Depositional Environments and the Hydrocarbon Generative ...confined to the Lower and Middle Triassic successions deposited in a deepwater shelf environment in the western part of

ISSN 0145�8752, Moscow University Geology Bulletin, 2014, Vol. 69, No. 1, pp. 1–10. © Allerton Press, Inc., 2014.Original Russian Text © D.A. Norina, A.V. Stupakova, T.A. Kiryukhina, 2014, published in Vestnik Moskovskogo Universiteta. Geologiya, 2014, No. 1, pp. 000–000.

1

INTRODUCTION

With the recent large hydrocarbon discoveries inthe Mesozoic reservoirs of the Barents Sea, the interestof many geologists is turning to Triassic shales as themost likely source rocks. Successful exploration in theregion will require assessing the distribution and lat�eral and vertical variation in the quality of the Triassicsource rocks. Because depositional environments havea strong influence on the type, quantity, and preserva�tion of organic matter in a sediment, i.e., on originalsource rock potential, we estimated the geochemicalparameters and lithofacies characteristics of the Trias�sic deposits for the entire Barents Sea basin.

In the late 1980s, studies were launched by Arktik�morneftegazrazvedka and VNIIOkeangeologiya toevaluate the quality of the Triassic source rocks usingcore and cuttings analysis from stratigraphic wellsdrilled in the Barents Sea and on the surroundingislands (Danyushevskaya, 1995). Numerous occur�rences and seepages of oil and bitumen in Triassicrocks reported from wells and outcrops have beenstudied at the All�Russia Petroleum Research Explo�ration Institute (VNIGRI) (Klubov et al., 1998). Rela�tionship between the quality of Triassic source rocksfrom different parts of the Barents Sea and their depo�sitional environments were discussed in previous pub�lications (Grigor’eva et al., 1998; Bjoroy et al., 2010;Leith et al., 1992).

MATERIALS AND METHODS

All geochemical analyses were performed in labo�ratories at the Faculty of Geology and Geochemistry

of Fossil Fuels at the Department of Geology of theMoscow State University. Twenty source rock sampleswere collected from Triassic outcrops during field�works on the Franz Josef Land (FJL) and Spitsbergenarchipelagos. Moreover, the study was supplementedby literature geochemical data and results of pyrolysisof Triassic samples collected from outcrops on Spits�bergen and from the Nagurskaya, Heiss, and Sever�naya wells on FJL (Danyushevskaya, 1995), and fromoffshore wells drilled in the Barents and Pechora seas(Official website of Norwegian…, 2010).

Study of Triassic depositional environments in theTriassic successions in the Barents Sea was based onoutcrops, core and cuttings descriptions, as well as welllog analysis. For the evaluation of the southeasternpart of the Barents Sea basin we also used the results ofour interpretation of seismic data (Kazanin et al.,2011) acquired by MAGE in 2008–2010. Lithofaciesmaps for the Early, Middle, and Late Triassic werecompiled using literature data (Atlas: Geological His�tory…, 2009; Glorstad�Clark et al., 2010).

The geochemical methods that were used in thisstudy included a combination of both qualitative andquantitative characterization of organic matter, suchas macro� and microscopic examination of rock sam�ples, Rock�Eval pyrolysis, luminescence microscopyand source rock extraction in chloroform, separationof asphaltene and malthene fractions of the extract.Normal and isoprenoid alkanes were analyzed usinggas�liquid chromatography (GC) on a Perkin�Elmergas chromatography system. Saturated and aromaticfractions of extracts were analyzed by gas chromatog�raphy/mass spectrometry (GCMS) using a Finnigan

Depositional Environments and the Hydrocarbon Generative Potential of Triassic Rocks of the Barents Sea Basin

D. A. Norina, A. V. Stupakova, and T. A. KiryukhinaDepartment of Geology, Moscow State University, Moscow, 119991 Russiae�mail: [email protected], [email protected], [email protected]

Received May 24, 2013

Abstract—With the recent large hydrocarbon discoveries in the Barents Sea, interest is turning to Triassicshales as the most likely source rocks. The results reveal the relationship between the quality of Triassic sourcerocks, the amount and type of organic matter, and the environments of deposition. The best source rocks areconfined to the Lower and Middle Triassic successions deposited in a deep�water shelf environment in thewestern part of the basin. Shallow�marine and deltaic argillaceous rocks exhibit fair to poor gas�generativepotential. Triassic fluvial�lacustrine deposits have little to no hydrocarbon generative potential.

Keywords: Triassic source rocks, geochemical studies, hydrocarbon generative potential, depositional envi�ronments, lithofacies zones, Barents Sea basin

DOI: 10.3103/S0145875214010062

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MOSCOW UNIVERSITY GEOLOGY BULLETIN Vol. 69 No. 1 2014

NORINA et al.

