Lithogeochemistry of the Vendian fine-grained clastic rocks in the southern Vychegda trough

ISSN 0024�4902, Lithology and Mineral Resources, 2011, Vol. 46, No. 5, pp. 427–446. © Pleiades Publishing, Inc., 2011.Original Russian Text © V.N. Podkovyrov, D.V. Grazhdankin, A.V. Maslov, 2011, published in Litologiya i Poleznye Iskopaemye, 2011, No. 5, pp. 484–504.

427

INTRODUCTION

The extended and relatively shallow�water Mezenforeland paleobasin existed in the Late Vendian infront of the Kanin–Timan fold�thrust belt at thenortheastern margin of the East European Platform.This basin accumulated tuffaceous–sedimentarysequences in the course of intense subsidence (Akse�nov, 1985; Grazhdankin, 2004; Maslov et al., 2008).Based on parametric drilling and geophysical data(Aplonov et al., 2006), the Upper Vendian rocksobserved as numerous exposures in the southeasternWhite Sea region (Grazhdankin, 2003), are tracedalong the northeastern periphery of the platform viathe Mezen paleobasin to the Verkhnyaya Kamadepression and again exposed in the Kvarkush–Kamennogorsk anticlinorium on the western slope of

the Central Urals (Grazhdankin et al., 2009). TheMezen paleobasin was bounded by the Volga–Kamamassif in the south and the intracratonic Moscowpaleobasin in the southwest. Similarity of the paleon�tological remains in sections of the southeastern WhiteSea region and the western slope of the Central Urals,as well as finds of the Belomorian fossil biota in thecore from boreholes drilled in the Mezen synecliseindicate the existence of steady biogeographical linkswithin the entire paleobasin in the Late Vendian(Grazhdankin et al., 2005a, 2007).

Along paleoslope toward the Kanin–Timan fold�thrust belt, thickness of the sedimentary fill of theforeland paleobasin increases from 500–600 m in thesoutheastern White Sea region to 1600 m in theVychegda trough (Fig. 1). Taking into account the

Lithogeochemistry of the Vendian Fine�Grained Clastic Rocksin the Southern Vychegda Trough

V. N. Podkovyrova, D. V. Grazhdankinb, and A. V. Maslovc

aInstitute of Precambrian Geology and Geochronology, Russian Academy of Sciences, nab. Makarova 2, St. Petersburg, 199034 Russia

e�mail: [email protected] of Petroleum Geology and Geophysics, Siberian Branch, Russian Academy of Sciences,

pr. Akademika Koptyuga 3, Novosibirsk, 630090 Russiae�mail: [email protected]

cZavaritskii Institute of Geology and Geochemistry, Uralian Branch, Russian Academy of Sciences, Pochtovyi per. 7, Yekaterinburg, 620075 Russia

e�mail: [email protected] June 21, 2010

Abstract—Lithogeochemical features of the Vendian mudstones and silty mudstones taken from BoreholeKeltma 1 in the southern part of the Vychegda trough of the Mezen syneclise are discussed. It is shown thatfine�grained clastic rocks of the Ust�Pinega, Krasavino, and Mezen formations have similar chemical com�positions, suggesting their accumulation in sufficiently similar settings. The main part of the studied sampleshas K2O/Al2O3 < 0.4. This fact, in combination with the absence of TM–FM and NPM–HM correlations,indicates a significant contribution of recycled aluminosiliciclastics in their composition. At the same time,the absence of correlation between CIA and indicator ratios of rock composition in the paleodrainage basins,such as Th/Cr and Th/Sc, indicates that CIA and some other lithochemical indicators appropriately reflectthe paleoclimatic conditions in source areas surrounding a basin. The CIA value in most of the analyzed sam�ples is no more than 70. Thus, the Keltma section is similar to Upper Vendian sequences of the Kvarkush–Kamennogorsk anticlinorium and the Shkapovo–Shikhany depression. It has been established that felsic andintermediate magmatic rocks coupled with a significant contribution of quartz�rich sediments served as thesource of fine aluminosiliciclastics for the southern Vychegda trough during the Vendian. High Ce/Cr valuesin the mudstones and silty mudstones suggest that the geochemically primitive Archean protoliths were notinvolved in the washout. In the SiO2–K2O/Na2O diagram, the Vendian mudstones and silty mudstones areplotted in the field of sediments of active continental margins. Typical low values of Mo/Mn and some otherredox indices in these rocks indicate that oxidizing environment predominated in bottom waters of the sedi�mentation basin during the entire Vendian. Analysis of variations of the lithochemical indicators upward theVendian sedimentary successions in borehole Keltma 1 made it possible to divide the section into threesequences of different lithofacies and paleontological compositions.

DOI: 10.1134/S0024490211050075

https://www.researchgate.net/publication/251099204_Sequence_stratigraphy_of_the_upper_Vendian_of_the_East_European_Craton?el=1_x_8&enrichId=rgreq-3f9ab1a0-e92d-4d08-a873-4584c9f16326&enrichSource=Y292ZXJQYWdlOzIyNzMzNzI3MztBUzoxMDM1MTc5NDc2OTUxMjFAMTQwMTY5MjAxMTAxOQ==

https://www.researchgate.net/publication/227199754_Late_Vendian_Miaohe-Type_Ecological_Assemblage_of_the_East_European_Platform?el=1_x_8&enrichId=rgreq-3f9ab1a0-e92d-4d08-a873-4584c9f16326&enrichSource=Y292ZXJQYWdlOzIyNzMzNzI3MztBUzoxMDM1MTc5NDc2OTUxMjFAMTQwMTY5MjAxMTAxOQ==

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LITHOLOGY AND MINERAL RESOURCES Vol. 46 No. 5 2011

PODKOVYROV et al.

great depths of rocks and their relatively poor study incores, the comprehensive investigations of thickUpper Proterozoic sequences in the Vychegda troughbecomes a key to understanding the Mezen paleobasinstructure and deciphering its sedimentary fill evolu�tion. In particular, study of the deep Storozhevsk andSeregovo parametric boreholes drilled in the Vychegdatrough showed a sharp thickening of the Upper Ven�dian fossiliferous sequence between the Redkino andKotlin horizons (Olovyanishnikov, 1998; Olovyanish�nikov and Grazhdankin, 1998). Drilling of BoreholeKeltma 1 yielded sensational results: it recovered theUpper Riphean stromatolite succession (more than2000 m thick) that represents so far a single locality ofthe unique Keltma fossil microbiota of the Vendianage (Vorob’eva et al., 2006, 2009a). This paper isdevoted to the analysis of lithogeochemical features ofthe Vendian fine�grained clastic rocks in the BoreholeKeltma 1 section.

STRATIGRAPHY

Researchers engaged in study of the Upper Prot�erozoic succession in Borehole Keltma 1 divide the

section into the following formations (Veis et al., 2006;Vorob’eva et al., 2006): Yshkemes (interval 4902–3943 m),Vapol (3943–2910 m), Vychegda (2910–2312 m),Ust�Pinega (2312–1880 m), Krasavino (1880–1725 m),

Mezen (1725–1512 m), and Padun (1512–1330 m)1.

It should be noted that the Yshkemes and Vapol forma�tions were distinguished in the adjacent structural�facies region on the Timan Ridge, but spatiotemporalrelations between these stratons and their age remaincontroversial (Gnilovskaya et al., 2000). Therefore,correlation of the platformal rocks in BoreholeKeltma 1 with the Yshkemes and Vapol formations ofthe folded framing seems to be insufficiently substan�tiated for the present. Moreover, the term “VychegdaFormation” according to (Tereshko and Kirillina,1990) is not recommended for the subdivision andcorrelation of the Borehole Keltma 1 section, espe�cially as opposed to the Ust�Pinega Formation,because the Vychegda Formation was distinguished bySolontsov et al. (1970) in the Borehole Kotlas section

1 We also adopted this division for the lithogeochemical descrip�tion of the Vendian fine�grained terrigenous rocks in BoreholeKeltma 1.

Yekaterinburg

EastEuropeanPlatform

Moscow

200 km

Timan–Pechora

plate

Uralianfoldarea

1

2

34

1

2

Southeastern WhiteSea region Kotlas

StorozhevskSeregovo

NorthernKeltma

525369

1623

1906

1136 1266 1330

2338

1550

2000 2070

2505

2309

2790

mrs4

1

Fig. 1. Distribution of the Upper Vendian sediments and tracing of the maximum regression surface (mrs4) in the southeasternEast European Platform. (1) Studied sections, (2) boreholes: (1) Kotlas, (2) Seregovo, (3) Storozhevsk, (4) Keltma 1.


