Lithogeochemistry of the Fine-Grained Siliciclastic Rocks of the Vendian Serebryanka Group of the Central Urals

ISSN 0016�7029, Geochemistry International, 2011, Vol. 49, No. 10, pp. 974–1001. © Pleiades Publishing, Ltd., 2011.Original Russian Text © A.V. Maslov, M.T. Krupenin, D.V. Kiseleva, 2011, published in Geokhimiya, 2011, Vol. 49, No. 10, pp. 1032–1062.

974

INTRODUCTION

The Vendian sedimentary successions of the westernslope of the Central Urals exposed along numerousright tributaries of the Chusovaya River are representedby two large groups, Serebryanka and Sylvitsa, whichare assigned to the Lower and Upper Vendian, respec�tively [e.g., 1–4] (Fig. 1). Sokolov [5, p. 60] noted that“there is still little evidence for the reconstruction ofenvironments and life in the zones of relative stability ofthe Early Vendian. Therefore, it is especially importantto explore the most complete Vendian sections and'transitional' Riphean–Vendian sequences. Perhaps,the most important objects are the sections of the Urals(Serebryanka Group) and, of course, the whole Arcticregion to the north of the Arctic Circle”. This was writ�ten 15 years ago but still remains an important issue.The lithogeochemical characteristics of the fine�grained siliciclastic rocks of the Sylvitsa Group allowingthe reconstruction of various aspects of the accumula�tion of sedimentary sequences have been investigated in

great detail in recent years [e.g., 6–13], whereas the sit�uation is basically different for the Lower Vendian of thewestern slope of the Central Urals. This paper is aimedat filling the existing gaps in the knowledge of thisregion.

LITHOSTRATIGRAPHY AND FORMATION CONDITIONS OF THE LOWER VENDIAN

OF THE WESTERN SLOPEOF THE CENTRAL URALS

The Serebryanka Group of the Kvarkush–Kamen�nogorsk meganticlinorium includes the Tany, Garevka,Koiva, Buton, and Kernos formations [1, 3]. The TanyFormation (up to 450–500 m thick) is dominated by til�lite�like pebble�poor conglomerates (diamictites)(Figs. 2a, 2b), feldspar–quartz sandstones, gravel�stones, siltstones, and silty shales. There are minoramounts of altered volcanogenic rocks: carbonate–

Lithogeochemistry of the Fine�Grained Siliciclastic Rocksof the Vendian Serebryanka Group of the Central Urals

A. V. Maslov, M. T. Krupenin, and D. V. KiselevaZavaritskii Institute of Geology and Geochemistry, Ural Branch, Russian Academy of Sciences,

Pochtovyi per. 7, Yekaterinburg, 620075 Russiae�mail: [email protected]

Received March 22, 2010

Abstract—Sedimentation environments were reconstructed for the Early Vendian successions of the westernslope of the Central Urals, which comprises one of the most complete sections of the terminal Precambriansystem in northern Eurasia. It was shown that, despite the presence of several diamictite levels in the sectionsof the Serebryanka Group, mature and multiply recycled fine�grained siliciclastic materials (CIA = 65–77)were delivered into the sedimentation basin over the whole Early Vendian. Based on the lithochemical char�acteristics of shales, the climate of Serebryanka time can be estimated as semiarid–semihumid, similar to thatdominating in Late Vendian paleocatchments. Based on relatively high Mo/Mn values (0.011�0.024), it wassuggested that anoxic or similar conditions existed in the basin of Buton time, whereas other sedimentarycomplexes of the Serebryanka Group were formed in well aerated environments. The systematics of Sr, Ba,Zr, Cu, and V in fine�grained siliciclastic rocks and Sr isotopic data for carbonate rocks indicate that the sed�iments were accumulated in a fresh�water basin. The values of trace�element indicator ratios, e.g., Th/Sc,La/Sc, Th/Cr and others, in the shales of the Serebryanka Group and Nd model age estimates indicate thata variety of mainly Early Proterozoic complexes, ranging from granitoids to basic rocks, occurred in the EarlyVendian paleocatchments. The basic rocks were eroded most extensively probably in the end of Serebryankatime. Based on the Ce/Ce* values of shales, it was concluded that submarine volcanism had no significantinfluence on sedimentation processes in the Early Vendian. An exception is Koiva and Kernos time, whenhematite�bearing shales were accumulated in association with pillow basalts in some zones of the basin. Thedistribution of the compositions of shales from various formations of the Serebryanka Group in discrimina�tion diagrams suggests that the Early Vendian sedimentary sequences were formed in passive geodynamic set�tings.

Keywords: fine�grained siliciclastic rocks, lithogeochemistry, Lower Vendian, Kvarkush–Kamennogorsk megan�ticlinorium, Central Urals.

DOI: 10.1134/S0016702911080040

GEOCHEMISTRY INTERNATIONAL Vol. 49 No. 10 2011

LITHOGEOCHEMISTRY OF THE FINE�GRAINED SILICICLASTIC ROCKS 975

chlorite, sericite–albite, and albite–chlorite–carbon�ate schists (Figs. 2c, 2d).

The Garevka Formation is made up of fine�grainedsandstones and phyllitic silty shales. According to [1],its thickness is up to 600–750 m.

It was widely claimed in the mid�1980s that the Tanyand Garevka formations of the Serebryanka Groupwere intruded by the Troitsk granosyenite massif.Although its relationships with the overlying formationsof the Serebryanka Group were not fully determined[14, 15], it was argued on the basis of indirect evidencethat the Troitsk granites predated the formation of theSylvitsa Group [16]. A whole�rock K–Ar age of 680 Mawas obtained for hornfels from the periphery of theTroitsk massif [14]. The Rb–Sr isochron method(whole�rock samples) yielded an age of 621 ± 12 Ma[14, 17]. Isochron 207Pb/206Pb ages of 650 ± 20 and630 ± 20 Ma were obtained for monomineralic zirconfractions from the Troitsk granosyenites [18]. TheSHRIMP II analysis of the U–Th–Pb system of zir�cons from the granosyenites indicated the existence oftwo age boundaries in the evolution of the massif [19].An age of 671 ± 24 Ma corresponding to the formationof euhedral zircon grains was interpreted as the mostprobable time of massif formation. Approximatelysimultaneously, older zircon cores with an age of 801 ±53 Ma were coated by younger zircon. It is also impor�tant to point out that there is currently no compelling

evidence for the active character of contacts betweenthe Troitsk massif and the Vendian sedimentarysequences. According to Petrov [19], the massif occursin the Late Riphean Baseg Group, which is made up oftrachybasalts, their tuffs, rhyolites of the ShegrovitskayaFormation (volcanics of this unit were transformed tohornfels and skarns during the emplacement of theTroitsk massif), arkosic sandstones of the Us’va Forma�tion, and dark gray phyllites of the Fedotov Formation,and the contacts of granosyenites and sedimentaryrocks are tectonic.

The Koiva Formation (up to 600–700 m) is made upof a fine intercalation of phyllite�like variegated and redshales, siltstones, and variegated limestones and dolo�mites (Figs. 2e, 2f). Alkaline basaltoids (tuffs, tuffites,pillow lavas, etc.), hematite shales, and diamictitesoccur in the section of this formation in the northernpart of the meganticlinorium.

The Buton Formation (150–350 m) is made up oflaminated dark gray carbon�poor shales with thin inter�beds of siltstones and fine�grained quartz and feldspar–quartz sandstones.

The Kernos Formation (200–1200 m) consists offeldspar–quartz sandstones with interbeds of gravel�stones and phyllite�like silt–clay rocks (Fig. 2g). In thenorthern part of the Kvarkush–Kamennogorsk megan�ticlinorium, the upper portion of the Kernos Formationcomprises abundant basic and ultrabasic volcanogenic

Devonian Takatin Formation

Ven

dian

Upp

erL

ower

Ser

ebry

anka

Gro

up

Sylvitsa Group: diamictites, sandstones, siltstones, shales, and mudstones

Kernos Formation: sandstones with interbeds of gravelstones and phyllite�like silt–clay rocks

Buton Formation: low�carbon shales with rareinterbeds of siltstones and sandstones

Koiva Formation: phyllite�like shales,siltstones, sandstones, and carbonate rocks

Garevka Formation: laminated bedded shales with fine�grained sandstones in the upper part

Tany Formation: diamictites, sandstones, siltstones, shales, and volcanogenic rocks

Late Riphean Baseg Group

Fig. 1. Schematic stratigraphic column of the Lower and Upper Vendian in the Kvarkush–Kamennogorsk meganticlinorium.

976


MASLOV et al.

rocks of the Dvoretskii complex [20]; diamictites werealso documented there. Karpukhina et al. [21, 22] per�formed the Sm–Nd and Rb–Sr dating of monominer�alic clinopyroxene fractions and whole�rock samples ofthe Dvoretskii trachyandesites and obtained ages of600–560 Ma, respectively. Ronkin [23] reported isoto�pic ages of 569 ± 42 Ma (whole�rock Sm–Nd) and559 ± 16 Ma (whole�rock Rb–Sr) for the trachyandes�ites of the Dvoretskii complex. A.A. Nosova (personalcommunication, 2009) obtained a Sm–Nd age of626 ± 50 Ma (MSWD = 1.5) for two whole�rock sam�ples of the volcanic rocks of the Dvoretskii complex andtwo monomineralic clinopyroxene fractions.

