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The post-Caledonian development of Svalbard andthe western Barents SeaDavid Worsley

Færgestadveien 11, NO-3475 Sætre, Norway

Abstract

The Barents Shelf, stretching from the Arctic Ocean to the coasts of northernNorway and Russia, and from the Norwegian–Greenland Sea to NovayaZemlya, covers two major geological provinces. This review concentrates onthe western province, with its complex mosaic of basins and platforms. Agrowing net of coverage by seismic data, almost 70 deep hydrocarbon explo-ration wells and a series of shallow coring programmes, have contributedgreatly to our understanding of this province, supplementing information fromneighbouring land areas. The late Paleozoic to present-day development of theregion can be described in terms of five major depositional phases. These partlyreflect the continuing northwards movement of this segment of the Eurasianplate from the equatorial zone in the mid-Devonian–early Carboniferous up toits present-day High Arctic latitudes, resulting in significant climatic changesthrough time. Important controls on sedimentation have involved varyingtectonic processes along the eastern, northern and western margins of theshelf, whereas short- and long-term local and regional sea-level variationshave further determined the depositional history of the province.

KeywordsBarents Sea; climatic change; geological

development; plate movement; Svalbard.

CorrespondenceDavid Worsley, Færgestadveien 11, NO-3475

Sætre, Norway. E-mail: [email protected]

doi:10.1111/j.1751-8369.2008.00085.x

The position of the Barents Shelf on the north-westerncorner of the Eurasian plate makes it a testing ground fora better understanding of the geological developmentof Europe, and of the entire Arctic Ocean. The shelf,covering an area of approximately 1.3 million km2, issurrounded by onland exposures with widely varyinggeology. Only a synthesis of these, together with availableknowledge of the subsurface of the shelf itself, can help usunderstand the geological development of this vastprovince, with its prognosed enormous—but as yet littleexplored and developed—petroleum potential (Fig. 1).

The Svalbard Archipelago, forming the subaeriallyexposed north-western margins of the shelf, covers a landarea of only 63 000 km2, which is less than 5% of thetotal area of the Barents Sea, but which displays a com-prehensive overview of the geology of the entire region(Steel & Worsley 1984; Worsley et al. 1986; Harland1997). Svalbard’s position immediately south of thepolar Euramerican Basin, and east of the Norwegian–Greenland Sea, puts it in a critical position to allow us torecognize many of the main features controlling thedevelopment of the western Barents Shelf. The generalplatform aspect of the archipelago makes it not entirelyrepresentative of areas further south, but many charac-

teristic features are highly relevant for understandingthe entire subsurface of the south-western shelf (Nøttvedtet al. 1993). Northern Norway, with its basement andLower Paleozoic outcrops, represents the northernmostpart of the Baltic Shield, with rocks affected by latePrecambrian and Caledonide orogenies (Ramberg et al.2008). This cratonic area was only occasionally onlappedduring the late Paleozoic and Mesozoic, but its erosionalproducts were important contributors to clastic UpperPaleozoic and Mesozoic hydrocarbon reservoirs on thesouth-western shelf.

Timan–Pechora to the south-east, with its foredeepsand inversion zones immediately adjacent to the develop-ing Uralides in the late Paleozoic, shows a varied geologywith many features of great relevance for eastern shelfareas (Ulmishek 1985). Novaya Zemlya is dominated byPermo-Carboniferous exposures in a complex facies array,perhaps reflecting the development of the archipelago as acomponent of the Ural–Taimyr orogeny, prior to Triassicwestwards-directed thrusting and emplacement into itspresent position (Otto & Bailey 1995; Sobolev & Nakrem1996). Franz Josef Land, with its exposures of Mesozoicsediments and volcanics, shows a development similar tothat of the north-eastern Svalbard Platform (Solheim

Polar Research 27 2008 298–317 © 2008 The Author298

mailto:[email protected]

et al. 1998), with the volcanism in both areas being closelyconnected with the opening of the polar EuramericanBasin during the Mesozoic.

The offshore Barents Shelf itself comprises two majorand highly disparate provinces (Fig. 2), with a north–south trending, generally monoclinal structure separatingeastern from western regions: this transition correspondsroughly with the politically disputed area betweenNorway and Russia. The eastern region, with its massive

South and North Barents basins, shows a developmentclosely linked to that of the Uralides, Timan–Pechora andNovaya Zemlya. The western province, the focus of thisreview, shows a much more complex tectonic deve-lopment (Faleide et al. 1984; Gabrielsen et al. 1990;Gudlaugsson et al. 1998). The mosaic of basins, platformsand structural highs in this area reflect the interplaythrough time between major tectonic processes along thewestern and north-western margins of the Eurasian plate.

Fig. 1 Land areas surrounding the Barents Sea have widely varying geologies (Mørk 1999). Map compiled by M.B.E. Mørk (see references in Mørk 1999).

Post-Caledonian Svalbard–Barents SeaD. Worsley

Polar Research 27 2008 298–317 © 2008 The Author 299

Changing tectonic and climatic controls onsedimentation: basement

Precambrian–Lower Paleozoic basement rocks of Sval-bard consist of sediments, metasediments and igneousrocks, ranging in age from the Riphean (1275 Mya) tothe Silurian. The entire succession has a maximumaggregate thickness of around 20 km, and has beenassigned to 20 different lithostratigraphical groups, col-lectively referred to as “Hecla Hoek”. This complexity inpart reflects the many nations and stratigraphical phi-losophies involved in the research, but also the geologicalreality that there are a wide variety of rocks and succes-sions exposed, grouped generally into three terranes. Thenorth-eastern terrane comprises Precambrian igneousand predominantly sedimentary rocks, including latePrecambrian glacial clastics and carbonates, and alsoLower Paleozoic sediments: all with clear affinities toexposures in north-east Greenland. The north-westernprovince is characterized by deep crustal metamorphics,including gneiss, migmatite and eclogite, whereas thesouth-western terrane is a complex mix of metasedi-ments, typical of subduction-zone environments.

