills.Although the entire rock column is affected by rifting,the effects are more gradual than when rifting isaccompanied by sill intrusion.

A model in which rifting at 125 Ma is notaccompanied by sill emplacement predicts that theBlaa Mountain Formation will generate hydrocarbons,indicating that the thermal changes due to rifting aresufficient to induce hydrocarbon generation. However,there are some significant differences in thehydrocarbon generation profiles for a model thatincludes the emplacement of sills. Without sills, thethermal effects of rifting initiate oil generation.Approximately 40 million tons of oil are producedover a time period of 4 Ma, from 125 to 121 Ma. TheBlaa Mountain Formation then enters into the gaswindow and produces about 9 million tons of gas.Not all of the oil is converted into gas; much of itremains as a residuum. The gas then diffuses awayfrom the source rock.

Sill intrusion not accompanied by riftingFig. 9B shows a version of the model with intrudedsills but without a rifting event. This results in a sharptemperature spike which decays relatively quickly. Theentire lithologic column is not heated evenly. The

strata closest to the sills are heated to significantlyhigher temperatures than the strata further away, wherethe temperature increase is almost negligible. Acomparison of Figs 9A and B shows rifting isresponsible for heating the entire lithologic column.Rifting also produces a long-term change in thegeothermal gradient, and thus the thermal profile ofthe region. Sill emplacement exhibits more localizedeffects, which decay quickly after intrusion.

Age of Sill EmplacementFigs 9C and D show temperature overlays from twomodels which illustrate the effects of changing theage of sill emplacement to 90 Ma and 110 Ma,respectively. Both models show the development oftwo temperature spikes — the first represents riftingand the second the sill intrusion. The riftingtemperature spike is rounded with gradual subsidence,and the sill intrusion peak is abrupt with a more rapidonset of decay. The difference between the modelsshown in Figs 9C and D is the time lapse betweenrifting and intrusion: they are otherwise identical.Where sills intrude at 90 Ma, a longer time lapse existsbetween the two temperature spikes than in the modelwith a sill emplacement at 110 Ma. The longer timelapse allows the effects of rifting to decay over a longerperiod of time and to a lower value before the sills areintruded.

Fig. 11. Oil and gas production overlain on the burial history. (Note: the quantities of hydrocarbons directlyreflect the model input parameters and the numbers should not therefore be quoted out of context).Main image (A) (with legends A and B): The Hare Fiord and Van Hauen Formations generate small quantities(about 0.3 million tons) of oil between 245-220 Ma and 240-210 Ma, respectively. This was rapidly convertedinto about 0.6 million tons of gas each (not shown). The Blaa Mountain Formation generated less than1million tons of oil between 165 and 125 Ma. The white box (B) shows that less than 0.2 million tons of gas wasproduced during that time. At 125 Ma, the Blaa Mountain Formation rapidly produces approximately 40million tons of oil due to the heat introduced by rifting and sill emplacement. This is several orders ofmagnitude above the legend (A) and results in a white band. Inserted in the white is band (C), correspondingto legend (C), which shows that the Blaa Mountain Formation subsequently rapidly produced approximately9 million tons of gas. The constant colour after 122 Ma indicates the total amount of gas produced thereafter.The sills are in magenta colour.

251S. Jones et al.

Varying the age of sill emplacement has an effecton the positions of the maturity zones. When sills areintruded at 90 Ma or 110 Ma, they do not affecthydrocarbon generation in this model. This is becausethe rifting at 125 Ma caused the Blaa MountainFormation to generate oil and gas millions of yearsprior to sill emplacement. When the age of sillemplacement is closer to the age of rifting, there arevisible effects in the model results. The Blaa MountainFormation begins to generate oil at 125 Ma, duringrifting. Upon sill intrusion, the oil generated cracksto gas, as shown in the maturity zone plots in the mainpanel in Fig.10.

