New stratigraphic and palaeogeographic data onUpper Jurassic to Cretaceous deposits from theeastern periphery of the Russian Platform(Russia)

Valentina S. VISHNEVSKAYAInstitute of the Lithosphere , Russian Academy of Science, ILSAN,

22 Staromonetny , Moscow, 109180 (Russia)valentina @i1san .msk .ru

Patrick DE WEVERLaboratoire de Geoloqle, Museum natio nal d'Histo ire nature lle,

43 rue de Button, F-75231 Paris cedex 05 (France)dewever@ mnhn.fr

Evgeniy VU. BARABOSHKINMoscow State University , Geologica l Facu lty,

Vorobjovy Gory, 119899 Moscow (Russia)barabosh@geol.msu.ru

Nikita A. BOGDA NOVInst itute of the Lithosphere, Russian Academy of Science, ILSAN,

22 Staromonetny, Moscow, 109180 (Russ ia)bogda nov @ilsan.msk.ru

Nikita VU. BRAGINGeological Institute of Russian Academy of Science ,

Pyzhevsky per ., 7, Moscow, 109017 (Russ ia)bragin@ginran. msk.ru

Lubov G. BRAGINAGeological Institute of Russian Academy of Science ,

Pyzhevsky per., 7, Moscow, 109017 (Russia)bragin@ginran.msk. ru

Alesia S. KOSTYUCHENKOTechnical Univers ity,

Leningradskoe shosse 112-1-1-211 , Moscow, 125445 (Russia)valentina @ilsan .msk. ru

Emmanue lle LAMBERTLaboratoire de Geo loqie , Museum national d'Histo ire natu relle,

43 rue de Button , 75231 Paris cedex 05 (France)geolhote @mnhn.fr

GEODIVERSITAS • 1999 • 21 (3) 347

Vishnevskaya V. S., De Wever P., Baraboshkin E. Vu. et al.

Yuriy M. MALlNOVSKYInstitute of the Lithosphere, Russian Academy of Science, ILSAN,

22 Staromonetny, Moscow, 109180 (Russia)barejko@ilsan.msk.ru

Kulyash M. SEDAEVAMoscow State University, Geological Faculty,

Vorobjovy Gory , Moscow, 119899 (Russia)koozminov @mtu-net.ru

Galina A. ZUKOVASimbirsk Geologica l Survey ,

3a Dovatora, Uljanovsk, 432000 (Russia)

Vishnevskaya V. S., De w ever P., Baraboshkin E. Vu. et al. 1999. - New stratigraphic andpalaeogeographic data on Upper Jurassic to Cretaceous deposits from the eastern peri­phery of the Russian Platform (Russia), in Crasquin-Soleau S. & De w ever P. (eds), Peri­Tethys: stratigraphic correlations 3, Geodiversitas 21 (3) : 347-363 .

348

KEYWORDS[ urassic,

Cretaceous,srrarigraphy,ammonites,radio laria ns,

for amini fera,nanno fossils,

palaeogeograp hi cal map.

ABSTRACTT he Late Ju rassic and Late Cre taceous were periods when, after prolongedcont inenta l eros ion, stable marin e sedimentat ion rook effect on the RussianPlatform. The sedirnents whi ch accumulated have diverse lith ological com­positions and a mixtur e of transient and endem ic faunas. Lith ological diversi­ty and a w ide var iety of facie s has led to prob lem s in s trat igra p h icalcorrelation of Late M esozoic sequences and discrepanci es in palaeogeograph i­ca! reconstructions, Different faunal groups belonging to a wide variety ofpalaeozoogeograph ic provinces exist within these deposits. T herefore, we useall availab le microfossils (rad iolarians, foram iniferas, nannoplan kron ) andmacrofossil gro ups (am monites, buc hias, inoceramides) in order to establishthe synchronic ity of anox ic and other events, ro propose biostr arigraph iczo nar io ns an d m odel the pal aeo geo gr aph y for Late Ju rass ic: low e rKimmerid gian and middle Volgian as well as Cretaceous time . We suggestthat th e Peri-T erhys of Eastern Euro pe is a unique area in which to solve th epro blem of srra tig raph ic co rrela tio n as it in corpor at es both Bor eal andT ransitional ro T erhyan palaeoclimatic provinces,

REsUMENo uuelles dounees stratigraphiques et pateogeograplJiqlles sur les depots juras­siques et cretacesde l'extronite oriel/tale de la Plate-forme russe (Russie).Le J urassiqu e supericur et le Crerace forment une period e ou, apres un elon gue erosio n conrinenrale, une sedimenta tio n marine stable s'i nsralle sur laplate-forme russe. Les sed imenrs accurnules ont des lith ologies variees et pre­sente nt un melange de faun es ende rniqucs ou transitionn elles. La d iversirelithologiq ue et la grande variere de facies our rendu com plexes les correla­tions srratigraphiques pour ces series du Mesozoique tardif et on t rnerne creede s desacco rd s d an s les recon stit utions paleogeogruph iques. Differentsgroupes fauniques, appartenant it un e grandc variere de provinces paleobio-

GEODIVERSITAS • 1999 • 21 (3)

MOTS CLESJurassique,

Crerace,srrat igrap hie,

ammonites,radiola ires,

forami niferes ,nannofossi les,

carte paleogeographique,

INTRODUCTION

Upper jurassic-C retaceou s of eastern Russian Platform

gcographiqucs existent dans ces depots. De ce fait, nous avons ete conduits auriliser rous les groupes disponibles de microfossiles (radiolaires, foramini­feres, nannoplancron ) et de macrofossiles (ammonites, buchias, inocera­mides) afin d'erablir le synchronisme des evene rnenrs, anoxiques ou autres,pour proposer des zonarions biosrratigraphiques et des modeles paleogeogra­phiques pour le Jurassique superieur : Kimmeridgien inferieur et Volgienmoyen ainsi que pour le Crerace. Nous pensons que la parrie peri-rerhy­sienne de l'Europe orienrale est un endroir unique pour resoudre les pro­blernes de correlation srratigraphique puisqu'il incorpore des elements fau­n iq ues de provinc es borea lcs et de la rran si ti on vers les prov incespaleoc limariques rerhysien nes.