Although the relationship between Svalbard andnorthern Norway during the main phase of Caledonian

movements in the Silurian is still uncertain, manyworkers now believe the hypothesis first suggested bythe late Brian Harland, and his Cambridge Arctic ShelfProgramme (CASP) co-workers (e.g., Harland & Wright1979; Harland 1997), that Svalbard’s basement com-prises three structural provinces that were broughttogether by large-scale lateral movements during thismain orogenic phase. A several-kilometre-thick succes-sion of post-orogenic “Old Red” facies sediments of lateSilurian to early Devonian age is essentially confined toa major graben on northern Spitsbergen, and suchsediments have not been identified elsewhere in thesubsurface of the western shelf. The shift from red togrey sediments around the early to mid-Devonian tran-sition is noteworthy, and indicates the transition fromthe southern arid zone to the equatorial tropics. Spits-bergen itself then saw a final phase of Caledoniandeformation in the late Devonian—the so-called Sval-bardian movements, which are correlative with theEllesmerian orogeny of Arctic Canada. CASP workers(e.g., Friend & Moody Stuart 1972) originally suggestedthat this phase also involved extensive lateral move-ments on the scale of 200 km, finally bringing togetherthe elements of the present archipelago into theirpresent position. However, this is now regarded as an

Fig. 2 Major structural elements of the Barents Sea.

Post-Caledonian Svalbard–Barents Sea D. Worsley


essentially compressive tectonic event, with little or nosignificant lateral movement.

Post-Svalbardian succession

The post-Svalbardian evolution of the archipelago—andof the southwestern Barents Sea—is summarized here interms of five main depositional phases, extending fromthe late Devonian to the Neogene, each demonstratedherein by palaeogeographical summary maps displayingessential features of the varying sedimentational regimes.The stratigraphical nomenclature used herein is basedon that of Worsley et al. (1988), Dallmann (1999) andLarssen et al. (2005) for Svalbard and the south-westernBarents Shelf.

These depositional phases partly reflect the continuingnorthwards movement of this segment of the Eurasianplate: Svalbard has moved from the equatorial zone in themiddle Devonian–early Carboniferous up to its present-day High Arctic latitudes, resulting in significant climaticchanges through time. Important tectonic controls onsedimentation have been imposed by the ongoing inter-play of varying processes along the shelf margins—firstbetween the compressive Uralide development to the eastand proto-Atlantic rifting in the west, and then by theopening of the polar Euramerican Basin to the north,and finally by transpression, transtension and the finalopening of the Norwegian–Greenland Sea along thewestern margins of the shelf. Both short- and long-termlocal and regional sea-level variations have further definedthe sequence development within this general framework.

The late Devonian to mid-Permian was characterizedfirst by widespread intracratonic rifting, following thelate Caledonian Svalbardian compressive movements,and then by the development of an immense post-riftcarbonate platform, stretching westwards to present-dayAlaska. Several large-scale basins—including the Nord-kapp Basin of the south-western Barents Shelf and theSverdrup Basin of Arctic Canada—developed along deep-seated sutures, and were the depositional sites of several-kilometre-thick evaporitic sequences, whereas thinnersabkha deposits and warm-water carbonates formed onthe intervening platform areas. A series of western highs,including the Stappen, Loppa and Sørkapp–Hornsundhighs, were tectonically active, and show a complexdevelopment. The mid-Permian saw a cessation ofevaporitic deposition, a shift first to cool-water carbonatesand then to clastic and organoclastic deposition, and anaccompanying general decrease in tectonic activity alongthe western margins. The entire Barents Shelf was thenmarked by a regional and deep-seated response to theUralide orogeny—reflected by greatly increased sub-sidence rates, especially in the eastern Barents basins.

Subsidence rates waned throughout the Triassic, andfollowing major deltaic progradations from severalprovenance areas, the late Triassic to mid-Jurassic saw astabilization of the entire area, with consequently rapidlydecreasing sedimentation rates, as extensional tectonismin the mid–late Jurassic established the major platformand basin pattern that we see today. The Jurassic–Cretaceous regional development, mostly dominated byfine clastic deposition, otherwise largely reflects thedevelopment of the polar Euramerican Basin on thenorthern margins of the shelf. Widespread magmatismalong the northern shelf margin was accompanied by ageneral northerly uplift, prior to break-up and oceanicdevelopment—although there is still considerable contro-versy as to how the Euramerican Basin actuallydeveloped. The area had steadily moved northwardsthrough temperate latitudes during the Mesozoic,approaching 60°N in the early Cretaceous. The latestCretaceous and Paleogene were dominated by changingtranspressive and transtensional regimes along thewestern plate suture, before the Eocene/Oligocenebreak-up and opening of the Norwegian–Greenland Sea.This was followed by the Neogene deposition of thickclastic wedges shed from the newly formed western shelfmargins, as a response to large-scale depression and upliftof the hinterland, related to repeated phases of glaciationand deglaciation of the shelf itself from the ?Mioceneonwards.