LITHOGEOCHEMISTRY OF THE VENDIAN FINE�GRAINED CLASTIC ROCKS 429

(interval 2217–2122 m) as the middle Member of theUst�Pinega Formation. In addition, the term “MezenFormation” is not also recommended for the Vendianrocks: the Mezen Formation was distinguished in theUpper Permian section of the Mezen syneclise in 1969based on the Mezen Horizon, which was establishedby A.A. Malakhov in 1940 (Molin et al., 1986).

Core material from Borehole Keltma 1 is scanty.Therefore, we cannot carry out a detailed subdivisionand facies–genetic analysis of rocks from this bore�hole. Nevertheless, the Vendian succession here can besubdivided into four sequences. The dolomitizedlimestones of the Upper Riphean Vapol Formation areoverlain by the following Vendian sedimentary succes�sion (from the base to top): (i) thinly interbedded graycross�bedded sandstones and dark gray mudstones(interval 2910–2790 m; thickness 120 m); (ii) thick(480 m) patchy (greenish gray and red�brown, withviolet tint in some places) sequence of thinly interbed�ded mudstones, siltstones, and sandstones (interval2790–2309 m); (iii) thick (580 m) sequence of thinlyand thickly interbedded (light gray fine�grained) cross�bedded sandstones (interbeds are up to 10–15 cmthick), siltstones, and dark gray mudstones (interval2309–1725 m). The Valdai Group section is crownedby the variegated sequence (interval 1725–1330 m) oflight gray thickly interbedded (medium�grained,cross�bedded) sandstones, greenish gray thin�beddedsiltstones, and bluish and brownish gray thin�beddedmudstones (beds are up to 20 cm thick).

The section of Borehole Keltma 1 is confidently cor�related with that of Borehole Storozhevsk located 156 kmnorthwest (Fig. 1). The most distinctly expressedboundary is the maximum regression surface (mrs4) atthe base of interval 2309–1725 m. It is traced in sec�tions of the adjacent boreholes owing to the sharpfacies change over the entire paleobasin. This bound�ary divides the Upper Vendian section in the Vychegdatrough into two sequences (facies series) defined as theUst�Pinega and Mezen formations (Olovyanishnikov,1998). Based on such correlation, interval 1725–1330 mof Borehole Keltma 1 can be correlated with the upperpart of the Mezen Formation that contains numerousremains of arumberiamorphs (Borehole Seregovo 40,intervals 1608–1603 m and 1545–1541 m). Thesequence of thinly interbedded mudstones, siltstones,and sandstones at 2790–2309 m (Borehole Keltma 1)correlates with the Ust�Pinega Formation of the Red�kino Horizon. It is noteworthy that thickness of theUst�Pinega Formation is relatively persistent (481 min Borehole Keltma 1, 435 m in Borehole Stor�ozhevsk, 450 m in Borehole Seregovo, and 432 m inBorehole Kotlas), whereas thickness of the MezenFormation (979 m, 804 m, 414 m, and 283 m, respec�tively) decreases with increasing distance from themargin of the East European Platform. Correlation ofthe Borehole Keltma 1 section with the adjacent bore�holes shows that the maximum regression surface atthe base of interval 2790–2309 m coincides with the

lowermost boundary of the Agma sequence (Grazh�dankin and Maslov, 2009).

The Keltma fossil biota was distinguished at 2790–2309 m in Borehole Keltma 1. It represents a specificmicrofossil assemblage containing acanthomorphicacritarchs of the early Ediacaran appearance, as well asspherical, clavate, and filamentous forms (Vorob’evaet al., 2006, 2009a). It is noteworthy that the upperpart of the underlying sequence of thinly interbeddedgray cross�bedded sandstones and dark gray mud�stones (interval 2910–2790 m) contains only filamen�tous and coccoid microfossils of a wide stratigraphicrange, whereas the lower part contains microfossilswith acanthomorphic acritarchs of the pre�Ediacaran(Late Riphean) appearance and fragments of macro�scopically flattened tubes with transverse structure. Atthe early stages of study, the age of the Keltma complexwas estimated at Early Vendian (Veis et al., 2006;Aplonov et al., 2006; Vorob’eva et al., 2006). It is nowconsidered that the interval of 2790–2309 m in Bore�hole Keltma 1 fills a stratigraphic hiatus between theLapland and Redkino horizons of the East EuropeanPlatform, the upper part of the interval of 2910–2790 mwith morphologically simple microfossils is ascribedto the Lapland Horizon, and the lower portion corre�lates with the terminal horizons of the Riphean rocksin the southern Urals (Sostoyanie…, 2008, Vorob’evaet al., 2009a, 2009b). However, our correlation of thesections likely indicates the Redkino age of the Keltmafossil microbiota.

The interval of 1725–1330 m in the BoreholeKeltma 1 section correlates with the upper part of theMezen Formation in sections of boreholes Stor�ozhevsk and Seregovo, where this sequence containsremains of the Late Vendian (Kotlin) arumberiamor�phs. Correlation of the interval of 1512–1330 m inBorehole Keltma 1 with the Padun Formation in thesoutheastern White Sea region seems to be improba�ble. First, the Padun Formation in the stratotype areahas a different structure and consists of the violet�brown, vinous�red, and red�brown (gray�brown insome places), fine�grained (locally, highly biotur�bated) sandstones with thin or thick, even, cross, fla�ser, and convolute bedding. Second, the Padun For�mation is characterized by traces of the vital activity ofDiplocraterion parallelum Torell, which, according tothe presently available data, appeared in the LowerCambrian (Alekseev et al., 2005; Grazhdankin andKrayushkin, 2007).

When the unified regional stratigraphic scheme wasaccepted in 1978, rocks transitional between the Red�kino and Kotlin horizons were known only in the Zim�nie Gory section (southeastern White Sea region). Theage of these rocks remained uncertain for a long time:they resembled rocks of the Kotlin section with respectto lithology, but contained the soft�bodied remains(Aksenov et al., 1978). In the new stratigraphicscheme of the European North of the USSR, the tran�sitional rocks were partly ascribed to the Ust�Pinega

430


PODKOVYROV et al.

Horizon. This version proposed instead of the Red�kino Horizon did not receive wide recognition (Verkh�nii…, 1986). Further specification of the stratigraphicscheme for the Vendian rocks in the Mezen synecliseresulted in identification of the Krasavino Formationwith following specific properties: its lower half haslithological and paleontological features inherent ofthe Redkino rocks, while the upper part resembles theKotlin Horizon (Burzin and Kuzmenko, 2000). Fur�ther, the base of the Chernyi Kamen Formation(Sylvitsa Group) in the Central Urals contains asequence with ambiguous stratigraphic position.Based on lithofacies features, some researchers ascribethis sequence to the Kotlin Horizon (Ablizin et al.,1982), but finds of casts and moulds of soft�bodiedorganisms allowed other researchers to accept theirRedkino age (Aksenov, 1985). Hence, the Redkinoand Kotlin horizons in the Mezen sedimentary basinand the western slope of the Central Urals are sepa�rated by a transitional sequence, which contains

diverse soft�bodied assemblage and reaches severalhundreds of meters in thickness. In our opinion, theinterval of 2309–1725 m in the Borehole Keltma 1section is ascribed precisely to this sequence.

Thus, despite inconsistency in the local UpperProterozoic stratigraphic scale for the Vychegdatrough, the Upper Vendian sequence of BoreholeKeltma 1 is rather confidently subdivided into regionalstratons. The interval of 2790–2309 m with theKeltma fossil microbiota is ascribed to the RedkinoHorizon. The interval of 2309–1725 m is ascribed tothe transitional (Redkino/Kotlin) rocks. The intervalof 1725–1330 m with macrofossils of arumberiamor�phs is ascribed to the Kotlin Horizon.

LITHOGEOCHEMISTRY OF THE SEDIMENTS

The core recovery in Borehole Keltma 1 was poorbut sufficient to obtain the relatively complete litho�geochemical characteristics of the section, reconstructthe general features of rock formation, and comparethe obtained data with similar investigations of theUpper Vendian sequences in the southeastern WhiteSea region and western slope of the Central Urals. Forthese purposes, we analyzed 80 samples of mudstonesand silty mudstones from the Vychegda, Ust�Pinega,Krasavino, Mezen, and Padun formations. The mainpart of these samples was taken by V.N. Podkovyrov.Some samples of mudstones and silty mudstones fromthe Vychegda and Ust�Pinega formations were kindlyprovided by N.G. Vorob’eva (Geological Institute,Russian Academy of Sciences, Moscow). Microscopicstudy showed that clay minerals in the Vendian fine�grained rocks are mainly represented by hydromicaand Fe–Mg chlorite. Fine silty fractions (10–25%)are dominated by quartz, microcline, and plagioclase.