MAIN LITHOFACI ES AND ST RATIG RA­PHY OF THE KIMMERIDGIAN

Our research team has undert aken field work inVolga River Basin (Aug us t 199 5, members offield work team were as follow: E. Baraboshk in ,N. Br agin , E. Lamb ert , V. V is h nevs kaya,G . Zukova; Au gu st 199 7 , V. Vi shn evskaya,G . Zukova) and in th e Ti ma n- Pecho ra Basin(Septem ber 1995 , A. Kosryuchenko, G . Sedaeva ,V. Vishnevskaya). All previous ly published andunpublish ed data conce rn ing of th ese regionswere revised and taken in to account.T he aim of our field trips was to collect preciseand well-located samples with fossil material inorder to establish accura te biostratigraphical cor­rel ati on s a nd to p ropose p al aeo geo gr aphi creconstruc tions which could provide a basis formodelling of palaeogeographic maps.During th e field work, we investigated and sam­pl ed the following ar eas in detail: ( 1) Kirn­meridgian-Vo lg ian portio n of the s tan d ardGo rod ische Sect ion of Volga River Basin andUkh ra out cr op as w ell as 21 outc rops a n d52 boreh ol es of the Volga-Kama and Tirnan­Pechora Basin (Figs 1-5 ); (2) middle Volgian ­Haurerivian sections near Go rodische and NewBerdianka villages (Figs 2, 3); (3) Aprian-Albiansec t io ns fro m boreh ol es of the Pen za region(10 km of Penza town , west of Volga River );(4) Barremian-Turonian section to th e north ofUlj anovsk city; (5) Ceno rnanian- Maas rrich tiansections near Shilovka settleme nt (50 km southofUljanovsk city) .

GEODIVERSITAS • 1999 • 21 (3)

The lower Kimmeridgian is represented by orga­nic shale (Fig. 5, borehole 18) with clay (Fig. 5,boreholes 15-1 7, 19,20, 22, 23, 25-27), glauco ­niti c sandsto ne, aleurolite (almost equivalent tosilt-sto ne in Russian literature) and clay (Fig. 5,boreholes 24, 28) , and micrite in th e outcrops ofthe Ukhta section. Rare phosphatic pebbles andpyritic concretions were also found .The time interval investigated correspo nds to th eearly Kimmeridgian in terms of standa rd ammo­n ite zo na t io n for t he Boreal Realm o f th eRussian Plate. Wi thin the Barents-Pechora area ,th e Amoeboceras rauni zo ne and in the Volga­Karna-Oka Basin , th e A. kitchini zo ne are pre­sent. Other cha racteristic am mo nites are Raseniatrimera Oppel and R. stepbanoidesO ppel.Kimmeridgian strata, which yielded radiolarians(Koz lova 1994; Vishnevska ya 1997), are wellrepresented in th e T irn an-Pecho ra Basin. ThePechora-Volga sed ime ntary basin was probablyproduced by a Late Jurassi c ph ase o f rifting(Kostiuchenko 1993), and was filled with radio­larian-bearing clay and sha le deposits in a sub­platform environme nt.The Kimmeridgian clay of Pech or a and Ukh raregions is also rich in glauconite and rnontrno­rillonite. Glauconite (15-30%), montmorillonite(10 -30 %), hydromica (I0-30 %) and chlorite (5­10 % ) are th e d omin ant co m po ne n ts inKim meridgian bituminous clay whereas glauco-

349

Vishnevskaya V. S.. De \Y/ever P.. Baraboshkin E. Vu. et id.

(~1

......'" Pechora ~ r~~~"~ f f- 7 @

'"(1i) ~ @v @ @l --~'---/ C1§ @ 16

®® • ®~ @@

Naryan MarCD@

~@ @ 36

:2 ® @@<t~ @;:= @@

@ 5

® (@) -

@ ~

@0@@ @

@0@

@

I--@44 47~

Ukhta•

\

FIG. 1. - The location of investigated boreholes and outcrops of Timan-Pechora Basin (the numbers corres pond to their officialrecord).

nite (30-40%), kao linire (25-30%), and rnon t­m orillon it e (2 0 -3 0 %) predomin ate in th eorganic-rich Volgian shale.The Kimm eridgi an cl ay (5-4 5 m) fro m th ePechora and Ukhta regions has a confo rma blestra tigraphic cont act with the underlyin g strata(Fig. 5) and demonstrates a succession of trans­gressive and regressive characters up to Volgianstrata.Radiol arian taxa make up only a minor part of

1

350

th e to tal fauna . Practically all taxa pr esent arekn own in th e Bo real provin ce of th e Ru ssianPlatform and C ircurn- Pacific Rim . T he lowerKimmeridgian radi ol ari an asse m blage of th eParuicingula vera zone of th e Barents-Pechora­U kh ra reg io n in clud es: A rchaeocenosp baerainequnlis (Rust) , Praeconocaryomma ex gr. spbae­roconus (Rust) , Pseudocrucella aff prava Blorne,Crucella crassa (Kozlova) , C. squama (Kozlova),C. aff mexicana Yang, Orbiculiforma cf iniqua

GEODIVERSITAS • 1999 • 21 (3)

U pper Jurassic-C reraceou s of eastern Russian Platform

LEGEND

~ Breccia..........

DIIillIillJ Sands

1mW] Sandstones

~ Siltstones

!El Clays---

~ Oil shales

~ Argillites- -

~ Marls. claye i marls

~ Limestones

1'-----r----,I Carbona te clays

~ Phosphorites

[IT] Bioturbation

~ Shell detrite

EJ Erosional surfaces

[ 10 cm

I' W" 'I Soflgrounds

. v . . .

. ±"-;' . .\:,I· ) · ~v_

... . . ">." ..~.

. . . ... . ..

Craspedi tessubditus

Craspeditesnodiger

W

-.J

oo

o>

z«

er:w0­

0­

:::::>

o>

z«

UPPERHAUTERIVIAN

FIG. 2. - The location of investigated sections of Volga Basin and stratigraphic column of the Volgian stage of the GorodischeSection.

GEODIVERSITAS • 1999 • 21 (3) 351

FIG. 3 . - Composite column of the Kimmeridgian-Hauterivianstages of the Gorodische Section.

recogni sed in the lowermost p arr of Ki m ­meridgian of th e Gorodische Standard SectiontBaylei zone of the Standard Scale).