These five late Paleozoic–Neogene sedimentationalregimes will now be described in some more detail, eachdemonstrated by palaeogeographical sketch maps display-ing the essential features of the development of the area.

Late Devonian–mid-Permian: evolutionof a carbonate platform

The south-western Barents Shelf formed a central part ofthe northern Pangean margin from the latest Devonianonwards. The definition of three lithostratigraphic groups(Fig. 3) reflects periods with distinct depositional regimes,punctuated by abrupt changes in tectonic and climaticconditions, and in relative sea level, with the latter result-ing both from Gondwanan glaciation and deglaciation,and from changing subsidence rates related to thedevelopment of the Uralide orogen (Stemmerik &Worsley 1995, 2005). Deposition of the predominantlynon-marine tropical humid clastics of the BillefjordenGroup started in the late Famennian to Viséan, continu-ing to the Serpukhovian. Regional uplift, and thesubsequent rifting in a series of local half-grabens, wasaccompanied by a climatic shift to arid conditions, fol-lowed by an ongoing regional sea-level rise. The resultingsediments of the Gipsdalen Group were first dominated



by clastics shed from faulted graben margins. Increasingtectonic quiescence and ongoing sea-level rises throughthe late Carboniferous then led to most of the shelfbecoming a warm-water carbonate platform, with abun-dant organic build-ups and the intermittent deposition ofsabkha evaporites at times of lowstand. The deep evapor-itic Nordkapp Basin developed at this time, and may haveformed an immense isolated salina during such lowstandperiods (as is also thought to be the case in the even largerCanadian Sverdrup Basin). A radical change in watertemperature and depth seems to have occurred aroundthe mid-Sakmarian, resulting in the deposition of thecool-water carbonates of the Bjarmeland Group, espe-cially in and around the subsiding margins of theNordkapp Basin. The late Permian was characterized byeven cooler water conditions, with deposition of siliceousshales.

Latest Devonian–Early Carboniferous:the Billefjorden Group

The Famennian to lower Serpukhovian BillefjordenGroup consists mostly of fluvial and lacustrine sedi-

ments deposited in humid and warm terrestrialenvironments over the western Barents Shelf (Fig. 4).Marine influence is only seen uppermost in the groupon the south-eastern Finnmark Platform, probablyreflecting the existence of a seaway through theNordkapp Basin that connected to the more openmarine environments known to prevail on the easternBarents Shelf at the time. The oldest deposits are onlyknown from isolated half-grabens on Bjørnøya andSpitsbergen: more widespread deposition started in theViséan, with the development of a large, humidhinterland that passed eastwards into shallow marineenvironments. Half-graben development continued tocharacterize the western shelf margins. The sedimentfill of these grabens shows a generally coarsening-upwards trend, from meandering river sandstones andfloodplain fines, into braided stream and alluvial fansandstones, and conglomerates. The Finnmark Platformalso shows an eastwards transition from continental todeltaic and shallow marine deposits (Bugge et al. 1995),passing into the fully marine environments of theeastern shelf, as displayed in Timan–Pechora andNovaya Zemlya.

Fig. 3 Upper Paleozoic sequences of the Norwegian Barents Shelf (modified from Larssen et al. 2005).



Thicknesses of around 400–600 m on the FinnmarkPlatform contrast with cumulative thicknesses of up to2500 m in the type area of the Billefjorden Trough, incentral Spitsbergen, whereas a composite thickness of600 m is preserved in the half-graben covering Bjørnøyaon the Stappen High, midway between northern Norwayand Spitsbergen (Worsley et al. 2001): the fluvial depositson Bjørnøya were clearly transported north-eastwardsalong the graben axis, probably towards a depocentreunder the present-day Sørkapp Basin.

Mid-Carboniferous–mid-Permian: the Gipsdalen andBjarmeland Groups

The mid-Carboniferous–lower Permian Gipsdalen Groupis dominated by shallow marine carbonates, sabkhaevaporites and local siliciclastics on the extensive plat-form areas of the shelf, whereas isolated deep and largebasins were the sites of halite deposition during most ofthis phase. The sediments of the group were deposited ina warm and arid climate, during a period characterized byfrequent sea-level fluctuations, reflecting the varyingphases of the contemporaneous Gondwanan glaciation.

Deposition of non-marine red beds commenced aroundthe Serpukhovian/Bashkirian transition in locally reacti-vated half-grabens following regional mid-Serpukhovian

uplift (Gjelberg & Steel 1981, 1983; Johannessen & Steel1992; Worsley et al. 2001). The red beds passed up intomarine carbonates in the mid-Bashkirian, and ongoingtransgression led to the submersion of the surroundingplatforms and local highs, during the Moscovian andGzhelian, although the Loppa, Stappen and Sørkapp–Hornsund highs in particular were to continue to betectonically active until the mid-Permian. The uncon-formable contact between the Billefjorden and Gipsdalengroups reflects major regional uplift, accompanied by arelatively abrupt climatic shift from humid to warm butarid regimes (Fig. 5). This uplift was followed by renewedrifting in pre-existing half-grabens, and also by the devel-opment and subsidence of the much larger Nordkapp andTromsø basins. The ensuing late Carboniferous regionalsea-level rise occurred in a global ice-house situation,and the Moscovian–Asselian platform was characterizedby shallow-water carbonate deposition at times of highglacioeustatic sea levels, whereas sabkhas and evensubaerially formed karsts and fossil soils developed attimes of lowstand (Fig. 6). Only limited quantities ofsiliciclastics were deposited locally immediately adjacentto isolated highs, which themselves gradually becametectonically quiescent. The resultant rhythmic parase-quences reflect these high-frequency and -amplitudesea-level variations: outer shelf areas are characterized by