The reconstructions of the formation conditions ofthe Late Precambrian sedimentary sequences in thewestern slope of the Central Urals have evolved consid�erably. They were regarded as miogeosyncline com�plexes in the mid�1960s and early 1970s [24, 25]. Thepublications of the 1980s and 1990s considered the his�tory of the Early Vendian sedimentary and volcanosed�imentary sequences of the western slope of the Central

Urals in the context of the processes of continental rift�ing. These ideas were most comprehensively discussedby Kurbatskaya et al. [26–32]. It was supposed that aslot�shaped continental rift was formed at the LateRiphean–Early Vendian boundary in the area consid�ered and filled with the sediments of sparagmite forma�tions, which probably can comprise the sedimentarysequences of the whole Serebryanka Group.

According to Bochkarev and Yazeva [33], a numberof nearly N–S�trending slow�spreading microrift zoneswith trachybasalt (Shpalorezovskii, Vil’venskii, andKolpakovskii complexes), trachybasalt–trachyte(Shchegrovitskii complex), and limburgite–trachyba�salt–trachyte volcanics (Dvoretskii complex) existed inthe Early Vendian in the area of the modern westernslope of the Central and North Urals. It is supposed thatthese microrift zones showed somewhat different geo�dynamic characteristics. During the formation of therift structure, the initial magmatic pulse produced thesubvolcanic rocks of the Krasnovisherskii complex inthe Polyudov Range. According to the above authors,

(g)(f)

(c)

(а) (b)

(d)

(e)

Fig. 2. (a, b) Diamictites and (c, d) tuff breccias in the sections of the Tany Formation, (e, f) piles of finely intercalated shales,siltstones, and sandstones in the sections of the Koiva Formation, and (g) sandstones with thin shale interbeds in the section ofthe Kernos Formation. The scale bar is 10 cm.



the structure propagated from north to south. Perhaps,the depth of magma generation decreased in the samedirection. In contrast, the data of Petrov et al. [20] sug�gest that the parental melts of the Dvoretskii, Shpalore�zovskii, and Kus’inskii complexes were derived from themaximum depths. Karpukhina et al. [22] also showedthat the composition of the mafic–ultramafic com�plexes of the western slope of the Central Urals is similarto the composition of alkali basalts from intraplate con�tinental settings.

The analysis of the area distribution of geochemicalcharacteristics in the Neoproterozoic magmatic com�plexes of the western slope of the Central Urals indi�cated that, in the Early Vendian, the region comprised asingle zone of alkaline magmatism producing the Bla�godat’, Troitsk, Kus’inskii, Dvoretskii, and Shpalore�zovskii complexes [20, 23], which are confined mainlyto the sequences of the Kernos Formation of the Sere�bryanka Group. Most of the aforementioned complexesare dominated by trachybasalts, alkaline plagioclase–amphibole picrites, and hyalomelanephelinites andcontain minor trachytes, trachyrhyolites, trachyandes�ites, teschenites, and carbonatites [34–36, 23, 20].

In the recent years, the suggestion that a lateralsequence of associations typical of an ocean basin canbe reconstructed for the Late Riphean of the region hasbecome more and more popular. Then, the easternboundary of the East European platform is imagined asa passive craton margin, which is changed to the east bya continental slope, oceanic complexes, and a series ofmicrocontinents. In the Vendian, the Cadomian orog�eny resulted in the formation of a foredeep and inter�montane depressions with molasses, extensive meta�morphism, and the development of thermal domes andophiolitic sutures [37, 38]. In our opinion, such a modelis most appropriate for the Vendian sections of the west�ern slope of the Southern Urals. Attempts of its directapplication to the Vendian sequences of the westernslope of the Central Urals are still controversial, whichis clearly exemplified by the absence of a single modelfor the correlation of various formations of the Asha,Serebryanka, and Sylvitsa groups.

The trace element systematics of the fine�grainedsiliciclastic rocks from the Lower Vendian of theKvarkush–Kamennogorsk meganticlinorium has beeninvestigated by ICP MS since the mid�2000s. Maslov etal. [9] presented the first data on the distribution of rareearth elements (REE), Th, Hf, Sc, Co, Cr, and Ni andNd model ages for the rocks of the Serebryanka andSylvitsa groups. It was shown that the chondrite�nor�malized REE patterns of the shales and silty mudstonesof the two groups are characteristic of post�Archeanfine�grained terrigenous sediments. The specific fea�tures of REE systematics may indicate heterogeneouscompositions of Vendian paleocatchments and theirvariations with time. The TNd(DM) values of rocks fromthe lower part of the Serebryanka Group are ~2.0 Ga,

whereas the higher levels of the Vendian section aredominated by rocks with TNd(DM) of 1.77–1.73 Ga.This indicates that, during the early stages of basindevelopment, fine�grained siliciclastic materials weredelivered into the sedimentation basin mainly from thewest, where Early Proterozoic crystalline complexeswere most widespread. The decrease in Nd model ageswas probably related to the addition of juvenile mantlematerial to the mature continental crust.

The petrochemical maturity of the rocks of the Ven�dian paleocatchments is further supported by theTh/Cr, Th/Sc, and LREE/HREE ratios [10]. On theother hand, the low Ti/Nb values in the fine�grainedsiliciclastic rocks of the Tany Formation are indicativeof the presence of material derived by the decomposi�tion of anorogenic basic or intermediate igneous rocks,which are widespread in intraplate continental settings.The maturity of rocks in the sources decreased signifi�cantly in post�Tany or post�Koiva time. The variabilityof Th/Cr in the fine�grained siliciclastic rocks of theSerebnyanka Group suggests that the conditions in theEarly Vendian were not favorable for the efficient mix�ing of fine�grained clastic materials and, consequently,indicates an unstable tectonic regime and a rather dis�sected relief in the sedimentation area.

The geochemical characteristics of the fine�grainedsiliciclastic rocks of the Early Vendian from theKvarkush–Kamennogorsk anticlinorium (Strakhovand Bostrom indexes, chondrite� and NASC�normal�ized REE patterns, LREE/HREENASC, Eu/Eu*NASC,Ce/Ce*NASC, Zr/Hf, Ce/La, etc.) were considered inmore detail by Maslov et al. [11]. It was shown that theshales of the Tany, Garevka, Koiva, and Buton forma�tions are free of exhalative materials and can be classed

as “normal” terrigenous sequences.1 Rocks with an

admixture of exhalative material and varieties with a sig�nificant fraction of eroded products of basic magmaticrocks were documented only in the Kernos Formation.At the same time, it should be pointed out that all theresults mentioned above are based on a limited amountof factual material. For instance, Maslov et al. [9] usedtrace element analyses of 33 shale samples from variouslithostratigraphic units of the Serebryanka Group (i.e.,from 3–4 to 10 samples for each formation). Approxi�mately the same data array was discussed in [10].Maslov et al. [11] analyzed trace element evidence fromhardly more than 40 samples of shales and fine�grainedclayey siltstones from various formations of the Serebry�anka Group (five samples from the Tany Formation, 13samples from the Koiva Formation, and 13 samplesfrom the Kernos Formation).

1 According to [39], hematite shales associating with pillowbasalts in some sections of the Koiva Formation show Strakhovand Bostrom indexes indicating a possible contribution of exha�lation components.

978


MASLOV et al.

SAMPLES AND ANALYTICAL METHODS

This paper is based on the analyses of 76 samples offine�grained siliciclastic rocks obtained by the ICP MStechnique at the laboratory of physicochemical meth�ods of the Zavaritskii Institute of Geology andGeochemistry, Ural Branch, Russian Academy of Sci�ences (analysts D.V. Kiseleva, N.V. Cherednichenko,O.A. Berezikova, and L.K. Deryugina) and 99 samplesanalyzed for major oxides by the XRF method at thesame laboratory (analysts N.P. Gorbunova, L.A. Tatar�inova, V.P. Vlasov, G.S. Neupokoeva, and G.M. Yatluk).

Analytical procedures were performed under cleanroom conditions. High�purity acids additionally puri�fied by sub�boiling distillation in a BSB�939�IR (Berg�hof) system were used for sample preparation and anal�ysis. Ultrapure water with a specific electric resistanceof 18.2 Mn × cm was obtained using RiOs�Elix andMilliQ (Milipore) systems.

Sandstone and shale samples were acid digestedusing the autoclave and microwave methods. A pow�dered sample (50–100 mg) was loaded into a Teflonvessel for autoclave decomposition and a PFA (CEM)Teflon vial for microwave decomposition. A 3 : 1 mix�ture of hydrochloric and nitric acids was added into thecontainers, and they were placed on a boiling water bathfor 10 min. Hydrofluoric acid was added to the hot mix�ture, and the container was left on the bath for another5 min. The vials and autoclaves were cooled to roomtemperature, closed with lids, and placed in protectivejackets.

Decomposition was conducted in an Ankon�ATautoclave system of sample preparation for 1.5 h at atemperature of 200°С and in a PLP (Ural�Gefest) lab�oratory microwave oven with programmed heating pro�viding a stepwise pressure increase to 450 kPa and expo�sure under these conditions for 10 min.

