the marine devonian in the northern part of western siberia

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ISSN 1028334X, Doklady Earth Sciences, 2009, Vol. 429, No. 8, pp. 1295–1298. © Pleiades Publishing, Ltd., 2009. Original Russian Text © B.I. Chuvashov, V.S. Bochkarev, A.M. Brekhuntsov, 2009, published in Doklady Akademii Nauk, 2009, Vol. 429, No. 2, pp. 234–237. 1295 Individual boreholes amidst a few drilled north of Siberian Uvaly (Spurs) yielded information on the reliable Paleozoic of Western Siberia [1]. For this rea son some researchers suggest a wide distribution of the Permian–Triassic formation in the northern part of Western Siberia [2]. Study of the core from the deep parametric borehole Yarudeiskaya 38 drilled 80 km south of the Gulf of Ob (Fig. 1) demonstrated the Devonian section of marine deposits composed of limestone–tuffvolcanic rocks with microfauna of a definite age. This Paleozoic sequence was penetrated by a borehole (BH) within the depth interval of 4382– 5010 m. The studied rocks are intensely dislocated, distinctly metamorphosed, and recorded in the seis mic field as an ordinary acoustic basement. Paleozoic rocks in the section are covered with gen tly dipping Upper Triassic, Jurassic, Cretaceous, and Paleogene deposits common for the Nadym–Taz Syn eclise. The late Paleozoic graben traced from the Gulf of Ob southward for nearly 200 km was revealed in the Paleozoic basement within the region of BH Yarude iskaya 38, which is located on its eastern slope. The section is subdivided into four members. Established from top to bottom are the following members: (1) tuffaceous–flysch, visible thickness 172 m; (2) tuffite–clastolava, visible thickness 170 m; (3) lime stone–conglomeratic within the depth interval of 4724–4794.8 m; and (4) andesite–basaltic, visible thickness 215.2 m. The angle of the dip of rocks varies from 90°–80° at the top to 40° at the base of the sec tion. The roof of Paleozoic rocks exhibits traces of intense weathering. The first member is composed of predominating sil iceous–clay shales, tuffites, and radiolarites. The color of the rocks varies from bluish green to dark gray and black. The bedding changes from banded to very fine due to color variations and lithological varieties. Clayey sandstone and gritstone are encountered in places. Serpentinite predominates in rock debris, and radiolarians are found in siliceous varieties. The second member is made of graygreen, red brown, and dark gray tuffites, tuff breccias, and small basalt bodies with greenstone alterations. The domi nant dip angle of rocks is 40°. Andesites were pene trated within the interval of 4641–4642 m. The third member is represented by marbled light gray and greenish limestones with valves of brachio pods (?) (depth 4790 m) and tentaculites (?), as well as interlayers of variegated conglomerate breccias with rock debris up to 2–7 m in size. Thin sections were made from limestones for extensive studies of foraminifers and algae. Limestone is biogenic and composed of calcareous algae Shu guria, Izhella, Renalcis, Epiphyton. This is a typical biocoenoses of Devonian organic structures. Identi fied among the foraminifers—common dwellers of algal biotopes—are Vicinisphaera angulata Antrop., V. squalida Antrop., Parathurammina aff. pusilla Byk., P. aff. scitula Tchuv., and Cribrosphaeroides sp. n. Especially abundant are sedentary forms Ivdelina elongata Malakh. Carbonates were dated at the Emsian of the Early Devonian. Biogenic limestones abound in numerous original interstices which at present are filled with secondary coarsecrystalline calcite–sparite. Sparite nests are up to 1 cm across. The rocks were formed in a wellilluminated zone of a shallow sea, but deeper than the zone of influence of regular waves on the sediment (>12–15 m). Periodic shoaling and sediment washout are revealed due to the presence of carbonate breccias. The fourth member is composed of andesites, basalts, and their tuffs. The rock color varies from dirty green to almost black. The rocks are massive, pyrox ene–plagioclase, with small rare amygdules and intense chloritization. The Marine Devonian in the Northern Part of Western Siberia Corresponding Member of the RAS B. I. Chuvashov a , V. S. Bochkarev b , and A. M. Brekhuntsov b Received May 4, 2009 DOI: 10.1134/S1028334X09080121 a Institute of Geology and Geochemistry, Ural Division, Russian Academy of Sciences, Pochtovyi per. 7, Yekaterinburg, 620151 Russia b OAO SIBNATs, ul. Permyakova 46, Tyumen, 625016 Russia GEOLOGY

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Page 1: The marine Devonian in the northern part of Western Siberia

ISSN 1028�334X, Doklady Earth Sciences, 2009, Vol. 429, No. 8, pp. 1295–1298. © Pleiades Publishing, Ltd., 2009.Original Russian Text © B.I. Chuvashov, V.S. Bochkarev, A.M. Brekhuntsov, 2009, published in Doklady Akademii Nauk, 2009, Vol. 429, No. 2, pp. 234–237.

