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ThepetroleumpotentialoftheRiphean–VendiansuccessionofsouthernEastSiberia

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Geological Society, London, Special Publications

doi: 10.1144/SP366.1p177-198.

2012, v.366;Geological Society, London, Special Publications  and Marcela G?mez-PérezJames P. Howard, Olga K. Bogolepova, Alexander P. Gubanov succession of southern East SiberiaThe petroleum potential of the Riphean-Vendian

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The petroleum potential of the Riphean–Vendian succession

of southern East Siberia

JAMES P. HOWARD*, OLGA K. BOGOLEPOVA, ALEXANDER P. GUBANOV &

MARCELA GOMEZ-PEREZ

CASP, West Building, 181a Huntingdon Road, Cambridge CB3 0DH, UK

*Corresponding author (e-mail: james.howard@casp.cam.ac.uk)

Abstract: The Siberian Platform covers an area of c. 4.5 million km2 in the East Siberia region ofRussia, up to 3.5 million km2 of which is prospective for hydrocarbons. We review the Archaean toNeoproterozoic evolution of the Siberian Platform and the potential oil and gas resources ofRiphean, Vendian and Infracambrian sediments. The Riphean was dominated by passive marginsedimentation and was intensely deformed during the Baikalian orogeny. Vendian strata recorda clastic transgressive sequence and the eventual re-establishment of carbonate platform sedimen-tation. The late Vendian–early Cambrian is characterized by carbonate deposition including thicksalt horizons, which form a regional seal. Hydrocarbon maturation and migration from Riphean andVendian source rocks occurred during the late Neoproterozoic and Early Palaeozoic, indicatingthat hydrocarbon reservoirs on the Siberian Platform may have hosted their reserves over a remark-able period of geological time. Despite many years of hydrocarbon exploration in East Siberia,many regions remain under-explored, and aspects of the proven hydrocarbon systems are poorlyunderstood. There are undoubtedly more major discoveries to be made in the region, and the Infra-cambrian succession of the southern Siberian Platform therefore represents an irresistible target forfurther hydrocarbon exploration.

Infracambrian sedimentary basins are a majorsource of hydrocarbons in many parts of the world,including Australia, India, Pakistan, Oman, Mauri-tania, the USA and East Siberia. Oil shows werenoted in East Siberia more than 200 years ago, andsince then East Siberia has become a world-classhydrocarbon province. Oil and gas in-place esti-mates are 4 billion barrels of oil (Bbbl) (Nakashima2004) and .38 trillion cubic feet (TCF) of gas(Ulmishek 2001a, b; Nakashima 2004). Oil in EastSiberia is of high quality, with a density of318API, sulphur content of 0.1–1.3% and low paraf-fin content (c. 1%) (Poussenkova 2007). The EastSiberian gas reserves differ from the gas fields ofWest Siberia in that they have a particularly highhelium content (0.2–0.6%) (Poussenkova 2007).Total helium reserves in East Siberia are estimatedto be between 1.9 and 2.5 TCF, exceeding thehelium reserves of the USA, which is currently theworld’s largest producer (Poussenkova 2007).

Predicted values of the total volume of hydro-carbon reserves in East Siberia vary substantiallydepending on the source of the data. Resource esti-mates by Nakashima (2004) suggest that oil reservesrange from 18.9 Bbbl (standard case) to 67.2 Bbbl(upside case), representing 13% of in-place Russianreserves (Dobretsov et al. 2007). Gas reserves areestimated at 386 TCF, or 18% of in-place Russianreserves (Nakashima 2004; Dobretsov et al. 2007).

Estimates of maximum oil and gas production alsovary significantly (Tables 1 & 2), especially thoseprovided by the Siberian Academy of Sciences andGazprom (Tables 1 & 2). For East Siberia, peakoil production is estimated to be 188 Mbbl/yr byGazprom and 450 Mbbl/yr by the Academy, whilepeak gas production is estimated to be 4.7 TCF/yrby Gazprom and 4.2 TCF/yr by the Academy (Pous-senkova 2007). Such differences probably reflect thelimited scale of exploration in East Siberia as well aspolitical factors. Current estimates of hydrocarbonreserves in southern East Siberia indicate the rela-tive importance of the three oil and gas plays asfollows: Riphean carbonates (3%), Vendian clastics(67%) and Vendian–early Cambrian carbonates(30%). However, Shemin (2007) concludes thatthe distribution of these reserves reflects the focusof earlier exploration, not the actual potential ofeach oil and gas complex. The opening of theESPO (East Siberian Pacific Ocean) pipeline islikely to further stimulate exploration in the region.

Geology

The Siberian Platform occupies an area ofc. 4 500 000 km2 and is bound by the Enisey–Khatanga trough to the north, the Enisey and Lenarivers to the west and east respectively and by the

From: Bhat, G. M., Craig, J., Thurow, J. W., Thusu, B. & Cozzi, A. (eds) 2012. Geology and Hydrocarbon Potentialof Neoproterozoic–Cambrian Basins in Asia. Geological Society, London, Special Publications, 366, 177–198.First published online January 19, 2012, http://dx.doi.org/10.1144/SP366.1# The Geological Society of London 2012. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics

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Central Asian Orogenic belt to the south (Fig. 1).The platform comprises Archaean basement over-lain by a platform succession consisting of four sedi-mentary ‘megacomplexes’ deposited in Riphean,Vendian–Silurian, Devonian–Carboniferous andJurassic–Cretaceous time. The platform marginsare characterized by a thick Riphean passive mar-gin succession.

The southern part of the Siberian Platform, whichcontains numerous proven and potential Infracam-brian hydrocarbon fields, forms the focus of thispaper. In this section we outline the geological evol-ution of six geological regions – the Baykit Anticlisethe Khatanga Saddle, the Cis-Sayan Syneclise, theAngara-Lena Step, the Nepa-Botuoba Anticlise,and the Cis-Patom Trough, which together form asubstantial part of the Lena-Tunguska oil and gasprovince (Fig. 1; Kontorovich et al. 1976). TheRiphean platform succession and passive marginsediments deposited along the platform marginsduring the Mesoproterozoic and Neoproterozoiccontain organic-rich intervals interpreted to havebeen the source of most of the hydrocarbons onthe platform. Thus, the problem of long-term preser-vation of Infracambrian hydrocarbons, which iscommon to Infracambrian hydrocarbon plays else-where, may be complicated by the need to establishlong-distance migration pathways from the platformmargins onto the platform itself.

The region remains under-explored away fromknown fields, and correlation of Riphean andVendian strata is hampered by rapid lateral facieschanges, limited biostratigraphic data and an

incomplete understanding of geological structures(Egorov et al. 2003). Correlation of well-exposedRiphean platform margin successions, interpretedas deepwater deposits, with the shallow marine plat-form succession observed in boreholes is especiallyproblematic (Frolov et al. 2010).

Tectonic evolution of East Siberia

The Siberian Craton formed by the accretion of 11Archaean and 2 Palaeoproterozoic crustal blocksin the period 2.1–1.8 Ga (Rosen et al. 2006; Glad-kochub et al. 2006). The subsequent tectonic evol-ution of the Siberian continent, and its locationand orientation with respect to other continents,has been the subject of much debate and research.It is assumed that the Siberian continent formedpart of the supercontinent Rodinia; however, its pos-ition with respect to Laurentia and the timing of itsseparation remain unclear. The lack of reliablepalaeomagnetic data from cratonic basement hasled to a number of different reconstructions for thetwo continents (Pisarevsky & Natapov 2003).Frost et al. (1998) and Rainbird et al. (1998) pointout that stable platform sedimentation from 1.8 Gacombined with the lack of Grenville age defor-mation (1.25–0.98 Ga) implies that the Siberiancontinent was on the northeastern periphery ofRodinia. It is believed that during Neoproterozoictime Siberia was located at equatorial/subtropicallatitudes, south of the palaeoequator (Pavlov et al.2002; Cocks & Torsvik 2007). At the beginning of

Table 1. Oil production (million barrels/yr)

2010 2020 2030 Reference Region

750–788 900–990 Kontorovich (2007) Yakutia, Krasnoyarsk, Irkuksk81.6 351.6 375 Dobretsov et al. (2007) East Siberia225 Poussenkova (2007) East Siberia

450 (peak – RussianAcademy of Sciences)

Poussenkova (2007) Yakutia, Krasnoyarsk, Irkuksk

188 (peak – Gazprom) Poussenkova (2007) Yakutia, Krasnoyarsk, Irkuksk

Table 2. Gas production (TCF/yr)

2010 2020 2030 Reference Region

2.5–2.8 2.6–3 Kontorovich (2007) Yakutia, Krasnoyarsk, Irkuksk1.7 3.5 4 Dobretsov et al. (2007) East Siberia1.8 Poussenkova (2007) East Siberia

4.2 (peak – RussianAcademy of Sciences)

Poussenkova (2007) Yakutia, Krasnoyarsk, Irkuksk

4.7 (peak – Gazprom) Poussenkova (2007) Yakutia, Krasnoyarsk, Irkuksk

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the early Cambrian the Siberian Platform began todrift slowly north (Shatsillo & Pavlov 2006).

The three main areas of basement outcrop inEast Siberia are the Aldan Shield (the StanovoyBlock), the Anabar Shield and the Olenek Uplift.A number of smaller uplifts exist along the southernand southwestern margins of the Siberian Platform.The rest of the platform is covered by Riphean,Vendian and Phanerozoic sedimentary successions.

Following the accretion of the Siberian Craton,a phase of regional extension resulted in the forma-tion of several intracratonic rifts (e.g. the Irkineeva-Chadobets and Urik-Iya rifts). A recent seismic line(Rudnitskaya et al. 2008) indicates that these maybe more extensive than previously thought. Thisline shows evidence for an elongate Riphean basin,named the Angara-Kotul Rift Basin, containing upto 15 km of Neoproterozoic to Mesozoic sedimentstretching from the Angara River (e.g. Irkineeva-Chadobets Rift) north across the craton (Fig. 2)(Rudnitskaya et al. 2008; Starosel’tsev 2009).

Passive margin sedimentation appears to havebeen established along the southeastern (Pri–Baikal–

Patom) and western (Enisey) margin of the cratonby the Mesoproterozoic time, whereas the onset ofsedimentation along the southern and southwest-ern margins (Pri-Sayan) of the craton appears tobe younger, established in Neoproterozoic times(Gladkochub et al. 2006). Gladkochub et al. (2006)propose that the onset of passive margin sedimen-tation in the SW records the breakup of Rodiniaand the opening of the Palaeo-Asian Ocean.