The content of the major rock�forming oxides andtrace elements in the mudstones and silty mudstoneswere determined by the X�Ray fluorescence (VRA�30;N.P. Gorbunova, L.A. Tatarinova, G. M. Yatluk, andV.P. Vlasov, analysts) and ICP�MS (ELAN 9000;D.V. Kiseleva, N.V. Cherednichenko, O.A. Berezik�ova, and L.K. Deryugina, analysts) methods at theZavaritskii Institute of Geology and Geochemistry,Uralian Branch of the Russian Academy of Sciences.Some statistical data on the chemical composition ofthe fine�grained clastic rocks are listed in Tables 1 and2. These data were plotted in the –log(Fe2O3/K2O) (Heron, 1988) and NPM�FM(Yudovich and Ketris, 2000) diagrams (Fig. 2), whichprovide a general information on the chemical com�position of mudstones and silty mudstones. In the firstdiagram, data points of the considered samples areplotted in the fields of shales and wackes. In the sec�ond diagram, most data points of mudstones and siltymudstones of the Vychegda and Mezen formations fallin the field of hydromica clays, whereas others are

log SiO2/Al2O3( )

1.5

1.0

0.5

0

–0.50

а

1

2

3

4

Fe�shales Fe�sandstones

ShalesW

acke

sArkoses Subarkoses

Sublitharenites

log(

Fe 2

O3/

K2O

)

log(SiO2/Al2O3)0.5 1.0 1.5

b1

0.1

0.010 0.2 0.4

III

II

I V

IVVI

NPM

FM

Fig. 2. Positions of data points of the Vendian mudstonesand silty mudstones in the Borehole Keltma 1 section inthe – and NPM–FM diagrams. Formations: (1) Vychegda, (2) Ust Pinega,(3) Krasavino, (4) Mezen.Fields of clay rocks: (I) mainly kaolinite rocks; (2) mainlysmectite rocks with the kaolinite and hydromica admix�ture; (III) mainly chlorite rocks with the Fe�hydromicaadmixture; (IV) chlorite–hydromica; (V) chlorite–smec�tite–hydromica; (VI) hydromica rocks with a significantamount of feldspars.

log SiO2/Al2O3( ) log Fe2O3/K2O( )



Tab

le 1

.C

onte

nts

(%)

of th

e m

ajor

roc

k�fo

rmin

g ox

ides

in th

e fi

ne�g

rain

ed c

last

ic r

ocks

of d

iffe

rent

Ven

dian

and

Cam

bria

n fo

rmat

ions

rec

over

ed b

y B

oreh

ole

Kel

tma

1

Com

po�

nent

Vyc

hegd

aU

st�P

ineg

aK

rasa

vino

Mez

enP

adun

Md

SD

Min

Max

Md

SD

Min

Max

Md

SD

Min

Max

Md

SD

Min

Max

Md

SD

Min

Max

SiO

261

.83

4.00

53.6

569

.14

62.3

51.

8259

.30

65.9

962

.44

0.49

61.7

862

.92

62.8

01.

5461

.81

66.2

461

.69

1.46

60.9

165

.67

TiO

20.

820.

260.

561.

810.

820.

080.

620.

940.

870.

020.

860.

900.

830.

020.

800.

870.

840.

030.

770.

87

Al 2

O3

16.0

81.

8911

.84

20.8

915

.81

0.96

14.0

217

.35

14.8

10.

2314

.54

15.0

514

.79

0.38

14.3

015

.32

15.1

30.

4814

.58

16.0

9

Fe 2

O3

tot

7.45

1.59

4.90

10.2

77.

340.

944.

768.

528.

370.

367.

878.

747.

540.

496.

567.

917.

510.

626.

328.

42

Mn

O0.

050.

050.

030.

210.

100.

040.

070.

180.

130.

020.

090.

140.

090.

030.

080.

150.

100.

030.

080.

15

MgO

2.09

0.70

1.67

4.33

2.86

0.19

2.33

3.15

3.08

0.07

3.02

3.19

3.02

0.22

2.55

3.16

3.04

0.11

2.75

3.14

CaO

0.54

0.95

0.30

4.90

0.80

0.37

0.33

1.63

1.09

0.04

1.05

1.12

0.83

0.32

0.78

1.59

0.94

0.39

0.64

1.84

Na 2

O1.

800.

430.

602.

401.

100.

320.

701.

701.

200.

081.

101.

301.

600.

680.

802.

601.

300.

420.

501.

70

K2O

4.32

0.75

2.78

6.07

3.55

0.59

2.53

4.66

3.18

0.14

3.03

3.34

3.63

0.43

3.00

4.08

3.67

0.44

3.34

4.51

P2O

50.

090.

060.

040.

280.

170.

190.

120.

970.

190.

000.

180.

190.

160.

010.

160.

190.

180.

010.

160.

19

L.O

.I.

4.40

1.18

2.60

8.20

4.56

0.57

3.60

5.52

4.75

0.24

4.50

5.00

4.41

0.48

3.60

4.80

4.85

0.42

4.00

5.40

n31

184

610

Not

es:

for

tabl

es 1

, 2,

an

d 4:

(M

d) m

edia

n, (

SD

) st

anda

rd d

evia

tion

, (M

in)

min

imum

val

ue,

(Max

) m

axim

um v

alue

, (n

) n

umbe

r of

an

alyz

ed s

ampl

es.

432


PODKOVYROV et al.

Tab

le 2

.C

onte

nts

(ppm

) of

som

e tr

ace

elem

ents

in th

e fi

ne�g

rain

ed c

last

ic r

ocks

of d

iffe

rent

Ven

dian

and

Cam

bria

n fo

rmat

ions

rec

over

ed b

y B

oreh

ole

Kel

tma

1

Ele

�m

ent

Vyc

hegd

aU

st�P

ineg

aK

rasa

vino

Mez

enP

adun

Md

SD

Min

Max

Md

SD

Min

Max

Md

SD

Min

Max

Md

SD

Min

Max

Md

SD

Min

Max

Li

49.1

415

.15

22.8

583

.62

40.3

814

.41

34.5

186

.27

51.1

813

.78

34.6

777

.17

36.8

911

.81

32.0

569

.43

32.8

04.

0329

.07

43.0

1

Be

2.92

0.84

1.47

4.92

1.64

0.98

0.83

5.27

1.69

0.17

1.38

1.85

1.63

0.24

1.32

1.93

1.48

0.19

1.27

1.93

Sc

13.5

84.

236.

8521

.29

11.2

93.

215.

2818

.07

10.6

32.

818.

9515

.14

11.8

71.

959.

5915

.85

12.3

91.

0210

.49

14.0

4

V93

.18

27.1

047

.78

153.

010

0.1

28.1

552

.15

163.

911

6.8

5.22

108.

612

3.1

100.

711

.73

87.9

212

4.4

105.

59.

2690

.74

120.

9

Cr

75.9

027

.82

45.7

116

3.6

61.4

923

.22

29.9

212

5.1

57.8

66.

6349

.23

67.4

345

.25

15.6

841

.48

89.0

453

.99

4.93

48.7

366

.22

Mn

359.

438

2.7

110.

115

0359

9.5

322.

827

3.6

1332

587.

713

3.8

390.

575

1.6

335.

919

5.9

306.

583

8.7

459.

914

4.5

313.

079

2.3

Co

17.1

06.

659.

6630

.31

15.6

13.

958.

4424

.29

16.2

61.

7815

.61

20.3

514

.03

2.79

12.0

921

.05

14.5

31.

4812

.85

17.6

2

Ni

26.7

922

.22

13.9

210

0.5

26.4

97.

8316

.76

47.9

126

.34

2.84

24.7

732

.46

22.9

53.

8718

.98

31.6

324

.83

2.51

21.9

530

.92

Cu

22.5

119

.82

10.9

992

.76

25.1

47.

4215

.09

40.0

238

.08

7.50

34.0

652

.97

37.5

68.

2221

.71

43.0

640

.92

38.4

59.

8113

0.5

Zn

79.6

519

.39

46.8

513

7.0

69.6

354

.93

46.6

526

5.8

74.1

18.

2070

.37

93.3

267

.61

14.6

452

.96

102.

466

.34

5.69

61.6

579

.63

Ga

22.6

83.

8714

.99

29.7

418

.14

5.27

9.73

32.7

418

.17

1.46

17.3

121

.50

16.6

72.

0114

.18

20.8

917

.64

1.26

16.3

620

.34

Ge

1.95

0.41

1.11

2.63

1.13

0.54

0.84

2.81

1.26

0.34

1.01

2.00

1.10

0.29

0.95

1.90

1.19

0.20

0.91

1.51

Rb

160.

540

.58

76.4

022

3.4

97.3

829

.76

27.8

214

7.5

74.3

713

.84

60.8

493

.92

90.2

316

.09

68.9

311

4.2

98.3

29.

7492

.88

122.

9

Sr

84.1

537

.43

51.5

221

9.9

96.0

529

.68

72.4

720

8.3

109.