МАТ�900 ХР mass spectrometer. The results ofgeochemical analyses were discussed in detail in ourprevious study (Kiryukhina et al., 2012).

The Triassic sequences were divided into lithofa�cies, each with a characteristic set of rock lithologies,structures, textures, thickness, flora and fauna fossils.The distinguished lithofacies zones were supported bylithostratigraphic columns generated for the Triassicsections based on well data and field outcrops on thebasin’s margins. The sea�level curves show cyclicalchanges from continental to shelf marine environ�ments (Fig. 1). Lithofacies zones in the undrilled areaswere interpolated from seismic data on the basis ofcontinuity, boundaries, thickness variation, and thecharacteristics of the seismic facies of the Triassic seis�mostratigraphic complex (Kazanin et al., 2011) with ageneral account of the regional tectonic and geologicalframework.

Triassic lithofacies zones. During the Triassic, theBarents Sea represented a large epicontinental basinwith water depths of up to 200 m, connected in thenorth with the open sea. Permian strata are overlainwith a minor hiatus by Triassic strata. The boundarybetween Permian and Triassic deposits is clearly visibleon seismic sections at the flanks of the basin (Kazaninet al., 2011), while the unconformity is not recogniz�able in the central part of the basin. Several intra�Tri�assic hiatuses were produced due to local uplift andgeneral shallowing of the basin during the Triassic.Subsequent widespread pre�Jurassic erosion tookplace during Rhaetian times near the incipient NovayaZemlya orogen (Kazanin et al., 2011), which experi�enced multiple phases of uplift since the Middle Trias�sic. The Upper and Middle Triassic deposits were par�tially removed as a result of differential uplift andintense erosion within the Barents Sea basin duringthe Late Cretaceous and Cenozoic.

During Triassic times, a continental, marginalmarine to marine depositional environment becameestablished in the Barents Sea shelf. One or severallithofacies zones were distinguished for each deposi�tional environment based on rock lithologies, sedi�mentary structures and textures, thickness, and fossilcontents (Fig. 1) (Gradzin�ski et al., 1980; Obstanovkiosadkonakopleniya…, 1990).

Lithofacies zones of erosion and fluvial–lacustrineplain are distinguished in the continental environ�ments. Zones of erosion tend to be dominated by ero�sional processes, so they act as a provenance of clasticsediments and plant detritus.

Fluvial–lacustrine plains have considerable lateraland vertical lithologic variation. Fluvial deposits con�sist of well�sorted sandstones, siltstones, and shales,commonly lenticularly interbedded, with conglomer�ate intercalations. The rocks are usually variegated tored colored due to the presence of hematite and ironoxides, the prevailing oxidizing environments andrapid burial. The sandstones and siltstones arepolymictic with clay and clay–carbonate cement and

common tangential or multi�directional cross�bed�ding. Lenticular bedding is the predominant sedimen�tary structure in sands and shales. Recognizable fossilsare scarce but include freshwater mollusk shells, fish,and reptile bones. Fragments of higher land plants,spores, and pollen occur.

The transitional marginal marine environments arecharacterized by a variety of lithofacies zones, includ�ing delta plains, delta fronts, prodeltas, tidal flood�plains, and lagoons, sand�banks, occasionally inun�dated by the sea. The deltaic environment is commonlydivided into three zones: delta plain, delta front, andprodelta, differing in the composition and characteris�tics of sediments. The delta plain includes distributarychannels with their subaerial levees, interdistributarymarshes and swamps, small lakes, and lagoons. Thedelta front is a narrow, steeply sloped submarine part ofthe delta where distributary channels meet the opensea. As a result of continuous sediment supply deltafront propagates basinward. The prodelta zone includesthe distal submarine part of the delta.

The delta plain deposits are mostly polymicticsands deposited in distributary channels and channel�mouth bars, typically dominated by tangential crossbeds, traces of erosion, and intercalations of peliticlayers; levee fine�grained sandstones and thin beddedsilts are also present. Delta plain marshes, lakes, andlagoons are dominated mainly by argillaceous thinbedded sediments, as well as coal lenses and bedsdeposited under humid climatic conditions. The deltafront deposits are well�sorted, tangentially cross�bed�ded sands and thinly bedded silts. The prodelta faciesare represented by thin�laminated silt and clay variet�ies with abundant plant debris and mica, but rarespores and pollen transported by rivers. Faunalremains are usually scarce, but include occasionalbivalves. Bioturbation is common in the lower part ofthe prodelta and lagoons.