Passive margin sedimentation continued intomid-Neoproterozoic times (between 850 and760 Ma), but by late Neoproterozoic times, boththe southwestern and southern platform margins hadtransformed into active margins. Island arcs andophiolites formed along the margins of the SiberianCraton between 750 and 650 Ma and were obductedonto the platform margins by 600 Ma, prior todeposition of the Vendian (Vernikovsky et al.2004). These events are collectively referred to asthe Baikalian orogeny; however, as discussed inVernikovsky et al. (2004), the accretionary eventsalong the margins of Siberia did not occur simul-taneously or have the same duration. Two fold

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Fig. 1. Tectonic regions in the southern part of the Siberian Platform (based on Mikulenko & Starosel’tsev 1979).Only oil and gas fields indicated in the text are shown. Inset map shows the platform margins and the area covered bythe main map. Uplifts on the Kamo Arch: 1, Kuyumba Uplift; 2, Tayga Uplift; 3, Chadobets Uplift. Sections describedin the text indicated by green dots: a, Goloustnaya; b, Biryusa and Tagul rivers.

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belts containing Neoproterozoic complexes cropout on the southern margin of Siberia: the EniseyRidge and Baikal–Vitam fold-and-thrust belt(Fig. 3).

The Enisey Ridge

The Enisey Ridge is a complex fold-and-thrustbelt that contains five terranes (East Angara,Central Angara, Isakov, Predivinsk and Angara-Kan; Fig. 3). The transformation from passiveto active margin occurred at c. 760 Ma and wasfollowed by several accretion events. The CentralAngara Terrane collided with Siberia between750 and 720 Ma. The Predivinsk island arc terranewas thrust eastwards onto the Angara-Kan between660 and 630 Ma, and the Isakov island arc wasobducted onto Siberia at 620–600 Ma (Verni-kovsky et al. 2004).

The Baikal–Vitam fold-and-thrust belt

The Baikal–Vitam fold-and-thrust belt resultedfrom the collision between the Barguzin micro-continent and the Siberian continent. This colli-sion event occurred over a prolonged period andwas preceded by the accretion of island arcsand ophiolites (the Baikal–Muya complex) toSiberia. Siberia’s southeastern passive margintransformed into an active margin during theLate Riphean, and the Baikal–Muya island arcsaccreted to the margin of Siberia during the latestRiphean or early Vendian (Khain et al. 1997).However, the main phase of deformation occurredwhen the Barguzin microcontinent collided withSiberia during the Early–Middle Palaeozoic.This collisional event resulted in gentle folding ofCambrian–Silurian sediments across the platformand, probably, the reactivation and uplift of the

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Fig. 2. Isopach map showing the distribution of Riphean sediments on the Siberian Platform, modified after Surkovet al. (1991). The thickness of Riphean sediments increases to 10–14 km along the platform margins (Khomentovskyet al. 1972). Inferred boundaries of the Angara-Kotul Rift Basin, after Starosel’tsev (2008), are also shown.

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Khatanga Saddle during the Late Silurian (Mel’ni-kov 1994).

Continental collisions around the platformmargins during the Neoproterozoic are associatedwith significant deformation of the interior of theSiberian continent, including rift inversion andblock uplift. Riphean strata are more heavilyfaulted than the overlying Vendian–Palaeozoicstrata (Frolov et al. 2011). The modern structuralframework of the Siberian Platform was establishedduring the Vendian and the most significant of thesestructures form the boundaries of the hydrocarbonprovinces shown in Figure 1.

Palaeozoic deformation on the platform ischaracterized by broad folding and vertical move-ments of large basement blocks. For example, the

Khatanga Saddle underwent uplift and reactivationduring the Silurian and subsequent subsidence dur-ing the Middle Carboniferous–Triassic (Mel’nikov1994). Smaller uplifts have also undergone phasesof Palaeozoic deformation; for example, in theBaykit region the Chadobets and Irkineeva Upliftswere active during the early Palaeozoic. At theend of the Palaeozoic, West Siberia underwentregional extension in response to the impact of amantle plume and eruption of the Siberian traps.

Stratigraphy of the Siberian Platform

Five phases of sedimentation can be recognized onthe Siberian Platform: Riphean, Vendian–Silurian,

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Fig. 3. Tectonic sketch map of Siberia modified after Vernikovsky et al. (2004) and Gladkochub et al. (2006). Areas ofPrecambrian exposure are indicated, together with the location of the main Baikalian faults.

RIPHEAN–VENDIAN OF SOUTHERN SIBERIA 181

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Devonian–Lower Carboniferous, Middle Carbon-iferous–Triassic and Jurassic–Cretaceous (Surkov1987). Up to 70% of the preserved thickness ofthe sedimentary cover of the Siberian Platformis represented by Vendian–Silurian rocks. In thissection we summarize the stratigraphic evolutionof the Siberian Platform.

Riphean

Where Riphean strata crop out (Fig. 3) they havebeen widely studied, and detailed stratigraphicdescriptions have been published (Semikhatov &Serebryakov 1983; Khomentovsky 1996; Podko-vyrov et al. 2002). However, relatively little isknown about the thickness and distribution ofRiphean strata across the platform where they areoverlain by Vendian and Palaeozoic strata. Theexceptions to this rule are the Kamo Arch andKhatanga regions, where extensive drilling is sup-ported by seismic data. The present-day distributionof Riphean sediments represents original deposi-tional geometries, the effects of Baikalian defor-mation and subsequent erosion prior to depositionof Vendian strata (Figs 2 & 4).

Riphean sediments are not preserved in thecentral parts of the Nepa-Botuoba High or on theAngara-Lena Step, and are much less abundant ontheir flanks in comparison with adjacent areas(Fig. 2). Elsewhere, Riphean strata range from 1 to4 km thick on the platform, but increase in thicknessto 10–14 km along the platform margins (Khomen-tovsky et al. 1972). Early models predicted thatsubstantial thicknesses of Riphean strata preservedon the platform were restricted to rifts (e.g. theIrkineeva-Chadobets and Urik-Iya rifts), but morerecent studies have increasingly recognized thatRiphean sediments are more widespread on the plat-form. Rudnitskaya et al. (2008) and Starosel’tsev(2008) propose an elongate Riphean basin, namedthe Angara-Kotul Rift Basin, extending acrossthe centre and west of the platform (Fig. 2), whileMel’nikov et al. (2005) describe the Chunya sedi-mentary basin that is bounded by the Baykit andKhatanga highs to the SW and SE, respectively,and Frolov et al. (2011) suggest a series of broadRiphean basins developed above early Ripheanrifts. Regardless of their names, these Ripheandepocentres occupy the same positions and, basedon seismic lines, are thought to contain almostcontinuous and thick (usually several kilometres)successions (Frolov et al. 2011). Consequently,these platform basins may be of great importanceas a source of hydrocarbons.

Along the southeastern margin of the platformin the Cis-Patom region, early Riphean strata arerepresented by fluvial sediments associated with vol-canic material, which are overlain by middle–late

Riphean sediments interpreted as continental shelfand slope deposits. The succession increases inthickness from 2800 m in the north to 8000 m inthe south and is interpreted to record deposition ona passive margin (Sovetov et al. 2007). This pas-sive margin succession was subsequently deformedinto a fold-and-thrust belt during the Baikalianorogeny.

On the southeastern part of the Angara-LenaStep, Riphean strata are 140–545 m thick and com-prise interbedded claystones, sandstones, blackshales and grey to black dolostones and limestones(Kontorovich 1995). These sediments thicken tothe south, and on the flanks of the Angara-LenaStep up to 3000 m of Riphean sediments uncon-formably overlie basement. These sediments con-sist of basal dolomites overlain by greywackes,sandstones, black shales and, in the upper part, brec-cias (Maslov & Kichko 1985; Flecker & Voronova1999). These sediments are interpreted to recorddeposition in shelf and slope environments and areinterpreted as late Riphean in age (Postnikov2001). Gladkochub et al. (2006) considered thesemarginal sediments as part of the Siberian Platformsequence; however, a marked change in palaeocur-rent orientations at the base of the late RipheanKachergatskaya Suite exposed in the Goloustnayasection indicates that the sediment was derivedfrom the south and east (Fig. 1; Flecker & Voronova1999). This implies sediment was shed into the evol-ving fore-arc basin, probably from the approachingBaikal–Muya island arcs, and the abrupt coarseningof sediment in the latest Riphean probably recordsthe onset of collision.

Along the southwestern margin of the platformin the Cis-Sayan region, some of the most completelate Riphean successions crop out along the Biryusaand Tagul rivers near Tayshet (Figs 1 & 5). Ripheanstrata are up to 5100 m thick (Mel’nikov 2005). Thesuccession has a basal clastic unit and becomesincreasingly carbonate-dominated upward, and isinterpreted as a passive margin succession (Fig. 5).This interpretation is supported by clinoformsobserved in a recent deep seismic profile acrossCis-Sayan (Mandelbaum et al. 1999).

The Enisey Ridge, to the west of the Baykitregion, contains the most complete Precambriansequences, reaching up to 12 km thick, from thePalaeoproterozoic to the Vendian (Mel’nikov2005). This clastic, carbonate and volcanic-sedi-mentary succession exposed in the East AngaraTerrane was deformed between 750 and 720 Maduring the collision between the Central AngaraTerrane and the Siberian continent (Vernikovskyet al. 2004). It is difficult to reconstruct the deposi-tional geometry; however, the westward thickeningof the succession and an increase in deepwaterfacies to the west supports a continuation of

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Fig. 4. Neoproterozoic to Early Palaeozoic sedimentary succession of the southern Siberian Platform (after Mel’nikov 2005, modified based on the author’s fieldobservations). Hydrocarbon systems are shown only for the Neoproterozoic–early Cambrian. Russian stratigraphic nomenclature is simplified (accepted Siberian regional stagesare shown in blue), and correlation with the International Chart is provisional. Note the limited lateral extent of the Riphean strata, in part due to erosion during the pre-Vendianunconformity. Vendian strata progressively onlap the unconformity and become increasingly widespread, recording a marine transgression. The stratigraphy of the Cis-Sayan regionremains uncertain. The Riphean stratigraphy of the Cis-Patom trough and the Cis-Sayan Syneclise contains numerous poorly constrained unconformities that are not includedin this figure.

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Fig. 5. Photographs showing representative features observed in the basement and Riphean strata exposed along the Tagul River near Tayshet. (a) Deformed metamorphicbasement to the SE of a major suture zone on the Tagul River. (b) Basaltic breccias of the Mesoproterozoic Subluk Formation. (c) Finely laminated stromatolitic dolostone of the lateRiphean Karagas Group. (d) General view of the monotonous thinly bedded clastic succession of the late Riphean Oselok Group along the Tagul River.

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passive margin sedimentation into this region(Gladkochub et al. 2006).