531

.61

82.9

616

3.7

121.

134

.44

107.

221

1.1

108.

113

.13

85.8

412

8.4

Y22

.24

7.20

6.78

37.2

415

.30

7.18

11.4

940

.17

14.4

44.

6510

.35

20.9

016

.92

5.01

15.4

030

.77

17.2

10.

9316

.22

18.9

6

Zr

195.

353

.17

88.1

227

4.4

112.

563

.79

76.1

632

1.9

130.

236

.05

88.6

019

7.7

120.

392

.59

96.4

637

7.1

115.

418

.76

88.5

314

0.1

Nb

17.2

027

.41

11.1

313

5.6

11.1

411

.36

4.78

55.3

19.

8354

.40

9.15

143.

58.

862.

537.

7615

.52

10.4

20.

858.

9711

.79

Mo

0.27

0.13

0.00

0.60

0.34

0.19

0.17

0.79

0.25

0.07

0.21

0.36

0.24

0.12

0.19

0.55

0.31

0.04

0.21

0.35

Ag

0.43

0.35

0.19

1.89

0.17

0.16

0.08

0.77

0.23

0.71

0.15

1.95

0.17

0.04

0.14

0.25

0.17

0.02

0.15

0.22

Cd

0.02

0.04

0.00

0.17

0.05

0.07

0.00

0.24

0.12

0.06

0.02

0.18

0.08

0.05

0.00

0.19

0.03

0.04

0.00

0.11

Sn

2.91

1.13

1.37

5.29

1.61

0.68

0.76

3.72

1.54

0.21

1.34

1.95

1.40

0.20

1.13

1.76

1.53

0.16

1.33

1.84

Sb

0.52

0.28

0.20

1.02

0.22

0.11

0.16

0.52

0.23

0.08

0.20

0.42

0.24

0.08

0.19

0.43

0.23

0.03

0.20

0.29

Te0.

020.

020.

000.

080.

030.

030.

010.

120.

050.

020.

040.

090.

040.

020.

030.

080.

040.

010.

020.

05

Cs

7.56

4.11

2.92

17.9

24.

201.

831.

038.

903.

420.

342.

973.

943.

120.

682.

284.

064.

000.

633.

425.

20

Ba

360.

519

5.4

133.

993

7.2

235.

818

7020

4.2

8185

243.

372

.65

172.

138

6.1

247.

967

.98

214.

842

5.2

230.

125

.26

208.

329

8.4



Tabl

e 2.

(Co

ntd

.)

Ele

�m

ent

Vyc

hegd

aU

st�P

ineg

aK

rasa

vino

Mez

enP

adun

Md

SD

Min

Max

Md

SD

Min

Max

Md

SD

Min

Max

Md

SD

Min

Max

Md

SD

Min

Max

La

36.0

611

.43

10.2

656

.63

25.4

99.

9911

.19

51.1

718

.49

4.01

13.4

621

.93

20.0

52.

6119

.28

27.0

123

.01

1.39

21.0

725

.49

Ce

75.6

322

.84

24.5

611

0.9

44.7

120

.33

25.4

210

2.6

33.9

710

.47

21.6

547

.93

44.5

26.

2142

.14

61.0

546

.73

5.21

37.2

951

.23

Pr

8.80

2.72

3.35

13.3

36.

272.

973.

2214

.83

4.77

1.06

3.56

5.70

5.09

0.90

4.96

7.63

5.71

0.28

5.28

6.17

Nd

33.7

210

.17

14.2

550

.75

23.4

612

.70

12.8

263

.62

18.4

94.

4314

.38

23.6

320

.17

4.18

19.4

732

.05

22.1

61.

0720

.72

23.9

1

Sm

6.08

1.82

2.92

8.56

4.12

2.84

2.57

14.2

83.

580.

932.

794.

763.

960.

963.

826.

684.

160.

193.

984.

56

Eu

1.07

0.35

0.58

1.77

0.83

0.54

0.56

2.72

0.80

0.21

0.65

1.10

0.89

0.22

0.84

1.50

0.90

0.04

0.86

0.96

Gd

4.82

1.54

2.54

7.60

3.19

2.68

2.51

12.6

23.

011.

042.

364.

723.

711.

123.

276.

783.

530.

203.

303.

84

Tb

0.70

0.23

0.30

1.13

0.47

0.28

0.33

1.48

0.45

0.13

0.36

0.64

0.50

0.16

0.48

0.94

0.51

0.03

0.48

0.56

Dy

4.37

1.37

1.76

6.94

3.08

1.51

2.17

8.20

2.93

0.85

2.25

4.23

3.36

1.01

3.06

6.14

3.43

0.13

3.24

3.63

Ho

0.90

0.28

0.30

1.47

0.61

0.26

0.43

1.43

0.57

0.17

0.44

0.85

0.68

0.20

0.62

1.24

0.67

0.03

0.64

0.72

Er

2.53

0.77

0.79

4.11

1.69

0.66

1.23

3.68

1.58

0.54

1.20

2.49

1.94

0.60

1.78

3.60

1.94

0.10

1.79

2.06

Tm

0.34

0.12

0.10

0.63

0.26

0.09

0.17

0.50

0.23

0.08

0.18

0.39

0.28

0.09

0.25

0.54

0.27

0.01

0.26

0.30

Yb

2.20

0.77

0.66

4.11

1.72

0.62

1.13

3.29

1.58

0.58

1.18

2.62

1.93

0.65

1.78

3.75

1.81

0.09

1.70

1.97

Lu

0.35

0.13

0.10

0.66

0.26

0.09

0.16

0.50

0.24

0.09

0.17

0.39

0.29

0.10

0.25

0.57

0.27

0.02

0.25

0.30

Hf

5.14

1.43

2.62

7.39

3.18

2.20

1.93

11.2

63.

580.

932.

665.

403.

162.

542.

6710

.27

3.02

0.37

2.68

3.93

Ta

1.91

0.85

0.71

4.95

0.70

0.77

0.29

3.13

0.65

1.83

0.53

5.17

0.57

0.43

0.47

1.75

0.58

0.08

0.50

0.80

W1.

460.

540.

792.

800.

790.

440.

382.

400.

820.

160.

671.

100.

700.

190.

531.

150.

720.

100.

660.

99

Tl

0.91

0.31

0.39

1.98

0.41

0.21

0.19

1.10

0.40

0.05

0.33

0.44

0.37

0.05

0.29

0.42

0.39

0.06

0.34

0.53

Pb

15.5

44.

417.

8225

.86

13.4

110

.57

5.02

51.0

112

.55

5.52

9.67

25.0

75.

922.

035.

0211

.23

7.20

29.4

26.

6310

0.4

Bi

0.31

0.23

0.13

1.28

0.18

0.09

0.10

0.40

0.19

0.03

0.15

0.23

0.14

0.06

0.11

0.27

0.15

0.03

0.12

0.21

Th

12.0

83.

533.

9816

.98

6.66

3.47

3.94

16.7

55.

001.

743.

858.

425.

921.

615.

3110

.28

6.12

0.55

5.77

7.57

U2.

510.

891.

264.

491.

701.

591.

056.

761.

530.

221.

201.

791.

440.

421.

242.

561.

350.

161.

261.

80

n25

186

810

434


PODKOVYROV et al.

localized in the field of chlorite–smectite–hydromicaclays.

Analysis of the available materials did not revealappreciable chemical differences between the fine�grained clastic rocks of the Ust�Pinega, Krasavino,and Mezen formations; the predominant part of mud�stones and silty mudstones of the Vychegda Forma�tion, as well as some amount of their samples from theMezen Formation, are characterized by elevatedNPM values, presumably indicating a significant con�tribution of potassic feldspar.

Let us consider now the variations of somelithochemical moduli and indicator ratios of majoroxides in the Vendian sedimentary succession in thesouthern Vychegda trough. The hydrolyzate module,HM (Al2O3 + TiO2 + Fe2O3 + FeO + MnO)/SiO2(Yudovich and Ketris, 2000) in the Vychegda Forma�tion section demonstrates a series of prominent excur�sions both toward higher (0.52–0.54) and lower(0.29–0.31) values relative to the median value (0.37)(Fig. 3a). Rocks in the Ust�Pinega Formation sectionshow significantly lesser and nonsystematic HM vari�ations (minimum 0.33, maximum 0.43, median0.38).The behavior of this parameter is similar in theKrasavino Formation (HMmedian = 0.38). The medianHM value is 0.37 (minimum 0.33, maximum 0.38) formudstones and silty mudstones in the overlying MezenFormation and 0.38 for the fine�grained clastic rocksof the Padun level. Thus, in terms of HM variations inmudstones and silty mudstones, the Vendian sequencerecovered by Borehole Keltma 1 is subdivided into two

intervals. The lower interval corresponding to theVychegda Formation is characterized by sufficientlywide HM variations, whereas the upper interval con�taining sediments of the Ust�Pinega, Krasavino, andMezen formations have significantly lesser HM varia�tions (0.29–0.54 and 0.33–0.43, respectively). How�ever, with allowance for standard deviations, themedian HM values for all formations distinguished inthe Borehole Keltma 1 section are statistically insig�nificant.