Extensive areas of the sea coasts were occupied bytidal floodplains and lagoons. Tidal plains are dissectedby a network of tidal channels through which seawaterrose and flooded the adjacent coastal flats. The tidalfloodplain boundaries are defined by tidal inundationrange. The deposits are thinly interbedded sands andshales with characteristic parallel and lenticular lami�nation. Shales are interpreted as highstand deposits,while sands are deposited in a lowstand or during theearly phases of sea�level rise. The sand deposited in thelower part of this zone exhibit well�sorting and bimo�dal tangential cross�bedding. A scarce, low�diversitymarine fauna is present; heavy bioturbation, siderite,and glauconite are also common.

The prevailing lagoonal facies are shales and silt�stones. The coarse clastic material could occur if hadbeen transported by fluvial systems from the continentor by tidal currents from the sea. Bioturbation is com�mon, a low�diverse marine fauna and plant remainsare present.


DEPOSITIONAL ENVIRONMENTS AND THE HYDROCARBON GENERATIVE 3

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NORINA et al.

Sand banks, periodically inundated by the sea, arelocated above the mean rising tide level and may becovered by saltmarshes mainly in temperate regions.These sediments represent the alternation of shalesand siltstones, in which primary sedimentary struc�tures were destroyed by bioturbation and plant�roottraces.

The marine environments are represented by innershallow shelf (up to 50 m) and outer deep�water shelf(50–200 m) facies. The inner shelf facies (upper sublit�toral zone) developed above the storm wave�base andwas subject to tidal wave action. This zone is domi�nated by the deposition of sand and silt varieties, withparallel or low�angle tangential cross stratification andcontain occasional shale beds.

The outer�shelf facies (lower sublittoral zone)developed below the storm wave�base under low�energy hydrodynamic conditions. This area is domi�nated by the deposition of dark grey to black shales,showing burrows and horizontal lamination and con�taining thin intercalations of fine sandstones as well aspyrite, phosphate, and calcareous concretions.Marine deposits contain abundant faunal remains ofcorals, sponges, brachiopods, gastropods, belemnites,and ammonoids.

Lower Triassic source rocks. During the Early Tri�assic, deposition in the southern (Pechora Sea) andnortheastern (Novaya Zemlya and North Kara paleo�land) areas of the basin occurred in fluvial–lacustrineenvironments (Fig. 2) under high�energy hydrody�namic and oxic conditions, dominated by red beds,mostly shales and siltstones, with coal lenses and highsand content. Such environments were detrimental tothe preservation of organic matter. The large riversbegan high in the Ural Mountains and Timan Ridgeand, possibly, on the North Kara paleo�land, risinginto multiple branches in the coastal area and makingup the main delta systems (Peschanoozerskaya andKolguevskaya wells). The transported material filledup the actively subsiding South Barents Sea basin andresulted in the deposition of a 2–4 km thick Lower Tri�assic sequence, which is clearly visible on seismic sec�tions. Sediments with high concentrations of plantremains (identified in thin sections as coal detritus)transported from the continent were deposited in deltaplain and delta front environments. Therefore, LowerTriassic source rocks from these lithofacies zones con�tain humic�type organic matter. The low organic mat�ter contents (0.002–0.2%) and low hydrocarbon gen�erative potential of shales in this zone reflect the pre�vailing oxidizing environments and, probably, largedilution effects due to high sedimentation rates.

The central parts of the South and North BarentsSea basins were inferred to represent the prodeltalithofacies zones with more favorable conditions forthe preservation of organic matter, which can beexplained by the accumulation of fine�grained materi�als, mostly silt� and clay�sized particles, which arecapable of absorbing organic matter, as well as by a

possible lower�energy environment as compared tothe delta and fluvio–lacustrine plains.

The deposition of variegated thinly intercalatedsand and shale beds occurred in the tidal floodplainenvironment along the margins of Novaya Zemlya, onthe northern slope of the Baltic shield, along the Fin�mark monocline and western flank of the Barents Seabasin (Fig. 2). The Lower Triassic shales of this litho�facies zone contain organic matter of the humic typebecause of the proximity to the provenance area. Thelow contents of organic matter (0.04–0.1% in theMurmanskaya well, 0.5% in the Severo Kildinskayawell, and 0.1–0.5% in Induan sediments of central andsouthern Spitsbergen) and extract (0.0006–0.16%) arecaused by poor preservation of primary organic matter inthe oxygenated water column due to high�energy hydro�dynamic conditions and tidal action. The shaly depositsof this lithofacies zone have very low hydrocarbon gener�ative potential (S1 + S2 = 0.12–0.56 mg HC/g rock), it isstill doubtful that they can be regarded as hydrocarbonsource rocks.