On the Baykit Anticlise, east of Enisey Ridge,Riphean strata are absent in the north but reach upto 4000 m thick in the south based on seismic anddrilling data (Kraevsky et al. 1991). The total thick-ness of Riphean rocks on the Khatanga Saddle is2000 m (Mel’nikov 2005). Riphean sediments cropout on the Chadobets Uplift, one of the smaller struc-tures complicating the anticlise (Fig. 1), and in theIrkineeva Uplift (Fig. 6a–d), a Riphean riftthought to have been inverted during the lateRiphean (Fig. 3), but are elsewhere buried underyounger strata. Riphean sediments on the BaykitAnticlise are dominated by interbedded carbonateand fine clastic beds and are interpreted to recordpassive margin sedimentation during early Neopro-terozoic time (Vernikovsky et al. 2004; Kochnevet al. 2007). The Enisey Ridge began to deformduring the late Riphean, and passive margin sedi-ments in the Baykit region are overlain by lateRiphean molasse (Vernikovsky et al. 2004).

At the end of the Riphean time, Siberia was anuplifted landmass from which clastic molassematerial was transported into surrounding basins(Mel’nikov et al. 2005). Uplifted collisional highsaround the platform margins provided a furthersource of clastic sediment. Riphean sedimentswere deformed in many areas and were partiallyand, in some areas (e.g. central Nepa-Botuoba),completely removed by erosion (Fig. 2).

Vendian

The Vendian succession records an overall trans-gressive regime with older formations restricted tothe platform margins and successively younger for-mations increasingly widespread across the craton(Fig. 4). Vendian sediments rest unconformably onvarious levels of the Riphean sediments and on crys-talline basement (Shenfel 1991).

During the Vendian, the Baykit and the Nepa-Botuoba basins are thought to have been locatedon the flanks of an uplift that occupied the centralpart of the Siberian Platform (Mel’nikov 1994).Between them was a less intensively subsidingregion, the Khatanga Saddle, which was invertedin the Late Silurian when the Barguzin microconti-nent collided with Siberia. This collisional eventresulted in deformation across the platform andhas important implications for petroleum migra-tion and trapping (see discussion of hydrocarbonpotential). The interpreted extent of these upliftsand their duration as topographic highs variesbetween publications (compare maps of Karnyush-ina et al. 2008 and Mel’nikov 1994). The thicknessof Vendian strata ranges from 160 m in the northernBaykit Anticlise to 1600 m in the southern and

southwestern Baykit Anticlise (Timoshina 2005)and the Nepa-Botuoba region (Mel’nikov 2005).

Vendian strata can be divided into four lithostra-tigraphic units: the Vilyuychan, Nepa, Tira regionalhorizons, which are clastic-dominated, and theNemakyt–Daldynian Danilovo Regional Horizon,which is characterized by carbonate deposition(Fig. 7; Mel’nikov 1994; Kochnev et al. 2007).Some progress has been made towards establishinga regional chronostratigraphy based on integratedd13C chemostratigraphy and establishing a tentativesequence stratigraphic framework (e.g. Knoll et al.1995; Pelechaty 1998); however, the older termi-nology is well established in the literature and ispreferred here.

Vilyuychan Regional Horizon

Strata belonging to the Vilyuychan RegionalHorizon are of uncertain age and lie between strataof known Riphean and Vendian age (i.e. the latestRiphean–early Vendian sensu Mel’nikov 2005).The sediments represent a post-Riphean molasseand are preserved only in marginal parts of theplatform (e.g. Nepa-Botuoba) where forelanddepressions formed adjacent and parallel to colli-sional belts formed by accretion of the Baikal–Muya ophiolites and island arcs during the latestRiphean and Vendian time (Vernikovsky et al.2004). Clastic sediment was derived both from theplatform and the surrounding orogens. Vilyuychanstrata are dominated by clastic strata everywhereexcept in the NE Cis-Patom region where marlsand shallow marine limestones and dolomites dom-inate the succession (Fig. 7). Karnyushina et al.(2008) use well data to reconstruct the distributionof clastic facies across the platform. Their map indi-cates that broad, conglomerate-dominated alluvialfans formed a fringe around uplifted areas and fedsediment onto a broad alluvial and lacustrine plain(Fig. 8a). Most of the clastic strata deposited on theAngara-Lena Step, Cis-Sayan and parts of the Nepa-Botuoba regions were eroded prior to deposition ofthe Nepa Regional Horizon (Mel’nikov et al. 1989).

Nepa Regional Horizon

Sediments belonging to the Nepa Regional Horizonare preserved over a much broader area than those ofthe underlying Vilyuychan Regional Horizon andextend into most parts of the southern Siberian Plat-form (Figs 7 & 8; Mel’nikov et al. 1989; Karnyush-ina et al. 2008). Erosional highs such as the KamoArch, central Siberia and parts of Nepa-Botuobaare fringed by sandstone-dominated successionsthat fine laterally into fine-grained alluvial plainand shallow marine successions (Figs 7 & 8). Themarked decrease in grain size combined with

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a

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Fig. 6. Field photographs showing outcrops of late Riphean and Vendian strata exposed on the Irkineeva Uplift atthe southern margin of the Baykit Anticlise. (a) Thinly bedded black shales of the middle Riphean UdereyFormation exposed on the Irkineeva River. In the subsurface this unit is a potential source horizon for the BaykitAnticlise. (b) Interbedded black sandy shales and sandy dolostones of the Upper Riphean Pogoryuy Formation exposedon the banks of the Nizhnyaya Terya River. (c) Thick succession of thinly bedded dolomites, sandstones and siltstonesfrom the late Riphean Kartochka Formation exposed on the banks of the Irkineeva River. (d) Organic-rich dolostonesand small reef bodies of the late Riphean Potoskuy Formation exposed on the Irkineeva River. This interval providesanother potential source of hydrocarbons to the Baykit Anticlise. (e) Outcrop of the Vendian Chistyakov Formation onthe Irkineeva River. Vendian strata overlie the Baikalian unconformity and are dominated by clastic strata. Thesecoarsening-upward, sandstone-dominated deposits are interpreted as a prograding clastic delta sourced from the EniseyRidge. Late Vendian carbonate units are not exposed in the Irkineeva Uplift.

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evidence for denudation of source areas (e.g. 60 mcliffs incised into Riphean strata on the KamoArch; Mel’nikov 1994) indicates that uplift of the

source areas had slowed or migrated furtherinland. Isopach data indicate that the subsidencealong the southwestern platform margin had

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Fig. 8. Palaeogeographic maps showing the southern Siberian Platform during Vendian time modified after Mel’nikov(1994). (a) Vilyuchan, (b) Nepa, (c) Tira, (d) Danilovo (Lower–Middle), (e) Danilovo (Upper). Maps are based ona review of well and outcrop data too numerous to show on the maps.

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migrated eastwards into the Cis-Sayan region(Mel’nikov 1994). In contrast, the Baykal–Patomdepression (in the Cis-Patom region) underwentcontinued subsidence in response to the ongoingcollision between the Baikal–Muya island arcsand Siberia and up to 600 m of sediment accumu-lated in an open shelf environment. The Cis-EniseyForedeep (east of the Enisey Ridge) also remainedactive and underwent periodic marine incursions(Fig. 8b). This final phase of subsidence occurredin response to the accretion of the Isakov and Predi-vinsk island arc terranes to Siberia (Vernikovskyet al. 2008).

Tira Regional Horizon

In the Tira Regional Horizon, the ongoing marinetransgression inundated large parts of the SiberianPlatform and only isolated land areas remained(e.g. Khatanga, Fig. 8c). Subsidence continuedacross the Cis-Enisey and Cis-Patom foredeeps andon the Angar-Lena Step and Cis-Sayan regions. Sedi-ments belonging to the Tira Regional Horizon arewidely preserved across the platform and are char-acterized by a broad mix of lithologies includingclastics, carbonates, sulphates and salt (Fig. 7).The margins of the platform are again dominatedby sandstones sourced from the now denudedsource areas in the SW and SE and from the EniseyRidge. In western areas, away from the clasticsources, much of the platform was dominated bydeposition of mud-grade sediment. Eastern Nepa-Botuoba and the Cis-Patom depression are character-ized by interbedded clastic and carbonate succes-sions. Sulphate and carbonate rocks occur in thedeepest part of the Cis-Patom depression. Salt depos-its up to 50 m thick were deposited in the westernmargin of the platform (e.g. Angara River) in lateTira time, and coeval anhydrite and anhydritic dolo-mites formed in the hypersaline shallow sea thatdominated the central and eastern parts of the plat-form (Mel’nikov 2005).

Danilovo Regional Horizon

The Danilovo Regional Horizon overlies a dis-conformable or unconformable basal contact withthe Tira Regional Horizon sediments (Fig. 7). Inthe Danilovo Regional Horizon the marine trans-gression finally inundated the platform and, apartfrom low-lying land areas along the platformmargins, sedimentation occurred across the wholeof thearea (Figs7&8d).The thickest sedimentsaccu-mulated in the Cis-Sayan where total thicknessesreach 600 m, and thick successions may also haveaccumulated in the Cis-Enisey Trough and Cis-Patom Depression. The lower part of the Danilovosuccession is dominated by sandstones derived

from highs at the platform margins (Sovetov et al.2007). Anhydrite or salt occur in all areas at the endof early Danilovo time. Carbonates were depositedacross much of the platform during middle–lateDanilovo time. The central part of the platform wasdominated by shallow-water, salt-bearing carbon-ates, whereas deeper-water conditions prevailedin the southern part of the platform (Mel’nikov1994, Fig. 8e).

Post Vendian stratigraphy

Following deposition of the Vendian, subsidencegreatly increased during Cambrian and EarlyOrdovician time and a 2200–3600 m thick succes-sion of evaporites and carbonates accumulated(Mel’nikov 1994). Subsidence rates decreasedduring the Middle Ordovician–Silurian, when amixed clastic and carbonate succession accumu-lated and parts of the platform underwent periodicuplift in response to the collision of the BarguzinTerrane with southern Siberia. Nepa-Botuoba,Angara-Lena and the northern Cis-Patom regionswere exposed sources of clastic sediment by lateSilurian time. The Khatanga region was alsoinverted during the Late Silurian. Vendian–Siluriansuccessions reach 2700–3100 m in Nepa-Botuoba,Baykit and Khatanga, 3900–4000 m in the Cis-Patom and Angara-Lena regions, and up to6000 m in the Cis-Sayan region (Mel’nikov 1994).

During the Devonian and Early Carboniferous,sedimentation was localized; up to 250 m accumu-lated in the northern flanks of the Kamo Arch,200 m in the Cis-Sayan region and 150 m in the Cis-Patom regions. The succession is dominated byclastic sediments eroding from exposed highs atthe margins of the platform and also within the plat-form, for example, in the Khatanga region.