Magmatic versus amagmatic petroleum systemFig. 10 compares maturity zone overlays for the DepotPoint L-24 models with sill intrusion and without sillintrusion. The main panel shows the maturity zonesfor the model with sills and rifting. There is a sharpjump in the positions of the zones upon rifting andsill intrusion. The Blaa Mountain Formation passesquickly through the oil and gas windows as shown bythe vertical, black, dashed line. Inset (B) shows thematurity zone plot for the model without sills. Notethat the Blaa Mountain spends a longer period of timein the oil and gas windows before passing into theovermature zone, and the dashed line is much lesssteep. An intermediate case is shown by Inset (A),where the sills intrude at 122 Ma. The jump in maturityzones is less pronounced than in the main panel, butmore so than in Inset (B); hence, the slope of thedashed line is intermediate between those two cases.The “with and without sills” models both produceapproximately 9 million tons of natural gas. The sillsdo not change the total amount of gas produced, butthey do strongly affect the rate at which the BlaaMountain Formation passes through the variousmaturity zones. In the simulation with sill intrusion,gas is rapidly generated; in the model without sillintrusion, the Blaa Mountain Formation generates oil,which then cracks to gas over a longer period of time,about 4 Ma.

The Sverdrup Basin is clearly a volcanic basin.This implies that these different scenarios existelsewhere in the basin, and may also explain thepredominance of natural gas plays within the basin.However, future work should include a more detailedsensitivity study to explore the effects of varying theheat flow values and the thicknesses of erodedlithologic units. Changing the position of the sourcerocks relative to the sills and to the surface changesthe potential for oil and gas production. The closeproximity of the Blaa Mountain Formation to sillsintruding the underlying Blind Fiord Formation allowsthe Blaa Mountain Formation to be affected stronglyby sill emplacement. The sediment-water interface

temperature and sea level appear to have a minimalinfluence on the model results.

DISCUSSION

The questions defining the scientific objectives of thisstudy were listed in the Introduction:

1. How can key observations on the hydrocarbon andmagmatic systems in the Sverdrup Basin beintegrated?Hydrocarbon generation requires source rocks to beheated into the oil or gas windows. In subsidingsedimentary basins, the thermal profile is a functionof conductivity and heat flow values. Because of thegeothermal gradient, deeper rocks reach highertemperatures than those closer to the surface (Hunt,1996). As a result, hydrocarbon generation dependson temperature, i.e. changes in the thermal conditionswithin the basin will affect the potential for oil andgas generation and/or under- or over-maturation(Archer et al., 2005). Thermal profiles for basinscontaining a significant volume of igneous rocks areaffected additionally by heat introduced by intrusiveand extrusive igneous rocks (e.g. Schutter, 2003;Malthe-Sørenssen et al., 2004). The Karoo Basin ofSouth Africa is a case in point (Svensen and Planke,2003). Some wells drilled in the Karoo Basin haveintersected source rocks which produced petroleumfollowing the emplacement of sill complexes. Contactaureoles around intrusive bodies show thedevelopment of fractured hornfels units which locallyact as aquifers. The fractured hornfels has reservoirpotential. Although flood basalts were erupted in theKaroo Basin, there was very little effect on thehydrocarbon system because of rapid cooling ofsubaerial lava flows. As in the case of the SverdrupBasin, intrusive sheets and dykes had a greater effecton the surrounding strata because the excess heat ofintruded magma is transferred efficiently to adjacentrocks during the cooling process (Schutter, 2003;Archer et al., 2005).

The contact aureoles of metamorphosed rockdocumented in the Depot Point L-24 well are causedby sill intrusion. Although the aureoles are notextensive, the heat generated by the intrusion willaffect kerogens or hydrocarbons well beyond thebaked contact with host sediments (e.g. Svensen etal., 2004). The distance of sills to source rocks andreservoirs is a critical factor because the thermalgradient decreases exponentially away from thesource; this is further complicated if magmatism isaccompanied by hydrothermal circulation (Schutter,2003). The effects of intruding igneous rocks musttherefore be considered in predictive models of oil andgas generation and potential in the Sverdrup Basin.


2. How and where in the evolution of the SverdrupBasin does sill emplacement affect the hydrocarbonsystem?Field observations (e.g. Fig. 4) indicate that the contactzones at chilled sill margins rarely exceeds a thicknessof one metre, and that the metamorphism is a localeffect. The contact-metamorphic zones form at veryhigh temperatures, as they are adjacent to the 1000-1200oC intruding magma. Oil and gas generationoccur at temperatures of 100-120oC and therefore donot correlate with the highly visible mineral reactions.However, the density of sill intrusion in the Mesozoicsuccession of the Sverdrup Basin (Fig. 3) suggeststhat there is likely to be a regional impact on thethermal profile. In the 1D model, the intrusion of sixsills at 1000ºC into the Depot Point L-24 columncauses significant changes in the thermal profile.There is a temperature spike at 125 Ma, related torifting and sill intrusion; this spike decays over time.The combined temperature spike affects the entire rockcolumn, not just the strata that contact the sills, and itheats the Blaa Mountain Formation, a potential sourcerock, to temperatures between 150 and 300ºC.