During the Lower Triassic, much of the BarentsSea basin consisted of shallow shelf environments(Fig. 2), which were more favorable for the preservationof organic matter in sediments. The organic matter con�tent in Lower Triassic rocks of the FJL (in the vicinity ofthe Nagurskaya well) is as high as 1.2%. The humic char�acter of organic matter (HI = 10–33 mg HC/g TOC) iscaused by the proximity of a large delta in the east.These rocks, although they have poor generativepotential (up to 0.3 mg HC/g ТОС), can be regardedas gas prone. Shallow marine shales of the Finmarkmonocline and Hammerfest basin (Havert Forma�tion) contain up to 0.4–1% of humic organic matter.Weakly oxic conditions in the sediments are indicatedby a number of geochemical indices, such as Pr/Ph,Pr/n�C17, and Ph/n�C18 (well 7124/3�1) (Fig. 3).

The Olenekian transgression in central Spitsbergenled to the deposition of shallow marine silty andargillaceous sediments (the Sticky Keep Formation).Dark grey mudstones here have typical TOC values ofup to 3%, extract contents of 0.4–0.8%, and organicmatter of the mixed humic–sapropelic type (HI =194–318 mg HC/g ТОС). The presence of a signifi�cant sapropelic component is caused by the absence oflarge rivers. The higher organic matter content of thesesource rocks reflect the prevalence of low�energy,weakly reducing conditions and the increased proppor�tion of pelitic�sized fractions in the basin sediment sup�ply. These sediments have Pr/Ph of 1.4–2, Pr/n�C17and Pr/n�C18 of 1.5–1.6 and 1.2–1.6, respectively(Fig. 3), suggesting the presence of mixed�typeorganic matter accumulated under weakly reducingconditions (Abdullah, 1999). Therefore, the Ole�nekian rocks deposited in this part of the archipelagocan be interpreted as having good source rock poten�tial (3.6–8.9 mg HC/g rock) (Fig. 2).

The outer deep�water shelf lithofacies zone occu�pied the eastern tip of Svalbard and extended south�



96°0′ E84°0′ E

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8Eastern

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Fig. 2. Comparison of geochemical data for Lower Triassic source rocks and lithofacies zones of Early Triassic age: 1, deep�watershelf (50–200 m); 2, shallow�water shelf (to 50 m); 3, tidal floodplain and lagoons; 4, sand banks periodically inundated by thesea; 5, prodelta, 6, delta plain and delta front; 7, fluvial–lacustrine plain; 8, areas of erosion; 9, present�day shoreline; 10, out�crops; 11, wells; 12, TOC values, % (recalculated to the initial values are denoted by subscript 0); 13, organic matter type(II, humic�sapropelic, III, humic); 14, extract content, %; 15, hydrocarbon generative potential, mg HC/g rock (recalculated tothe initial values are denoted by subscript 0).

ward and southwestward into the Norwegian shelf andNordkapp basin (Fig. 2). The eastern and southernlimits of this zone are defined by the westernmostedges of Lower Triassic clinoforms (Glorstad�Clarket al., 2010). Predominantly argillaceous facies of Ole�nekian age deposited on eastern Spitsbergen, Edge, andBarents islands have high organic matter contents (up to6%, mixed humic–sapropelic type) and good hydrocar�bon generative potential (average S2 = 12 mg HC/g rock)(Bjoroy et al., 2010). On the Norwegian shelf, theorganic matter content is up to 1.7–2% in the Induanmudstones and up to 2–8% in the Olenekian mud�stones, with HI of up to 500 mg HC/g TOC. The C27,

C28, and C29 sterane ratios suggest an open�sea envi�ronment (Official website of Norwegian…, 2010). Assuggested by Bjoroy et al. (2010), the hopane distribu�tion of these rocks indicates marine deposition underhighly reducing conditions and is similar to thatreported from eastern Svalbard. This correlation sug�gests that good source rocks were deposited during theEarly Triassic throughout the entire outer deep�watershelf zone.

Middle Triassic source rocks. During the MiddleTriassic, deposition in the southern and southeasternBarents Sea shelf occurred on fluvial�lacustrine, del�taic and coastal plains (Fig. 4). The Middle Triassic

78°0′ E72°0′ E66°0′ E60°0′ E54°0′ E48°0′ E42°0′ E36°0′ E

6


NORINA et al.

succession is composed of greenish grey, fine� tomedium�grained sandstones interbedded with varie�gated shales and occasional beds of black pyritizedshales (Grigor’eva et al., 1998), which are characterizedby poor hydrocarbon generative potential (<0.4% TOC)and extract content of 0.006–0.03% (Murmanskayaand Severo–Kildinskaya wells).