Value of the chemical index of alteration, CIA (100 ×Аl2О3/(Аl2O3 + СаО* + Na2O + K2O) (Nesbit andYoung, 1982; Young, 2001) insignificantly increasesfrom the base (2312 m) of the Ust�Pinega Formation(mudstones and silty mudstones) to a depth of approx�imately 2120 m (thickness about 190 m) and thendecreases to the top of the Krasavino Formation(thickness about 360 m) (Fig. 3b). In the Mezen For�mation section (thickness 213 m), CIA first increases(from 65 to 67), then decreases to 60, and againincreases to 69. Rocks of the underlying the Ust�Pin�ega Formation exhibit more prominent CIA varia�tions: the value increases from 65 to 69 at 2822–2774.6m, whereas silty mudstone and mudstone samplestaken at 2732.8, 2730.6, and 2729 m are characterizedby lower CIA values (56, 47, and 58, respectively).Similarly low CIA values are typical of mudstone K�63taken from a depth of 2562 m due to the presence ofcarbonate admixture in the rocks (CIA values recalcu�lated on the carbonate�free basis for the indicatedsamples increases to the typical values). In general, the

C1512 m

1725 m

1880 m

2309 m

2910 m

Md = 0.38

Md = 0.37

(а) (b) (c)

1

0 0.2 0.4 0.6 60 70 80 90 100 0.04 0.08 0.12

Area

with values

typical

of fine

clastics from

the humid

climate

regions

~

Ve

nd

ia

n

Fig. 3. Variations of HM (a), CIA (b), and TM (c) in the Vendian and Cambrian fine�grained clastic rocks recovered by BoreholeKeltma 1. (1) Padun Formation. (Md) Median. Other symbols are shown in Fig. 2.



fine�grained clastic rocks of the Ust�Pinega–Mezeninterval are characterized by the median CIA value of67 ± 2, which is sufficiently close to data obtained forthe Upper Vendian rocks in the Shkapovo–Shikhanydepression and the Kvarkush–Kamennogorsk anticli�norium (Maslov et al., 2006; Maslov and Krupenin,2007). It is highly possible that the paleodrainagebasins, which supplied fine aluminosiliciclastics in theVychegda segment of the Mezen basin during theentire Vendian, were characterized by semiarid cli�matic conditions. The absence of correlation betweenCIA and indicator ratios, such as Th/Cr and Th/Sc,indicates that CIA variations are controlled by the cli�matic factor rather than the source rock composition.For instance, the correlation coefficient between CIA,Th/Cr, and Th/Sc is –0.14 and –0.01, respectively, forthe fine�grained aluminosiliciclastic rocks of theVychegda Formation. This parameter is –0.47 and –0.19, respectively, for the Ust�Pinega Formation.

The Upper Vendian Sylvitsa Group in the CentralUrals shows a more complex CIA variation upward thesection (Fig. 4). The Staropechny–Perevalok intervalshows successive decrease and increase of this param�eter. The CIA values again decrease in the silty mud�stones of the Vilukha Member (Chernyi Kamen For�mation). Data on the Shurysh–Cheremukhovo inter�val of this formation are lacking, but the absence ofsignificant changes in this interval is suggested by thefollowing fact: rocks from the upper part of theVilukha Member and lower levels of the Sinii KamenMember have similar CIA values. The fine�grainedclastic rocks from the Sinii Kamen, Konovalovka, andKrutikha members (Chernyi Kamen Formation) andpossibly Ust�Sylvitsa Formation contain severalmedium�scale cycles of CIA variations. However, CIAvalues in the considered interval of the Sylvitsa Grouplack any prominent increase or decrease of this param�eter upward the section. The Upper Vendian (andLower Cambrian) mudstones of the Belomorian–Kuloi plateau exhibit a steady upward growth of CIA:from 66 in the Lyamitsa Formation to 71 in the ErgaFormation and 77 at the Padun level (Grazhdankin etal., 2005b, Maslov et al., 2006).

The titanium module, TM (TiO2/Al2O3) shows adifferent pattern in mudstones and silty mudstonesfrom Borehole Keltma 1 (Fig. 3c). Upward theVychegda Formation section, its value decreases from0.076–0.099 to 0.048–0.056 (median 0.052 ± 0.012).At the higher stratigraphic levels, TM grows from0.038–0.053 at the Ust�Pinega Formation base to0.059–0.060 in the fine�grained clastic rocks of theKrasavino Formation (median 0.052 ± 0.005 for thefine�grained rocks of the Ust�Pinega Formation and0.059 ± 0.001 for the rocks of the Krasavino Forma�tion). The Mezen–Padun interval, in contrast, showsome increase in TM from 0.058 at the bottom to0.054–0.056 at the top (median 0.056 ± 0.001 and0.055 ± 0.002, respectively).

The K2O/Al2O3 ratio, an indicator of the maturitydegree of fine aluminosiliciclastics (Cox et al., 1995),significantly varies in mudstones and silty mudstonesof the Vychegda Formation. For example, this ratio is0.19–0.23 in samples K�81, K�68, K�67, HB�15,K�58, and K�53 taken from a depth of 2795, 2648,2606.6, 2450, 2446, and 2350.5 m, respectively. Thus,the Vychegda Formation section shows three cycles ofvariations of this parameter from high to low valuesand vice versa at intervals of 2901–2730, 2730–2563,and 2563–2348 m (Fig. 5). The median K2O/Al2O3

value is 0.27 ± 0.04 for the fine�grained clastic rocks ofthe Vychegda Formation. Mudstones and silty mud�stones from the overlying Ust�Pinega Formation haveK2O/Al2O3median = 0.23 ± 0.02. This also contains sev�eral cycles with variations of this parameter between0.18 and 0.27, with a general trend of decrease upwardthe section. The fine�grained clastic rocks of theKrasavino Formation presumably preserve this trend(K2O/Al2O3median = 0.22 ± 0.02). In contrast, rocks ofthe Mezen–Padun interval show a gradual upsectiongrowth in K2O/Al2O3. This parameter varies from 0.20

2000 m

0 mU

pp

er

V

en

di

an

(S

yl

vi

ts

a

Gr

ou

p)

1

2

3

4

5

6

50 60 70 80 90 100

CIA

= 7

0

Areawith values

typicalof the fine

clastics fromthe humid

climateareas

Fig. 4. Variations of CIA in the fine�grained clastic rocks ofthe Sylvitsa Group of the Kvarkush–Kamennogorsk anti�clinorium. Formations and members: (1) Staropechny, (2)Perevalok; (3–5) Chernyi Kamen: (3) Vilukha Member;(4) Shurysh and Cheremukhovo members; (5) SiniiKamen, Konovalovka, and Krutikha members; (6) Ust�Sylvitsa.

436


PODKOVYROV et al.

to 0.24 at the base of the Mezen Formation andreaches 0.28–0.29 at 1376–1370 m.

The K2O/Al2O3 values in the fine�grained rocksfrom the Borehole Keltma 1 section indicate the pre�dominance of lithogenic material (Cox et al., 1995);i.e., rocks subjected to more than one cycle of weath�ering and redeposition. This conclusion is confirmedby the relations between lithochemical moduli deter�mined for the mudstones and silty mudstones. It isknown that the rocks reworked by only one sedimen�tation cycle show positive correlation between TM(TiO2/Al2O3) and FM (Fe2O3 + FeO + MnO)/(TiO2 +Al2O3), and no correlation between NPM (Na2O +K2O)/Al2O3 and HM (Yudovich and Ketris, 2000). Inthe fine�grained rocks of the Vychegda Formation, thecorrelation is absent (r = –0.02) for the TM–FM pairand only 0.19 for the HM–NPM pair. In mudstonesand silty mudstones of the Ust�Pinega Formation,these pairs show positive correlations (0.67 and 0.23,respectively). Correlation coefficients between thesemoduli were not calculated for mudstones and siltymudstones of the Krasavino and Mezen formationsbecause of small number of samples. Mudstones andsilty mudstones of the Padun Formation are charac�terized by rTM–FM and rNPM–HM values of 0.68 and 0.41,respectively. This fact also suggests the predominanceof the fine lithogenic aluminosiliciclastic material intheir composition.