The geothermal gradient predicted from the burialhistory heated the deepest source rocks totemperatures well above the oil and gas maturity zones(Hare Fiord and Van Hauen Formations; Fig. 10 and11). Rifting and sill intrusion occur almost 100 Maafter hydrocarbon generation ceased in bothformations, and thus did not affect the hydrocarbonsproduced by these formations. The Blaa MountainFormation, a shallower source rock, undergoes itsmain phase of hydrocarbon generation at 125 Ma, atthe time of minor renewed rifting and sill intrusion inthe eastern Sverdrup Basin (Stephenson et al., 1987;Villeneuve and Williamson, 2006). The sensitivitystudy shows that the changes in the thermal profile ofthe Depot Point L-24 column due to rifting aloneinitiate oil generation and later gas generation in theBlaa Mountain Formation. The emplacement of sillsincreases hydrocarbon generation rates in the BlaaMountain Formation and promotes the generation ofgas rather than oil. By 0 Ma, the heat spike hassubsided and the geothermal gradient has decayed tolevels expected prior to rifting and sill emplacement.

3. How do the results obtained in the numerical modelvary when sills are not introduced in the stratigraphiccolumn, or when the age of sill emplacement isdifferent?The heat spike in the original Depot Point L-24 modelrepresents the combined effects of minor renewedrifting and sill emplacement late in the history of theSverdrup Basin. The entire lithologic column isaffected rather than just the host rocks in contact withthe intrusions. When the sills are omitted from the

model, the rifting temperature spike is isolated. Thechanges in this thermal profile cause slower oilgeneration in the Blaa Mountain Formation, and gasgeneration begins after about 4 Ma.

Varying the age of sill emplacement separates thethermal effects of rifting from the thermal effects ofigneous intrusion, resulting in two temperature spikes(Fig. 9). The intrusion of sills causes rapid gasgeneration in the Blaa Mountain Formation. If therifting and sill intrusion are coeval, as in the originalDepot Point L-24 model, the Blaa MountainFormation has increased hydrocarbon generation rates.If the sills are introduced shortly after rifting, the BlaaMountain Formation begins producing oil, and at thetime of sill intrusion begins rapid gas generation.Overall, the emplacement of sills increases thehydrocarbon generation rates in the Blaa MountainFormation, and promotes the production of naturalgas rather than oil. The quantity of gas produced bythe Blaa Mountain Formation is consistent for all ofthe Depot Point L-24 model variations, about 9 milliontons. The hydrocarbon generation histories differ ineach of the model variations. The Blaa MountainFormation spends different amounts of time in the oiland gas windows in each of the models, but the endvolumes are similar.

The heat flow values and the eroded stratigraphicsuccession are expected to have a significant influenceon the thermal history of the Depot Point L-24 lithologiccolumn and will be the subject of future work.

4. Can the modelling of the effects of igneousactivity on the hydrocarbon system be extrapolatedto other parts of the Sverdrup Basin, and to otherArctic basins?The numerical modelling process applied in this studydoes not provide a unique quantitative solution to thescientific questions listed in the introduction. Althoughthe model results provide the user with a range ofscenarios, these numbers reflect the input parametersselected for one-dimensional analysis. A morecomprehensive study could use the same approach andtest varying model input parameters within appropriateranges of values. The construction of the one-dimensional model allows the user (i) to explore thelimitations and knowledge gaps associated with thesimulation; and (ii) to compare the effect of differentdata sets such as heat flow and time-temperaturemodels from fission-track analysis, and in the future,from (U-Th)/He dating. Limitations are due to thecurrent lack of reliable data sets. For example, thevitrinite reflectance values used as model input arenot well defined and there are no Rock-Eval dataavailable for the Depot Point L-24 well. Overall, theapplication of a 1D modelling approach to the DepotPoint L-24 lithologic column results in a set of robust

253S. Jones et al.

qualitative observations on the thermal processes andinteractions that affect the petroleum system on AxelHeiberg Island, and provides a frame of reference foradditional modelling of wells in the central andwestern Sverdrup Basin. Comparative studies of theMesozoic successions in the Canadian ArcticArchipelago, Svalbard and the Barents Sea haveestablished important similarities between theseonshore and offshore basins (Leith et al., 1993;Beauchamp and Mayr, 1997). Further applications ofthe model in 2D and 3D on a regional scale wouldyield semi-quantitative results, and allow acomparative study of the impact of sills on thepetroleum system of Circum-Arctic and northernAtlantic volcanic basins.