20

- (3 - ___

~-;::')t~~~:; 61- 0 .5­

"-"B,, t:» 59 2.5

-=.-=- a_-_ 4-1

N

g 6- 0.5(') . ~ - .- 5 10 .1-z :...-;-- -':'- .-- .0'>a ' ~ ',,-<:>, ,,-'-po 8-7 0-0.<<5 10- 0.5­> " " ., . ,, ' 11 0 .8u:i '" . " " 12- 0.3-i'i . ' Q • 17 0.5~ <o : ', ' '" . ' 20 08o, p-:..-!~~~~-.: - . -::::> ' " . ". " •• 22 1

~ =-=-=-=:2: - - -~ -_-_~- 80- 12-

; - - - 0 -=--~ 72 18

~ -=-'--:---9-:~ - - - - - - -

;;> - - - -a:wf-::::>«I

.....:wa:()

~-'

klimovi

fulgens

Zones

niki tini

sokolovi

virgatus

eudoxus

pseudo­scvthica

inversus

subdi tus

cymodoce

syzranicus

nodiger

D Sand m Radiol aria. ' .

1--=-1 Clay 101 Nannoplankton- -

0 Limestone lID if I Ammonites

1---.-1 Oil shale ~ Buchia

~ Phosphatic pebbles

Blorne, o.? retusa (Kozlova), Pantanellium tierra­blankaense Pessagno & McLead, Parvicingulainornata Blorne, P cf blowi Pessagno, P hneckeli(Pan ranelli), P burnensis Pessagno & W ha len,P pizbmica Kozlova, P pusilla Kozlova, P papula­ta Kozlova, P santabarbarensis Pessagno, P? enor­mis Yang, P? blackhornensis Pessagn o & W hale n,Excingula? bifizria Kozlova.T he lower Kim me ridg ian Paruicingula vera zoneof the Bare n ts-Ti rnan-Pecho ra Bas in (V ish ­nevskaya & De Wever 1996 ) is probably equiva­len t ro the lower Kim meridg ian Crucella crassaassem blage of Kozlova (1994) and co rrelates wi thth e Buchia concentrica zo ne , A . rauni am mon itezone and Epistomina unzbensis for aminiferal zon eas well. T his interval probably co rrespo nds ro th eKim meridge Clay H yd ro carbon Forma tio n ofthe Nort h Sea which cont ains abunda nt P jonesi(Dyer & Copesrake 1989).A study of Paruicingula distr ibution shows a pre­dominan ce of thi s genus in the Kim me ridgia n ofthe T iman-Pecho ra and Barents regions. Speciesof th is genus are represented by a wide range ofmorphorypes. T he eo-occurrence of Arcro-Borealfora mi niferal assem blages rogethe r with Jurassicradio larians and Buchias confirms the possibiliryof using Paruicingula as palaeoc lirnaric ind icaro r(V ish n evskaya 19 96) . For exam ple, the mainKim meridgian re p resentatives of the Moscowregion are Paruicingula vera Pessagno & W halen ,P inornata Blorne, P elegans Pessagn o & W halen.Parvicingu lides preva il, compris ing 50% of th isasse m b lage and in the m iddle Volgian of theM oscow Basin , are represented by P baeckeli(Pa n ra ne ll i), P hexagonata (Hei tze r) (Brag in1997).In th e Go ro d is ch e Sec t io n (Vo lga Bas in )Pnruicingula j onesi (Pessag no) is th e dominantspecies in th e Kimmeridgian and th e percentageof parvicingu lides in th e total radi olari an faunareaches 50-60%.Radiolar ian-bearing organic black sha le an d bitu­mi no us clay w hic h were d ep osited in anoxicenviro nme n ts a re ass ig ne d to t he low e rKimmer idgian (Cymodoce zone) . T h is intervalex h ib its b lack sh ale layers with a high TOC(more 10% ) content and good petroleum poten­tial (Baud in et al. 1996) . Ammonite horizo nsco ntain ing P densicostata and P baylei can be

352 GEODIVERSITAS • 1999 • 21 (3)

UpperJura ssic-Cr eraceou s o reastern Russian Platform

• Benthos

D Necton

~ Oil shales

Samples Total amo unt of samples

o 20 40 60 80 100

Y95/11-7Y 95/11-8Y 95/11-9

Y 95/11-11Y 95/11-20

Y 95/11-10-4

Y 95/11-10-2

Y 95/11-22

OS Y 95/11-24, 10­Y 95/11-25

OS Y 95/11-2Y 95/11-31

OS Y 95/11-3

OS Y 95/11-4Y 95/11-41Y 95/11-43

Species divers ity

o 5 10 15I I I ~O

SIZE-FREQUENCY DISTRIBUTIONOFLoripes fischeria nus

(sample Y 95/10-2)

SIZE-FREQUENCY DISTRIBUTIONOFLoripes fischeria nus

(sample Y 95/11-26)

l.enqth s ­mm

Length 5

mm4 - 4

3 - 3

2 -I1 -

0 - L,-!-,-'=TTT1"TTT"I"TTTTTTl,-!,1 Sampies30

11 I

14

SIZE-FREQUENCY DISTRIBUTIONOF Oorsoplani tes sp.

(sample Y 95/11-26)

0-,

Diam eter B-

mm 7 -

6­

5­

4 -

3­

2-

1 -:-r--f'Ta,-ar'Y~...,...........I........1,..,Samp les-rr-rr-r-r-rr-r-r-r-f-r- Sampl es26

SIZE-FREQUENCY DISTRIBUTIONOFScurria maeotis(sample Y 95/1 1-38)

0.5

0.0

2.5

1.5

2.0

1.0

Length 3.0

mm

FIG. 4. - The distribution of samp ling and percentages of macrofauna in the Gorodische Section.

GEODIVERSITAS • 1999 • 21 (3) 353

Vishnevskaya V. S., De W ever P., Barahoshkin E. Yu. er ,d.

Th e upp er Kimm eridgian i Eudoxus-Au tis ­siodorensis am m o n ite zo nes) seq ue nces o f theGorod ische Section are rep resented by clay mar!with abunda nt nannofossils. Tergestie/la margereli,Watznaueria communis and ~v. britannica are thedominant spec ies. The cha rac te ristic spec ies areStephanoiiibion bigoti, Discorhabdus tub us,Podorhabdus cylindratus, P decussatus, P cuuillieri,as well as th e smallest indi vid uals of NflIlIlOCOllUSsteinmanni (= N. colomi) . This nannoplan kronassemblage is s im ila r to th e N W Eu ro pea nVekshinella stradneri assemblage of Bern ard & H ay(I974). A more precise Kimmeridgian rad iolarianzona tion may be developed in the near future.The North C aucasus Kimmeridgian-Tithonianasse m blages include only ra re P. dhimenaensis(Baum garrne r) and Berriassian assem blages in­clude P boesii (Parona) (Vishnevskaya et al. 1990).The conte nt of parvi cingulides is less th an 5% ofthe to tal assemblage in th e Terhyan Realm.