The vials and autoclaves were cooled, their contentwas transferred into Teflon containers, and the reactionchambers were carefully rinsed with deionized water.The wash water was added to the first solution portion.The content of the containers was evaporated at a tem�perature of 140–150°С to obtain dry salts. The residuewas carefully mixed with concentrated nitric acid, afterwhich it were evaporated to dryness. The operation wasrepeated for the more complete removal of silicon. Theobtained dry salts were mixed with 1 ml nitric acid and15 ml deionized water and heated at 90°С for one hour;the obtained solution was mixed with 0.1 ml of 30%hydrogen peroxide solution and kept at the same tem�perature for 5–10 min. The prepared solutions werediluted with 1% nitric acid solution and transferred into50�ml polypropylene containers. Indium solution,which was used as an internal standard, was added up toa concentration of 10 µg/l.

Element contents were determined using an ELAN9000 (PerkinElmer Instruments) quadrupole mass

spectrometer. Solution was introduced into the massspectrometer using a pneumatic cross flow nebulizer.High�purity argon (99.999%) was used for measure�ments. Before the beginning of measurements, theinstrument was optimized to achieve the maximumsensitivity for М+ and minimize signals from М2+,МО+, and background at m/z = 220.

The ELAN 9000 mass spectrometer operated underthe following conditions during the multielement anal�ysis of geologic samples: 1.3 kW power, 0.7 amu spectralresolution, and Ni or Pt cones. All measurements wereperformed in a quantitative analysis mode with the con�struction of calibration curves. Standard multielementsolutions (PerkinElmer Instruments) certified to com�ply with the ISP 9001 requirements were used to obtaincalibration dependences. The analytical procedureincluded the following operations: (1) analysis of a con�trol (blank) sample (1% HNO3 solution used for thepreparation of standard solutions and sample dilution),(2) analysis of calibration solutions and construction ofcalibration curves (element concentration in the solu�tion was 10 µg/l), (3) analysis of ten solutions of interestwith preliminary analysis of a respective control (blank)sample containing reagents that were used for samplepreparation, (4) recalibration, (5) analysis of 10 solu�tions of working samples, etc. The sample introductionsystem was cleaned between measurements for at least2 min.

The quality of trace element analysis was controlledusing standard rock samples OU�10 (greywacke, Bay�ston Hill Quarry, Shrewsbury, Great Britain) andMGT�1 (granite, Central Geological Laboratory, UlanBator, Mongolia) provided by the International Associ�ation of Geoanalysts (IAG) within the GeoPT programand prepared in accordance with requirements forinternational reference materials.

The attested and measured contents of elements insamples OU�10 and MGT�1 are compared in Fig. 3.The relative standard deviations of the measurementresults were no higher than the permissible values(OST 41�08�212�04); no sources of systematic errorswere revealed.

LITHOCHEMICAL CHARACTERISTICS OF THE FINE�GRAINED SILICICLASTIC

ROCKS OF THE SEREBRYANKA GROUP2

Evidence on the chemical composition of the fine�grained siliciclastic rocks of the Serebryanka Group issummarized in Table 1. Based on the SiO2/Al2O3 andFe2O3/K2O ratios in the available samples of fine�grained siliciclastic rocks from various lithostratigraphic

2 The term lithochemical data (characteristics) refers to the con�tents and ratios of major (rock�forming) elements in sedimen�tary rocks; lithogeochemical data (characteristics) include thecontents and ratios of trace elements in rocks [40].



units of the Serebryanka Group, they can be classed asshales and less common wackes (Fig. 4a). This allows usto use their lithogeochemical characteristics for variousreconstructions, because it is commonly believed that,owing to efficient mixing typical of sedimentary pro�cesses, fine�grained clastic rocks (shale, siltstone–mudstone, mudstone, and fine�grained clayey siltstone)reflect in a specific manner the composition of theupper continental crust over considerable areas,whereas the chemistry of sandstones is controlledmainly by local sources [45].

General chemical characteristics. In the (Na2O +K2O)/Al2O3–(FeO + Fe2O3 + MgO)/SiO2 diagram[42], the compositions of shales from various forma�

tions of the Serebryanka Group plot mainly in field V(Fig. 4b). The relations of normalized alkalinity index,(Na2O + K2O)/Al2O3, and femic index, (FeO + Fe2O3 +MgO)/SiO2, in this field correspond to the composi�tions of the most common clay rocks consisting of chlo�rite–montmorillonite–illite mixtures. The authors ofthe diagram argued that rocks with such compositionsare not related to weathering zones. A smaller numberof points fall within field VI (illite�bearing clay rockswith variable amounts of finely dispersed feldspar,which are characteristic mainly of arid weatheringzones of the Late Precambrian [46]) and the overlapregion of fields II (rocks dominated by montmorillonitewith subordinate amounts of kaolinite and illite) and V.

1000

0.1 1000

100

10

1

1 10 100

1000

0.1

100

10

1

Mea

sure

d, p

pm

Certified, ppm

y = 1.00258x + 0.00429R2 = 0.9990

Ti

Mn

BaRb

CrZr

LiCe

Sr

Zn

LaPb

ThNd

GaCs

Y

Sn

VNiNb

SmPr

BeCu

ScU

GdDy

HfCo

MoTa

ErTl

YbBi

GeHo

TbW

EuLu

Sb

Tm

Ti

Mn

Ba

RbCr Zr

LiCe

Sr

LaPb

ThNd

Ga

Cs

Y

V

Ni

Nb

SmPr

Be

Cu

Sc

U

Gd

DyHf

Co

MoTa

Tl

Yb

HoTb

Eu

Lu

Tm

y = 1.00393x – 0.03382R2 = 0.9995

MGT�1

Cd

OU�10

Mea

sure

d, p

pm

Er

Fig. 3. Comparison of certified and analyzed contents of elements in standard samples OU�10 and MGT�1.

980


MASLOV et al.

These observations are in adequate agreement with dataon the mineral composition of the fine�grained silici�clastic complexes of the Serebryanka Group obtainedby the analysis of the distribution of shale compositionsin the K/Al–Mg/Al diagram [43] (Fig. 4c).

In the (Na2O + K2O)–HI diagram [42] (Fig. 4d),most of the compositions of fine�grained siliciclasticrocks of the Serebryanka Group fall within the field ofnormohydrolyzates (0.33 < HI < 0.48) at Na2O + K2Ofrom 3.75 to 7.75%. The median hydrolyzate index (HI)values in the rocks of the Tany, Koiva, and Kernos for�mations are close to each other: 0.43 ± 0.09, 0.43 ±

0.08, and 0.40 ± 0.07, respectively.3 The median of HI

is somewhat lower in the shales of the Garevka Forma�tion (0.35 ± 0.07), but, if standard deviations are takeninto account, this value is statistically indistinguishablefrom the above data. On the other hand, the matrix ofdiamictites from the Tany Formation shows HI =0.26 ± 0.01, which allows us to consider these materialsas hypohydrolyzates and is in good agreement with theirsuggested marine–glacial nature [49, 50]. The diamic�tite matrix of the Tany Formation is also different fromthe fine�grained siliciclastic rocks of the SerebryankaGroup in the total of alkalis (4.06% versus 5.26–5.95%).

3 In this paper, we use median values for the contents and ratios ofvarious oxides and elements, because this statistical parameterprovides a generalized estimate for small analytical samples ofunknown distribution [47, 48].

As can be seen from Table 1, the shales of mostlithostratigraphic units of the Lower Vendian of theKvarkush–Kamennogorsk meganticlinorium do notshow significant differences in the median contents ofmajor oxides, taking into account standard deviations.As will be shown below, there are some exceptions,including SiO2 in the Buton Formation, TiO2 and Al2O3

in the Garevka and Buton formations, Fe2O3(tot) andMgO in the Buton and Kernos formations, CaO in theGarevka and Buton formations, and K2O in the Koivaand Buton formations. The available information doesnot support the suggestion on elevated P2O5 contents inthe rocks of the Buton and Kernos formations; however,this could be related to the fact that we did not samplesections with basic volcanics. According to Kurbatskayaet al. [26, 28, 29, 31, 1], most phosphate occurrences(e.g., Bobrovskaya suite of the Lower Kernos Subfor�mation) are related to these volcanics.