The Middle-Carboniferous–Triassic time wascharacterized by widespread uplift and erosion ofCarboniferous and Silurian sediments. Subsidenceincreased in the south of the platform during thePermian when 300–500 m of coal-bearing clasticswere deposited in the Cis-Sayan region. The Cis-Patom and Angara-Lena regions continued to actas an uplifted sediment source at this time. Thelatest Permian and Early Triassic of northernSiberia is dominated by deposition of the Siberiantraps, and during Middle–Late Triassic time thewhole of southern Siberia was uplifted and under-went erosion with the removal of 150–300 m ofEarly Palaeozoic sediments (Mel’nikov 1994).

During Early–Middle Jurassic, Late Creta-ceous and Early Palaeogene times, thin sedimentsaccumulated across the southern part of the SiberianPlatform; however, Mel’nikov (1994) suggests that,on balance, erosion outstripped sediment accumu-lation in the southern Siberian Platform.

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Petroleum potential

The Lena Tunguska oil and gas province contains 99known hydrocarbon fields, of which 29 are oil andgas fields and 60 are gas condensate fields (Naka-shima 2004). Most of these fields are located inthe Nepa Arch and Kamo Arch, including the fivelargest oil and gas fields, which together accountfor 85% of the proven oil reserves in East Siberia.The remaining fields are located in the KhatangaSaddle and Angara-Lena Step (Fig. 1).

These fields are hosted in Riphean–Cambrianstrata, which, based on regionally distributed reser-voirs and seals at several stratigraphic levels, maybe subdivided into three distinct oil and gas plays,each with their own reservoir and top seal. Theseare (i) a Riphean play in which carbonate reservoirsare sealed by early Vendian clastic sediments; (ii) aVendian play consisting of four clastic reservoirs inthe Vilyuychan, Nepa and Tira Regional Horizonswith a muddy carbonate seal in the lower part ofthe Danilovo Regional Horizon; (iii) a Vendian–Cambrian play with two carbonate reservoirs inthe Middle and Upper Danilovo and Lower Cam-brian succession. A regional seal is provided bysalt bearing dolomites.

In this section we summarize potential sourceand reservoir units for each of the hydrocarbonplays before outlining the likely maturation his-tory. The exploration potential for each region ofthe southern Siberian Platform is also discussed.

Source rocks

Riphean strata are recognized by most authors as aprimary source for hydrocarbons on the SiberianPlatform, with some estimating that they accountfor up to 90% of known hydrocarbon reserves(Drobot 1988). Riphean source rocks are knownboth on the platform and in the deformed remnantsof foreland basins and back-arc basins around theplatform margins. In the platform succession, goodsource rock intervals occur at the base of deposi-tional cycles at several levels on the Kamo Archand Khatanga saddle, where Riphean strata havebeen widely studied in wells. Highly prospectiveintervals include the Lower–Middle Riphean Vedre-shev and Madra formations (mean TOC 1.2%), theLate Riphean Iremeken Formation (mean TOC8.27%) on the Kamo Arch, and the late RipheanAyan Formation (mean TOC 1.45%) on theKhatanga Saddle (Filiptsov et al. 1998; Timoshina2005). These source rocks are characterized bygreat lateral and vertical variability, leading to avery irregular distribution of organic matter (Frolovet al. 2011). The source potential of Riphean plat-form sediments deposited in deeper basins (e.g. theAngara-Kotul Rift Basin/Chunya Basin and the

Cis-Sayan Syneclise) that have not been drilled isuncertain. However, based on the presence ofgood source intervals on their margins, and thetrend to deep marine depositional environments inthe basin centres, they must be considered good can-didates for source rock deposition. Riphean succes-sions preserved at the deformed platform marginsinclude thick intervals with excellent source poten-tial and great lateral extent. In the Cis-PatomTrough, Middle–Late Riphean carbonaceous mud-stones have TOC values .10% (Khabarov 1995).In the Cis-Enisey Trough, thick accumulations ofblack shale, subsequently deformed and uplifted aspart of the Enisey Ridge, contain source rock inter-vals with TOC values of 5–10%, occasionally ashigh as 20% (Voronova & Tull 1993).

Potential hydrocarbon source rock intervals arealso known from Vendian strata. Early Vendian sedi-ments on the Siberian Platform are dominated bycontinental red beds that have low organic content.However, mudstones in the Middle VendianOskoba Formation have TOC values up to 14% onthe Kamo Arch (Timoshina 2005). Vendian sedi-ments on the Cis-Sayan region have not beenwidely drilled; however, it seems likely that intervalswith source potential were deposited in this deepbasin during late Vendian time (Fig. 8). The Cis-Patom Trough remained a marine basin throughoutthe Vendian and contains two potential source inter-vals. Vendian black mudstones with TOC values of4–5% are reported and, in a 10 m thick black mud-stone unit at the top of the Nepa Horizon, meanTOC reaches 5.6% (Drobot 1988; Mel’nikov1994). This suggests that Vendian source rocks,despite being less rich in TOC than Riphean sourcerocks, are probably widespread in the overthrustzone of the Patom Highlands (Mel’nikov 1994).

Palaeozoic source rocks are not reported insouthern Siberia, although Silurian strata are con-sidered important in the Tunguiska Basin to the NW.

Reservoirs

The three hydrocarbon plays are distinguishedbased on the assessment of probable reservoirunits. In this section we discuss the reservoir poten-tial of each of these plays in general terms; mechan-isms of trap formation vary from region to regionand are discussed later.

Riphean clastic and carbonate units have gener-ally low reservoir potential across the platform dueto depositional heterogeneity and subsequent altera-tion during millions of years of deformation andfluid flow. There are, however, two situationswhere alteration of Riphean strata increases porosityand permeability to the point that they becomeviable reservoirs. Reservoirs are reported withinthe Riphean succession where tectonic fracturing

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of carbonate units leads to leaching and cavernousporosity. The Bysykhtakh Field in the eastern Siber-ian Platform is the only example of this field type.The future potential of such reservoirs is uncertain;some authors (e.g. Surkov et al. 1991) consider themimportant while others (e.g. Frolov et al. 2011)dismiss them as exploration targets. In contrast,the potential of reservoirs developed by karstifica-tion of exposed Riphean strata prior to depositionof the Vendian is undisputed following discoveryof the Yurubchen and Kuyumba Fields on the KamoArch. On the Kamo Arch the palaeo-karst developedbelow the unconformity and penetrated up to 500 mbelow the top of the succession (Voronova & Tull1993). The porosity is largely the result of leachingduring exposure and, combined with later fractur-ing, has produced cavernous reservoirs with poros-ities as high as 10% (Kuznetsov & Skobeleva2005). Riphean strata were eroded over wide areasof the Siberian Platform; consequently, karstifiedRiphean reservoirs are predicted around themargins of the Baykit Anticlise, Khatanga Saddleand around the Angara-Lena Step (Fig. 2).

Where preserved, Vendian clastic reservoirsare considered the most important target for hydro-carbon exploration on the southern SiberianPlatform. Sandstone reservoirs occur at several stra-tigraphic levels and are usually named according tolocal stratigraphic schemes. They are commonlystratigraphically sealed by interbedded siltstoneand evaporite beds, and a regional seal is providedby muddy carbonates in the lower part of the Dani-lovo Horizon. Correlation of sandstone reservoirsbetween fields is problematic due to an absence ofregional seismic data and a paucity of fauna.

Late Vendian–Cambrian reservoirs are mostsignificant in areas where the clastic Vendian isabsent, such as in Central Nepa-Botuoba, wherecavernous algal dolomites with porosities between7 and 9% occur, and the Vilyuychan Saddle (innortheastern Nepa-Botuoba), where limestone anddolomite reservoirs have porosities of 10–25%(Mel’nikov 1994). Particularly high porositiesoccur where carbonates were sub-aerially exposed,leading to karstification; examples are the trapforming reefs in the basal part of the early CambrianOsa Formation in the Talakan–Verkhnyaya–Chonafield (Mel’nikov et al. 2005). In the Khatangasaddle, Vendian carbonates of the Soba, Tetre andOka formations are sealed by salt in the upperUsolka Formation, although these reservoirs havegenerally low permeability (Mel’nikov et al. 2008).

Maturation and migration

The importance of Riphean source rocks in thehydrocarbon systems of East Siberia presents ahuge span of geological time for hydrocarbon

maturation and migration to occur. The literatureis dominated by two migration models, one invok-ing Vendian–Cambrian maturation and the otherproposing Early Palaeozoic maturation. The differ-ence between these models lies in the significanceattached to Riphean source rocks on the platformmargins.

If Riphean strata in the Pre-Enisey Trough andthe Cis-Patom Trough are an important source ofhydrocarbons to reservoirs on the platform, then amodel invoking early generation, migration andtrapping must be invoked, because these sourceregions were substantially deformed during theBaikalian orogeny.

Most authors agree that source intervals in thePre-Enisey Trough passed into the oil window(and possibly into the gas window) during theRiphean, and that the hydrocarbons generatedwould have migrated up dip onto the platform.There is, however, significant disagreement as tothe potential for early hydrocarbons to be trappedand preserved on the platform. Trapping and preser-ving early hydrocarbons through the Baikalianorogeny and subsequent deformation events pre-sent significant problems. In particular, the pro-cesses of karstification and structuration thatcreated the Riphean reservoirs on the Kamo Archoccurred during the Baikalian orogeny, and theseals are provided by the basal Vendian strata.Consequently, it seems likely that hydrocarbonsgenerated during the Riphean must have beendestroyed by erosion during the creation of thepre-Vendian unconformity (Frolov et al. 2011).Bitumens resulting from the weathering of hydro-carbons are seen in Riphean–Triassic strata acrossthe Siberian Platform and are testimony to thevolume of hydrocarbons lost during the long evol-ution of the hydrocarbon systems (Bazhenova &Tull 1995). Other authors suggest that althougha substantial proportion of the early generatedhydrocarbons were destroyed, there is the potentialfor some of them to have been trapped withinthe Riphean succession, and from there they mayhave subsequently migrated into the present reser-voirs (Surkov et al. 1991). Timoshina (2005) recog-nized two distinct hydrocarbon families on theSiberian Platform, one of which was restrictedto the Riphean fields on the Kamo Arch. Kontoro-vich et al. (1988) established that organic materialof Riphean age was the source of hydrocarbonsdiscovered in Riphean clastic reservoirs by tracingabnormally high contents of 12–13-mono-methy-lalkanes present in oils from the Yurubchen fieldand also in bitumen extracts from Riphean sourcerocks, which implies a Riphean source unique tothis region.