1295

Individual boreholes amidst a few drilled north ofSiberian Uvaly (Spurs) yielded information on thereliable Paleozoic of Western Siberia [1]. For this rea�son some researchers suggest a wide distribution of thePermian–Triassic formation in the northern part ofWestern Siberia [2]. Study of the core from the deepparametric borehole Yarudeiskaya 38 drilled 80 kmsouth of the Gulf of Ob (Fig. 1) demonstrated theDevonian section of marine deposits composed oflimestone–tuff�volcanic rocks with microfauna of adefinite age. This Paleozoic sequence was penetratedby a borehole (BH) within the depth interval of 4382–5010 m. The studied rocks are intensely dislocated,distinctly metamorphosed, and recorded in the seis�mic field as an ordinary acoustic basement.

Paleozoic rocks in the section are covered with gen�tly dipping Upper Triassic, Jurassic, Cretaceous, andPaleogene deposits common for the Nadym–Taz Syn�eclise. The late Paleozoic graben traced from the Gulfof Ob southward for nearly 200 km was revealed in thePaleozoic basement within the region of BH Yarude�iskaya 38, which is located on its eastern slope.

The section is subdivided into four members.Established from top to bottom are the followingmembers: (1) tuffaceous–flysch, visible thickness 172 m;(2) tuffite–clastolava, visible thickness 170 m; (3) lime�stone–conglomeratic within the depth interval of4724–4794.8 m; and (4) andesite–basaltic, visiblethickness 215.2 m. The angle of the dip of rocks variesfrom 90°–80° at the top to 40° at the base of the sec�tion. The roof of Paleozoic rocks exhibits traces ofintense weathering.

The first member is composed of predominating sil�iceous–clay shales, tuffites, and radiolarites. The

color of the rocks varies from bluish green to dark grayand black. The bedding changes from banded to veryfine due to color variations and lithological varieties.Clayey sandstone and gritstone are encountered inplaces. Serpentinite predominates in rock debris, andradiolarians are found in siliceous varieties.

The second member is made of gray�green, red�brown, and dark gray tuffites, tuff breccias, and smallbasalt bodies with greenstone alterations. The domi�nant dip angle of rocks is 40°. Andesites were pene�trated within the interval of 4641–4642 m.

The third member is represented by marbled lightgray and greenish limestones with valves of brachio�pods (?) (depth 4790 m) and tentaculites (?), as well asinterlayers of variegated conglomerate breccias withrock debris up to 2–7 m in size.

Thin sections were made from limestones forextensive studies of foraminifers and algae. Limestoneis biogenic and composed of calcareous algae Shu�guria, Izhella, Renalcis, Epiphyton. This is a typicalbiocoenoses of Devonian organic structures. Identi�fied among the foraminifers—common dwellers ofalgal biotopes—are Vicinisphaera angulata Antrop.,V. squalida Antrop., Parathurammina aff. pusilla Byk.,P. aff. scitula Tchuv., and Cribrosphaeroides sp. n.Especially abundant are sedentary forms Ivdelinaelongata Malakh. Carbonates were dated at theEmsian of the Early Devonian. Biogenic limestonesabound in numerous original interstices which atpresent are filled with secondary coarse�crystallinecalcite–sparite. Sparite nests are up to 1 cm across.The rocks were formed in a well�illuminated zone of ashallow sea, but deeper than the zone of influence ofregular waves on the sediment (>12–15 m). Periodicshoaling and sediment washout are revealed due to thepresence of carbonate breccias.

The fourth member is composed of andesites,basalts, and their tuffs. The rock color varies from dirtygreen to almost black. The rocks are massive, pyrox�ene–plagioclase, with small rare amygdules andintense chloritization.

The Marine Devonian in the Northern Partof Western Siberia

Corresponding Member of the RAS B. I. Chuvashova, V. S. Bochkarevb, and A. M. Brekhuntsovb

Received May 4, 2009

DOI: 10.1134/S1028334X09080121

a Institute of Geology and Geochemistry, Ural Division, Russian Academy of Sciences, Pochtovyi per. 7, Yekaterinburg, 620151 Russiab OAO SIBNATs, ul. Permyakova 46, Tyumen, 625016 Russia

GEOLOGY

Page 2: The marine Devonian in the northern part of Western Siberia

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DOKLADY EARTH SCIENCES Vol. 429 No. 8 2009

CHUVASHOV et al.

The mentioned rock association from the BHYarudeiskaya is best correlated with the Tur’in Forma�tion from the Tur’in Subzone of the Tagil structural–facies zone. Volcanosedimentary rocks of the Tur’inFormation were formed in the Silurian rift structurewith a tendency to shoaling by the initial MiddleDevonian. Radiolarite interlayers found in the BHYarudeiskaya are typical of the Tur’in Formation aswell.