VOLG IAN BIOSTRATIGRAPHY OF TH EPECHORA BASIN AND GO RO DISCHESTAN DA RD SECT ION

Volgian stra ta have a tr an sgressive cha rac ter inth e Pech ora regio n (Fig , 5). Among rad iolar ian swhi ch occ u r w it h in th e middl e Vo lgia nDorsopla nites p anderi a m mo n i te zo ne,Parv icingula pap ulata Koz lo va , P. conica( K h a ba kov) , P. cristata Ko zlo va , P. rugosaKozlova, P simplicim Kozlova are th e dominantspec ies , Par vicingul id es ag ain co m p rise up to90 % of faun as in the Bar ents- Pechora reg ion .Ammon ites, buc hias and foraminife ra are alsoabundant in th ese strata.T he G orod ische Sta ndard Sect ion is the sectionwh ich has been most completely processed formacro- and microfauna (Figs 2-4),Stud ies of th e macrofaunal assem blage from theGorod ische Sectio n show (cf. Micra 1993), thatstra ta in th e sec tio n can be co nfide n tly assignedto two a m mo n ite su bz o nes of th e ( mi d d leVo lg ia n) Dorsoplani tes p anderi zo ne: Th ePaulouia pauloui bottom subzo ne and Zaraiskiteszarajskensis to p subzone, which were establishedby Gerasimov & Micha ilov (1966) .T he paoloui subzo ne (layers 6 1-59) is characreri-

354

sed by clayey-ca rb onate successio n wi th th inphosphori te a nd m arcasit e ho rizons (F ig . 3).Several erosio na l surfaces are recognised in th esubzo ne. O the r am mo ni tes include Zaraiskitessp., Z. cf. tschernyschovi, Z. cf. michnlskii,Dorsoplanites aff panderi, D. sp., Paulouia sp.,numerous ros tr ums of Lagollibelus (L.) paruulatogether wi th a benrhic faunal assem blage of th ebivalves Loripes fiscberianus, Buchia russiensis,Oxy tomn sp . , Protocardia cancin na, Gresslynnlduini, gas tro pods Eucyclus sp., Apporhais sp.,brach iop ods Lingula s p ., R usie lla sp"Rhy nchonella loxie; scaphopods Laeuidentali um,as well as serpulids. These assemblages permit usto cha racte rise sed ime ntary conditions as weakl yanoxic shallow water.A somewhat rich er fossil complex is pr esent inthe zarajsleensis subzone (layers 58-23), The rocksof thi s su bzo ne have rh ythmi cal s t r uc t u re ,Rh ythms usually begin wi th horizons of rewo rk­ed and dissolved fauna, They are ove r!ain by car­bonate clays to pped with o il sha le. T he qu antityof o rgan ic matter inc reases from 1-1. 5% up toalmos t 22% at the back ground of decrease ofcarbo na te matter (Fig. 3). Rh ythmic cha nges inth e benrhic assem blage occ ur from a prevalen ceof benrhos to an up sect ion inc rease of nekton(Fig. 4) . In th e o il sha les young populati ons oflost Loripesfischerianus and Scurria maeotis usual­ly prevai l, toge the r wit h ne pio nic am mon ites,T h is d emonstrates a s t ro ng anoxic impul seduring th e oi l sha le form ation . The fo llowingfaun al asse m blage was d et ermined fro m thatinterval : a m m o n i tes Zaraisleites cf. scytbicus,Z. p ilicensis , Z. qu enstcdti i , Z. stchuleinensis,Dorsoplanitespanderi; belemnites LagonibelllS (L.)lI1agnifica, L. (Holcobeloides) uolgensis, L. (L. ) cf.rosanoui; biva lves A starte sp. , Gresslyn alduini,Bu chin mosquensis, B, russiensis, Oxy tomn sp .,Loripes [ischeriauus, N ucula sp., Panopra sp"Limatula consobrina, Liostrea plastica: gastropodsScu rria tnaeatis, Eucyclus s p .; sca p h o p o d sLneuidentalium sp.; b rachiopods Lingula sp. ,Rhynchonella rouillieri and o the r fauna.T he rad iolar ians Orbiculijorma ex gr. mclaughli­n i Pessagn o , Sticbocapsat de uo rata ( R ust),Phormocampe jauosa Kh udyaev, Paruicingulabexagonntn (Heirzer) , P cristata Kozlova, P conica(Kha ba kov) , P aff, alata Kozlova, P. multipara

GEODIVERSITAS • 1999 • 21 (3)

26 2223

-0'0

<:IJ>_

T3 1-_- _-

TJI -- -- -

20 21 15 18 16

J1l111ro. ~ ; . 0 ~~~~~ ~~:-;. 0 ~_\~ ' .'0·°'

. . . 0 . . .. ' 0 · .. 0 B70,0 I a4 :...· ~ .:.. -= -:: -:: _ _ _ c'o: .0:

Cf,-.. .1: I IK '!. I ~ .::.-.1 . J~ ,'> 1-=----1 K1

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24 25 28

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01'" ':- : : ·~ ·I 01:-: .0

00 Q f'\., O 00 '0

K 11'~ a-a4 '.W::X r K v :::"'-:-';;;:XrI krtl -<>- r -K

J30X X G<pJ3 1_-_-_ / C4 -- .