In the Cis-Patom Trough the main stage of colli-sional deformation occurred during the Palaeozoic;

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consequently, there is greater potential for hydro-carbons generated in this basin to be preserved.Generation of hydrocarbons from Riphean sourcerocks is thought to have begun during the Ripheanand to have been completed during the Vendianbut, as discussed above, much of the early gen-erated hydrocarbons are likely to have been lostduring formation of the pre-Vendian unconformity(Mel’nikov 1994). The main stage of migrationfrom Riphean source rocks into Vendian andVendian–Lower Cambrian reservoirs on theSiberian Platform occurred during late Vendian–early Cambrian time, after the formation of theregional seals (Mel’nikov 1994). Vendian sourcerocks in the Cis-Patom Trough began to generatehydrocarbons in the late Cambrian, and peak gener-ation and migration was reached during the Silurian(Kontorovich et al. 1981).

Riphean source intervals deposited in basins onthe platform (Cis-Sayan and Angara-Kotul Rift/Chunya Basin) underwent less pre-Vendian ero-sion and, due to the increasing Vendian overburden,they probably passed through the oil window duringthe Vendian. Ultimately, Riphean and Vendiansource intervals were buried deep enough duringthe Palaeozoic to exhaust their hydrocarbon poten-tial (Frolov et al. 2011). The hydrocarbons producedin these basins will have been destroyed by thermalalteration unless they migrated to shallower strati-graphic positions. Cambrian salt inhibits upwardmovement, so lateral migration to the basin mar-gins is the only pathway available. This has clearimplications for targeting hydrocarbon explorationin these basins.

The timing of hydrocarbon generation fromRiphean source rocks on the Kamo Arch is wellconstrained. Lower–Middle Riphean source rocksof the Vedreshev and Madra formations, whichunderlie the pre-Vendian unconformity, are lateor post mature. They are directly overlain byVendian sediments that are within peak maturityfor organic matter (Filiptsov et al. 1999; Timoshina2005). This categenic unconformity suggestsLower–Middle Riphean units reached maximummaturity during pre-Baikalian time. In contrast, agradual increase in kerogen maturation is recordedbetween Late Riphean source rocks (e.g. theIremeken Formation) and Vendian source rocks,suggesting they reached maturity post Baikaliantime (Filiptsov et al. 1999). Frolov et al. (2011)show that Late Riphean source intervals on theKamo Arch began to generate oil in the Vendianand peaked during the upper Cambrian or Ordovi-cian. Peak gas generation followed during theOrdovician–Silurian, and the main phase for gasmigration probably occurred in the Triassic,related both to emplacement of the Siberian Trapsand cracking of earlier oil.

Regional hydrocarbon potential

Cis-Patom Trough

The Cis-Patom Trough can be traced along theeastern boundary of the Siberian Platform (Fig. 1),and is 1000 km long and up to 150 km wide. Thisdepression formed in response to collisions duringthe Baykalian orogeny and contains thick Early–Middle Riphean passive margin sediments overlainby a Late Riphean–Vendian active margin and fore-land basin succession that contains known sourceintervals. Sediments in the Cis-Patom Troughwere intensely deformed during the collision ofthe Barguzin microcontinent and Siberia duringthe Silurian, and the inner slope and base of thedepression are buried beneath thrust sheets thattectonically juxtapose Vendian outer shelf andslope deposits on coeval sabka evaporites (Pele-chaty 1998).

The Cis-Patom Trough is considered to be animportant regional kitchen from which hydrocar-bons generated in Riphean and Vendian sourceintervals charged oil, gas and gas condensate fieldson the Nepa-Botuoba Anticlise and Angara-LenaStep. The Cis-Patom Trough underwent continuedsubsidence from Riphean to Silurian times, andhydrocarbon generation probably began in the lateRiphean and continued until the Silurian when thebasin closed.

The charging of reservoirs in the Nepa Archand Angara-Lena Step from source rocks in theCis-Patom Trough requires a lateral migration ofup to 300 km. The architecture of the SiberianPlatform during the Vendian–Cambrian was favo-urable to such long-distance migration, becausethe thick carbonates and clastic successions depos-ited on the platform margins provided a fairwayfor up-dip migration onto the elevated flanks ofthe platform.

The Bysykhtakh gas field in the northern part ofthe foredeep probably formed in a thrust-relatedanticline (Ulmishek 2001a). No other hydrocarbonfields are known from this area and it has lowexploration potential due to the intensity of Siluriandeformation.

Nepa-Botuoba Anticlise

The Nepa-Botuoba Anticlise, located in the SE of theplatform, is 800 km long and 380 km wide and iscovered by early Vendian–early Palaeozoic clasticunits. Following Baikalian uplift, Riphean stratawere eroded from the crest of the Nepa-BotuobaAnticlise, and clastic Vendian strata onlap themargins of the high. A number of small structures,including the Nepa Arch and Verkhnyayan ChonaUplift, formed on the crest of the anticlise during

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this deformation event. Successful exploration inNepa-Botuoba has focused on oil and gas depositshosted in Vendian sandstone reservoirs. Severallarge fields have been discovered, mainly locatedon the Nepa Arch. These include the four largestoil fields in East Siberia; Verkhnyaya-Chona(1220 Mbbl, 1.1 TCF), Chayanda (730 Mbbl, 5.6TCF), Talakan (570 Mbbl, 1 TCF) and SrednyayChandayaa Botuoba (440 Mbbl, 5.5 TCF) (Naka-shima 2004). Carbonate reservoirs are less importantin this region, and only in the Vilyuchansk regionhave hydrocarbons been found in dolomite reser-voirs (Mel’nikov 1994; Drobot et al. 2004).

The most important reservoirs on the Nepa-Botuoba Anticlise belong to the clastic Vendianplay. Sandstone reservoir units occur at several hor-izons, but most have limited lateral extent. Theycommonly wedge out as they onlap the high andshale out to the SE. Abrupt changes in the reservoirproperties of the sandstones result from diagenesis,including silicification, halitization and sulphatiza-tion, which are irregular and unpredictable. Diagen-esis is thought to have occurred after the first phaseof hydrocarbon migration and to have sealed exist-ing reservoirs, protecting them against subsequenttectonic movement (Vinogradov 1978).

Hydrocarbon fields in the Nepa-Botuoba regioncan be divided into anticlinal and sheeted types.Anticlinal traps, which drape over basement highs,characterize hydrocarbon fields on the crest ofthe Nepa-Botuoba Arch (Ulmishek 2001a). Thesefolds deform Vendian and often early Cambriansediments and are interpreted to have formedduring the Early Palaeozoic in response to terraneaccretion along the southern margin of Siberia.The timing of their formation is critical to the viabi-lity of the early hydrocarbon migration model.Lithological variation in reservoir properties formsthe main trapping mechanism in non-anticlinalfields on the Nepa-Botuoba Anticlise, where trapsdue to simple stratigraphic pinchouts are rare (Mel’-nikov 1994). Many fields, particularly those in theMirnin area in northeastern Nepa-Botuoba areaffected by faults that compartmentalize reservoirs.These faults probably formed during Early Palaeo-zoic compressional deformation and represent a sig-nificant risk to a Vendian–Cambrian hydrocarboncharge. However, the combination of significantreservoir heterogeneity and the presence of Cam-brian salt, which forms a self-sealing trap, providesprotection to early hydrocarbon accumulations.

Hydrocarbon accumulations in the Vendian–Cambrian play generally occur where the clasticVendian play is thin or absent. The Vendian–Cambrian play forms important reservoirs in twoareas: (i) in central Nepa–Botuoba, where caver-nous algal dolomites occur with porosities between7 and 9% (slightly reduced by secondary halite);

(ii) the Vilyuychan Saddle in northeastern Nepa-Botuoba, where limestone and dolomite reservoirsare less affected by secondary halite, resulting inporosities of 10–25% and more continuous lateralextent (Mel’nikov 1994). Particularly high poros-ities occur where carbonates were sub-aeriallyexposed, leading to karstification, such as the trap-forming reefs in the basal part of the early CambrianOsa Formation in the Talakan-Verkhnyaya Chonafield (Mel’nikov et al. 2005). Accumulations insuch reservoirs clearly require a late Cambrian oryounger charge. It is possible that reservoirs of theVendian–Cambrian play were charged by second-ary migration of hydrocarbons from reservoirs inthe Vendian play on the flanks of the Nepa-BotuobaAnticlise, for example, when older reservoirs over-flowed or where seals were breached during Palaeo-zoic faulting.

The main phase of hydrocarbon maturation andmigration from Riphean source rocks in the Cis-Patom Trough into the Nepa-Botuoba Arch isthought to have occurred during the Riphean–early Cambrian (Mel’nikov 1994). Owing to theage of the reservoirs (Vendian–Cambrian) and thelater structuration, the preservation potential ofthese hydrocarbons appears low. Maturation andmigration of Vendian hydrocarbons began in theVendian and continued into the Silurian; con-sequently, these hydrocarbons have a much greaterpreservation potential. However, geochemical stu-dies suggest a Riphean source for the majority ofthe hydrocarbons on the Nepa-Botuoba Anticlise,with Vendian source rocks providing only around30% of the total (Drobot et al. 2004). The problemsinherent in preserving hydrocarbons derived fromthe Cis-Patom Trough lead us to suggest that theremay be a contribution from Riphean source rockson the platform that were less deeply buried andconsequently matured later. Riphean strata areabsent across the Nepa-Botuoba region, but arewidespread to the west and NW (Fig. 2).

Angara-Lena Step

The Angara-Lena Step (Fig. 1) lies at the southernend of the Siberian Platform, covering a territoryof c. 350 000 km2, and it shares many geologicalcharacteristics with the Nepa-Botuoba Arch(Ulmishek 2001a). Three giant gas condensatefields, thought to have been charged from sourcerocks in the Cis-Patom Trough, have been dis-covered on the Angara-Lena Step: the Kovykta,Bratsk and Atovo fields (Fig. 1).

The Vendian Chora Formation (equivalent to theNepa and Tira regional horizons) contains four pro-ductive sandstone beds: Bokhan, Shaman, Parfenovand Bratsk (Mel’nikov et al. 2005). The sandstonesare grey/red and separated by siltstone and

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anhydrite, and range from 3 (Bokhan) to 80 m thick(Parfenov). The major reservoir in all three fieldsis the Parfenov bed, which lies in the upper part ofthe clastic Vendian play, although commercial gasflows have been achieved from the older horizonsin some wells.