The K2O/Al2O3 variation in the section of theSylvitsa Group of the Kvarkush–Kamennogorsk anti�clinorium (Fig. 6) shown for comparison demon�strates a more complex pattern. This parameter is

marked by the following trend: decrease from 0.20–0.27 to 0.18–0.22 in the lower part of the Upper Ven�dian sequence (Staropechny and Perevalok forma�tions); distinct growth from 0.18–0.19 to 0.27 in thefine�grained clastic rocks of the Vilukha Member(Chernyi Kamen Formation); decrease in theShurysh–Sinii Kamen interval (Chernyi Kamen For�mation); and several intervals of growth and decreaseat higher intervals of the section. In the southeasternWhite Sea region, the Upper Vendian sequence recov�ered by Borehole Tuchkino 1000 shows upsectionincrease in the median K2O/Al2O3 ratio from 0.22 ±0.03 (Lyamitsa Formation) to 0.28 ± 0.01 (Erga For�mation), whereas the silty mudstones of the CambrianPadun Formation have median K2O/Al2O3median of0.25 ± 0.03.

Information on the chemical composition of themudstones and silty mudstones provides insight intothe possible rock composition of source areas. Among

the available discrimination diagrams, the F1–F22

diagram (Bhatia, 1983; Getaneh, 2002; Yan et al.,

2 Here, F1 = 30.638 × TiO2/Al2O3 – 12.541 × Fe2O3tot/Al2O3 +7.329 × MgO/Al2O3 + 12.031 × Na2O/Al2O3 + 35.402 ×K2O/Al2O3 – 6.382, while F2 = 56.5 × TiO2/Al2O3 – 10.879 ×Fe2O3tot/Al2O3 + 30.875 × MgO/Al2O3–5.404 × Na2O/Al2O3 +11.112 × K2O/Al2O3 –3.89.

C1512 m

1725 m

1880 m

2309 m

2910 m

0 0.2 0.4

~

Ve

nd

ia

n

K2O

/Al 2

O3

= 0

.3

Fig. 5. Variations of K2O/Al2O3 in the Vendian and Cam�brian fine�grained clastic rocks recovered by BoreholeKeltma 1. Symbols are shown in Figs. 2 and 3.

Fig. 6. Variations of K2O/Al2O3 in the fine�grained alumi�nosiliciclastic rocks of the Sylvitsa Group on the westernslope of the Central Urals. Symbols are shown in Fig. 4.

2000 m

0 m

Up

pe

r

Ve

nd

ia

n(

Sy

lv

it

sa

G

ro

up

)0 0.2 0.4

K2O

/A2O

3 =

0.3



2007; Al�Harbi and Khan, 2008; Huntsman�Mapila etal., 2009) is most frequently used in recent years. Thisdiagram shows compositional fields of the fine�grained clastic rocks related to the disintegration ofpaleodrainage basins of magmatic (basic, intermedi�ate, and felsic) and sedimentary rocks containing asignificant amount of quartz. In the considered case,the latter parameters could serve as the main source offine aluminosiliciclastics in the sedimentation basin,with some contribution of igneous felsic and interme�diate rocks (Fig. 7).

Based on chemical composition of mudstones andsilty mudstones from Borehole Keltma 1, weattempted to estimate the paleogeodynamic nature ofthe Vendian rocks using diagrams SiO2–K2O/Na2O

and F3–F43 (Bhatia, 1983; Roser and Korsch, 1988)

(Figs. 8a, 8b). In the first diagram, most data points ofthe mudstones and silty mudstones fall in the field ofsediments of active continental margins. This is con�sistent with the viewpoint that the considered territoryrepresented a part of the foreland basin of Timanidesin the Vendian (Grazhdankin, 2004; Maslov et al.,2009). In contrast, most data points in the second dia�gram are plotted in the field of passive continentalmargins. The low La/V ratio observed in the Sc/Cr–La/V diagram (Fig. 8c) for mudstones and silty mud�stones of the entire section suggest their formation insettings similar to oceanic island arcs, though they arecomparable with sediments of the passive and activecontinental margins in terms of the Sc/Cr ratio.

Using some trace element data on mudstones andsilty mudstones from the Vendian sedimentarysequence in the Borehole Keltma 1 section, we con�structed variation plots for Th/Cr, Ce/Cr, LaN/YbN,and Eu/Eu* that reflect the rock composition in thepaleodrainage basins. Based on the upsection varia�tion in Th/Cr and Ce/Cr (Figs. 9a, 9b), the sectioncan be subdivided into three intervals. The first inter�val corresponds to the Vychegda Formation and showswide variations of Th/Cr and Ce/Cr at a general trendof decrease upward the section. In rocks of the secondinterval (Ust�Pinega Formation and the lower part ofthe Krasavino Formation), variations of Th/Cr andCe/Cr ratios are insignificant, and their upsectiondecreasing trend is less expressed as compared to rocksof the Vychegda Formation. Rocks of the third interval(upper part of the Krasavino Formation and entireMezen Formation) exhibit growth of Th/Cr andCe/Cr ratios. The Th/Cr ratio typical of mudstonesand silty mudstones of the entire section of BoreholeKeltma 1 suggests the predominance of the intermedi�

3 F3 = 0.303 – 0.0447 × SiO2 – 0.972 × TiO2 + 0.008 × Al2O3 –0.267 × Fe2O3 + 0.208 × FeO–3.082 × MnO + 0.14 × MgO +0.195 × CaO + 0.719 × Na2O –0.032 × K2O + 7.51 × P2O5,whereas F4 = 43.57 – 0.421 × SiO2 + 1.988 × TiO2 – 0.526 ×Al2O3 – 0.551 × Fe2O3 – 1.61 × FeO + 2.72 × MnO + 0.881 ×MgO–0.907 × CaO – 0.177 × Na2O – 1.84 × K2O + 7.244 ×P2O5.

ate rocks (diorite–granodiorites) in the paleodrainagebasins (Interpretatsiya…, 2001). The Cr/Cr ratio neverfall below 0.4 in 57 analyzed samples and is usually lessthan 0.4 in erosion products of the primitive Archeanprotoliths (Maslov, 2007).

Distribution of LaN/YbN across the Borehole Keltma 1section has a slightly different character (Fig. 9c). In thelower part of the Vychegda Formation (interval 2906–2601 m), this parameter varies from 7.15 to 8.85. TheLaN/YbN ratio reaches 17.56 at 2563.8 m (sample K�64), decreases to 13.79 1.8 m upward the section (sam�ple K�63), and again increases to 17.36 at the pointlocated 4 m upward the section (sample K�62). Thispattern presumably shows that the source areasincluded a new type of rocks compositionally close togranodiorites. In general, the LaN/YbN ratio in mud�stones and silty mudstones of the Vychegda Formationgradually declines upward the section and reachesalmost the PAAS value (9.2) near the top. The medianLaN/YbN ratio in the fine�grained clastic rocks of theVychegda Formation is 8.55 ± 2.88. Such drastic vari�ations are absent in the Ust�Pinega and Krasavino sec�tions. The median LaN/YbN ratio is 9.29 ± 1.75 inmudstones and silty mudstones of the Ust�PinegaFormation and slightly lower (7.50 ± 1.10) in compo�sitionally similar rocks of the Krasavino Formation.Mudstones and silty mudstones of the Mezen Forma�tion have the median LaN/YbN ratio of 7.08 ± 0.88. Allthese facts and the data on Th/Cr ratios presentedabove indicate that the integral composition of therocks eroded in the paleodrainage basin during theVendian was close to the average composition of theupper continental crust.

8

2

5

–1

–4

–7

–10 –5 0 5 10 15 20

F1

F2

Quartz�richsedimentary rocks

Igneousfelsicrocks

Igneousintermediate

rocks

Ign

eous

maf

icro

cks

Fig. 7. Positions of the data points of the Vendian andCambrian mudstones and silty mudstones recovered byBorehole Keltma 1 in the F1–F2 diagram. Symbols areshown in Figs. 2 and 3.

438


PODKOVYROV et al.

The Eu/Eu* ratio in mudstones and silty mud�stones from the lower part of the Vychegda Formation(interval 2906–2601 m) varies from 0.52 to 0.62 andincreases to 0.65–0.75 at 2563.8–2348 m (Fig. 9d).The median Eu/Eu* ratio is 0.62 ± 0.06 in the fine�grained rocks of the Vychegda Formation. At the base ofthe Ust�Pinega Formation (interval 2302–2297.6 m),the negative Eu anomaly varies from 0.62 to 0.44 andshows wide variations (0.65–0.73) for the remainingrocks (median 0.69 ± 0.07). The trend of some upwardgrowth of Eu/Eu* is preserved in the lower part of theKrasavino Formation. The median Eu/Eu* ratio is0.74 ± 0.02 in the fine�grained clastic rocks of the for�mation. Mudstones and silty mudstones of the MezenFormation, which crowns the Vendian sequence, havea slightly higher Eu/Eu* (0.70 ± 0.02).