Comparison with PAAS. Normalization to post�Archean average Australian shale (PAAS [45]) showedthat the shales of the Tany Formation are rather similarto PAAS in SiO2, TiO2, Al2O3, total iron, MgO, andK2O, but are significantly depleted in MnO and CaO(MnOmedian = 0.36 × PAAS and CaOmedian = 0.25 ×PAAS at a minimum of 0.09 × PAAS) (Fig. 5a). Thecontents of Na2O and P2O5 range from 0.42 to 4.45 ×PAAS and from 0.37 to 5.37 × PAAS, respectively. Themedian of the chemical index of alteration, CIA =100 × Аl2О3/(Аl2О3 + СаО* + Na2O + K2O) [51, 52],

Table 1. Median contents of major oxides in the fine�grained siliciclastic rocks of the Serebnyanka Group, wt %

Compo�nent

Formation

Tany Garevka Koiva Buton Kernos

Med SD Med SD Med SD Med SD Med SD

SiO2 60.52 4.89 65.24 2.99 61.59 3.81 55.93 1.96 63.20 3.82

TiO2 0.81 0.16 0.97 0.25 0.72 0.14 0.92 0.04 0.72 0.13

Al2O3 18.03 2.22 15.91 1.96 17.94 3.18 20.96 0.52 17.06 2.18

Fe2O3 tot 7.01 1.90 6.89 2.09 7.29 1.77 5.02 1.10 5.35 2.32

MnO 0.04 0.02 0.04 0.02 0.05 0.02 0.07 0.06 0.04 0.06

CaO 0.32 0.33 0.15 2.69 0.30 0.49 0.54 0.31 0.28 0.36

MgO 2.23 0.91 2.30 0.53 2.09 0.36 1.91 0.27 1.95 0.41

Na2O 1.43 1.14 2.00 0.35 1.26 0.57 2.23 1.56 1.79 0.77

K2O 3.93 1.35 3.26 0.54 4.09 1.50 4.73 1.09 3.86 1.14

P2O5 0.19 0.18 0.12 0.06 0.14 0.11 0.24 0.11 0.13 0.14

LOI 3.67 0.82 3.40 1.82 3.70 0.57 3.82 0.45 3.50 0.85

n 22 5 35 8 31

Note: n is the number of analyzed samples, Med is median, and SD is standard deviation.



is 69 (minimum 62 and maximum 77) for the fine�grained siliciclastic rocks of the Tany Formation.

The diamictite matrix of the Tany Formation issomewhat enriched in SiO2 relative to PAAS (median is1.14 × PAAS), but its median contents of TiO2, Al2O3,Fetot, MnO, CaO, MgO, and K2O are generally lowerand range from 0.54 to 0.82 × PAAS. These rocks aredifferent from the shales of the same level in highermedian SiO2 and CaO contents and significantly lowercontents of TiO2, Al2O3, Fetot, MgO, and K2O. Forinstance, the median Al2O3 content is ~18% in the Tanyshales and 12.51% in the diamictite matrix. Theseparameters for K2O are 3.93 and 2.47%, respectively.The CIA value of the diamictite matrix of the Tany For�mation ranges from 58 to 69.

The median contents of SiO2, TiO2, Fetot, and MgOin the fine�grained siliciclastic material of the Garevkalevel are similar to PAAS (from 0.98 to 1.06 × PAAS,Fig. 5b). The median contents of some components are

lower than the PAAS values, including Al2O3 (0.84 ×PAAS), K2O (0.88 × PAAS), MnO (0.36 × PAAS), and

CaO (0.12 × PAAS). The minimum and maximumNa2O contents in the shales of the Garevka Formationare in contrast higher than the PAAS level. Comparedwith the Tany shales, the rocks of similar grain�sizecharacteristics from the Garevka Formation are richerin SiO2 (60.52 and 65.24%, respectively) and poorer inAl2O3 (18.03 and 15.91, respectively) and CaO (0.32and 0.15%, respectively). The CIA values of theGarevka shales range from 65 to 73, one of the samplesshows a low CIA value of 41 at 6.25% CaO and 3.27%MgO.

The shales of the Koiva Formation are similar toPAAS with respect to median SiO2, Al2O3, Fe2O3 tot,MgO, Na2O, and K2O contents (Fig. 5c), whereas themedian contents of TiO2 and P2O5 are 0.72 × PAAS and0.88 × PAAS, respectively, and MnO and CaO are sig�nificantly depleted relative to PAAS. Compared withthe underlying rocks of similar grain size from the

0.6

0 1.2

0.4

0.2

0.4 0.8

Mg/

Al

(c)Chlorite

Kaolinite Illite Illite + K�feldspar

K/Al

2.0

–1.02.5

1.0

0

0.5 1.0

log(

Fe 2

O3

tot/

K2O

)(a)

log(SiO2/Al2O3)

1

0.0010.6

0.1

0.01

0.2 0.4

FM

(b)

NKM

0.6

0 15

0.4

0.2

5 10

HI

(d)

Na2O + K2O, wt %

0 1.5 2.0

Fe�shales

Fe�sandstones

Sub�arkoses

Sub�

Arkoses

Wackes

Shales

0

I

II

III IV

V

VI

1

2

3

4

5

6

Superhydrolyzates

Normohydrolyzates

Hypohydrolyzates

Fig. 4. Compositions of the shales of the Serebryanka Group and the fine�grained matrix of the diamictites of the Tany Formationof the Kvarkush–Kamennogorsk meganticlinorium in the (a) log(SiO2/Al2O3)–log(Fe2O3tot/K2O) [41], (b) NKM–FM [42],(c) K/Al–Mg/Al [43], and (d) (Na2O + K2O)–HI [42] diagrams. Fields in the NKM–FM diagram (clays): I, mainly kaolinite;II, mainly montmorillonite with minor kaolinite and illite; III, mainly chlorite with minor Fe illite; IV, chlorite–illite; V, chlo�rite–montmorillonite–illite; and VI illite with a significant fraction of dispersed feldspars. The K/Al and Mg/Al values for kaolin�ite, illite, and chlorite were calculated using the data of [44]. Formations: 1, Tany; 2, diamictite matrix of the Tany Formation;3, Garevka; 4, Koiva; 5, Buton; and 6, Kernos.

982


MASLOV et al.

Garevka Formation of the Serebryanka Group, theshales of the Koiva Formation are slightly depleted inSiO2, TiO2, and Na2O (median values are 65.24 and61.59%, 0.98 and 0.72%, and 2.00 and 1.26%, respec�tively) but enriched to some extent in Al2O3 (15.91 and17.94%, respectively) and CaO (0.15 and 0.30%,respectively). The median CIA value for the shales ofthe Koiva Formation is 71 ± 6 (minimum 55 and maxi�mum 71). The MgO and Na2O contents of variegatedhematite shales associating with pillow basalts are 3.1–3.3% and 3.0–3.9%, respectively. According to the data

of Yudovich and Kertis [42], this indicates the presenceof camouflaged pyroclastic material [39].

In the northern part of the Kvarkush–Kamen�nogorsk meganticlinorium (upper reaches of the Us’vaRiver), we described a layer�bay�layer section of theKoiva Formation with a total thickness of ~400 m andcollected 15 shale samples from it. This provided a basisfor the analysis of variations in K2O/Al2O3, hydrolizateindex, and CIA in the vertical section of this lithostrati�graphic unit of the Serebryanka Group (Fig. 6). TheK2O/Al2O3 ratio is lower than 0.30 almost throughout

0.1SiO2 LOI

10

1

TiO2

Al2O3FeO3 tot

MnOCaO

MgONa2O

K2OP2O5

Buton Formation (d)

0.1

10

1

(c)

0.1

10

1

(b)

0.1

10

1

(a)

Diamictite matrix

Fig. 5. PAAS�normalized distribution patterns of major oxides in fine�grained siliciclastic rocks from various levels of the Sere�bryanka Group. Formations: (a) Tany, (b) Garevka, (c) Koiva, and (d) Kernos.



the whole Koiva section, which indicates the domi�nance of lithogenic components in the composition offine�grained siliciclastic materials. The HI values are0.50–0.53 in the shales from the base of the section(lowest 7–20? m) (superhydrolyzates according to [42])and remain almost constant (0.40–0.41) in the 20?–125 m interval. Upsection (125–260 m), HI increasesto 0.43–0.48 and shows rather significant variations toboth higher (0.55) and lower (0.39) values in the upper�most levels. The CIA value is 68–71 in the 0–40 minterval and varies from 71 to 76 in the overlying stratabetween 40 and 210 m. Shales with similarly high CIAvalues reappear in the section of the Koiva Formation at320–360 m. Since there is no correlation of CIA valuesin the section of the Koiva Formation with suchgeochemical indicators of paleocatchment composi�tion as Th/Cr, La/Sc, and Th/Sc (rCIA–Th/Cr = –0.45,

rCIA–La/Sc = –0.13, and rCIA–Th/Sc = –0.14), the pre�sented CIA values can be considered as a climate signalrecorded in fine�grained clastic rocks. Thus, the sectionis dominated by fine�grained siliciclastic materialsformed in paleocatchments under semiarid–semihu�mid climate conditions.

In the basin of the Mezhevaya Utka River, the totalthickness of the Koiva Formation decreases by morethan an order of magnitude [1]. In contrast to the sec�tion described above, lenses and interbeds of fine�grained iron�poor dolomites occur there in red and var�iegated siltstones and fine�grained sandstones. Thedolomites can be tentatively interpreted as lacustrinedeposits on the basis of their geochemical and Sr iso�tope characteristics (87Sr/86Sr from 0.7209 to 0.7243;A.B. Kuznetsov, personal communication, 2005).