Strong variability of organic matter types and con�tents in the Middle Triassic shallow shelf facies tendsto reflect variations in their source rock potential. Forexample, argillaceous facies in the eastern part of theHammerfest basin contain up to 1.5% organic matter ofthe humic type. However, moving farther northwardfrom the provenance area (Baltic shield), in the more sta�ble shallow marine settings, the organic matter content ofthese rocks increases to 3% (Nordkapp basin). The valuesof the Pr/n�C17 and Ph/n�C18 ratios (wells 7124/3�1 and7226�11) indicate the dominantly humic type of organicmatter (Fig. 3) (Official website of Norwegian…,2010).

During the Middle Triassic, thick sequences (up to2 km) of alternating sandy, silty and argillaceous rockswith abundant mica flakes and shell fragments, weredeposited in the east of the FJL under shallow marineenvironments in the proximity to their provenancearea (Figs. 1, 4). Shale beds contain up to 0.1–1%organic matter. The peak of n�alkane distribution inthe C21–C22 range, a predominance of both high� andlow�molecular�weight odd�numbered alkanes, as well

as the presence of a pronounced naphthene hump inthe region of polycyclic aromatic compounds alto�gether indicate a predominance of humic�typeorganic matter formed in a marginal marine environ�ment (Fig. 5). The low generative potential of theserocks (up to 0.53 mg HC/g rock) is due to the high�energy depositional regime (wavy and cross�lamina�tion, frequent intercalations), the oxidizing conditionsin the sediment (the presence of siderite), as well asdilution effects. The data from earlier works (Dany�ushevskaya, 1995) show that the TOC values of theAnisian rocks encountered in the Heiss and Severnayawells do not exceed 0.7%, while those of the Ladinianrocks are not greater than 0.9%. These rocks generallyshow little remaining hydrocarbon generative poten�tial (up to 0.28 mg HC/g rock). The remaining gener�ative potential for highly mature rocks was recalcu�lated to the early oil window. Middle Triassic rocksfrom FJL have initial TOC values of 0.8–2.1% (a cal�culation factor of 1.5–2, according to the data ofT.K. Bazhenova) and HI of up to 130 mg HC/g TOC.These values correspond to poor–fair initial genera�tive potential, based on the classification of Peters andCassa (up to 2.7 mg HC/g rock).

Dark grey to black thin�laminated mudstonesdeposited in central Spitsbergen in a shallow�marineprodelta to lagoonal environment (carbonate inter�beds, bioturbation) have a present�day organic mattercontent of up to 1.4–1.7% and fair to good hydrocar�bon generative potential (S1 + S2 = 2.3–6.2 mg HC/grock) (Fig. 4). Since these rocks are thermally mature(approaching the late oil window), initial values werehigher. TOC values calculated for the early oil windowmay have been as high as 3.5% and the hydrocarbongenerative potential could be very high. These calcula�tions are consistent with the literature data on lessmature rocks: up to 7% TOC, excellent generativepotential (>29 mg HC/g rock), extract content of>1.2% (Abdullah, 1999).

The humic–sapropelic type of organic matter(HI = 130–337, initial HI up to 450 mg HC/g ТОС),bimodal n�alkane distribution (peaks at n�C20 andn�C31) (Fig. 5), a pronounced naphthene hump, and apredominance of high� molecular�weight odd�num�bered alkanes (CPI 2 = 2C29/(C28 + C30) > 1) are indic�ative of the increased input of continental componentsfrom the westerly deltas, whereas Pr/Ph (1.4–2) andPr/n�C17 and Ph/n�C18 suggest a moderately reducingdepositional setting (Fig. 3) (Abdullah, 1999).

The outer deep�water shelf lithofacies zone, whichextends along the western basin margin (Fig. 4), repre�sents the best source rocks of Middle Triassic age. OnEdge Island and Norwegian shelf, they comprisemostly black shales, which have organic matter con�tents (for the early oil window maturity) of 4–10% and8–16%, respectively. Present�day TOC values are slightlylower for the rocks of the Norwegian shelf (2–6%) due tohigh thermal maturity of mixed�type organic matter,which shows a significant input of the sapropelic com�

10

8

64

2

0.3

0.2

0.4

0.16320.60.3 0.40.2 0.8

Ph/n�C18

Pr/n�C17

0.60.8

1

Deg

ree o

f deg

radati

on

Humic OM

Mixed

OM

Marine OM

Postmat

ure

Mat

ure

Imm

ature

Deg

ree o

f mat

urity

1 4 5 8 10

123

456

78

Fig. 3. Pr/n�C17 vs. Ph/n�C18 plot for extracts from Trias�sic source rocks: 1–3, Lower Triassic: 1, Spitsbergen;2, Nordkapp basin, well 7226/11; 3, Hammerfest basin,well 7124/3�1; 4–6, Middle Triassic: 4, Spitsbergen,5, well 7226/11�1, 6, well 7124/3�1; 7–8, Upper Triassic:7, well 7226/11�1, 8, well 7124/3�1.