Traps in the Angara-Lena Step are simple anti-clines in which Vendian and Cambrian stratadrape basement blocks, with minor faulting (e.g.Bratsk and Atovo fields) or stratigraphic traps intilted fault blocks (Kovykta field). The anticlinesand faulting are presumed to have formed duringthe Early Palaeozoic collisional events in theBaikal–Vitam Fold-belt. The resources of thegiant Kovykta gas-condensate field are estimatedto contain up to 1.9 TCF gas, plus 450 Mbbl ofgas condensate. The gas from the Kovykta field con-tains 0.28% helium, 37–42% of Russia’s totalhelium reserves (Poussenkova 2007). Reservoirthickness ranges from 5 to 30 m and it is possiblethat the Kovykta field might not simply be a field,but may instead form part of a huge condensatereservoir up to 200 km in diameter. Recoverableresources of this greater Kovykta reservoir couldbe as high as 10 TCF (Poussenkova 2007).

Overlap in the timing of hydrocarbon migrationfrom the Cis-Patom Trough and the formation ofreservoirs and traps on the Angara-Lena Step, thelong migration distances required and subsequentdeformation all suggest that the preservation poten-tial of Riphean–Vendian hydrocarbons is low.However, the high helium content of the Kovyktagas field on the Angara-Lena step (0.28%) is signifi-cant. Helium may be derived either from uraniumdecay in Vendian reservoir lithics or from basementrocks, and to reach such high concentrationsrequires a long-lived, efficient trap that would alsoprotect an early hydrocarbon charge.

Khatanga Saddle

The Khatanga Saddle is between 125 and 225 kmwide and 200 and 400 km long, and lies betweenthe Nepa-Botuoba Anticlise and the Baykit Anti-clise. The Khatanga Saddle contains part of theRiphean–Vendian Chunya sedimentary basin(Mel’nikov et al. 2008; coincident with part of theAngara-Kotul Rift Basin) but was inverted in lateSilurian–Early Carboniferous time. It underwentfurther subsidence during the Middle Carbonifer-ous–Early Triassic.

Two producing oil and gas fields exist withinthe Khatanga Saddle: the Payga and Soba fields(Fig. 1). Commercial quantities of oil havealso been obtained from individual wells in otherareas of the saddle. The Payga and Soba fieldslie on the eastern margin of the Chunya Basinwhere Riphean strata eroded on the flanks of the

Nepa-Botuoba Anticlise subcrop Vendian sand-stones of the Vanavara Formation (Nepa RegionalHorizon). These sandstones form reservoirs withporosities ranging from 2.3 to 22% (in the Sobafield) that are sealed by anhydritic dolomite of theoverlying Oskoba Formation. The trap is an anti-cline that has been complicated by faulting produ-cing three separate block structures (Bitner et al.1990). The timing of the faulting remains uncertain,but it is likely to postdate trapping and relate toblock uplifts in Silurian–Early Carboniferous time.

The primary source rocks in the Khatanga Saddleare considered to be Riphean strata preserved in theChunya Basin (Mel’nikov et al. 2005). UpperRiphean sediments beneath the Soba field containhighly carbonaceous rocks (Filiptsov et al. 1998)that occur in the 140 m thick Ayan Formation asblack mudstone with marl interbeds with a meanTOC of 1.45%. As discussed above, hydrocarbonsproduced within the Chuna Basin cannot migratevertically due to Cambrian salt, so instead migratelaterally into fields at the margins of the basin (i.e.the Khatanga Saddle and the Baykit Anticlise).

The Khatanga Saddle is the focus of renewedexploration, particularly within the Ilimpeya pet-roleum zone to the north of the Soba and Paygafields. The main prospects are (i) late Riphean kar-stified carbonates sealed by Vendian mudstones(analogous to the Yurubchen–Tokhoma petroleumaccumulation zone), (ii) the Vendian play recog-nized in the Soba and Payga fields, and (iii) lateVendian carbonates of the Vendian–Cambrianplay, although these suffer from low porosity andpermeability in the area (Mel’nikov et al. 2008).

Cis-Sayan Syneclise

South of the Baykit Anticlise is the Cis-SayanSyneclise (Fig. 1), which covers an area ofc. 192 000 km2. Its western and southwestern mar-gins are formed by the eastern Sayan and EniseyRidge fold-belts. To the west it is bounded by theAngara-Lena Step. The Cis-Sayan basin is a deepEarly Palaeozoic depression in which the basementoccurs at depths of 5–7 km (Mel’nikov 1994).

No hydrocarbon fields have yet been discoveredin the Cis-Sayan Syneclise; however, the area con-tains a thick Riphean and Vendian succession thathas been buried to sufficient depths for hydrocarbonmaturation to occur during Vendian–Early Palaeo-zoic time. The Riphean succession is likely toinclude potential source units similar to those inthe Chunaya Basin to the north and there is particu-lar interest in late Vendian strata exposed SW of theBiryusa River where the clastic succession (ShamanFormation) contains bitumen (Zolotov 1969; Mel’-nikov et al. 2005; Samsonov & Larishev 2008).Hydrocarbons generated within the Cis-Sayan

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Syneclise may have migrated into the surroundinghighs in the Angara-Lena Step, Baykit Anticliseand southern Nepa-Botuoba Anticlise, but there isgreat potential for stratigraphic, lithological (e.g.reefs) and structural traps around the margins ofthe syneclise itself and therefore good potential forhydrocarbon exploration in the region.

Baykit Anticlise

The Baykit Anticlise lies in the western part of theplatform, east of the Enisey Ridge and north of Cis-Sayan Syneclise. It occupies an area of 155 000 km2.The major structures of the Baykit Anticlise havebeen mapped using seismic surveys: Central KamoArch, Kuyumba Uplift, Tayga Uplift and ChadobetsUplift (Fig. 1). Several large oil and gas fields areknown in the Baykit Anticlise, mainly located onthe Kamo Arch in the Yurubchen–Tokhoma Pet-roleum Accumulation Zone (PAZ).

Riphean strata on the Baykit Anticlise are up to3000 m thick and are unconformably overlain bythin Vendian deposits. The clastic Vendian is thinor absent, so the Riphean play is the main focus ofexploration in the region.

The structure of the petroleum reservoirs iswell understood based on extensive well data (Kon-torovich et al. 1994; Kuznetsov 1997). Ripheanstrata consist of a deformed succession of 12 alter-nating clay–carbonate, carbonate and clay units.The reservoir interval is a fractured Riphean dolos-tone represented by stromatolitic, intraclastic andmicrogranular varieties. Riphean strata were sub-aerially exposed for a long period during the earlyVendian, and an extensive palaeo-karst has devel-oped below the unconformity. Leaching duringexposure, combined with later fracturing, producedcavernous reservoirs with porosities as high as10% (Kuznetsov & Skobeleva 2005). Oil and gashave only been found in areas of well-developedpalaeokarst and subsequent fracturing, so theboundaries of the Yurubchen–Tokhoma PAZ arelargely defined based on the distribution of thepalaeo-karst (Voronova & Tull 1993; Mel’nikovet al. 2008). High-quality seals are provided bymudstones in the overlying Vanavara Formation(Vendian), sulphate- and carbonate-bearing clasticsof the Oskoba Formation (Vendian) and widespreadlower Cambrian salt (Voronova & Tull 1993).

The Vendian succession, represented by mud-stones interbedded with sandstones and siltstones,is thin (160–200 m) in the north and central partof the Baykit Anticlise and thick (750–1400 m) inthe south and the SW, close to its boundaries(Timoshina 2005). Exploration in Vendian stratafocuses on the Vanavara Formation (where its thick-ness exceeds 30 m, Mel’nikov et al. 2008) andthe overlying Oskoba Formation. The Vanavara

Formation contains five levels of oil- and gas-bearing sandstones sealed with a thick sulphatemember of the Oskoba Formation. The Oskoba For-mation contains a highly radioactive sandstone bedthat has provided an economic gas flow in theOmora field (Mel’nikov et al. 2008). LateVendian–Early Cambrian potential reservoirs arefound in the Soba, Tetere and Osa carbonates,with the salt-bearing upper part of the Usol’e For-mation acting as a regional seal. However, these car-bonates have low porosity and permeability,limiting their potential. The Vendian–Cambrianboundary is conformable; however, its exact strati-graphic position has not been identified.

There are four hydrocarbon source regions withthe potential to charge reservoirs in the Baykit Anti-clise: the Cis-Enisey Trough to the west, the Cis-Sayan Syneclise to the south, the Chunya Basin tothe NE and the Baykit Anticlise itself.

Timoshina (2005) and Kontorovich et al. (1988)established that fields hosted by Riphean sedimentson the Kamo Arch belong to a distinct hydrocarbonfamily, implying a distinct source that has notcharged fields in adjacent regions. The ChunyaBasin is a source of hydrocarbons to the KhatangaSaddle so is unlikely to be the source of a uniquehydrocarbon family on the Baykit Anticlise. Hydro-carbons sourced from the Chunya Basin do, how-ever, represent a major play (the Chunku-UchamiPetroleum Accumulation Zone) along the northeast-ern flanks of the Bakyit Anticlise (Mel’nikov et al.2008). Source intervals in the Cis-Enisey Trough,Cis-Sayan Syneclise and on the Baykit Anticliseitself therefore represent potential sources forhydrocarbons in known fields.

As discussed earlier, the preservation potentialfor hydrocarbons generated in the Cis-EniseyTrough is low because maturation occurred priorto formation of both the karst reservoir andVendian seal. Riphean and Vendian sources on theBaykit Anticlise are mature (Frolov et al. 2011),but the distribution of organic matter is patchy andtheir potential is therefore uncertain. The Cis-SayanSyneclise has very good source potential, assuminga similar maturation history to that proposed for theChunaya Basin (Mel’nikov et al. 2008). However,migration of hydrocarbons from the Cis-SayanSyneclise onto the Baykit Anticlise may have beenimpeded by deformation along the IrkineevaUplift, which was repeatedly reactivated in earlyPalaeozoic time.

In addition to the Riphean source rocks dis-cussed above, there are Vendian source rocks,including the late Vendian Oskoba Formation,which has TOC values of up to 14% on the KamoArch (Timoshina 2005). These Vendian sourcerocks are likely to be the source of oil and gasreserves in the Kuyumba field that are genetically

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distinct from hydrocarbons found in Riphean reser-voirs (Bazhenova & Tull 1995).

Discussion

The recent interest in hydrocarbon exploration inEast Siberia has supported increased levels of geo-logical research in the region. The results of thisresearch have revealed the geological complexityof this region by highlighting, and beginning toresolve, problems in our understanding of EastSiberia’s tectonic history, stratigraphy and hydro-carbon systems. Recent research has proven thepotential for Riphean source rocks on the platformand mapped the depocentres in which hydrocarbonmaturation and migration from these sources hasoccurred.