Fig. 4 Palaeogeographic sketch map showing Late Devonian–Early Carboniferous depositional environments.



algal-, fusulinid- and sometimes crinoid-rich wackestonesand packstones, between subaerial exposure surfaces,whereas more grainstones occur updip, interbedded withpalaeoaplysinid/phylloid algal build-ups and associatedlagoonal deposits. Frequent exposure led to extensivedolomitization and karstification, with accompanyingkarst collapse and breccia formation, whereas freshwaterflushing led to the early formation of secondary porosity.The entire group shows significant preserved thicknessvariations from 0 to 600 m on platforms and highs, andup to 1800 m in the Billefjorden Trough of central Spits-bergen; only small (<10-m-thick) organic build-ups areobserved onland, draping the graben margins. Offshore,this sequence can be up to 1500 m thick, and build-upsthat developed on ramps adjacent to highs can reach acomposite thickness of several hundred metres.

The base of the mid-Sakmarian–upper ArtinskianBjarmeland Group is marked by a major flooding event,which coincided with a significant shift from shallowwarm waters to the more temperate conditions thatdetermined the cool water biotic composition of thecarbonates of this group. This transgressive event marksthe end of the high-frequency rhythms of the GipsdalenGroup, and the transgression itself was probably relatedto the final waning and disappearance of the Gondwananice cap. The abrupt change in depositional regimes wasprobably also related to changes in circulation in theBoreal Ocean as a result of the closing of the seaway toTethys, along the developing Uralide suture zone. Thegroup is best developed along major basinal margins, andongoing transgression flooded most areas by the Artin-skian: large Tubiphytes/bryozoan build-ups developed,all with pervasive early diagenetic marine calcite cement.The group is much thinner or absent over inner platformsand structural highs (e.g., Spitsbergen and the southern

Finnmark Platform). In these areas there was reneweduplift during the Sakmarian/Artinskian, again leading tokarstification and freshwater flushing of the underlyingcarbonates. The deep basinal development of the Bjarme-land Group is still uncertain.

Late Permian–middle Triassic: from carbonatesto clastics

The Kungurian saw a shift to the deposition of cold- anddeep-water fine clastics and silica-rich spiculites, influ-enced by the development of the Uralides and theopening of intracratonic seaways along the western shelfmargins. The early Triassic was dominated by the depo-sition of non-siliceous shales and mudstones that contraststrongly with the underlying siliceous units. Although theupper Permian Tempelfjorden Group and the lower tomid-Triassic Sassendalen Group show strikingly differentlithologies and faunas, both contain shales that are locallyrich in organic matter: the Botneheia/Kobbe formationsof western areas deposited during the Anisian/Ladinianare particularly organic-rich, and constitute importanthydrocarbon source rocks.

Latest Permian: the Tempelfjorden Group

The middle–upper Permian (Kungurian–Capitanian/?Wuchiapingian) Tempelfjorden Group overlies asignificant subaerial exposure surface on platform areas(Fig. 7), where there was significant renewed flooding,whereas basins and basin margins show abrupt deepen-ing, with a significant shift to cool- and deep-waterspiculitic shale deposition. Interbedded minor units ofsandstone and limestone are associated with local highsand platform margins (Fig. 8). The limestones showdistinctive and spectacular assemblages of bryozoans,together with spiriferid and productid brachiopods. Thisdramatic depositional change, from the carbonate envi-ronments that had prevailed for almost 40 million years,reflects the development of the Urals and the closure ofseaway connections to the warm waters of Tethys. Majorplate reorganization resulted in greatly increased subsid-ence rates in the region, whereas intracratonic seawaysdeveloped along the western shelf margins, connectingthe Boreal Realm to the central European ZechsteinBasin.

The distinctive spiculites of the group, rich in biogenicsilica, are found throughout the northern Pangean shelfmargins. In the Sverdrup Basin they have been ascribedto the development of extremely cold water conditions,much colder than would normally be expected fromthe relevant palaeolatitudes of around 35°N. This mayperhaps be related to the development of northern winter

Fig. 5 Lower Carboniferous clastics of the Billefjorden Group are sharply

overlain by red beds, which pass gradually up into marine carbonates,

Landnørdingsvika, Bjørnøya. (Photo by David Worsley.)



sea ice as a result of cold-water oceanic upwelling,accompanied by a landward surge of the thermocline(Beauchamp & Desrochers 1997): established as a resultof major plate reorganization, and of changed oceaniccirculation patterns accompanying the Uralide orogeny.A contemporaneous increase in subsidence and sedimen-tation rates has also been related to the Uralides, but notas a result of the development of the western Barentsshelf as a foreland basin—the area affected is much too

large for that—but perhaps instead reflects the depressionof the 660-km mantle discontinuity, caused by subduc-tion along the Uralide suture. Whatever the triggeringmechanism, the group shows thickness variations fromzero or near zero, on local highs and inner platforms,up to 900 m in the southern Hammerfest Basin, withthe thickest successions on Spitsbergen being 360 and480 m in the St. Jonsfjorden and Billefjorden troughs,respectively.