The REE distribution pattern in mudstones andsilty mudstones of different Vendian formations in thesouthern part of the Vychegda trough, relative to theaverage post�Archean Australian Shale (PAAS), areshown in Table 3 and Fig. 10. In terms of REE pat�terns, the fine�grained aluminosiliciclastic rocks of theVychegda Formation are fairly close to PAAS. Themedian (La/Yb)PAAS in them is 0.93 ± 0.31,(Gd/Yb)PAAS is 1.18 ± 0.31, and (Eu/Eu*)PAAS is alsoclose to 1 (0.95 ± 0.10). As compared to PAAS, mud�stones and silty mudstones of the Ust�Pinega Forma�tion are relatively enriched in MREE, while(Eu/Eu*)PAAS is 1.06 ± 0.10. The fine�grained rocks ofthe Krasavino Formation are slightly depleted inLREE relative to PAAS. The median (La/Sm)PAAS is0.72 in rocks of this level, 0.81 in the underlying rocksof the Ust�Pinega Formation, and 0.90 in rocks of theVychegda Formation. Some LREE depletion and theabsence of MREE enrichment is also observed inmudstones and silty mudstones of the Mezen andPadun formations.

Some common geochemical features of the Ven�dian fine�grained siliciclastic rocks in the southernpart of the Vychegda trough, southeastern White Searegion, and western slope of the Central Urals areshown in Fig. 11. In terms of Ni–Cr correlation, aswell as GdN/YbN and Eu/Eu* ratios, rocks of all threeobjects described above are close to the typical post�Archean compositions, whereas mudstones and siltymudstones of the Sylvitsa Group have higher contentsof Ni and Cr than analogous rocks recovered by Bore�hole Keltma 1. Position of the data points in theLa/Sc–Th/Co diagram confirms the previous conclu�sion concerning the predominance of felsic and inter�mediate rocks in the source areas of all three regionsduring the accumulation of the Vendian sedimentarysequences.

The redox settings are reconstructed usingMo/Mn, Ni/Co, V/Cr, and other indicator ratios(Kholodov and Nedumov, 1991; Hatch and Lev�enthal, 1992; Jones and Manning, 1994; Rachold andBrumsack, 2001; Rimmer, 2004). It is believed that theMo/Mn ratio is more than 0.01 in sediments of stag�

50 60 70 80 90SiO2

100

10

1

0.1

Passivecontinental

margins

Activecontinental

marginsIsland�arc

settings

K2O

/Na 2

O

8

4

0

–4

F4

F3

12

–8–6 –1 4 9

Passivecontinental

margins

Island�arc

settings

Activecontinental

margins

Continentalvolcanic arcs

oceanic

4

3

2

1

La/

V

Sc/Cr

5

0 0.2

Passivecontinental

marginsActive

continentalmargins

Continentalvolcanic arcs

Oceanicisland arcs

0.4 0.6 0.8 1.0

(а)

(b)

(c)

Fig. 8. Positions of data points of the Vendian and Cambrianmudstones and silty mudstones recovered by boreholeKeltma 1 in the SiO2–K2O/Na2O (a), F3–F4 (b), and (c)Sc/Cr–La/V diagrams. Symbols are shown in Figs. 2 and 3.



nant basins and significantly less than 0.001 in sedi�ments from the well�aerated basins. Ni/Co < 5 pointsto the formation of sediments under oxidizing condi�tions; Ni/Co = 5–7, in disoxic conditions; and Ni/Co >7, in anoxic conditions. The oxidizing settings in thebasin is also suggested by V/Cr < 2, whereas values of2–4.25 and >4.25 indicate sedimentation under thedisoxic and suboxic–anoxic conditions, respectively.

The median contents of Mo, Mn, Ni, Co, V, andCr in the fine�grained Vendian aluminosiliciclasticrocks of Borehole Keltma 1 are given in Table 4. Thepredominant part of the studied samples are charac�terized by Mo/Mn < 0.001 (Fig. 12a), which indicatesthe lack of stagnant settings in the near�bottom waterin the basin. A good aeration of the near�bottomwaters in the basin was also noted for the Upper Ven�dian in the southeastern White Sea region. However,this is not always the case for the Upper Vendian sedi�mentary successions in the Central Urals, especiallyits upper levels (Vilukha, Sinii Kamen, and Krutikhamembers of the Chernyi Kamen Formation). Ni/Co < 5in the studied sections (Fig. 12b) testifies that initialsediments were accumulated in oxidizing conditions.The V/Cr value gradually increases upward the section(Fig. 12c) and reaches ~2 or more in mudstones of theKrasavino–Padun interval, which seemingly points tothe accumulation of initial sediments in the oxidizingand disoxic conditions. Thus, there is sufficientground to state that the entire Vendian sedimentarysequence in the southern part of the Vychegda troughwas mainly accumulated in a well�aerated basin.

Several conclusions can be drawn from the datapresented above. Mudstones and silty mudstones ofthe Ust�Pinega, Krasavino, and Mezen formations arevery similar in chemical composition, suggesting their

C1512 m

1725 m

1880 m

2309 m

2910 m

(а)

0 0.1 0.2 0.3

~V

en

di

an

0.4

Th/Cr = 0.11(diorites)

Th/Cr = 0.018(basic rocks)

(b)

0 1 2

Ce/Cr = 0.4

(c)

10 18

LaN/YbN = 9.2(PAAS)

(d)

0.5

Eu/Eu*

(PAAS)= 0.66

1.0

Fig. 9. Distribution of Th/Cr (a), Ce/Cr (b), LaN/YbN (c), Eu/Eu* (d) in the Vendian–Cambrian fine�grained aluminosiliciclas�tic rocks recovered by Borehole Keltma 1. Symbols are shown in Figs. 2 and 3.

Table 3. Some parameters of the PAAS�normalized REE dis�tribution in the Vendian–Cambrian mudstones and siltymudstones recovered by Borehole Keltma 1

(La/Yb)PAAS (Gd/Yb)PAAS (Eu/Eu*)PAAS

Vychegda Formation

Ust�Pinega Formation

Krasavino Formation

Mezen Formation

Padun Formation

Note: Median and standard deviation are given in the nominatorand denominator, respectively.

0.930.31�� 1.18

0.31�� 0.95

0.10��

1.010.19�� 1.20

0.31�� 1.06

0.10��

0.820.12�� 1.17

0.09�� 1.13

0.04��

0.770.10�� 1.14

0.07�� 1.07

0.03��

0.930.04�� 1.13

0.06�� 1.09

0.02��

440


PODKOVYROV et al.

(а)10

1

0.1(b)

10

1

0.1(c)

10

1

0.1(d)

10

1

0.1

10

1

0.1

(e)

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Fig. 10. The PAAS�normalized REE distribution in the fine�grained aluminosiliciclastic rocks of the Vychegda (a) Ust�Pinega(b), Krasavino (c), Mezen (d), and Padun (e) formations.



Ni

10000

1000

100

10

Cr

Eu

/Eu

*

GdN/YbN

1.4

1 3

1 10 100 1000

Zone of thepost�

Archean composition1

2

3

La/Sc

10

1

0.1

0.01

Th

/Co

0.1 1 10

Field with values typical

of erosion productsof felsic rocks

Field withvalues typical

of erosion productsof basic rocks

2

1.2

1.0

0.8

0.6

0.4

0.2

0 4

Field of post�Archeancratonic sediments

Fig. 11. Positions of data points of the Vendian mudstonesand silty mudstones in different discrimination diagrams.(1) Southern part of the Vychegda trough; (2) Kvarkush–Kamennogorsk anticlinorium; (3) Belomorian–Kuloiplateau.

deposition in analogous settings. The fine�grained ter�rigenous rocks of the Vychegda Formation contain ahigher content of the detrital potassic feldspars thanthe overlying Vendian rocks. Most of the studied sam�ples of the fine�grained clastic rocks, which composethe Borehole Keltma 1 section, have K2O/Al2O3 <0.4.Together with the lack of TM–FM and NPM–HM correlations, this fact indicates that fine alumino�siliciclastics in their composition underwent multiplesedimentation episodes. The absence of positive cor�relation between CIA and such indicators of sourcearea composition, as Th/Cr and Th/Sc ratios, indi�cates that the CIA value of the Vendian mudstones andsilty mudstones in the southern Vychegda trough, aswell as some other lithochemical indicators of thematurity of fine aluminosiliciclastics (HM and oth�ers), primarily reflect the paleoclimatic environmentsin the paleodrainage zones around the consideredVendian basin segment.