The potential for widespread Riphean andVendian source intervals on the Siberian Platformprovides an alternative to models invoking earlymaturation and migration from the platformmargins. However, despite problems reconcilingthe timing of maturation and migration with thetiming of trap formation in the Baykit Anticliseand the problems inherent to preserving hydro-carbon reservoirs filled during Neoproterozoic–Cambrian time, it remains likely that some fieldsin East Siberia have achieved this longevity. Themain factors supporting the preservation of ancienthydrocarbon reserves in East Siberia are as follows.

† Since the development of the base Vendianunconformity when substantial loss of earlyhydrocarbons occurred (Mel’nikov 1994), someareas of the platform have not been substantiallydeformed. Palaeozoic deformation, particularlyduring the Silurian (uplift) and Permian (exten-sion), was mainly localized at the edge of base-ment blocks, and over much of East SiberiaNeoproterozoic and Early Palaeozoic strata aredeformed only into long-wavelength folds.Faulting within these blocks is not intense, andalthough it probably breached early seals insome fields (e.g. Yurubchen), many fieldsremain largely unfaulted.

† The high helium content found in gas reserves onthe Angara-Lena Step (Kovykta field) indicatesthat excellent trap integrity was sustained overextended periods of geological time. Such trapswould also be capable of preserving an earlyhydrocarbon charge.

† Late Vendian argillaceous evaporate-rich car-bonate beds, together with early Cambriansalts, form excellent regional seals. These are amajor factor contributing to the preservation ofhydrocarbon pools in Riphean and Vendianreservoirs over very long time periods, becausesalt formations are self-sealing and consequently

difficult for faults to breach. The presence of thisregional seal increases the chance of re-trappinghydrocarbons leaking from early accumulationsbreached by later deformation events.

† Widespread secondary mineralization inNepa-Botuoba is thought to post-date the earlyhydrocarbon charge. Secondary mineralizationreduces porosity around hydrocarbon fields,improving the seal and making the fields lesssusceptible to breaching by subsequent folding,tilting or faulting.

† Organic-rich Riphean and Vendian sediments inthe Cis-Patom Trough represent the only knownsource rock capable of charging reservoirs ineastern Nepa-Botuoba. Hydrocarbons sourcedfrom these rocks migrated during the Vendian–Cambrian.

† The composition of oil in reservoirs on theSiberian Platform indicate it is derived predomi-nantly from Riphean source rocks. In mostregions Riphean source rocks were producinghydrocarbons during Vendian–Early Palaeozoictimes. The large reserves discovered suggestsome of the early hydrocarbons must have beenpreserved.

† The influence of magmatic rocks on Infracam-brian strata is not very well understood;however, it appears to have been minimal. TheSiberian Platform has undergone several phasesof extensive intrusive and extrusive volcanismculminating in the Permian–Triassic eruptionof the Siberian traps (Mel’nikov et al. 1995). Insome areas, magmatic rocks are thought to com-prise large volumes of the preserved section (e.g.up to 20% in the Baykit region; Shemin 2007).However, the effects of these intrusions on thehydrocarbon systems are likely to be limitedbecause in most cases intrusions are hosted instrata of Cambrian and younger age and arerarely found in Infracambrian strata. Magmaticepisodes also post-date the main phases ofhydrocarbon maturation and migration, so theeffects of high heat flow associated with theimpact of a mantle plume on the base of theSiberian Craton are not a major influence onhydrocarbon maturation in the region. The highheat flow may have resulted in cracking of oilin reservoirs increasing the volume of gas(Frolov et al. 2011).

Hydrocarbon exploration on the Siberian Platformhas largely focused on the Vendian clastic succes-sion with the exception of the Baykit region wherethe Riphean play is the primary target. Despiteextensive drilling and seismic surveys, much ofthe southern Siberian Platform remains unexploredand many geological questions remain. The discov-ery of a major Riphean basin covering .40 000 km2

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with significant potential for hydrocarbon gener-ation, as recently as 2003–2005 (Mel’nikov et al.2008; Rudnitskaya et al. 2008; Starosel’tsev2008), indicates the potential gaps in our currentgeological understanding of the region. Furtherbiostratigraphic and chemostratigraphic work isrequired to refine stratigraphic correlations acrossthe platform and to accurately locate key boundarieswithin the succession. Only when strata can be accu-rately correlated across the region can the relation-ships of hydrocarbon systems from different areasbe fully understood.

Our existing knowledge of Infracambrianhydrocarbon resources on the Siberian Platformreflects the narrow focus of past exploration. Byexpanding the search for hydrocarbons into newareas such as the NW Baykit Anticlise, the north-western Nepa-Botuoba Arch and the Cis-SayanSyneclise, and increasing the targeted successionto include the promising regional Riphean andVendian–Cambrian play, there are probably morelarge discoveries to be made in the region.

References

Bazhenova, T. & Tull, S. J. 1995. Organic Geochemis-try of the Upper Precambrian–Palaeozoic Sequencesof the Siberian Platform. CASP Russian StratigraphicSeries Report 613.

Bitner, A. K., Krinin, V. A. et al. 1990. Hydro-carbon Potential of Ancient Productive Complexesof the Western Siberian Platform. SNIIGGiMS,Yeniseyneftegazgeologiya.

Cocks, L. R. M. & Torsvik, T. K. 2007. Siberia, the wan-dering northern terrane, and its changing geographythrough the Palaeozoic. Earth Science Reviews, 82,29–74.

Dobretsov, N. L., Kanygin, A. V. & Kontorovich,A. E. 2007. Economics and Environment as factorsof sustainable development of Siberian mineralresources. In: Briskey, J. A. & Schulz, K. J. (eds)Proceedings, Workshop on Deposit Modeling,Mineral Resource Assessment, and Sustainable Devel-opment, U.S. Geological Survey Circular, 1294, 143.

Drobot, D. I. 1988. History of Oil and Gas Generationand Evaluation of the Oil and Gas Content of the Pre-cambrian and Cambrian of the Siberian Platform.IGiG, Novosibirsk [in Russian].

Drobot, D. I., Pak, V. A., Devyatilov, N. M., Khoklov,G. A., Karpyshev, A. V. & Berdnikov, I. N. 2004.Precambrian petroliferous deposits on the southernSiberian Platform: exploration for extractable hydro-carbons. Russian Geology and Geophysics, 1, 98–108.

Egorov, V. A., Vinogradov, V. I., Kolesnikov, E. M.,Murav’ev, V. I. & Bujakaite, M. I. 2003. Multistagealterations of pre-Vendian oil-bearing rocks of theBaykit Anticlise (Siberian Platform) based on Rb–Srand K–Ar data. Lithology and Mineral Resources,38/5, 394–402.

Filiptsov Yu. A., Boldushevskaya, L. N., Petrishina

Yu. V., Krinin, V. A. & Kontorovich, A. A. 1998.

Alteration grade of organic matter and prediction ofthe phase composition of oil in fields of differentages in the Siberian Platform and the West SiberianPlate, Krasnoyarsk Region. In: Geology and MineralResources of the Krasnoyarsk Region. KNIIGGiMS,Krasnoyarsk, 79–94.

Filiptsov Yu. A., Petrishina Yu. V., Bogorodskaya,L. I., Kontorovice, A. A. & Krinin, V. A. 1999.Estimation of catagenesis and petroleum potential oforganic matter in the Riphean and Vendian depositsof the Baykit and Khatanga petroliferous areas. Geolo-giya I Geofizika, 40/9, 1362–1374 [in Russian].

Flecker, R. & Voronova, L. 1999. Precambrian Sedi-ments of the SE Siberian Platform: Initial FieldResults and Facies Analysis. CASP Arctic andRussian Studies Report 694.

Frolov, S. V., Akhmanov, G. G., Kozlova, E. V.,Krylov, O. V., Sitar, K. A. & Galuskkin, Y. I.2011. Riphean basins of the central and western Siber-ian Platform. Marine and Petroleum Geology, 28,906–920, doi: 10.1016/j.marpetgeo.2010.01.023.

Frost, B. R., Avchenko, O. V., Chamberlain, K. R. &Frost, C. D. 1998. Evidence for extensive Proterozoicremobilization of the Aldan Shield and implications forProterozoic plate tectonic reconstructions of Siberiaand Laurentia. Precambrian Research, 89, 1–23.

Gladkochub, D. B., Pisarevsky, S. A., Donskaya, T. V.,Natapov, L. M., Mazukabzov, A. M., Stanevich,A. M. & Sklyarov, E. V. 2006. The Siberian Cratonand its evolution in terms of the Rodinia hypothesis.Episodes, 29/3, 169–174.

Karnyushina, E. E., Korobova, N. I. & Mardanova,S. R. 2008. Facies zoning of Vendian petroliferousterrigenous strata in central and southern areas ofEast Siberia. Moscow University Geology Bulletin,63/6, 402–404.

Khabarov, E. M. 1995. Sedimentary environmentsof black shale source rocks in the tectonically differ-ent Riphean sedimentary basins (south of EastSiberia). In: Abstracts of Chinese–Russian Symposiumon Palaeozoic and Proterozoic Petroleum Potential,Bejing, Chinese Oil Corporation, 158–182 [inRussian].

Khain, V. E., Gusev, G. S., Khain, E. V.,Vernikovsky, V. A. & Volobuev, M. I. 1997.Circum–Siberian Neoproterozoic ophiolite belt.Ophioliti, 22, 195–200.

Khomentovsky, V. V. 1996. Event-based stratigraphyof Neoproterozoic of Siberia and China. Geologiya IGeofizika, 37/8, 43–56 [in Russian].

Khomentovsky, V. V., Shenfil, V. Yu., Yakshin, M. S.& Butakov, E. P. 1972. Base Sections of the UpperPrecambrian and Lower Cambrian Deposits of Siber-ian Platform. Nauka, Moscow [in Russian].

Knoll, A. H., Grotzinger, J. P., Kaufman, A. J. &Kolosov, P. 1995. Integrated approaches to terminalProterozoic stratigraphy: an example from the OlenekUplift, northeastern Siberia. Precambrian Research,73, 251–270.

Kochnev, B. B., Nagovitsin, K. E. & Faizullin Sh.,M. 2007. The Baikalian and Vendian sequences inthe Lower Angara area (southwestern SiberianPlatform). Russian Geology and Geophysics, 48,933–940.

RIPHEAN–VENDIAN OF SOUTHERN SIBERIA 197

by guest on March 25, 2013http://sp.lyellcollection.org/Downloaded from

Kontorovich, A. 2007. Eastern prospects of Russia’soil industry. Oil of Russia, 2 international quarterlyedition.