The Permian/Triassic transition is still poorly understoodthroughout the region, but it appears that there was asignificant hiatus in the latest Permian (Lopingian), par-ticularly on highs and platforms. Freshwater leaching ofthe underlying spiculites seems to have locally given rise tosecondary reservoir porosity, with implications for hydro-carbon accumulation. The abrupt change from highlycemented spiculitic shales to the overlying non-siliceousshales of the Sassendalen Group is dramatic, both in theoutcrop and on seismic data. The so-called “Permian ChertEvent” was now at an end, and oceanic waters warmedsignificantly. Perhaps, as suggested by many authors, thiswarming was a contributory factor leading to the latePermian major marine extinction. The soft, poorly fossil-iferous basal shales of the overlying group apparentlycontain a Lopingian (Tatarian) palynoflora on outer plat-forms, and in basinal situations, although their sparsemacrofaunas have a Mesozoic aspect.

Fig. 6 Late Carboniferous regional palaeogeography.

Fig. 7 The mid–late Permian saw a regional transgression that onlapped

and overstepped all of the older units: on Bjørnøya, Lower Carboniferous

tectonized sandstones are directly overlain by Upper Permian deposits.

(Photo by David Worsley.)



Early–middle Triassic: the Sassendalen Group

As noted above, the basal shales of the SassendalenGroup may be of latest Permian age, at least where theyhave been penetrated by exploration wells and shallowstratigraphic coreholes on the margins of the NordkappBasin. In more positive platform areas, includingSvalbard, an Induan age is suggested. A generallytransgressive trend, punctuated by repeated coastal pro-gradations, throughout the early Triassic led to the onlapand submergence of positive features, such as theSørkapp–Hornsund and Stappen highs by the Olenekian(Fig. 9). The Loppa High only became the site of marinesedimentation in the Anisian/Ladinian.

The entire group is dominated by non-siliceous fineclastics—indeed this time span has been referred to asrepresenting the “Early Triassic silica gap”. The south-western Barents Sea was now isolated from centralEuropean basins, as the late Permian Zechstein seawaywas closed by the uplift of the mid-Norwegian andeastern Greenland shelves (Doré 1991). High subsidenceand sedimentation rates continued across the entireBarents Shelf during this depositional phase, a featuremost marked in the southern and northern Barentsbasins of the Russian sector. Thicknesses range from60–150 m on pre-existing structural highs to 700 m inwestern Spitsbergen, and are over 1500 m on the south-western shelf and several kilometres in the eastern basins.Sediment transport to these deep basins in the east seems

to have been from the central Urals, along the axis of theTiman-Pechora depression, and not from Novaya Zemlyaitself. Indeed, limited seismic data suggest a pattern ofthinning in the Triassic section towards Novaya Zemlya,leading some workers to suggest that the archipelagooriginally formed in the late Paleozoic as part of acontinuous Ural–Taimyr chain, and was then thrust west-wards into its present position during the early to mid-Triassic, subsequent to the main development of the Urals(Otto & Bailey 1995).

Significant sandstone intervals on Spitsbergen areapparently related to repeated coastal progradation fromGreenland to the west, and several barrier bar–deltaicsandstone units are exposed along the western coast(Mørk et al. 1982). Through much of the early to mid-Triassic, most of the south-western shelf was distal to anoscillating, but generally north-westerly prograding,coastline, with sand provenance being first from theBaltic Shield and then increasingly from the Urals. Bythe mid-Anisian, a NNE-trending system of clinoforms,extending over the Hammerfest Basin and on to theBjarmeland Platform, may have been situated close to thepalaeocoast, with the possibility for sand deposition indelta-front/shoreface environments (Fig. 10). The newlydiscovered hydrocarbon-bearing sandstones in the KobbeFormation of the StatoilHydro Obesum find belong to thistrend. The Obesum hydrocarbon source rocks are not yetin the public domain, but they are likely to be organic-rich shales, which are time-equivalents of the Botneheia

Fig. 8 Late Permian regional palaeogeography.



Fig. 9 The Mesozoic and Cenozoic development of the south-western Barents Sea, modified from Nøttvedt et al. (1993), with the geological time scale

based on Gradstein et al. (2004).



Formation of central and eastern Svalbard, and whichcontain up to 10% of organic carbon. Early workers inthe area called this unit the “Oil Shale” because of thepresence of free oil in septarian concretions.

Late Triassic–Late Cretaceous: development ofthe polar Euramerican Basin

This depositional phase contains several sandstone unitswith significant hydrocarbon reservoir potential, espe-cially in the lower part of the section, which thenbecomes more shale-dominated upwards. The Ladinian–Bathonian Kapp Toscana Group is locally rich insandstones of varying origins. The lower StorfjordenSubgroup (Ladinian/Carnian) has a deltaic character,with sandstone provenance from widely differing areas(Fig. 11). Units assigned to the overlying Norian–BajocianStorfjorden and Norian–Bathonian Wilhelmøya sub-groups display a wide variety of coastal/shallow marinesettings, often with mineralogically and texturally maturesandstone units. Regional transgression in the Bathonian/Callovian led to deposition of the shale-dominatedAdventdalen Group, which has significant organic carboncontent, especially in the upper Jurassic units. Sandstoneswere now largely confined to the margins of the tempo-rarily emergent highs and platforms around the Jurassic/Cretaceous transition, and to northern shelf areas in theBarremian. The latter are clearly related to the uplift ofnorthern shelf margins, which, together with extensivevolcanism in the same areas, clearly presaged and accom-panied the opening of the present polar Euramerican

Basin. The Jurassic/Cretaceous transition also saw thecataclysmic meteoric impact that formed the Mjølnircrater in the central Barents Sea, an impact that may havehad long-term implications for the regional depositionalenvironment. Ongoing uplift resulted in a major hiatusfrom the Albian/Cenomanian to the basal Paleogene overmuch of the north-western shelf. The clay-dominatedsequences of the Upper Cretaceous Nygrunnen Group arerestricted to south-western basinal areas.