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-.:. -.:. _ / J2

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l-?- ~I Radiolarians ~ Flora E:J Bioturbations

J1-2 1.-dPC;. "

T3 1- - -- -c

-o

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VJV1V1

FIG. 5. - The dist ribut ion 01Jurassic fac ies within the sect ions of the north -eastern part of the Russian Platform. For the location 01boreholes see in Fig . 1. For legend 01columns 1­14 see Vishnevskaya (1998) , 29-52 see Vishnevskaya & Sedaeva (1999) . P, Permian; T, Triassic; J , Jurassic; K, Cretaceous; 0 , Tertiary; a. Aptian ; ai , Alb ian; hob, Hauterivian­Barremian; bs- v , Berriassian-Valanginian ; ne, Neocomian; v , Volg ian ; o x-km , Oxlordian-Kimmeridgian; c l , Cal lovian .

s..~

~~

;Al~

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c-e;;-

3"­3

(Kh udyaev), P. aff. haeckeli (Panta ne lli), P. aff.spinosa (Grill & Kozur), PlathYClJphalllS?pumilusRust , Lithocnmpe cf. terniseriata Rust were reco­ve red from within the D orsoplnnites panderiammonite zone in the Z. zarajskensis subzone ­th e uppermost part of nannofossil \Vatznaueriacommunis zone of the Gorodische Sect ion, wh eredominant species of coccolirhs are W martelae,W strigosa, W tubulata, W ouata.H igher in th e section (layers 22-20) thin mem­bers of quartz-glauconitic sands and sandsto nesbuild up the succession . They contain horizonswith reworked phosphorires. Faun as are locatedpredominantly in rewashed pebbles. In layer 20 ,remains o f s t ro n gly reworked zo n a l in dexVirgatites geraSJimovi were found together withLoripes sp. and dissolved rostrums of Lagonibelus(H .) volgensis. There ar e man y radio lariansreworked from the Z. zarajsleensis subzo ne wit hinthe phosphorite pebbles.Ammon ites from the succeeding Virgatites virga­tus next zone were not discovered. H owever, onth e basis of srratigra phic posit ion in a detailedsect io n, this zo ne m ost likely occu rs bet weenlayers 18 and 20.The uppermost parr of sec t io n is co m p risesd en se thin members o f carbo na te sa nds ro rieswith hu ge am monites Epivirgatites biplicijormisand E. nikitini (layers 17-12) fro m the middleVolgian E. nikitini zone.Sandsrones of the upper Volgian Kachpuritesfit/­gem zo ne lie above an eros io nal surface . Theycontain Craspedites nelerassoui, C. sp. and Kach­pu rites lulgens associated with Buchia p iochii,B. sp., belemnites Acroteuthis (A .) russiensis an dA. (A.) mosquensis, which were fou nd in layers 11and 10.Overlapping layers 7, 8 also lie above erosionalsurfaces erosion and are characterised by rework­ed Craspedites cf. okensis, which is the diagnosticform of th e upper Volgian Craspedites subdituszone . T he belemnites Acroteutb is (A .) mosquensisand bivalve Buchia piochii and B. tenulcollis occurtogether with these ammonites. Radiolarian spe­cies P. cristata Kozlova, P. alata Kozlova, P. blowi(Pessag no) and St ichocapsa deuorata (Rus t) arecommon within the se strata in which th e parvi­cing ulid conte nt is 50-60%.No ammo nite fauna was found in layers 6-5 , bur

356

based on existing literature (Mesezhnikov 1984),th ese stra ta ca n be co rrela te d wi th th e upperVo lg ian Craspedites nodiger zo ne a nd lo we rValang inian Temnoptycbites syzranicus zone. T heuppermost part of Volgian stage is character isedby app earance, within the radiol arian microfauna,of the Med iterranean species P boesii (Parona),The appea rance of this M editerran ean spec iestaxon notwithstanding, radi olarian assem blagesare dominantly Boreal in cha racter and th e typesof radi olari an assemblages present have not beendescribed p rev iousl y. Th e prop o sed middl eVolgian Paruicingula haeckeli zone is closely cor­related to th e Parvicingula papulata zone of th ePechora Regi on (Koz lova 1994) . It co rrelateswith the am mon ite Dorsoplnn ites pa nderi zo newhi ch ca n , in turn , be correlated w it h th eEuolutinella emeljanzeui- Tracbammina septentrio­nalis or Saracenaria pra uoslnuleui foraminiferalzo ne (Koz lova 199 4 ) in the Pech ora Basin ,Lenticulina biexcauata zone (Ljurov 1995) in th eSysola hydroca rbon Basin , and Parhabdolithusembergeri nannopl ankron zone in M idd le Volgah ydro carb on Basin . We ca n t race last zo nethrough both So u the rn Engla n d and No rr hFrance (Vishnevskaya & De Wever 1996 ). Dueto th e presence of index species , it is possible tocorrelate th is interval with bu ch ias Bucbia mos­quensis-B. russiensiszone of th e Russian Platform(Sey & Kalacheva 1993).The proposed upper Volgian Paruicingula bloioizo ne probab ly co r res po n d s to th e Pseudo­cralan i u m plan ocep h a la assembl age o f th ePechora and N ort h Siberia regions which wasesta blishe d by Kozlova (1994) and can be corre­lated with Buchia piochi i-B. terebratuloides zoneof the Russian Platform (Sey & Kalacheva 1993).

JURASSIC PALAEOGEOGRAPHY

The Jurassic str a t ig rap h ic seq ue nces in th eTiman-Pechora Basin (Fig . 5 ) clearly show atransgressive dep osirional syste m start ing withEarly-Midd le jurassi c sands and d eep en in gup ward to th e accum ulatio n of th e higher gradeso urce rocks in the Vo lgia n tim e . T he m assextinc tio n, observed here and especially in th eGorod isc he Sec tio n of the Vo lga-Ura ls Basin

GEODIVERSITAS • 1999 • 21 (3)

40° N

50° E 60°

70° N

CJ.. ··':: : ", :

UpperJurassic-C reraceou s of eastern Russian Platform

40° N

1- I 2 1---.-1 3 [34

40° N

FIG. 6. - Schematic palaeofacies location map of the Kimmeridgian time (adopte d after Sedaeva & Vishnevskaya 1995). 1, coas talmarine sandstone and siltstone; 2, marine clay ; 3, anoxic organ ic shale; 4, lignite coa l and organic detritus; 5, phosphate; 6, sup­posed land; 7, location of sections from Fig. 5 (number in circle); 8, location of the Gorod ische outcrops (letter in circle) .