ponent (HI of up to 525 mg HC/g TOC). The distri�bution of n�alkane with a maximum in the low�molec�ular�weight region and a minor naphthene hump areindicative of a predominance of sapropelic organicmatter (Fig. 5). The deposition of excellent sourcerocks (S2 = 2.5–57 mg HC/g rock, 19 mg HC/g rock)in this lithofacies zone is caused by the increased con�tent of pelitic material that is capable of absorbingorganic matter and low�energy, predominantly reduc�ing conditions.

Upper Triassic source rocks. Towards the end ofTriassic time, a general shallowing of the basin resultedin the widespread deposition of terrigenous rocksenriched in humic organic matter (Fig. 6). Theamount and rate of clastic deposition decreased in theLate Triassic. The fluvial–lacustrine shale interbeds

deposited in the southeast of the basin cannot beregarded as good source rocks due to their very loworganic matter content (<0.8%). An extensive tidalfloodplain occupied the central and western parts ofthe study area. Upper Triassic shales in the South Bar�ents Sea basin and on the FJL generally have low gasgenerative potential, but in some isolated lagoons andswamps conditions promoted better preservation oforganic matter (for example, Carnian black shales andcoal layers in the vicinity of the Severnaya well on theFJL) (Fig. 6). Black shales have high content oforganic matter (up to 11%) of predominantly humictype (HI = 214 mg HC/g TOC) and excellent hydro�carbon generative potential (up to 24 mg HC/g rock).Similar depositional settings may have existed withinthe Nordkapp and Hammerfest basins, as suggested by

Bit.: 0.03%

Bit.: 0.07–0.1%

7219/9�1

7128/4�1

7124/3�1

1.6

4.5

7–10

0.5

3

0.4

1.5

0.6

S1 + S2 = 2.3–6.2(S1 + S2)0 = 8–15

S1 + S2 = 0.03–0.532

6Southern

Medvezhiy Isl

Fersman


Heiss

Ganza cape

II–III

Land

Spitsbergen

II–III

III

well

Varandey�more

Pechora syneclis


CentralSpitsbergen

Wilhelm

III


Murmanskaya well

III

Nagurskaya well

Arkticheskaya well

North Karasyneclise


Severnaya well


Kolguevskaya well

Bit.: 0.006%

0.15

7226/11�1

EasternSvalbard

III–II

S1 + S2 = 0.1–0.3

Bit.: 0.47–0.59%S1 + S2 = 4.3–57

1.7

1.41.57

1.2

0.9Bit.: 0.024–0.035%

S1 + S2 = 0.7

(S1 + S2)0 = 0.4–2.7

0.7

10.8

0.1

0.9

0.4

0.9

0.7

TOC0 to 2%

TOC0 to 7%

II–III

South Barents basin

high

Vernadskiihigh

Svalbardsyneclise

Lunin saddle

North Barents basin

North Siberianthreshold

basin

III

96°0′ E84°0′ E

72°0′ E60°0′ E

48°0′ E36°0′ E

30°0′ E24°0′ E18°0′ E12°0′ E6°0′ E0°0′ E

82°0′ N

78°0′ N

74°0′ N

70°0′ N

Admiralteisky swell

Bjarmeland platform


Fedynski high

Nordkappbasin

Kola

monocline

Hammerfest

Fig. 4. Comparison of the geochemical data of Middle Triassic source rocks and lithofacies zones of Middle Triassic age. The leg�end is the same as in Fig. 2.

78°0′ E72°0′ E66°0′ E60°0′ E54°0′ E48°0′ E42°0′ E36°0′ E

8


NORINA et al.

Fig. 5. Gas chromatograms of source rock extracts of Anisian mudstones from Spitsbergen and FJL outcrops.