CONCLUSIONS

We present the results of 1D numerical modelling thatexplores the effects of rifting and magmatic eventson the thermal history and petroleum generation atthe Depot Point L-24 well near Eureka Sound, AxelHeiberg Island (79o23’40”N, 85o44’22”W). Themodelling study represents the first investigation ofthe potential interaction between the petroleum systemand igneous intrusions in the eastern Sverdrup Basin,Canadian Arctic Archipelago. The thermal history wasconstrained using vitrinite reflectance and fission-track data, and knowledge of the tectonic history. Thesimulation identifies the time intervals during whichhydrocarbons were generated, and illustrates theinterplay between hydrocarbon production andigneous activity associated with renewed rifting andthe widespread intrusion of sills in the easternSverdrup Basin during the Early Cretaceous. Thecomparison of the petroleum and magmatic systemsin the context of previously proposed models of basinsubsidence and renewed tectonism during the lateMesozoic was an essential step in the interpretationof results for the Depot Point L-24 well.

The model results show that rifting and sillintrusion occur after hydrocarbon generation ceasedin the Hare Fiord (~7900-8200 m depth at 125 Ma)and Van Hauen (~7200-7900 m depth at 125 Ma)Formations; thus, rifting and sill emplacement willnot affect the generation potential of these deeperformations in the Sverdrup Basin. In the case ofshallower source rocks such as the Blaa MountainFormation (3000-4400 m depth at 125 Ma), rapidgeneration of natural gas occurred at 125 Ma, duringthe time of rifting and sill intrusion. A sensitivity studyinvolving variations in the timing of sill intrusion andrifting shows that the emplacement of sills increasedhydrocarbon generation rates in the Blaa MountainFormation and facilitated the production of gas ratherthan oil.

We conclude that the application of a one-dimensional model to the Depot Point L-24 lithologiccolumn results in a set of robust qualitativeobservations that describe the thermal processesaffecting hydrocarbon plays on Axel Heiberg Islandduring the Early Cretaceous. The study provides aframe of reference for petroleum studies in other partsof the Sverdrup Basin and in Circum-Arctic volcanicbasins of Mesozoic age targeted for exploration.

ACKNOWLEDGEMENTS

The first author wishes to thank scientists andtechnical support staff at the Geological Survey ofCanada, Bedford Institute of Oceanography, for theirsupport in 2005-2006, particularly Gordon Oakey,Frank Thomas and staff at the BIO Library; andmembers of the faculty and technical staff at DalhousieUniversity and Saint Mary’s University whoinfluenced the direction and quality of this study:Grant Wach, Andrew MacRae, Patrick Ryall andGordon Brown. We thank Tom Brent, ChristopherHarrison and Keith Dewing, GSC Calgary, for accessto unpublished map and well data for Axel HeibergIsland; and Wolf Rottke and Thomas Leythaeuser(Integrated Exploration Systems), for their feedbackand generous technical support during research withPetroMod. The authors are grateful to StevenBergman, Nicolai Lopatin, Patrick Potter and JohnShimeld for their thorough reviews of the manuscript.

This project was funded through a NaturalSciences and Engineering Research Council ofCanada (NSERC) Undergraduate Student ResearchAward, 2005; and a Natural Resources Canada, EarthSciences Sector, project: New Energy Options forNortherners (NEON). The project was completedunder the umbrella of NSERC and PetroleumResearch Atlantic Canada (PRAC) CRD grant CRDPJ305606 – 03 to MZ; and benefited from field supportto M-C.W and MZ provided by the Polar ContinentalShelf Project and Nunavut Research Institute.

This is a Geological Survey of Canada contributioncarried out as a collaborative project between GSCAtlantic and the Department of Earth Sciences atDalhousie University, Halifax, Canada.

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IMPACT OF MAGMATISM ON PETROLEUM SYSTEMS IN THE SVERDRUP BASIN, CANADIAN ARCTIC ISLANDS, NUNAVUT: A NUMERICAL MODELLING STUDY