Late Triassic: the Storfjorden Subgroup

Deposition of organic-rich shales continued throughoutthe Ladinian on the Svalbard Platform, with most of thesouth-western Barents Shelf already dominated by thedevelopment of prodelta shales in front of the north-westerly prograding systems noted above. Deltaic andfloodplain environments were rapidly established overmuch of the province, with still high, but decreasing,subsidence and sedimentation rates, and a complexpalaeogeographic pattern developed. Deltas still pro-graded from the west, affecting the westernmost parts ofSpitsbergen (and Bjørnøya), but these waned markedlythroughout the Carnian. New seismic evidence (Riis et al.2008 [this issue]) suggests that major sediment inputfrom the Urals continued, leading to the establishmentof delta-plain environments over much of the northernshelf, and extending to the north-eastern parts of theSvalbard Archipelago (Figs. 12, 13). The existence of anorthern volcanic provenance area to the north-east(presumably north of present-day shelf margins) is nowin doubt, although fieldwork in Svalbard in 2008 willhopefully clarify this question. The resultant Carniansandstones, although prolific, are usually texturally andmineralogically immature, with high primary contents offeldspathic, volcanic and lithic fragments, making themsusceptible to extensive diagenetic alteration, and oftenrendering them essentially impermeable, especially ifsubjected to appreciable burial. Areas further to the southin the Norwegian sector may have been affected by con-tinued progradation from the Baltic Shield: Carniansandstones recently encountered in the Nordkapp Basinand on the Finnmark Platform apparently show betterreservoir properties than their northern equivalents.These channel and coastal sands were derived frommature provenance areas on the Baltic Shield, and theirprimary reservoir quality was probably enhanced bymarine reworking at times of highstand, especially innear-coastal environments. Subsidence rates were stillhigh throughout the entire area, and earlier Paleozoichighs were now inverted: exploration wells on the LoppaHigh, for example, show an Upper Triassic successionthat, although incomplete because of subsequent erosion,

Fig. 10 The nunatak of Austjøkeltinden (foreground) on the margins of

the Sørkapp–Hornsund High shows a complete Triassic succession,

younging from the saddle to the left through a condensed Sassendalen

Group (terminating in black Anisian/Ladinian shales), and then through a

thick Storfjorden Subgroup deltaic sequence, ending (nearest camera) in

highly condensed (<10-m-thick) representatives of the Wilhelmøya

Subgroup. (Photo by David Worsley.)



Fig. 11 Mid-Triassic regional palaeogeography.

Fig. 12 Late Triassic regional palaeogeography.



is almost as thick (about 1300 m) as the complete equiva-lent sequence in the Hammerfest Basin, to the south ofthe high (1410 m). The basins in the eastern sector con-tinued to subside, but now also with the newly emplacedNovaya Zemlya as a significant provenance area. It isinteresting that sandstones throughout the region show aconvergence of lithologies upwards in this sequence,perhaps reflecting increasing marine reworking andmixing of the components from the different provenanceareas (Mørk 1999; Riis et al. 2008). Increasing localtectonic activity also led to a breakdown of the geographi-cally synchronous transgressive/regressive sequences thathad hitherto characterized Triassic deposition in theregion (Mørk et al. 1989; Egorov & Mørk 2000; Mørk &Smelror 2001). Indeed, in the Storfjorden Group, thebase of the progradational sequences stretches from theLadinian base Snadd Formation in south-eastern areas tothe Carnian prodeltaic shales of the Tschermakfjellet For-mation on Spitsbergen.

Latest Triassic–Middle Jurassic: the Realgrunnenand Wilhelmøya subgroups

A supra-regional relative sea-level rise in the earlyNorian—the so-called “Rhaetian” transgression of centralEurope—established marine connections between theTethyan and Boreal oceans along the proto-Atlanticseaway. This was accompanied by a major shift in struc-tural regimes and depositional systems throughout theentire circum-Arctic province. The Barents Shelf sawgreatly decreased subsidence and sedimentational rates(only 5% of those of the earlier Triassic regimes). TheUralian-sourced progradational systems were no longerdominant, and shallow marine and coastal environmentswere established throughout the province. Although stillwith multiple provenance areas, the resultant sandstonesreflect extensive reworking, and are texturally and

mineralogically mature (Bergan & Knarud 1993), withexcellent primary reservoir properties, such as those inand around the Snøhvit Field in the southern Hammer-fest Basin. However, in areas subjected to greatermaximum burial (e.g., western Spitsbergen and thewestern Hammerfest Basin), the same units show exten-sive quartz overgrowth, resulting in well-cementedquartzites. This entire sequence shows a rhythmicdevelopment of migrating barrier-bar and coastal envi-ronments. The individual units are patchily preservedover platform areas, reflecting intermittent primary depo-sition as migrating bars or banks, at times of relativehighstand, and subsequent erosion following the initia-tion of differential block movements in the mid-Jurassic.Highly condensed remanié deposits are also common onthese platforms, for example in central Spitsbergen. Localand unpredictable thicker developments may representsand infill of incised valleys that probably formed alongplatform margins during lowstand, and/or as a result ofthese movements.