200

140

120

100

80

60

40

20

160

180

Central Spitsbergen

Eastern Spitsbergen

nC17

nC18

nC19

nC20

nC21

nC22

nC23nC24

nC25

nC26

nC27

nC28

nC19

nC30nC31

nC32

nC33

nC34

nC35

nC36 nC37nC38

Pr

Ph

nC19

10095

80

65

50

35

20

50

4628262218 2016 24Time, min

Rel

ativ

e ab

udan

ce

10

9085

7570

6055

4540

3025

15

30 32 34 36 38 40 42 44

c�16

i�c�18

c�17

c�18

c�19

Pr

c�20c�21 c�22

c�23c�24

c�25

c�26

c�27

c�29

c�30

c�31c�32

c�28

Ph

nC19

40

35

30

25

20

15

10

5

08570655040 4535 55 75 8060

nC17

nC18

nC19

nC20

nC21nC22

nC23

nC24

nC25

nC26

nC27

nC28

nC19 nC30

nC31

nC32

PrPh

nC29

Franz Josef Land

14.22

20.02

22.39 23.2224.67

25.78

29.65

32.1332.98 35.11

38.9036.83 40.72 42.27 44.23 47.29c�



Pr/n�C17 and Ph/n�C18, indicating mixed�typeorganic matter (Fig. 3).

Shallow�marine shales of the Upper Triassic suc�cessions in the western part of the basin are character�ized by high contents of humic�type organic matter;on the Norwegian shelf they have present�day TOCvalues of 0.9–5% and initial TOC values of 2–10%(Fig. 6). The limited connection to the open sea andrestricted water circulation promoted preservation oforganic matter and the excellent hydrocarbon genera�tive potential of these rocks on the Norwegian shelf.On Spitsbergen, Upper Triassic rocks have lowerorganic matter contents (0.5–1.2%) and poor genera�tive potential (0.6 mg HC/g rock) caused by high�

energy water circulation and proximity to the open sealocated to the north of the study area.

CONCLUSIONS

1. Lateral and vertical variations in the amount andtype of organic matter in Triassic source rocks of theBarents Sea shelf are a function of the depositional set�tings. The best source rocks (up to 7–16% organic mat�ter of the mixed humic–sapropelic type) with excellentinitial generative potential are confined to the outerdeep�water shelf lithofacies zone, which during theEarly and Middle Triassic formed an N–S�trendingstrip in the western part of the basin. These facies com�prise Olenekian and Anisian rocks in eastern Spitsber�

96°0′ E84°0′ E

72°0′ E60°0′ E

48°0′ E36°0′ E

30°0′ E24°0′ E

18°0′ E12°0′ E6°0′ E0°0′ E

82°0′ N

78°0′ N

74°0′ N

70°0′ N

Bit.: 0.0025–0.62%

Bit.: 0.009%

Bit.: 0.018%

Bit.: 0.045–0.7%

Bit.: 0.0002–0.0025%

7219/9�1

7321/7�1

7128/4�1

7226/11�17124/3�1

1.3

3.9

0.9

0.7

1.15

0.7

1.7

0.1

0.74

0.2

1

(S1 + S2 )0= 3–17

S1 + S2 = 0.06–0.57

S1 + S2 = 0.67

S1 + S2 = 0.6

S1 + S2 = 0.4–24

1.6

1.9 EasternSouthern

Medvezhiy Isl


South Barents

Heiss

Ganza cape

III

II–III

SvalbardSpitsbergen

III

III

well

basin

Kolguevskaya well

Varandey�more

Pechora syneclise

Nordkapp

Hammerfest basin


CentralSpitsbergen

Wilhelm Land


Murmanskaya well

III

Nagurskaya well


Arkticheskaya

North Karasyneclise


Fedinsky high

Fersman rise

Admiralteisky swellNorth Siberian

threshold

Severnaya well

Lunin saddle

Svalbardsyneclise

Vernadskiihigh


North Barents basin

well

Sentralsbankenhigh

0.3

0.4

basinII–III

Shtokman–Ludlovmegasaddle

0.5

1.2

2.3

2.9

1.1

4.7

1.34

1.15

10.8

5.6

0.67III

0.16

TOC0 = 2–10%

III–II

Kola

monocline

Bjarmeland platform

Fig. 6. Comparison of the geochemical data from Upper Triassic source rocks and lithofacies zones of Late Triassic age. Thelegend is the same as in Fig. 2.

78°0′ E72°0′ E66°0′ E60°0′ E54°0′ E48°0′ E42°0′ E36°0′ E

10


NORINA et al.

gen and the Norwegian shelf. This zone, which ischaracterized by deposition of predominantly peliticmaterial, low�energy or sometimes stagnant reducingwater conditions, promoted better preservation oforganic matter.

2. Shaly rocks of shallow�marine lithofacies zones,which occupied much of the basin during the Triassic,have moderate contents of humic organic matter (1–2%)and fair to poor gas�generative potential. These faciescomprise the Induan sediments on Spitsbergen andthe Norwegian shelf, as well as the Lower and MiddleTriassic rocks on the FJL. Similarly to the Upper Tri�assic rocks of the Norwegian shelf, stagnant�watershallow�marine conditions in this area may have beenfavorable for better preservation of organic matter andhigher generative potential of these rocks.