GEODIVERSITAS • 1999 • 21 (3) 357

Vish ncvskaya V. S., Dc \'Vc\"er P.. Baraboshkin E. Yu. et 111

(only about 40 species of ammonites, 20 speciesof aucellids , 22 species of benrhic foraminiferasand 20 spec ies o f pl anktoni c fo ra m in ife ras ,10 species of belernnires, 5-40 calcareous nan no­fossil taxa, 20 species of radiolarians and severalspec ies of algae were recogni sed within Dorsa­planitespanderi zone), probably resulted from thecum ulative effects of a constant alternation oftransgressive and regressive episodes. T his type ofsedimenta tion and palaeoenvironm ent s surv ivedinto late Volgian tim e, but a cha nge of condi ­tions had already appeared by the end of Volgiannme.The proposed schematic palaeogeographi c map sof the Kimm eridg ian and Volgian time (Figs 7 ,8) in dic ate the locati on of th e easte rn rim ofsha llow sea with excellent environments for oilan d fuel-ric h organic source roc ks (Figs 5, 6).Similar to Recent seas and to an ancient sea, forexample, the Devo nian Sea (Vishnevskaya 1993),the maximum concentrations of phyroplankron ,siliceo us plankton and benrho s, carbonace ousplankton , nekton and benthos were found in thewater imm ediately bordering the continent. T histype of relative increase in the proporrion of lipidrich organic matte r in the bottom sediments andits good preservation probably took place in res­ponse to the preservative character of phospho­rus, th e content of whi ch is very high in thesestrata (Baudin et al. 1996 ).It is well-know n that in the Teth yan Realm thegenus Paruicingula is rare whereas the content ofthis genus in the Boreal (Khydjaev 1931; Sedaeva& Vishnevskaya 1995) and Australian provinces(Baumgarrner 1993) is much greater. From theseda ta, we can assume th at cold water env iro n­m ents domin at ed th e north-east ern RussianPlat fo rm Jurassic oil-sha le-bea ring basin . Thepreponderance of parvicingulides possibly indi ­ca tes up welling co nd it ions which have couldexisted offs ho re (F igs 6 -8) . T he ab u nda n tremains of sponge spicules, which settled alongthe shelf edge confirm this conclusion.

J URASSI C BI O STRATI GRA P H Y ANDPALAEO GEO G RAPHY

Detailed analysis of taxonomi c variety of faunal

358

assemblages and some morphological peculiari­ties of shells allow us to establish biostratigraphi ccorrela tio ns and to reconsrruct th e possibl ebathyrnerric and topographic features of sedi­mentary basins. One would notice that Jurassicrad io lar ian fauna was fi rstl y foun d fro m theGoro dische Standard Section of the Volga Basin.It repres ents new data on th e palaeontologicalcha rac te rist ics of th e Upper Ju rassic Ru ssianRegion al Volgian Stage . The lower Kimmerid­gian ammonite Amoeboceras kitchini (Salfeld) istypical of the Arctic (No rrhern Siber ia, Sub polarUrals) and Boreal-Atlanric Provinces (EuropeanRu ssia). Bucbia is a cha racte ris t ic element ofArctic and Boreal realms. Foraminiferas are alsotypical of the Boreal-Atlanti c Province. A typicalfeatu re of radi olar ian assemb lages (abundancean d high taxo nomi c d ive rs it y of t he gen usParvicingl/la) indica tes Boreal affinity. T he pre­sence of the genus Aspidoceras in the Volga-O kaBasin , well-know n in th e Western Europe andMediterranean Region , is the onl y indicato r ofpossible Terhyan influence.Some peculiarities were common for sedimentsof the Pechora and Volga basins:1. Sedimentary lithologies and their th icknessesindicate uneven subs idence on the periph ery ofRussian Platform.2. Alternation of deep-water and shallow-watersed iments and numerous gaps ind icate eustaricvanano ns.3. Geoc hemica l data exhibit enr ichment in orga­nic matter.New siliceous microfossil radiolarian assemblageshave been obtained from the Volgian as dated byammonites and calcareous nannofossils.T he eo-occ urrence of radio lari an s with calca­reous nann ofossils represent s the first well-da tedradiolarian assemblage of th is age at such a highlatitude on the Russian Platform.As might be expected many new radiola rian spe­cies of the Boreal Province are encount ered.

LOWER C RETACEOUS ST RAT IG RAPHYOF ULJANOVSK-PENZA REGI O N

Berri asian strata are pro bably rewor ked in th eGorodische Section, although they were marked

GEODIV ERSITAS • 1999 • 21 (3)

Upper j urassic-Crcraccous of eastern Russian Platfor m

50° E

~ 2~

[I]10

r===lI..=.....=.J

W 11

I~I 5 mtttII 6 ~ 7 1--:::..-1 8!CEJ 13 c:EJ 14 ~1 5 W1 6

FIG. 7. - A detail palaeogeographic map of the Volgian time. 1, marl; 2, sand; 3, clay; 4, limestone; 5, oil shale; 6, land; 7, sponge;8, auce lline; 9, ammonite; 10, foraminifera; 11, radiolaria; 12, bivalve; 13, glauconite; 14, phosphate; 15, buchia; 16, gypsum.

GEODIVERSITAS • 1999 • 21 (3) 359

Vishnevskaya V. S.. De \'<'ever P., Baraboshkin E. Yu. et Ill.

(?mapped) accord ing to Mesezhnikov (1984).From our point of view, the presence of Berria­sian deposits here is improbable becau se the sec­tion is strongly condensed. Mo st probably, Ber­riasian ammo nites which are pr esent in th esestrata were reworked into the base of Valanginian.T he sec tio n is te rminate d by bl ack clays(layers 4-1) with siderite and lim on ite concre­t io ns, con tain ing lar ge weathered am mo ni tesSpeetoniceras (5.) uersicolor and S. (5.) subinuer­sum, wh ich are ascr ibed to th e Speetonicerasinuersum zone of the rop Haurerivian.An anoxic eve n t occu rred wi th in th e lowerAptian Deshayesites deshayesizone. The remaind erof the lower and middle Aptian is characterisedby anaerobic condi tions. A late Albian rad iola­rian assemblage was found amongst the Albianblack clay of Uljanovsk Sectio n. It is represente dby Orbiculiforma mu ltangula Pessagn o, Theo­campe cylindricn Smirnova & Aliev, Obeliscoitesturris (Squinabol).T he Barremi an-A1bian int ervals were also investi­gated in two (7, 10) boreholes in the Penza area.At a depth of 89 m in borehole 10, the radiola­rian s Orbiculiforma maxima Pessagno , Distylo­capsa m icropora (Squinabol ) , sim ilar to lateAlbian Te thya n forms (0' Dogheny 1995);Dictyomitrn communis (Sq uinabol) and Obesa­capsula sp. cf. 0. zantoraensis Pessagno were reco­vered . A t a d epth o f 10 5 .5 m in th e sa mebo reho le, typ ical late Albian radiolar ian speciesPorodiscus kauilkinensis Aliev, Arcbneodictyomitrasimplex Pessagn o , Dictyomitra gracilis (Sq u i­na bol), Dictyomitra [erosia allgusta Sm irnova,Th eocamp e cylin drica Sm irn ova & Ali ev wer erecognis ed. At a depth of 106.8 m within bore­hole 10, the radiolarian faun a is char acterised bySpumellaria only.Within borehole 7, at a depth of 113.3 m, radio­lar ians Orbiculiformn neuadaensis Pessagn o ,Obeliscoites perspicnus Squinabol, 0. cf. uinassai(Squ ina bo l), Xitus a n telop ens is Pessagn o,X.? asymbatos Forema n, wh ich are character isticspecies of the A1b ian to early Ce nornanian, werefound. At a dep th of 120 m (borehole 7) rad iola­rian s are represented by th e species Orbiculi­j orm a neunda ensis Pessagno an d typi cal lateAlbian Theocampe cylindricn Smirnova & Aliev,T simplex Smirnova & Aliev.