Basinal areas were the sites of more continuous sedi-mentation, although uppermost sandstones in the groupcontain numerous remanié horizons, reflecting theonset of mid-Jurassic movements. These further definedpresent-day structural features, and also accentuated thepre-existing differentiation between platform and basinalareas: for example, the entire sequence thins from 500 min the Hammerfest Basin to less than 50 m on the centralBjarmeland Platform. An extreme example of this varia-tion can be seen onshore in Svalbard, with dramaticvariations in thickness and development over the Billef-jorden Lineament. Western platform areas show onlya few metres of a highly condensed and incompleteNorian–Bajocian sequence, which thickens rapidly east-wards across the lineament to over 200 m on Kong KarlsLand. Phosphatic conglomerates are common at severalhorizons, the most noteworthy being the well known“Lias Conglomerate” (Brentskardhaugen Bed) uppermostin the sequence, which contains phosphatic nodules withremanié fossils of Toarcian–?Bajocian age (Bäckström &Nagy 1985).

Mid-Jurassic–mid-Cretaceous:the Adventdalen Group

Renewed regional transgression in the Bathonian cut offthe supply of coarse clastics, and marine calcareousmudstones gave way to the anoxic black shales of theHekkingen and Aghardjellet formations during theCallovian/Oxfordian (Fig. 14). All earlier highs and plat-forms were now submerged, but thickness variations—from almost 400 m in the south-western HammerfestBasin to less than 100 m over central highs on the basinal

Fig. 13 Storfjorden Subgroup deltaics on Hopen: a fluvial channel cutting

into delta-plain overbank deposits. (Photo by David Worsley.)



axis—reflect earlier and ongoing Jurassic tectonism.Similar thickness variations are seen onshore in Svalbard(Dypvik et al. 1991). The Upper Jurassic black shales areexcellent source rocks for petroleum in western parts ofthe Barents Shelf, with marine-dominated kerogens andorganic contents of up to 20%. The subsequent burialhistory of the region indicates that significant oil genera-tion has only occurred in the deeper western basinal areas,and perhaps locally in deeper parts of the Nordkapp Basin.

A major change in depositional environments aroundthe Jurassic/Cretaceous boundary seems to be related to alowering of sea level, and the general development ofmore open marine environments with better bottom cir-culation, except in locally restricted basinal areas. TheMjølnir meteor impact on the north-eastern BjarmelandPlatform may have had short-term catastrophic conse-quences over a large area (Dypvik et al. 1996; Smelroret al. 2001; Dypvik et al. 2004), as well as heralding thisgeneral environmental shift. Local sandstone fans werealso built out from platform margins into the adjacentbasins at this time.

The early Cretaceous was otherwise dominated by thedeposition of fine clastics over much of the province,with up to 700-m-thick basinal shales that have someorganically enriched intervals. Platform areas have muchthinner and more carbonate-dominated sequences. Mostmarked features of this sequence are seen in northernshelf areas, where a Barremian southerly directed deltaicprogradation overlies an unconformity, heralding theonset of northern margin uplift, and this was accompa-nied by extensive extrusive magmatism along the same

northern margins, reflecting the break-up prior to theopening of the polar Euramerican Basin (Fig. 15). Delta-plain environments characterize the development of thesandstones of the Helvetiafjellet Formation in northernand central Spitsbergen (Gjelberg & Steel 1995), butspectacular synsedimentational collapse features aroundKvalvågen in south-east Spitsbergen (Nemec et al. 1988)mark the southernmost extent of fluvial sandstones, withexposures further south passing into marine sandstonesand thicker more shale-rich sequences. Large-scalesouthwards-directed clinoforms seen on seismic linesfrom the Bjørnøya Basin may represent distal equivalentsof this sequence. An Aptian regional sea-level rise signifi-cantly cut off coarse-clastic supply, even in the north.Northern uplift continued, however, so that a 190-m-thick condensed Aptian/Albian shale-dominated wedgein central Spitsbergen thickens to over 1000 m in south-ernmost land exposures, and then thickens further to1400 m and extends through to the Cenomanian in thesouth-western Barents margin.

Late Cretaceous: the Nygrunnen Group

The uplift and erosion of northern shelf areas continuedthroughout the late Cretaceous, so that basement, Devo-nian and Upper Paleozoic rocks dominate exposuresthere, with only an occasional thin veneer of youngersediments. From Longyearbyen and southwards on Spits-bergen, Paleogene basal conglomerates rest directly onlower Cretaceous units of varying Aptian–Albian ages(Fig. 16). The only areas with significant deposition werethe western marginal basins, where exploration wells inthe Tromsø Basin have encountered up to 1200 m ofclaystones with thin limestone interbeds. The entiresequence thins eastwards to 50–250 m in the HammerfestBasin, where condensed calcareous to sandy units bearwitness to intermittent deposition, only at times ofmaximum transgression.

Paleogene: transtension, transpression and theopening of the Norwegian–Greenland Sea

The Paleogene development of the region was dominatedby tectonic activity along the western shelf margins, priorto the final opening of the Norwegian–Greenland Sea inthe Eocene/Oligocene. The opening occurred after theformation of the compressive Tertiary orogenic belt ofSpitsbergen and the north-western shelf, which entailedcrustal shortening estimated to around 30 km. Mean-while, southern shelf margins (south of 76°N) showed agenerally passive and subsiding character throughout thePaleogene, apart from volcanism and marginal uplift

Fig. 14 Helvetiafjellet, central Spitsbergen: Upper Jurassic organic-rich

black shales pass up, at the break of the slope, into much leaner Lower

Cretaceous black shale. A major difference from the southern shelf areas

is the development of Barremian deltaic sandstones prograding south-

wards, but with a delta front over south-eastern Spitsbergen. These are

overlain by transgressive Aptian shales with thin storm-deposited sand-

stones. (Photo by Atle Mørk.)



prior to and accompanying the break-up that finally pro-duced oceanic crust to the west.