Felsic and intermediate magmatic rocks withabundant quartz�rich sedimentary rocks served assources for fine aluminosiliciclastics in the southernVychegda trough during the entire Vendian. The max�imum median Th/Cr value (0.15) in mudstones andsilty mudstones of the Vychegda Formation is slightlyhigher than the value in diorites (~0.1) and consider�ably lower than that in granodiorites (~0.45) (Interpre�tatsiya…, 2001). The minimum median Th/Cr (0.09)typical of the Krasavino Formation rocks is signifi�cantly higher than that in the basic rocks (0.018)(Interpretatsiya…, 2001). This conclusion is supportedby the REE distribution in the Vendian mudstones andsilty mudstones from Borehole Keltma 1. The medianLaN/YbN value in these rocks vary from 9.29 (Ust�Pin�ega Formation) to 7.08 (Mezen Formation). In gen�eral, this parameter is 8.5 for the entire succession and9.2 for PAAS (Taylor and McLennan, 1988). HighCe/Cr values (median values for the formations andindividual values in separate samples) exclude thecontribution of geochemically primitive Archean pro�toliths in their composition.

Positions of the compositional data points of thefine�grained aluminosiliciclastic rocks from theVychegda, Ust�Pinega, Krasavino, and Mezen forma�tions in different discrimination diagrams do not allowus to make confident conclusion about the geody�namic nature of the Vendian sedimentary successionin the Vychegda trough. It is noteworthy that datapoints of the Vendian mudstones and silty mudstonesof the study region in the SiO2–K2O/Na2O diagramare plotted in the field of sedimentary complexes ofactive continental margins. This field also includesOligocene and Miocene terrigenous rocks of the Swissmolasse basin in the Alpine foreland basin (von Eynat�ten, 2003), South Uralian segment of the Late VendianMezen foreland basin (three upper formations of theAsha Group), Late Vendian L’vov–Kishinev depres�sion (three lowermost formations of the KanilovGroup, according to unpublished data of A.V. Sochava

442


PODKOVYROV et al.

C1512 m

1725 m

1880 m

2309 m

2910 м

(а)

0 0.001 0.002

~

Ve

nd

ia

n Mo/Mn = 0.001

0.003

(b)

4 8

(c)

0 1 2 3 4 5

12

3

0

Fig. 12. Distribution of Mo/Mn (a), Ni/Co (b), and V/Cr (c) in the Vendian and Cambrian fine�grained aluminosiliciclasticrocks recovered by Borehole Keltma 1. (1) Field with values typical of oxidizing settings; (2) the same for disoxic settings; (3) thesame for the sub� and anoxic settings. Symbols are shown in Figs. 2 and 3.

and L.V. Korenchuk), and sediments of some otherbasins formed at the collisional stage.

In the majority of analyzed samples, the CIA valueis no more than 70, suggesting the predominance ofthe fine�grained aluminosiliciclastics unaffected bysignificant transformations under humid climaticconditions in the Vendian section of Borehole Keltma1. This fact suggests that the Keltma section is similarto the Upper Vendian sequences in the Kvarkush–Kamennogorsk anticlinorium and Shkapovo–Shikh�any depression, on the one hand, and is different fromthe Belomorian–Kuloi plateau sections characterizedby upsection CIA increase, on the other hand (Grazh�dankin et al., 2005b). It is noteworthy that drastic CIAincrease is noted in the Belomorian sections from thePadun Formation base. Therefore, the absence ofrocks with high (>70) CIA values in the BoreholeKeltma 1, Kvarkush–Kamennogorsk anticlinorium,and Shkapovo–Shikhany depression base can berelated to the absence of the Lower Cambrian rocks inthese regions.

Low values of stagnation coefficient (Mo/Mn) andsome other indicators of redox settings in the Vendianmudstones and silty mudstones from Borehole Keltma1 suggest the predominance of oxidizing conditionsnear the bottom layers during sedimentation. In thisrespect, the southern Vychegda segment of the LateVendian sedimentation basin was fairly close to theMiddle Uralian and White Sea segments.

CONCLUSIONS

The Vendian sequence recovered by BoreholeKeltma 1 is subdivided into three sequences with spe�cific lithofacies, paleontological, and lithogeochemi�cal characteristics.

The first sequence (interval 2790–2309 m) is com�posed of the thinly interbedded patchy mudstones,siltstones, and sandstones. The sequence contains theKeltma fossil microbiota represented by acanthomor�phic acritarchs of the Early Ediacaran appearance, aswell as spherical, clavate, and filamentous forms. It ischaracterized by prominent variations of HM, CIA,Th/Cr, and Ce/Cr; gradual upsection decrease of TM,GdN/YbN, and Eu/Eu*; and significant variations ofK2O/Al2O3.

The second sequence (2309–1725 m) consists ofthe thinly� and thickly interbedded light gray fine�grained cross�bedded sandstones, siltstones, and darkgray mudstones. They are traced in the adjacent bore�holes (Yarensk, Storozhevsk, Seregovo, and Kotlas),which contain abundant assemblages of the soft�bod�ied organisms. This sequence is marked by relativelystable values of HM, CIA, and K2O/Al2O3; gradualgrowth of TM; decrease in GdN/YbN, and significantvariations of the Th/Cr, Ce/Cr, and Eu/Eu* ratios,except for the upper part of the interval.

The third sequence (1725–1330 m) comprises thethickly interbedded light gray medium�grained cross�bedded sandstones, greenish gray thin�bedded silt�stones, and bluish or brownish gray thin�bedded mud�stones. In the adjacent boreholes, the analogous



Tabl

e 4.

Con

tent

s (p

pm)

of s

ome

indi

cato

r tr

ace

elem

ents

in th

e fi

ne�g

rain

ed c

last

ic r

ocks

from

dif

fere

nt V

endi

an fo

rmat

ions

rec

over

ed b

y B

oreh

ole

Kel

tma

1

Ele

�m

ent

Vyc

hegd

aU

st�P

ineg

aK

rasa

vino

Mez

enP

adun

PA

AS

Md

SD

Min

Max

Md

SD

Min

Max

Md

SD

Min

Max

Md

SD

Min

Max

Md

SD

Min

Max

Mo

0.27

0.11

0.12

0.60

0.34

0.19

0.17

0.79

0.25

0.07

0.21

0.36

0.24

0.12

0.19

0.55

0.31

0.04

0.21

0.35

1

Mn

359

383

110

1503

599

323

274

1332

588

134

391

752

336

196

307

839

483

839

326

3130

1100

Ni

2722

1410

126

817

4826

325

3223

419

3225

6722

238

55

Co

177

1030

164

824

162

1620

143

1221

1538

1313

623

V93

2748

153

100

2852

164

117

510

912

310

112

8812

410

59

9112

115

0

Cr

7628

4616

461

2330

125

587

4967

4516

4189

5415

749

550

110

n25

186

810

444


PODKOVYROV et al.

sequence contains specific fossil arumberiamorphassemblage. In terms of lithogeochemistry, the thirdsequence resembles the underlying rocks. Unlike thesecond sequence, it demonstrates a gradual growth ofK2O/Al2O3, Th/Cr, and Ce/Cr ratios.

Comparison of the Borehole Keltma 1 section withthe coeval sections in the southeastern White Searegion, Shkapovo–Shikhany depression, and westernslope of the Central Urals revealed some litho�geochemical differences, indicating a great role oflocal factors, such as the provenance composition andspecific features of the clastic material mobilizationand transportation during the deposition of sedimentsin different segments of the paleobasin. At the sametime, difference in the behavior of lithogeochemicalparameters, e.g., CIA, in the upper part of sections inBorehole Keltma 1 and southeastern White Sea regioncan be caused by the absence of sediments coeval withthe Padun Formation in the southern Vychegda seg�ment.

Analysis of lithogeochemical characteristicsallowed us to determine the position and formationcondition of the Vychegda Formation recovered byBorehole Keltma 1 in the summary section of the pre�Paleozoic rocks in the Vychegda trough. In particular,the chemical composition of mudstones and siltymudstones indicates that fine aluminosiliciclastics inthe southern Vychegda trough during the evolution ofsedimentary fill were derived from the felsic and inter�mediate magmatic rocks. However, high Ce/Cr valuesexclude the input of geochemically primitive Archeanprotoliths in the provenance composition. In terms oflithogeochemistry, the Vychegda Formation resemblesthe Valdai rocks formed in a distal setting of the fore�land basin in front of the Timanides. In this respect,the pre�Redkino age of the Vychegda Formationseems to be improbable. Lithogeochemical features ofthe fine�grained clastic rocks of the Vychegda Forma�tion revealed by our investigations do not contradictthe concept of the Redkino age of rocks containing theKeltma fossil microbiota.

ACKNOWLEDGMENTS

We are grateful to E.G. Dovzhikova for help in pro�cessing the core of Borehole Keltma 1.

This work was supported by the Russian Founda�tion for Basic Research, project no. 09�05�00279 andProgram 25 of the Presidium of the Russian Academyof Sciences.

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