The study of rock katagenesis (metamorphism)showed that siliceous–clayey shales from the depthof 4429 m are characterized by vitrinite reflectivityof 4.28%. (Determinations were carried out byA.N. Fomin.) The rocks experienced apokatagenesisof AK3 gradation, i.e., metamorphism. Overlyingdeposits of the cover represented by Upper Triassic

mudstones yielded the following values: depth 3974 m,0.78% (MR2); depth 4030 m, 1.09% (MR3).

The data confirm that there is an intense jump inkatagenesis when passing from the cover to the base�ment.

The new data obtained are well correlated from thestandpoint of events with the southern Yamal Penin�sula where siliceous complexes with Devonian radi�olarians are developed on the Verkhorechensk area(BH 35) and to the north, there are mainly limestonesequences with the fauna of all Devonian series on theNovyi Port area [4]. Moreover, 200 km east of BHYarudeiskaya 38, Middle Devonian marine depositswith brachiopod fauna were revealed in BH Yubilein�aya 200, and there is one more BH Nadymskaya 7between the mentioned sections, in which the terrige�

Location of boreholes in the northwestern part of Western Siberia. (1, 2) Boreholes with paleontological data (1) and that men�tioned in the text (2).

67

36 8119329

9040

10374

853

74

4

1

1305

201

10

101

200 38 7

5

1

11

77

1001

200

35PR

Verkhorechenskaya area

SALEKHARD

Yubileinaya

Nadymskaya Yarudeiskaya

North�Pak�Yuganskaya

Akhtyn�Turskaya

Talinskaya

Lovinskaya

Filippovskaya

Andreevskaya Frolovskaya

East Pravdinskaya

Lekuminskaya4

1

2

115017

33

KHANTY�MANSIYSK

Page 3: The marine Devonian in the northern part of Western Siberia

DOKLADY EARTH SCIENCES Vol. 429 No. 8 2009

THE MARINE DEVONIAN IN THE NORTHERN PART OF WESTERN SIBERIA 1297

nous dislocated sequence penetrated below Jurassicdeposits of the cover. The sequence comprises diabasesand a jasper member with radiolarians, which we arbi�trarily correlate with the Tel’pos Formation of theOrdovician [3].

Silurian and Lower Devonian, in places MiddleDevonian, marine deposits are widely developed in thesouthern regions of Western Siberia [5, 6]. Only indi�vidual boreholes are shown in the figure.

It should be noted that, unlike the southern Tran�suralian regions [7], Devonian marine facies at the lat�itude of Khanty�Mansiysk and Ivdel in the Urals notonly dominate in some areas but make up carbonateplatforms (the Frolov structural–facies zone) andreefs. The fauna from Devonian marine facies wasfound in sections of boreholes Talinskaya 67, EastElizarovskaya 75, Em–Egovskaya 853, Gorelaya 41,Lovinskaya 811, Lovinskaya 9329, Ubinskaya 3552,West Frolovskaya 4, 33, and others. In the Shaimregion, Lower Devonian carbonate sections [8] areadjacent to Silurian–Devonian and Ordoviciansequences [9]. According to our data, Emsian fora�minifers from the Lower Devonian were identified inpinkish limestones with interlayers of fine�clastic car�bonate breccias in BH Lovinskaya 9173 within thedepth interval of 2339.8–2343 m.

Due to rock folding and subsequent erosion, Devo�nian complexes are rarely encountered, but the stud�ied sections would suffice to resolve a series of impor�tant problems.

Firstly, the Caledonides, which are characterizedby Devonian continental facies, cannot be distin�guished on the territories mentioned above [10].

Secondly, the marine sections we have listed char�acterize grabens and horsts, which rules out the presenceof a Kazakhstan�type continent east of the Urals, as istraced by proponents of the plate tectonics model [11].

Thirdly, formations typical of the Uralides aremapped from the Yarudeiskaya area in the north toTobol’sk in the south.

West of the Yarudeiskii Trough, basement rockshave a zonal structure. Anticlinoria were revealedthere, which are made of old gneisses and crystallineschists (BH Mshistaya 1, Puikovskaya 31, and others)with granitoids of Permian–Triassic age (BH Tan�opchinskaya 2, 3; Kunovatskaya 10, 16). Contiguouson the east with the anticlinorium is a synclinoriumcomposed of middle Paleozoic volcanics and calcare�ous–clayey shales (BH Poluiskaya 200, 202, 204;Lak’’yuganskaya 101; Kutop’eganskaya 1, and oth�ers). Occurring in the synclinorium core is the Yarude�iskii intermontane trough with Permian deposits com�prising flora imprints (BH Yarudeiskaya 4�R), as wellas spores and pollen (BH 5). The deposits are coal�bearing (BH Shuginskaya 7).