1

360

Between 123.45 and 123.50 m, the radio lariansPorodiscus inflatus Smirnova & Aliev, Obeliscoitesturris (Squinabol) are present.At a depth of 133.15 to 133.25 m the radiol a­rians Dictyomitra [erosia allgllSta Sm irn ova an dStichomitra communis Squinabol were recovered.W ithin the interval 129.75 to 129.90 m, A1bianspecies Crolanium cuneatum (Smirnova & Aliev),C. triquetrum Pessag no , Porodiscus inflatusSmirnova & A1iev were met.At a depth of 136 m, the only spec ies recoveredwas Orbiculijorma multangula Pessagno occurred.Fro m t he above d ata we cons ider t hat th eApti an-Albian Crolnnium cuneatum zone can berecogn ised in the Uljanovsk-Penza Region.

U PPER CRETACEOUS BIOST RATI GRAPHYOF VO LGA BASIN

Upper Cre taceo us rad iolarians were studied fromth e Shi lovka Sect ion in th e Uljanovsk Regionand fro m core sections of boreh oles (28, 502)from th e Volgograd Region. T hree radiolari anassemblages were det ermin ed: Archneosp ongo­przt llu m bipa rt itu m -Alieui um superbu m(Turoni an-Coniacian), Pseudoaulophncus jlo resen­sis-Eu chi t on ia santonica (l ate Co n iaci a n ­Sa nro nia n or Sa n to n ia n) an d Amphipyndnxtylotus-Patellula planoconuexa (late Ca rnpanian).Age data were supported by foraminife ral an dnann oplankr on assem blages, which have affinitywith Euro pean ones. T hese assem blages are simi­lar to Western Siberian Boreal associa tions, butinclude some Terhyan taxa.The ea rly Santonian Eu chiton ia san tonica­A lievium praegallowayi zone was established byVishnevskaya (1997). It is a characteristic Borealzone and is widespread both in Siberian, Russianplat forms and in the Pre-Caucasus. Wi th in theShilovka Section, it correspo nds to th e foramini­feral Gauelinella infrasantonica zone or nanno­plan kto n Marthasterites [urcatus zo ne. T he lateSa nto n ia n -ea rly Ca m pa n ia n fo ra m in ifera lGauelinella stelligera zone can be correlated withthe Orbiculiforma qundrata-Lithostrobus rostouze­vi zone. T he upper part of this zone may be cali­brated with the nannoplankton Arkhallgelskiellaspecillata zone in the Shilovka and Tushna sec-

GEODIVERSITAS • 1999 • 21 (3)

Upperjurassic-Cretaceou s or easter n Russian Plartorrn

Barents

Sea

I0OI~

~

C7l2~

8 ~9

1=-=3 3 I, ! , I 4 I~ I 5 ImREl 6 [rIJ 7

[I] 10 [±]11 [[I}12 [L[] 13 [I]14

FIG. 8. - A detail palaeogeographical map of Kimmeridgian time . Legend: see on Fig. 7, only 1, gravellite.

GEODIVERSITAS • 1999 • 21 (3) 361

Vishnevskaya V. S., De Wever P., llaraboshkin E. Yu. et at.

tions. C am pa nian Prunobrach iu m articulatu mzone (Lipma n 1952) or Amphibrachium siberi­cum zo ne and Spongoprunum angustum zo nes(Amo n & De Wever 1994) have no analogues inthe Tethyan Region . Neve rtheless, the Terhya nspecies Afens liriodes Riedel & Sanfilippo wasfound in th e interval of th is zo ne within th eShilovka Section.

CONCLUSION

The proposed biostrat igraphi c subdivisions basedon new palaeontologi cal dat a are clearl y defi­nable. They have a proven wide geographic d is­tr ibution and can be useful for co rrelation ofsedimenta ry sequences as well as bioti c and abio­ne events .T he direct correlation of Peri-Tethyan radiolarianzona tions wit h ocea nic ones and those of th eTerhyan region is very difficult owing to provin­ciality of species. Only on e Jurassic zon e, th eupper Volgian -lower Berriasian Parvicingulablotoi zo ne, ca n probabl y be co mpa red withzonarions of Baumgartner (1993) for the ArgoBasin. The upper Berriasian -lower ValanginianParvicingula khabakovi- Williriedellum salumicumzone (Vishnevskaya 1996), which is widespreadin the Russian and Siberian platforms within theammonite Bojarkia mesezhnikovi zone, can becompare with some Terhyan ones owing to thepresence of numerous Parvicingula boesii.Biosrrat igr aphic co rrelations of mic ro foss ils(radiolarians, foraminiferas and nannoplankron)and macrofossils (ammo nites, buchias) is propo­sed in order to establish the syn chronicit y ofevents and conseq uently of more genera l geologi­cal processes.

AcknowledgementsWe ex p ress our gra t i tu d e to ProfessorA. Nikishin and anonymous reviewers for theirst im u lat ing co m me n ts a nd criti cism on thepaper. We are grateful to J . Aitchison who helpedus to improve the English. Special thanks are dueto Peri-Terhys Programme (grants 95 18 and 95­96/ 18) an d Ru ssi an Fo u n da t io n for Basi cResearch for financial support (Grant RFFI 97­05-65 566) and to CNRS-ESA 7073.

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REFERENC ES

Amon E. & De Wever P. 1994. - Upper Cretaceousbio strarigraphy of the borders of the Ura l belt s:Wes tern Sibe rian and Eastern Volga-Ural Basins :229-262 , in Roure F. (ed.), Peri-Tetbyan Platforms.Tec hnip ed., Paris.