300

0

200

100

0.2 0.4

50–55

44–49

43

42

40–41

34–39

29–33

22–28

20, 21

17

16

15

14

13

12

11

1–10

20 m

K2O/Al2O3 HI СlA

K2O

/Al 2

O3

= 0

.3

0 0.2 0.60.2 50 75 100

1

2

3

4

5

6

Values characteristic of

fine�grainedsiliciclastic

materials from humid climate

zones

Values characteristic of

fine recycled siliciclasticmaterials

СlA

= 7

0

Fig. 6. Variations in K2O/Al2O3, hydrolizate index, and CIA from bottom to top in the section of the Koiva Formation. (1) Inter�calation of green and gray sandstones, siltstones, and shales; (2) unexposed interval; (3) green and gray siltstones; (4) intercalatedred sandstones, siltstones, and shales; (5) red siltstone; and (6) red sandstone.

984


MASLOV et al.

The fine�grained siliciclastic materials of the ButonFormation are similar to PAAS in median SiO2, TiO2,and Al2O3 contents (Fig. 5d). At the same time, they aresomewhat depleted in total iron and MgO and slightlyenriched in Na2O, K2O, and P2O5. The contents ofMnO and CaO in the shales of the Buton Formation, aswell as in the rocks of all underlying units of the Sere�bryanka Group, are significantly lower than the PAASvalues (0.38 and 0.35 × PAAS, respectively). Themedian TiO2, Al2O3, CaO, and Na2O contents in theButon shales are somewhat higher than those of theKoiva rocks of the same grain size (0.91 versus 0.72%,20.95 versus 17.94, 0.45 versus 0.30%, and 1.68 versus1.26%, respectively). The contents of SiO2 and totaliron are higher in the rocks of the Koiva Formation(55.89 versus 61.59% and 4.90 versus 7.29%). The CIAof the Buton shales ranges from 67 to 70.

The Kernos shales are similar to PAAS with respectto median SiO2, Al2O3, MgO, and K2O contents(Fig. 5d). They are somewhat depleted relative to PAAS

in TiO2, Fetot, and P2O5, and the median contents ofNa2O, MnO, and CaO are ~1.5, 0.37, and 0.21 × PAAS,respectively. Compared with the shales of the ButonFormation, the rocks of similar grain�size characteris�tics from the Kernos Formation show higher medianSiO2 contents (55.89 and 63.20, respectively), butsomewhat lower TiO2, Al2O3, CaO, and K2O contents.The CIA of the fine�grained siliciclastic rocks of theKernos Formation is 69 ± 3 (minimum 59 and maxi�mum 73).

It is evident from the data presented above that SiO2

and Al2O3 contents show the most pronounced anti�thetic variations in the composition of fine�grainedsiliciclastic rocks from the generalized section of theSerebryanka Group. Considerable variations were alsoobserved for Fe2O3 tot, the median contents of which inthe shales of the Tany, Garevka, and Koiva formationsare from ~6.9 to ~7.3% and decrease to 4.9–5.35% inthe Buton and Kernos rocks of similar grain size(Fig. 7).

Paleogeodynamic setting. According to SiO2–K2O/Na2O relationships, a significant fraction of thefine�grained siliciclastic rocks of the SerebryankaGroup was formed in active continental margin envi�ronments [53] (Fig. 8a). The respective points form anarray approximately parallel to the lines separating thefields of major geodynamic environments (K2O/Na2Odecreases with increasing SiO2 contents in the rocks).Also shown in this diagram are the fields of syncolli�sional fine�grained siliciclastic materials from the Ven�dian and top Upper Riphean of the Yenisei Range(unpublished data of A.D. Nozhkin, Institute of Geol�ogy and Mineralogy, Siberian Branch, Russian Acad�emy of Sciences); the Devonian of the Xicheng basin,China [54]; the Neoproterozoic Lake Maurice andUngoolya groups, Officer Basin, Australia [55]; and theNeoproterozoic Hammamat Group, Egypt [56]. Thefields of the above sequences are extended mostly in avery different direction: except for the Neoproterozoicsediments of the Officer Basin, K2O/Na2O tends toincrease with increasing SiO2 content in all of the com�plexes.

In the K2O/Na2O–SiO2/Al2O3 diagram [57], mostof the shale compositions from the Serebryanka Groupalso plot in the field of typical passive continental mar�gin sediments (Fig. 8b). In the F1–F2 diagram [58], thecompositions are almost equally distributed betweenthe fields of passive and active continental margins(Fig. 8c). On the other hand, with respect to Sc/Cr–La/Y relationships [58] (Fig. 8d), the sequences consid�ered here tend to plot near the field of sediments frompassive geodynamic settings. The above considerationsallow us to suppose that, in terms of geodynamic set�ting, the sequences of the Serebryanka Group can beassigned to passive regime complexes, predating in the

0

Tan

y

5%

Gar

evka

But

on

Ker

nos

Koi

va

15

20%

60

65%

SiO2Al2O3

Fe2O3tot

TiO2

CaOMgO

Na2OK2OP2O5

Fig. 7. Variations in the median contents of major oxides infine�grained siliciclastic rocks from various formations ofthe Serebryanka Group.



Vendian section the syncollisional sequences of theschlieren suite of the Sylvitsa Group [13].

GEOCHEMISTRY OF THE FINE�GRAINED SILICICLASTIC ROCKS

OF THE SEREBRYANKA GROUP

The median contents of a wide range of trace ele�ments in the fine�grained siliciclastic rocks of all forma�tions of the Serebryanka Group and correspondingstandard deviations are given in Table 2. These data canbe used to evaluate indicator element ratios in the shalesof various lithostratigraphic units of the SerebryankaGroup and reconstruct the main characteristics of the

formation of the Early Vendian sedimentary sequencesof the Kvarkush–Kamennogorsk meganticlinoriumand, first of all, the compositions of rocks in the prove�nances.

Compositions of rocks in plaeocatchments. The fine�grained siliciclastic rocks of the Serebryanka Groupshow considerable sample�to�sample variations inTh/Sc, from 0.14–0.16 to 4.45 (Fig. 9a). The medianvalues of this ratio are much less scattered: from 0.77(Garevka Formation) to 1.97 (diamictite matrix fromthe Tany Formation). Taking into account the data of[59, 60], this indicates that the paleocatchments ofSerebryanka time comprised a variety of rocks rangingfrom basic to granitic compositions.

100

0.150 90

10

1

60 70 80

12

–8–6 9

8

4

0

–4

–1 4

(a)

K2O

/Na 2

O

SiO2, wt %

б

в

г

а

Passive continental margins

Active continental margins

Island�arcettings

8

01 100

6

4

10

(b)

SiO

2/A

l 2O

3

K2O/Na2O

Passive continentalmarginsActive

continental margins

2

F2

F1

Passivecontinental margins

Oceanicisland�arc settings

Continentalvolcanic arcs

5

0 1.0

4

3

2

1

0.2 0.4

La/

Y

Sc/Cr

Passive continentalmargins

Active

Continentalvolcanic arcs

0.6 0.8

Oceanic island arcs

continental margins

1234

5

(c) (d)

Active continental margins

Fig. 8. Compositions of shales from various formations of the Serebryanka Group in geodynamic discrimination diagrams for sed�imentary complexes. Formations: (1) Kernos, (2) Garevka, (3) Koiva, (4) Buton, and (5) Kernos. The SiO2–K2O/Na2O diagramalso shows the fields of (a) syncollisional fine�grained siliciclastic rocks of the Vendian and upper Upper Riphean of the YeniseiRange (unpublished data of A.D. Nozhkin); (b) Devonian of the Xicheng basin, China [54]; (c) Neoproterozoic Lake Mauriceand Ungoolya groups, Officer basin, Australia [55]; and (d) Neoproterozoic Hammamat Group, Egypt [56].

986


MASLOV et al.

Table 2. Median trace element contents in the fine�grained siliciclastic rocks of the Serebryanka Group, ppm