Kontorovich, A. A., Kontorovich, A. E. et al. 1988.The Yurubcheno–Tokhoma zone of gas and oilaccumulation – an important object of concentrationof regional and prospective work in the Upper Proter-ozoic of the Lena-Tunguska oil and gas province. Geo-logiya I Geofizika, 29/11, 45–55.

Kontorovich, A. A., Surkov, V. S. et al. 1994. Oiland gas bearing basins and regions of Siberia. Nepa-Botuoba Region. In: Kontorovich, A. A. (ed.) Oiland Gas Bearing Basins and Regions of SiberiaRussian Academy of Sciences, Volume 1. UIGGM,Novosibirsk.

Kontorovich, A. E. (ed.) 1995. Oil and Gas Basins andRegions of Siberia. Irkutsk Basin, Novosibirsk, 8 [inRussian].

Kontorovich, A. E., Mel’nikov, N. V. & Starosel’-

tsev, V. S. 1976. Oil and gas regions of the SiberianPlatform. Geologiya Nefti I Gaza, 2, 6–16 [inRussian].

Kontorovich, A. E., Surkov, V. S. & Trofimuk, A. A.1981. The Petroleum Geology of the Siberian Platform.Nedra, Moscow [in Russian].

Kraevsky, B. G., Pustyl’nikov, A. M. & Krinin, O. A.1991. New data on the Riphean stratigraphy ofBaykit Anticlise. Geologiya I Geofizika, 6, 103–110[in Russian].

Kuznetsov, V. G. 1997. Riphean hydrocarbon reservoirsof the Yurubchen–Tokhom zone, Lena-Tunguska pro-vince, NE Russia. Journal of Petroleum Geology, 20/4, 459–474.

Kuznetsov, V. G. & Skobeleva, N. M. 2005. Silicifica-tion of Riphean Carbonate sediments (Yurubcha-Tokhomo zone, Siberian Craton). Lithology andMineral Resources, 40/6, 637–665.

Mandelbaum, M. M., Mishen’kin, B. P. et al. 1999. AStudy of the Southern Siberian Platform and BaykalRift Zone Using Deep Seismic Sounding. UIGGiM,Novosibirsk, 10–21 [in Russian].

Maslov, V. K. & Kichko, A. I. 1985. Ore zonations ofmiddle-upper Riphean deposits in the Baikal areaWest and North-West. Lithology and MineralResources, 6, 83–96.

Mel’nikov, N. V. 1994. The Vendian geology and hydro-carbon potential of the southern Siberian Platform.CASP Russian Stratigraphic Series Report 583.

Mel’nikov, N. V. (ed.) 2005. Stratigraphy of Oil and GasBasins of Siberia. Riphean and Vendian of SiberianPlatform and its Folded Margins. Novosibirsk, 428[in Russian].

Mel’nikov, N. V., Egorova, L. I. & Killina, L. I. 1989.The Cambrian stratigraphy of the Bakhta megaswell.Geology and Geophysics, 3, 9–21 [in Russian].

Mel’nikov, N. V., Filiptsov Yu. A., Valchak, V. I.,Smirnov, E. V. & Borovikova, L. V. 2008. Petroleumpotential of the Riphean–Vendian Chunya sedimen-tary basin in the western Siberian Platform. RussianGeology and Geophysics, 49, 176–182.

Mel’nikov, N. V., Sitnikov, V. S., Vasil’ev, V. I., Dor-

onina, S. I. & Kolotova, L. V. 2005. Bioherms ofthe Lower Cambrian Osa Horizon in the Talakan–Upper Chona zone of petroleum accumulation

(Siberian Platform). Russian Geology and Geophysics,46, 834–841.

Mel’nikov, N. V., Voronova, L. G. & Tull, S. J. 1995.The Influence of Igneous Rocks on the Hydrocarbon-Bearing Deposits of the Siberian Platform. CASPRussian Stratigraphic Series Report 631.

Mikulenko, K. I. & Starosel’tsev, K. S. 1979. TectonicMap of Sedimentary Cover of the Siberian Platform.Scale 1:200 000, SNIIGGiMS, Novosibirsk [in Russian].

Nakashima, K. 2004. Petroleum Potential in the EastSiberian Region, Institute of Energy Economics, Japan.

Pavlov, V. E., Gallet, Y., Petrov, P., Yu., Zhuravlev,D. Z. & Shatsillo, A. V. 2002. The Ui Group and LateRiphean sills in the Uchur–Maya area: isotope andpaleomagnetic data and the problem of the Rodiniasupercontinent. Geotectonics, 36, 278–292.

Pelechaty, S. M. 1998. Integrated chronostratigraphy ofthe Vendian system of Siberia: implications for aglobal stratigraphy. Journal of Geological Society,155, 957–973.

Pisarevsky, S. A. & Natapov, L. M. 2003. Siberia andRodinia. Tectonophysics, 375, 221–245.

Podkovyrov, V. N., Kovach, V. P. & Kotova, L. N.2002. Mudrocks from the Siberian hypostratotypeof the Riphean and Vendian: chemistry, Sm–Ndisotope systematic of sources and formation stages.Lithology and Mineral Resources, 37/4, 344–363.Translated from Litologiya I Poleznye Iskopaemye, 4,397–418.

Postnikov, A. A. 2001. The History of the Baikal-VilyuiBasin in the Late Precambrian, in Supercontinentsand Geological Evolution of Precambrian. Instituteof the Earth Crust, Siberian branch of the RussianAcademy of Sciences, Irkutsk, 208–212.

Poussenkova, N. 2007. The Wild, Wild East. East Siberiaand the Far East: a new petroleum frontier? CarnegieMoscow Center, 4.

Rainbird, R. H., Stern, R. A., Khudoley, A. K., Kropa-

chev, A. P., Heaman, L. M. & Sukhorukov, V. I.1998. U–Pb geochronology of Riphean sandstoneand gabbro from southeast Siberia and its bearing onthe Laurentia–Siberia connection. Earth and Plane-tary Science Letters, 164, 409–420.

Rosen, O. M. 2003. The Siberian craton: tectonic zonationsand stages of evolution, Geotectonics, 37/3, 175–192.

Rosen, O. M., Levskii, L. K. et al. 2006. Paleoprotero-zoic accretion in the northeast Siberia craton: isotopicdating of the Anabar Collision System. Stratigraphyand Geological Correlation, 14, 581–601.

Rudnitskaya, D. I., Val’chak, V. I., Starosel’tsev,V. S., Goryunov, N. A. & Shcherbakov, V. A.2008. [Investigation into the deep crustal structure ofpetroleum provinces in East Siberia, from seismicdata]. Geofizika, 3, 13–17 [in Russian].

Samsonov,V.V.&Larishev, A. I.2008.Prospectivepetro-leum complexes and zonation of southern Siberian Plat-form. Neftegazovaya Geologiya, 3 [in Russian] http://www.ngtp.ru/

Semikhatov, M. A. & Serebryakov, S. N. 1983. GIN ANSSSR. Stratigrafical Hypostratotype of Riphean Depos-its. Nauka, Moscow, 367 [in Russian].

Shatsillo, A. V. & Pavlov, V. N. 2006. Paleomagnetismof Vendian rocks in the southwest of the Siberian Plat-form. Russian Journal of Earth Sciences, 7.

J. P. HOWARD ET AL.198

by guest on March 25, 2013http://sp.lyellcollection.org/Downloaded from

Shemin, G. G. 2007. Geology and the Vendian and EarlyCambrian Petroleum Potential of the Central Parts ofSiberian Platform (Nepa-Botuoba and Baykit anti-clises, and the Khatanga Saddle. Russian Academyof Science, Novosibirsk [in Russian].

Shenfel, V. Y. 1991. Late Precambrian of the SiberianPlatform. Science Academy of USSR, Novosibirsk[in Russian].

Sovetov Yu. K., Kulikova, A. E. & Medvedev, M. N.2007. Sedimentary basins in the southwestern SiberianCraton: Late Neoproterozoic–Early Cambrian riftingand collissional events. In: Linnemann, U., Nance,R. D., Kraft, P. & Zulauf, G. (eds) The Evolutionof the Rheic Ocean: From Avalonian–CadomianActive Margin to Alleghenian–Variscan Collission.The Geological Society of America. Special Paper,423, 549–578.

Starosel’tsev, V. S. 2009. Identifying paleorifts aspromising tectonic elements for active oil and gas gen-eration. Russian Geology and Geophysics, 50,358–367.

Surkov, V. S. 1987. Megacomplexes and Deep Structureof the Earth Crust in Petroleum Provinces of the Siber-ian Platform. Nedra, Moscow [in Russian].

Surkov, V. S., Grishin, M. P. et al. 1991. The Ripheansedimentary basins of the Eastern Siberia Province andtheir petroleum potential. Precambrian Research, 54,37–44.

Timoshina, I. D. 2005. Geochemistry of Organic Matter ofoil Source Rocks and Oils from Upper PrecambrianStrata of Southern East Siberia. GEO, Novosibirsk[in Russian].

Ulmishek, G. F. 2001a. Petroleum Geology andResources of the Nepa-Botuoba High, Angara-LenaTerrace, and Cis-Patom Foredeep, SoutheasternSiberian Craton, Russia. U.S. Department of theInterior, U.S. Geological Survey. Document 2201-C.

Ulmishek, G. F. 2001b. Petroleum Geology andResources of the Baykit High Province, East Siberia,Russia. U.S. Department of the Interior, U.S. Geologi-cal Survey. Document 2201-F.

Vernikovsky, V. A., Vernikovskaya, A. E., Pease, V. L.& Gee, D. G. 2004. Neoproterozoic Orogeny along themargins of Siberia. In: Gee, D. G. & Pease, V. L. (eds)The Neoproterozoic Timanide Orogen of EasternBaltica, Geological Society, London, Memoirs, 30,233–248.

Vernikovsky, V. A., Vernikovskaya, A. E. et al. 2008.Late Riphean alkaline magmatism in the westernmargin of the Siberian Craton: a result of continentalrifting or accretionary events? Doklady Earth Sciences,419/1, 226–230.

Vinogradov, L. D. 1978. State of the Problem of For-mation of Diagenetically Sealed Oil and Gas Poolsand Their Exploration. VIEMS, Moscow [in Russian].

Voronova, L. G. & Tull, S. J. 1993. The Hydrocarbon-Bearing Riphean Succession of the Baykit Region,SW Siberian Platform. CASP Russian StratigraphicSeries Report 570.

Zolotov, A. N. 1969. Geological structure of the TulunCis-Sayan and the history of its development duringthe Early Palaeozoic. Geology and Petroleum Poten-tial of East Siberia. Nedra, Moscow, 69–88 [inRussian].

RIPHEAN–VENDIAN OF SOUTHERN SIBERIA 199

by guest on March 25, 2013http://sp.lyellcollection.org/Downloaded from