3. Delta plains developed due to the enhancedinput of clastic material eroded from the Ural and PayKhoy mountain ranges. Shale beds in these succes�sions contain predominantly humic�type organicmatter. Oxic conditions and sediment dilution wereresponsible for the poor hydrocarbon generativepotential of Lower and Middle Triassic rocks from theSouth and North Barents Sea basins. Good sourcerocks can be confined to the maximum flooding sur�faces, which are readily visible on seismic data as high�amplitude continuous reflectors (Kazanin et al.,2011).

4. Shaly deposits of tidal floodplain lithofacieszones have low organic�matter content, which iscaused by high�energy waters and prevailing oxic con�ditions. A general shallowing of the basin and thewidespread establishment of these depositional set�tings by the Late Triassic could be responsible for thepoor generative potential of the Upper Triassic rocksof the Barents Sea basin. At the same time, therestricted lagoon environments may have promotedthe preservation of large amounts of organic matter ofboth the humic and humic–sapropelic types. Forexample, the Carnian black shales on the FJL gener�ally exhibit good to excellent gas�generative potential.

5. Since the higher�energy oxidizing conditions insediments of fluvial–lacustrine plains were unfavor�able for the preservation of organic matter; Triassicrocks in the south and southeast of the study area havelittle or no hydrocarbon generative potential.

REFERENCES

Abdullah, W.H., Organic facies variations in the Triassicshallow marine and deep marine shales of centralSpitsbergen, Svalbard, Mar. Pet. Geol., 1999, vol. 16,pp. 467–481.

Atlas: Geological History of the Barents Sea, Smelror, M.,Petrov, O.V., Larssen, G.D., and Werner, S., Eds.,Trondheim: Geological Survey of Norway, 2009.

Bjoroy, M., Hall, P.B., Ferriday, I.L., and Mork, A., Triassicsource rocks of the Barents Sea and Svalbard, Searchand Discovery Article. AAPG, 2010, no. 10218, pp. 1–6.

Glorstad�Clark, E., Faleide, J.I., Lundschien, B.A., andNystuen J.P., Triassic seismic sequence stratigraphyand paleogeography of the western Barents Sea area,Mar. Pet. Geol., 2010, vol. 27, pp. 1448–1475.

Gradzin�ski, R., Kostecka, A., Radomski, A., and Unrug, R.,Sedimentologiya (Sedimentologia), Moscow: Nedra,1980.

Grigor’eva, V.A., Eremin, N.A., and Nazarova, L.N.,Paleogeography and Oil�and�Gas Potential of TriassicDeposits of the Shelf Zones of the Pechora and BarentsSeas, Geol. Nefti Gaza, 1998, no. 9, pp. 10–17.

Danyushevskaya, A.I., Oil and Gas�producing strata ofPhanerozoic deposits of Arctic Islands, Geokhimiya,1995, no. 10, pp. 1495–1505.

Kazanin, G.S., Pavlov, S.P., Shlykova, V.V., et al., Seis�mogeologicheskoe stroenie Pechorskogo i Yugo�Vostoch�noi chasti Barentseva morei na osnove interpretatsiikarkasnoi seti seismicheskikh profilei MOB OGT 2D(Seismogeological structure of Pechora and the south�eastern part of the Barents Seas based on interpretationof the data from 2D CDP seismic reflection profiles),Moscow: GEOS, 2011.

Kiryukhina, T.A., Bol’shakova, M.A., Stupakova, A.V.,et al., Mesozoic oil and gas source deposits in the oil�and�gas potential basin of the Barents Sea, Geol. NeftiGaza, 2012, no. 3, pp. 24–35.

Klubov, B.A., Bezrukov, V.M., Garib’yan, E.V., andTaninnskaya, N.V., Active oil shows at the Franz JosefLand Archipelago and their most probable nature,Lithol. Miner. Resour., 1998, vol. 33, no. 4, pp. 386–390.

Leith, T.L., Weiss, H.M., Mork, A., et al. Mesozoic hydro�carbon source rocks of the Arctic region, in Arctic geologyand Petroleum Potential, Amsterdam: Elsevier, Norwe�gian Petroleum Soc., 1002, pp. 1–25.

Official web�site of Norwegian Petroleum Directorate.URL: http://www.npd.no. Cited May 1, 2010.

Sedimentary Environments and Facies, Reading, H.G., Ed.,New York: Elsevier, 1978.

Translated by N. Kravets

Documents

Depositional Environments and the Hydrocarbon Generative ...confined to the Lower and Middle Triassic successions deposited in a deepwater shelf environment in the western part of