Element

Formation

Tany Garevka Koiva Buton Kernos

Med SD Med SD Med SD Med SD Med SD

Li 46.39 18.94 – – 58.42 17.26 – – 24.79 9.28

Be 2.05 0.61 2.77 0.51 2.02 1.31 1.87 0.77 2.20 4.79

Sc 8.83 3.69 19.34 2.01 13.95 7.04 14.51 6.29 5.95 55.21

V 91.77 22.24 124.17 17.69 89.25 57.63 78.08 38.34 81.73 95.88

Cr 126.34 36.07 141.79 27.63 116.27 43.86 112.46 34.51 124.84 398.77

Co 13.40 4.80 16.33 6.26 14.70 4.26 4.67 1.96 13.26 10.01

Ni 46.81 16.81 71.82 12.74 42.86 13.41 26.71 3.77 29.46 21.81

Cu 15.95 9.25 30.72 4.53 21.95 13.76 16.87 65.04 38.08 49.12

Zn 69.20 20.11 102.38 2.58 88.35 29.72 65.47 14.13 76.70 27.29

Ga 19.77 4.57 27.41 2.18 23.31 9.82 23.51 1.79 23.05 5.19

Rb 88.05 44.13 132.36 22.49 144.70 81.65 121.34 42.03 80.11 43.61

Sr 33.30 34.43 76.57 47.06 45.64 15.82 52.57 26.74 41.29 32.65

Y 10.36 9.67 26.40 2.08 17.29 9.74 19.88 8.02 8.28 7.31

Zr 180.04 43.46 160.89 19.61 152.63 102.74 229.36 36.61 188.27 48.29

Nb 16.72 21.55 20.18 2.34 15.04 16.50 20.93 3.74 19.01 8.46

Mo 0.30 0.70 0.37 0.06 0.14 1.80 0.85 0.57 0.29 0.99

Cd 0.01 0.01 – – 0.03 0.04 – – 0.06 2.85

Sn 2.15 0.63 – – 2.39 1.18 – – 2.88 2.42

Sb 0.17 0.12 – – 0.30 0.18 – – 0.61 1.90

Te 0.08 0.16 – – 0.08 0.19 – – 0.46 238.12

Cs 2.30 1.07 3.80 0.90 3.07 2.01 3.55 0.58 4.53 1.87

Ba 499.90 176.73 607.64 285.74 477.61 386.39 670.80 165.28 438.70 651.70

La 26.98 22.79 49.56 8.69 35.77 19.21 46.14 15.35 17.97 11.40

Ce 52.80 46.41 95.03 26.87 68.17 37.52 83.39 29.86 42.34 21.30

Pr 6.32 4.87 11.37 1.88 8.42 4.57 10.33 3.39 4.64 2.44

Nd 22.29 18.41 41.21 6.61 31.99 17.30 37.05 11.98 19.85 8.64

Sm 3.52 3.17 6.94 1.04 5.65 2.89 6.01 1.90 3.68 1.81

Eu 0.66 0.71 1.39 0.36 1.09 0.57 1.01 0.34 0.65 0.42

Gd 2.19 2.76 5.64 0.75 3.73 2.03 4.39 1.58 2.06 1.43

Dy 2.32 1.84 4.75 0.34 3.27 1.86 3.27 1.25 2.26 1.15

Er 1.31 0.83 2.61 0.21 1.85 1.09 1.92 0.76 1.34 0.71

Tm 0.20 0.11 0.36 0.04 0.28 0.17 0.27 0.11 0.19 0.13

Yb 1.35 0.69 2.36 0.24 1.81 1.09 1.85 0.71 1.32 0.66

Lu 0.20 0.10 0.35 0.04 0.27 0.16 0.28 0.11 0.21 0.21

Hf 4.81 1.04 4.48 0.57 4.59 3.21 6.19 0.81 5.55 1.35

Ta 1.35 0.55 1.28 0.14 1.02 1.53 1.25 0.23 1.47 1.24

Tl 0.61 0.22 1.28 0.29 0.69 0.36 0.73 0.53 0.72 0.24

Pb 6.04 5.04 14.95 11.92 7.20 5.17 14.57 8.74 9.92 7.93

Bi 0.15 0.09 0.21 0.10 0.18 0.41 0.11 0.05 0.26 0.38

Th 8.95 4.41 14.39 2.43 12.07 6.74 13.20 5.69 6.35 3.31

U 1.72 0.61 1.90 0.29 1.56 1.27 1.86 1.18 2.07 1.22

n 16 6 26 6 17

Note: n is the number of analyzed samples, a dash means no data, Med is median, and SD is standard deviation.



1.6

0tn kr

1.2

0.8

0.4

tnmatrix gr kv bt

Ce/

Ce*

Typical values of sequences from continental margin zones

(g)25

0tn kr

20

10

5

tnmatrix gr kv bt

LR

EE

/HR

EE

Typical values of erosion products of

(h)

8

0

6

4

2

Th

/Co

(e)

0.20

0

0.15

0.10

0.05

Th

/Cr

(c)

6

0

4

2

Th

/Sc

(а)

Granites

Basites

Basites

Diorites

Diorites

Syenites

15

mainly basicigneous rocks

Typical values of erosion products ofmainly silicicigneous rocks

0

4

4

Cr/

Zr

(f)

Granites

Basites

0

25

20

5

La/

Co

(d)

Diorites

Syenites

0

30

20

10

La/

Sc

(b)

Granodiorites

Syenites

15

10

Granites

Basites

Basites

Fig. 9. Variation ranges of some indicator ratios of trace elements in the fine�grained terrigenous rocks of various formation of theSerebryanka Group and the diamictite matrix of the Tany Formation (indicator ratios for various types of igneous rocks are givenafter [59]). Formation: tn, Tang; tnmatrix, diamictite matrix, Tany Fm.; gr, Garevka; kv, Koiva; bt, Buton; and kr, Kernos.

A similar conclusion can be drawn from the distribu�tion of La/Sc values in the shales of the SerebryankaGroup (Fig. 9b). This parameter is most variable in therocks of the Kernos Formation (0.41–24.79) and fine�

grained diamictite matrix (3.78–19.76) of the TanyFormation, whereas, for instance, the full range ofLa/Sc values in the Garevka shales is 2.47–2.93. Themedian La/Sc values are ~8.6 in the fine�grained matrix

988


MASLOV et al.

of the Tany diamictites and from 2.64 (Garevka Forma�tion) to 4.04 (Tany Formation) in the shales.

The dominance of basic and intermediate rocks inthe provenances over the whole Serebryanka time issupported, taking into account the data of [59], by theTh/Cr indicator ratio of shales (Fig. 9c). The medianTh/Cr values in the fine�grained siliciclastic rocks of theTany and Kernos formations (0.071 and 0.049, respec�tively) are approximately two times lower than those inthe Garevka, Koiva, and Buton rocks of the same grainsize.

The La/Co ratio shows a somewhat different behav�ior in the section of the Serebryanka Group (Fig. 9d).The median values of this parameter in the rocks of theTany, Garevka, Koiva, and Kernos formations are sim�ilar (1.50–3.10, indicating the dominance of basic rocksand diorites in the paleocatchments), but increase up to~9.9 in the shales of the Buton Formation. The maxi�mum/minimum ratio of La/Co in the fine�grainedrocks of the Buton and Kernos formations is ~9–50.Similar variations were observed for the Th/Co ratio inthe Lower Vendian section (Fig. 9e).

The variations of Cr/Zr in particular samples of fine�grained rocks from various formations of the Serebry�anka Group (Fig. 9f), as well as the data on Th/Sc andLa/Sc indicator ratios, suggest that the Early Vendianpaleocatchments comprised a wide range of rock com�positions (from basic rocks to granites).

The median value of Ce anomaly in the fine�grainedsiliciclastic rocks of the Serebryanka Group is from 0.89(Buton Formation) to 0.97 (Tany Formation) (Fig. 9g).Even in the Kernos shales, in which the presence ofexhalation material was previously established on thebasis of HREE enrichment in the NASC�normalizedREE patterns and the presence of a negativeCe/Ce*NASC anomaly [11], this parameter does notindicate a considerable role of exhalation processes insedimentogenesis. Taking into account the data of [61,62], this observation and the examination of structuraland textural characteristics of the Early Vendian rocks[63–65] indicate that, in general, Early Vendian sedi�mentation occurred in a shallow basin and the crust ofthe basin was not highly permeable.

The dominance of silicic rocks in provenances overthe whole Early Vendian is further supported by the dis�tribution of the LREE/HREE ratio in the shales of var�ious formations of the Serebryanka Group (Fig. 9h).The maximum and minimum median values of thisparameter were observed in the shales of the Buton For�mation (15.58) and the fine�grained rocks of the KernosFormation (10.33).

Variations in some of the aforementioned trace�ele�ment indicator ratios in the sections of various lithos�tratigraphic units of the Serebryanka Group are illus�trated by the example of the Koiva Formation, the sec�tion of which was described by us in the upper reaches

of the Us’va River (Fig. 10). For instance, the maxi�mum Th/Sc values (0.94–1.04) were observed in theshales of the lower portion of the section, whereasTh/Sc is no higher than 0.92 in the upper part. In gen�eral, throughout the whole section studied, the Th/Scvalues are somewhat higher than those of Proterozoictonalite–trondhjemite–granite associations. TheTh/Co ratio shows a somewhat different behavior in thesection of the Koiva Formation. In the lower part of thesection (0–210 m), Th/Co is rather constant (0.76–1.04) and close to the level of Archean and ProterozoicTTG associations (0.80 and 0.83, respectively). TheTh/Co value of fine clastic rocks increases up to 1.41–1.55 in the upper part of the section and decreases againto 1.00 in the topmost 25–30 m. The Ce/Cr valueincreases somewhat upsection. The median Ce/Crvalue is 0.69 in this section (full range from 0.55 to0.79), which indicates the absence of any significantfraction of fine�grained Archean siliciclastic materialsin the shales (their Ce/Cr is usually lower than 0.4 [67]).In contrast, the LaN/YbN ratio exhibits a slight gradualincrease upsection. For instance, fine�grained clasticrocks with 12.26 < LaN/YbN < 14.91 dominate in theinterval 0–170 m (mean LaN/YbN of Archean grani�toids is 15.2 [66]), whereas shales from the higher levelsshow 10.61 < LaN/YbN < 12.76; this may indicate agradual increase in the fraction of Proterozoic TTGassociations in the provenances. The magnitude of Euanomaly is 0.83 in sample US�112�9 collected 1.5 mabove the bottom of the section, decreases to 0.69within 1.5–117 m, and recovers up to 0.80. Upsection,to the level of 340 m, the Eu/Eu* values of the fine�grained siliciclastic rocks of the Koiva Formation aresimilar to the negative Eu anomaly of the average

Archean cratonic shale (0.73 [66]).4 Only in sample us�

112�1 collected 382 m above the bottom of the section,the Eu anomaly becomes again intermediate betweenthe values of PAAS (0.66) and the average Archean cra�tonic shale (0.73). The shales of the section consideredshow also variable GdN/YbN, which is almost identicalto the PAAS value in some samples, approaches thelevel of the Archean cratonic mudstone in one sample,and is close or higher than the value of the Early Prot�erozoic continental crust (1.77 [66]) in several samples.