Taking into account new data on BH Yarudeiskaya38, the rock composition of the basement and itsstructure suggest the extension of the Uralides east�ward from the Urals to Nadym. The sedimentary coverin eastern regions, like along the Polar Urals, beginswith Upper Triassic deposits. These data confirmA.L. Yanshin’s opinion [12] about consolidation of thebasement in the Middle Triassic or at the terminalEarly Triassic.

In the northern part of Western Siberia, the base�ment was penetrated, in addition to the above�men�tioned boreholes, in BH 77 on the Lenzitskaya area atthe Gulf of Ob and in BH 1001 on the Medvezh’efield. Both boreholes crossed the phyllite and green�schist sequence attributed to the Upper Cambrian.The cover in both sections begins with Jurassic depos�its overlain by Cretaceous.

As is evident from the foregoing, on vast areas theboreholes penetrate Precambrian and Paleozoic com�plexes and not Permian–Triassic trapps as reported in[14, 2]. The actual material does not confirm infer�ences about wide development of Permian–Triassicvolcanics in the northern part of Western Siberia.

The correlation of Ordovician sections (BH Akhtyn–Turskaya 201, Filippovskaya 9040) with middle Paleo�zoic complexes represented by marine facies andwidespread along the lower reaches of the Ob Rivershows that all are characteristic of the eastern slope ofthe Urals and reflect not the oceanic but rift environ�ments where ultrabasic rocks are developed in places,as well as horst environments with abundant carbonateplatforms.

These materials prove once again that the territoryof the West Siberian Plate was not underlain by theoceanic crust in the Paleozoic and Precambrian, butevolved according to the scenario of riftlike ensimaticgeosyncline belts involving miogeosyncline�typezones with the granite–gneiss basement as inferred byA.L. Yanshin [15]. In the east, the Uralides border theAltaides.

ACKNOWLEDGMENTS

This work was supported by the Russian Founda�tion for Basic Research, project no. 09�05�00344.

REFERENCES

1. V. S. Bochkarev, A. M. Brekhuntsov, and N. P. Desh�chenya, Geol. Geofiz., No. 1/2, 120–143 (2003).

2. N. L. Dobretsov, Geol. Geofiz. 46 (9), 870–890 (2005).3. V. S. Bochkarev, in Geology and Oil� and Gas�Bearing

Capacity of the Nadym–Pur�Taz Interfluve (Tyumen,1995), pp. 179–206 [In Russian].

4. V. S. Bochkarev and V. G. Krinochkin, in Precambrianand Paleozoic Formations in Western Siberia. Tectonics

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CHUVASHOV et al.

of Platform Areas (Nauka, Novosibirsk, 1988) [in Rus�sian].

5. V. S. Bochkarev, A. M. Brekhuntsov, L. G. Peregoedov,and L. V. Smirnov, Nature of Carbonate Devonian Sedi�ments on the Right Bank of the Shchuch’ya River andNovoportovskoe Deposit of the Yamal Peninsula. Stratig�raphy and Paleontology of Siberia (Novosibirsk, 2000)[in Russian].

6. B. I. Chuvashov and E. A. Yatskanich, Dokl. Earth Sci.389 (2), 164–169 (2003) [Dokl. Akad. Nauk 388 (6),784–787 (2003)].

7. N. B. Malyutin, E. P. Smirnov, and M. N. Degteva,Geological Structure and the Stratified Base in the MiddleTransurals (Nedra, Moscow, 1977) [in Russian].

8. K. S. Ivanov, Yu. N. Fedorov, S. G. Zakharov, et al., inCarbonate Sedimentary Successions and Adjacent Areas:Sedimentogenesis, Lithogenesis, and Minerageny (Inst.

Geol. Geokhim. UrO RAN, Yekaterinburg, 2004),pp. 52–60 [in Russian].

9. K. S. Ivanov, Yu. N. Fedorov, and E. O. Amon, Gor.Vedomosti 6 (25), 86–97, (2006).

10. Eurasian Tectonics, Ed. by A. L. Yanshin (Nauka, Mos�cow, 1966) [in Russian].

11. V. A. Koroteev, R. G. Yazeva, K. S. Ivanov, andV. S. Bochkarev, Otechestv. Geol., No. 6, 50–57(2001).

12. K. A. Kleshchev and V. S. Shein, Prospects of Oil� andGas�Bearing Capacity of the Base of Western Siberia(VNIGNI, Moscow, 2004) [in Russian].

13. M. V. Muratov, Geotektonika, No. 1, 6–29 (1965).14. S. I. Stupakov, V. A. Simonov, V. S. Bochkarev, et al.,

Gor. Vedomosti, No. 1(44), 6–10 (2008).15. A. L. Yanshin, Izv. Akad. Nauk SSSR, Ser. Geol.,

No. 4, 511–538 (1936).