Baudin F., Hanrzpergue P., Min a V., Ol feriev A. &Zakharov V. 1996 . - Biostratigraphi c correlationsand black shale deposits of the Upper Jurassic fromthe Ru ssian Platform . Abstracts of Peri- TethysConference, Amsterdam: 7, 8.

Baum garrner P. O. 1993. - Lower Cre taceous radio­larian biostrarigraph y and biogeograph y of north­western Australian (ODP sites 765 and 766 andDSD P si te 26 1), Argo Abyssa l Plain and lowerExmourh Plateau. Proceedings ofthe ODP, Scien tijicResults, W ashin gton 123: 299-342 .

Berna rd T. & Hay W , 1974. - O n Jurassic cocco­liths: tentat ive zonation of the Jurassic of SouthernEngland and No rth France. Eclogae geologicea helve­ticae, Basel 67 (3): 563-585.

Bragin N. Y, 1997. - Radiolaria from the phospho­ri tes basal ho rizon s of the Vo lgia n Stage in th eMoscow region , Revue de Micropaleontologie, Paris40 (4) : 285-296.

Dyer R. & Co pesrake P. 1989. - A review of latestJurassic to earliest Cretaceous Radiol aria and theirbiostratigraphic pot enr ial to petroleum explorationin the North Sea. Northwest European Micro ­paleontology and Palynology, London: 2 14-235 .

Ge rasimov P. A. & Mikhailov N. P. 1966. - VolgianStage and the geostra tigraphical scale for the UpperSeries of the Jurassic System. Proceeding of Academyof Sciences USSR, set. geol. , Moscow, No. 2: 118­138 [in Russian].

Khudyaev J. 1931. - O n the Radi olar ia in phos­ph a tes in t he regi on of th e Sysso la Ri ver.Transactions ofthe Geological and Prospecting ServiceofUS.S.R., Moscow, Fascicle 46: 1-48.

Kosti uchenko S. L. 1993. - T he cont inenta l platetectonic mod el of th e Timan-Pech or a provin ceba sed on integrat ed deep ge o physica l st udy .Z onenshnin memorial Conference on Plate Tectonics,G EO MAR, Kid : 85, 86.

Kozlova G. E. 1994. - Mesozoic radiolarian assem­blage of the Ti man-Pechora oil field. Proceeding ofSnnkt-Petersbnrg International Conference, Sr­Petersburg: 60-75.

Lipm an R. X. 1952. - Materi als on mon ographicstudy of U ppe r C re tace ous radi ol ari an s fro mRussian platform. Paleontology and Stratigraphy,Gosgeolisdat, Mo scow: 24-51 [in Russian] .

Ljurov S. B. 1994. - Division of Jurassic sequencesof the Middle Vichegda. Abstracts of InternationalSymposium "Biostratigraphy ofoil fields", Dece mber1994 , St-Petersburg: 59, 60 .

Mesez h n ikov M . S. 19 8 4 . - Exc u rs io n 060.Boundary beds of J urassic and Cretaceous in the

GEODIVERSITAS • 1999 • 21 (3)

Middle Povolzhie and Riazanian region : 38-49, inTh e C entral re gion s of Eu ro pea n part of th eRSFSR. The summalY guidebook of excu rsions 059,060, 066 XXVII International Geological Congress.Nauka, Moscow.

Mina V. V. 1993. - Ammonites and zona l stratigra­phy of th e Middle Vo lg ia n of Cen tra l Russia .Naukova Durnka, Kiev, 132 p. [in Russian].

O 'Dogherty L. 1995. - Biochronology and paleon­tolo gy of Mid-Cretaceous radiol ari an s fromNorthern Apennines (Italy) and Betic Cordillera(Spain) . Mem oires de Geologie, Lausanne, n° 2 1,4 15 p.

Sedaeva G . M. & V ishn evskaya V. S. 1995. ­Jurassic paleoenvironments of rhe North-EasternEuropean platform. Z onenshain Conference on PlateTectonics, GEOMAR, Kiel: 205 .

Sey 1. I. & Kalach eva E. D. 1993 . - Buchiids andzonal srrarigraphy of the Upper [urassic deposits ofth e northern Far East of Ru ssia. Geolog ia andGeofizica, N ovosibirsk, 34 (8), 12 p. [in Russian] .

Vishnevskaya V. S. 1993. - Model of sedimentarybasin for the Dornanik-rype deposits: new version .Z onemhain memorial Conference on Plate Tectonics,GEOMAR, Kiel: 151-1 52.

- 1996. - Parvicingula as indicator of J urassic toEarly Cr etaceous paleogeographical and sedirn ento­lo gi cal paleoenvironments with in North Per i-

GEODIVERSITAS • 1999 • 21 (3)

U pper j urassic-C reraccous of eastern Russian Platform

T erhys. A bstracts of M oscow Peri-Tetbys Workshop,Mo scow: 30, 3 1.

- 1998. - The domanikoid facies of th e Ru ssianplatform and basin paleogeography, in Crasquin­Soleau S. & Barrier E. (eds}, Peri-Terhys memoir 3:Stratigraphy an d ev o lu t io n of Pe r i-T'er h ya nPlatforms, Memoi res du Museu»: national d 'Histoirenat ure/le, Paris, 177 : 45-69.

Vishn evskaya V. S., Agarkov Yu. V., Za kariadze G. S.& Sedaeva K. M. 1990 . - Late j u rass ic­Cretaceous radiolarians of the Great Caucasus askey to determine age and paleoenvironment of th eLesser C au casu s ophiolites. Rep orts of RussianA cademy of Science, Moscow 3 10 (6) : 141 7-1 421 .

Vishne vskaya V. S. & De W ever P. 1996. - Aboutpossibility to correlate North Peri-Terhyan radiol a­rian events with others zo nat io ns . Abstracts ofMo scow Peri-Tethys Workshop , Moscow: 3 1, 32.

Vi shnevskaya V. S. & Sedaeva K. M. 1999. ­Reconstructions of sediment ary paleoenvironmenrsof th e north-eastern European platform and adjoi ­nin g areas for some intervals of Jurassic: 94-98 , inGeology and mineral resources of Eu ropean No rth­Eastern Ru ssia: New results and new perspe cti ves,Proceed ing of XII! Geological Co ngr ess of Ko miRespub lica . Volume 2. Geological In stitute ofUral ian Bran ch of Russian Acad emy of Sciences,Sikrivkar.

Submitted fOr p ublication on 22 April 1997;accep ted on 3 0 Ju ne 1998.

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