With respect to Th–La relations (Fig. 11a), the fine�grained terrigenous rocks of the Serebryanka Group aretransitional between UCC, PAAS, average Archeancratonic shale, and Archean granitoids. In the Ni–Crdiagram (Fig. 11b), most of the points cluster nearPAAS away from both the average Archean cratonicshale and UCC. Only some shale compositions fromthe Kernos Formation approach UCC in Cr and Nicontents. In contrast, in the Sc–Th/Sc diagram, the

4 Taylor and McLennan [45] argued that the average Archeanmudstone shows Eu/Eu* ~ 1.0.



Fig

. 10.

Var

iati

ons

of s

ome

indi

cato

r tr

ace

elem

ents

in th

e se

ctio

n o

f th

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tor

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r va

riou

s ge

och

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]; E

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49

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40–

41

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20,

21

17 16 15 14 13 12 11

1–10

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/Sc

Th/Sc = 0.83 (PRTTG)

Th

/Co

Th/Co = 0.8 (ARTTG)

Th/Co = 0.83 (PRTTG)

Ce/

Cr

La N

/Yb N

LaN/YbN = 8.3 (PRγ)

LaN/YbN = 10.5(PRTTG)

LaN/YbN = 15.2 (ARγ)

Eu

/Eu

*

PAAS

ARshl

PR

TT

G

AR

TT

Gи

AR

2β

Gd

N/Y

b N

PAAS

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0.5

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812

160.

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751.

001

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49

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40–

41

34–

39

29–

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20,

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17 16 15 14 13 12 11

1–10

20 m

Th

/Sc

Th/Sc = 0.83 (PRTTG)

Th

/Co

Th/Co = 0.8 (ARTTG)

Th/Co = 0.83 (PRTTG)

Ce/

Cr

La N

/Yb N

LaN/YbN = 8.3 (PRγ)

LaN/YbN = 10.5(PRTTG)

LaN/YbN = 15.2 (ARγ)

Eu

/Eu

*

PAAS

ARshl

PR

TT

G

AR

TT

Gan

d A

R2β

Gd

N/Y

b N

PAAS

EPCARshl

Th/Co = 0.02 (AR2β)

990


MASLOV et al.

Early Vendian shales form a linear array extending fromArchean granitoids to the average Archean cratonicshale. The compositions of PAAS and UCC also plot inthis array (Fig. 11c). With respect to La/Sm and Sc/Thvalues, the rocks are similar to PAAS, UCC, andArchean granitoids (Fig. 11d). The distribution of shalecompositions from the Serebryanka Group in theCo/Hf–Ce/Cr diagram indicates the absence of anysignificant fraction of Archean fine�grained siliciclasticmaterials in most of our samples. The above two param�eters are close to the average composition of Archeancratonic shales only in one sample (us�119�2) from ourcollection; some samples show Ce/Cr < 0.40, but theirCo/Hf ratio is close to PAAS. The dominance of silicicigneous rocks in the source regions and, correspond�ingly, the mature geochemical character of the paleo�catchments are clearly illustrated by the distribution ofthe compositions of Serebryanka shales in the La/Sc–Th/Co diagram (Fig. 11f). Similar to La/Sm and Sc/Thvariations, the La/Yb–Th/Ta relationships in the fine�grained siliciclastic rocks from the Lower Vendian of theKvarkush–Kamennogorsk meganticlinorium are rathersimilar to those in such model geochemical objects asPAAS, Archean granitoids, and average Archean cra�tonic shale (Fig. 11g).

In the GdN/YbN–Eu/Eu* diagram, most of thecompositions of shales from the Serebryanka Groupoccur in the field of 1.0 < GdN/YbN < 2.0 and 0.5 <Eu/Eu* < 0.85 (Fig. 12a); i.e., these rocks show somecharacteristics of post�Archean fine�grained siliciclas�tic materials. Two shale samples from the Kernos For�mation (us�118�1 and us�119�2) have negative Euanomaly values of 0.41 and 0.42; taking into account thedata of [45, 66], this may indicate a contribution oferoded Archean granitoids to their compositions. Thissuggestion is supported by the low Ce/Cr values (0.12)in these samples. According to Taylor and McLennan[45], the average Archean cratonic shale has Ce/Cr =0.12; Condie [66] reported a lower, although onlyslightly, value of 0.095. The Eu/Eu* value of sample us�108�5 is 0.94, as compared with 0.97 for Late Archeanbasalts and 0.96 for Middle Proterozoic basalts [66]. Anumber of shale samples from the Tany Formation aresignificantly depleted in HREE (their GdN/YbN rangesfrom 2.17 to 3.30); according to [45], this is a character�istic feature of Archean fine�grained siliciclastic rocks.The GdN/YbN ratio is somewhat lower in several shalesamples from the Buton (2.03–2.59), Garevka (2.03–2.41), and Koiva (2.05–2.14) formations.

Based on the position of Serebryanka shale compo�sitions in the YbN–LaN/YbN diagram (Fig. 12b), it canbe suggested that the Early Vendian fine�grained silici�clastic materials were produced mainly by the erosion ofpost�Archean granitoids and rocks similar in composi�tion to Proterozoic tonalite–trondhjemite–graniteassociations. However, it should be kept in mind that

the YbN value of Proterozoic granites is 14.1 [66],whereas, the maximum values in our data set are nohigher than 12.

It can be clearly seen in the Eu/Eu*–LaN/YbN dia�gram that most of the compositions of fine�grainedsiliciclastic rocks of the Serebryanka Group show rela�tively high LaN/YbN values, significantly higher thanthose of Late Archean basalts, Archean cratonic shales,and PAAS (Fig. 12c). This indicates a significant petro�geochemical maturity of the rocks of Early Vendianpaleocatchments. On the other hand, their Eu/Eu* val�ues are intermediate between the Eu anomalies of theaforementioned model objects.

The main characteristics of chondrite�normalized[45] REE patterns in the fine�grained siliciclastic rocksof various lithostratigraphic units of the SerebryankaGroup are given in Table 3. The REE diagrams areshown in Fig. 13. Based on these data, it can be con�cluded that the main source of the Early Vendian fine�grained siliciclastic rocks was the geochemically maturecomplexes of the base of the East European platform.The maximum LaN/YbN values in the Tany and Butonshales range from 27.42 to 29.63, significantly above themean value of Archean tonalite–trondhjemite–graniteassociations (~18.2 [66]). The minimum LaN/YbN val�ues in most lithostratigraphic units of the SerebryankaGroup do not decrease below 8.40, and are as high as15.66 in the Buton shales. On the other hand, the min�imum LaN/YbN value in the fine�grained siliciclasticrocks of the Kernos Formation is 6.82. These rocks alsoshow a significantly lower median LaN/YbN value of11.67 (as compared with 18.69 in the underlying rocksof the Buton Formation). This indicates the possibleappearance of basic rocks in the paleocatchments of theend of Serebryanka time. However, their contributionto the development of the sedimentary sequence of theKernos Formation was not very significant.

The median Eu/Eu* values of the fine�grainedsiliciclastic rocks of the Garevka, Buton, and Kernosformations are rather close to the PAAS level (0.66[45]). This parameter is slightly higher in the shales ofthe Tany and Koiva formations.

The Garevka and Buton shales are different from therocks of similar grain�size characteristics from otherlithostratigraphic units of the Serebryanka Group inhaving higher GdN/YbN values, 1.93 and 1.95, respec�tively, versus 1.47–1.67 for the rocks of the Tany, Koiva,and Kernos formations. Two of the four samples of theGarevka Formation analyzed by us and three of the sixsamples of the Buton Formation show significantHREE depletion. The shales of the Tany Formation arecharacterized by the maximum scatter of GdN/YbN val�ues: from 0.95 (slight HREE enrichment) to 3.30 (sig�nificant HREE depletion). In our opinion, this isrelated to the insufficient averaging of rock composi�tions in provenances by erosion and weathering during



the initial stages of formation of the Serebryanka sedi�mentary sequence and the presence of Archean com�plexes in the catchments [9]. On the other hand, thediamictite matrix of the Tany Formation shows a some�

what lower median LaN/YbN value compared with theshales of the same level (13.42 versus 17.11) but similarvalues of other characteristics of chondrite�normalizedREE patterns.