Paleocene–Oligocene: the Van Mijenfjordenand Sotbakken groups

Paleogene sediments on the north-western shelf are pre-served in the Central Basin of Spitsbergen, and in several

isolated smaller basins in south-western and north-western parts of the island. With a preserved thickness of1900 m, the clastic deposits of the Van MijenfjordenGroup in the Central Basin (Fig. 17) reflect alternatingtranstensional and transpressive regimes along thewestern shelf margin (Steel et al. 1985). This depositionalepisode culminated in the progradation of shallowmarine to alluvial sands from the west that finally filledthe basin in the Eocene. Other Paleogene units in localbasins seem to have developed during the main compres-sive movements that followed the development andfilling of the Central Basin (Nøttvedt et al. 1988;Dallmann et al. 1993). A similar development has beenidentified southwards to about 76°N, where the entireshelf margin changes character from a compressive topassive aspect (Bergh & Grogan 2003). Volcanism in theVestbakken Province between 75 and 72°N is apparentlyrelated to this transition. The south-western shelf is char-acterized by the claystone-dominated Sotbakken Group,which is largely confined to the western basins andouter shelf margins, although thin units are apparentlyalso preserved throughout the south-western NordkappBasin, and sporadically in the north-eastern arm of theNordkapp Basin. The sequence thickens westwardsthrough the Hammerfest Basin from 180 to 770 m;western basins show even thicker developments, up to900 m in the Tromsø Basin, 1000 m in the Bjørnøya

Fig. 15 Earliest Cretaceous–Barremian composite regional palaeogeography.

Fig. 16 Base Paleogene, central Spitsbergen. Upper Cretaceous deposits

are totally missing from the northern shelf areas: here, a Paleogene basal

conglomerate rests directly on eroded Albian marine shales and storm

siltstones. (Photo by Atle Mørk.)



Basin and over 2800 m in the Sørvestsnaget Basin(Ryseth et al. 2003). Recent studies suggest that therewas some uplift of shelf areas associated with the Tertiaryorogeny and opening of the Norwegian–Greenland Sea(Fig. 18). The Hammerfest and Nordkapp basins wereapparently least affected, but uplift of 1–2 km may haveaffected the northern platform areas.

Neogene: glaciation and uplift,and renewed volcanism

The Neogene saw the development of a massive wedgedeposited over and off of the western shelf margins, fedby clastics derived from large-scale and predominantlyglacially related repeated shelf depression and uplift

delta plain, often tide-dominated

wave-dominated delta

front barrier coast

prodelta

turbidites, slumps from western uplift

tide-dominated delta

(proximal)

offshore bar complex

(distal)

HOLLENDAR-

DALEN FM.

prodelta

prodelta(lower)

F-U

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(upper)delta plain

delta front

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EN

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AN

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.

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SO

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.

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ING

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AN

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Large-scale

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response

to West

Spitsbergen

Orogeny

Fig. 17 The Paleogene succession of the Central Basin, Spitsbergen (from Steel et al. 1985).



(Faleide et al. 1996; Dimakis et al. 1999). Late Quater-nary volcanism in north-western Spitsbergen may berelated to the Yermak hot spot to the north-west of thearchipelago.

Miocene–Pleistocene: the Nordland Group

The Neogene throughout the entire shelf was charact-erized by repeated glacially induced subsidence anduplift, with sedimentation restricted to the western shelfmargins, and spilling over onto the newly formed oceaniccrust (Fig. 19). This is true of marginal areas north andsouth of 76°N, where up to 5 km of fine-grained depositsof the Nordland Group accumulated along the entirewestern Barents Shelf margin (Faleide et al. 1996). Theseerosional products reflect glacial erosion and periodic iso-static uplift caused by erosional unloading during thePliocene and Pleistocene (Vorren et al. 1991; Mangerudet al. 1996). The Hammerfest Basin and south-westernNordkapp Basin were least affected, with an uplift ofless than 2 km, whereas platform areas to the northexperienced an uplift and erosion of up to 3 km. Thesedifferential movements have had significant effects onpre-existing hydrocarbon accumulations, and are impor-tant risk factors now being addressed in currentexploration activity (Nyland et al. 1992).

Afterword and acknowledgements

This brief review is based on a series of presentationsdirected mainly towards the petroleum industry overrecent years. It draws on a multitude of sources, inaddition to the author’s own research and industrialexperience since 1970. I have therefore chosen torestrict references to only a few works, without intend-ing any offence to all of the other importantcontributors to this field of Arctic research over theyears.

Thanks are overdue to past students, many of whichare now present colleagues, for their boundless enthusi-asm for Arctic geology through the years—not least AtleMørk and Hans Arne Nakrem, who were the main driversof the Boreal Triassic Conference. Long-term cooperationwith Lars Stemmerik, Geological Survey of Denmark andGreenland, has greatly improved my understanding ofthe Upper Paleozoic carbonate development, and I amgrateful to Ashton Embry and his colleagues in Calgaryfor giving me a better circum-Arctic overview. The mapshave evolved in cooperation with collaborators at SAGEXPetroleum, especially with Dirk van der Wel. A specialthanks to the ever-patient Turid Oskarsen for her excel-lent drafting, and to my ever-patient wife and colleagueRosalind Waddams.

Fig. 18 Late Paleogene regional uplift.



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