8

0 15

6

4

2

5 10

100

0.1 100

10

1

1 10

Sc/

Th

La/Sm

AR2β

PAAS

ARγ

10

0.011 100

1

0.1

10

1

2

3

4

5

6

Th

/Ta

La/Yb

ARγPAAS

AR2β

ARshl

1000

10.1 100

100

10

1 10

10

0.01 100

1

0.1

1 10

101 1000

100

10 100

Th

/Sc

AR2β

ARγ PAAS

ARshl Th

/Co

ARshl

PAAS

ARγ

Typical values oferosion products ofsilicic igneousrocks

La

PAAS

ARshl

AR2β

ARγ

UCC

Cr

Ni

PAAS

UCC

ARshl

0 15

2

5 10

Ce/

Cr

Co/Hf

PAAS

ARshl

(a)

(c)

(d)

(b)

(e)

(f)

(g)

Th

Sc La/Sc

Fig. 11. Compositions of fine�grained siliciclastic rocks from various formations of the Serebryanka Group and the fine�grainedmatrix of diamictites from the Tany Formation in discrimination diagrams. PAAS is the post�Archean average Australian shale[45]; ARshl is the average Archean cratonic shale [66]; ARγ is Archean granitoids [66]; AR2β is Late Archean basaltoids [66]; andUCC is the upper continental crust [68]. Other symbols are the same as in Fig. 4.

35

AR2β

992


MASLOV et al.

Redox conditions in the sedimentation basin. Themedian Mo/Mn value is ~0.0007 in the fine�grainedsiliciclastic rocks of the Tany Formation and 0.001,0.0004, and 0.0022 in the shales of the Garevka, Koiva,

and Kernos formations, respectively. Using the criteriaof [69], the sequences of all the aforementioned units ofthe Serebryanka Group can be considered as complexesdeposited in a well aerated sedimentary basin. Themedian Mo/Mn value in the carbon�poor dark grayshales of the Buton Formation is significantly higher(0.016), which indicates the existence of anoxia or sim�ilar conditions in the basin [6].

Paleosalinity. Without reliable paleontological evi�dence, the reconstruction of the salinity of Late Pre�cambrian sedimentary basins is an almost insurmount�able problem. However, some insight into paleosalinitycan be gained from geochemical data, provided that thesedimentary strata considered were formed in a singlesedimentary basin and at invariable provenance compo�sitions and paleoclimate [70, 71]. Then, B content inthe fine�grained fraction of clay rocks [72–75] or con�tents and ratios of B, Rb, Ga, V, and Li in the same frac�tion [76–80] can be used as paleosalinity indicators. Inour case, a fine (<0.001 mm) fraction could not be sep�arated from the rocks affected by late catagenesis–metagensis. Therefore, we analyzed the proportions ofSr, Ba, Zr, Cu, and V in the bulk samples of fine�grainedsiliciclastic rocks of the Serebryanka Group, althoughwe are aware that the obtained inferences can be con�troversial. It is believed that marine and freshwatermudstones have distinctly different Sr/Ba ratios: 3.5–18 in the former and no higher than 1 in the latter [81–83]. According to the same authors, Zr/Cu ranges from3.0–3.5 to 8 in freshwater mudstones and decreases to1.0–3.5 in typical marine mudstones. On the otherhand, the V/Zr ratio is 0.1–1.2 in the former rock typeand 0.5–4.0 and even higher in the latter type. In theZr/Cu–V/Cu diagram (Fig. 14a), most of the composi�tions of the fine�grained siliciclastic rocks of the Tany,Garevka, Koiva, and Buton formations lie at Zr/Cu >3.5, whereas the shales of the Kernos Formation showZr/Cu values both higher and lower than 3.5. The V/Zrratio of most of our samples is lower than 1 (medianV/Zr is 0.54, 0.81, 0.61, 0.32, and 0.49 in the rocks ofthe Kernos, Garevka, Koiva, Buton, and Kernos for�mations, respectively). On the whole, these observa�tions give grounds to believe that most of the sedimen�tary complexes of the Serebryanka Group were accu�mulated mainly in freshwater basins. This suggestion issupported by rather low (unusual for marine mud�stones) Sr/Ba ratios in the fine�grained rocks of theTany, Koiva, and Kernos formations (median Sr/Bavalues are 0.10, 0.11, and 0.09, respectively) (Fig. 14b).

Clarkes of concentration of trace elements. To obtaina general geochemical portrait of fine�grained siliciclas�tic rocks from various lithostratigraphic units of theSerebryanka Group, we analyzed clarkes of concentra�tion (Cc) for a wide range of trace elements: Li, Be, Sc,V, Cr, Co, Ni, Cu, Zn, Ga, Ge, Rb, Sr, Y, Zr, Nb, Mo,

40

0 1.0

30

20

10

0.4 0.8

La N

/Yb N

Eu/Eu*

(c)

ARγ

PAAS ARshl

AR2β

120

0 30

40

80

10 20

La N

/Yb N

YbN

(b)

PRγPRTTG

ARTTG

Archean tonalite–trondhjemite–granite association

Post�Archean granitoids

1.2

0 4

0.4

0.8

1 2

Eu

/Eu

*

GdN/YbN

(а)

ARγ

Eu/Eu* = 1.0ARshl

3

PAAS

Gd

N/Y

b N =

2.0

AR2β

Fig. 12. Compositions of fine�grained siliciclastic rocksfrom various formations of the Serebryanka Group and thefine�grained matrix of diamictites from the Tany Forma�tion in the (a) GdN/YbN–Eu/Eu*, (b) YbN–LaN/YbN,and (c) Eu/Eu*–LaN/YbN diagrams. ARTTG is ArcheanTTG association, PRTTG is Proterozoic TTG association,and PRγ is Proterozoic granitoids [66]. Other symbols arethe same as in Figs. 4 and 11.



Cd, Sn, Sb, Cs, Ba, REE, Lu, Hf, Ta, Tl, Pb, Bi, Th,

and U.5 In addition to purely scientific interest, the

analysis of Cc values for trace elements is significant forpractical applications, because it provides informa�tion on the provenance of sedimentary materials.There are almost no publications on Cc in the EarlyVendian sedimentary sequences of the western slopeof the Central Urals, and the data presented belowcan partly fill this gap.

The fine�grained siliciclastic rocks of the Tany For�mation show a weak enrichment in Li (Cc median =2.37) and Ta (Cc median = 1.51) (Table 4). The medianCc values of most other trace elements range from 0.11to 1.44 (Fig. 15). The median Cc values of REE are nohigher than 0.90. The Ccc max/Cc min ratio, which isconsidered as an index of the heterogeneity of Cc distri�bution for a particular element (H), is higher than 5 forSc, Co, Cu, Rb, Sr, Y, Nb, Mo, Sb, all REE, Tl, Pb, Bi,and Th and between 2.5 and 5.0 for Li, Be, Cr, Ni, Zn,Cd, Cs, and Ba. The fine�grained matrix of diamictitesfrom the Tany Formation shows no distinct geochemi�cal specialization. Its REE contents are significantlylower than those of shales from the same level, whichcan be considered as indirect evidence for the domi�nance of finely dispersed non�clay minerals in its com�position. The Garevka shales show weak enrichments inCo, Ni, Zn, Ga, Rb, Nb, La, Ce, Pr, and Nd. Their Hvalues are 2.89 for Co, 3.59 for Sr, and higher than5 only for Pb.

The fine�grained siliciclastic rocks of the Koiva For�mation are moderately enriched in Li and weaklyenriched in Rb. The median Cc values of other trace ele�ments in these rocks range from 0.12 to 1.33. In theshales of the Tany Formation, 27 of 43 trace elementsshowed H > 5, i.e., were distributed rather heteroge�neously in the available data set, whereas 36 elementswith H > 5 were detected in the rocks of similar grainsize from the Koiva Formation (Table 4).

The Buton shales show a slight Nb enrichment(Cc median = 1.75). The median Cc values of othertrace elements range from 0.22 to 1.50. A strongly het�erogeneous distribution (H > 5) was observed only forCu, and H ranges from 2.60 to 4.29 for Sc, Co, Rb, Sr,Y, Mo, Er, Tm, Yb, Lu, Tl, Pb, Th, and U. Other traceelements show H < 2.5. The fine�grained siliciclasticrocks of the Buton Formation are slightly light REEenriched and heavy REE depleted relative to UCC.

The Kernos shales are slightly enriched in Nb andTa. Similar to the Tany rocks of similar grain size, theREE contents of the Kernos shales are significantly

5 According to V.I. Vernadsky, the clarke of concentration is theratio of chemical element content in a particular geochemicalsystem to its abundance in the Earth’s crust [84].

lower than the UCC values. Strongly heterogeneousdistributions (H > 5) were observed for Li, Be, Sc, V, Cr,Co, Cu, Zn, Ge, Rb, Sr, Y, Mo, Cd, Sn, Sb, Ba, Eu,Gd, Tb, Tm, Lu, Ta, Pb, and Bi. Fifteen other trace ele�ments show significantly heterogeneous distributions(2.5 < H < 5) (Table 4).

Table 3. Main parameters of chondrite�normalized REEpatterns for the fine�grained siliciclastic rocks of the Sere�bryanka Group

Parameter LaN/YbN LaN/SmN GdN/YbN Eu/Eu*

Tany Formation

Med 17.11 4.78 1.47 0.72

SD 5.44 1.28 0.69 0.08

Min 8.40 3.08 0.95 0.67

Max 29.63 8.33 3.30 0.94

Garevka Formation

Med 14.16 4.66 1.93 0.68

SD 3.37 0.21 0.38 0.08

Min 11.00 4.32 1.51 0.64

Max 19.14 4.80 2.41 0.81

Koiva Formation

Med 14.22 4.36 1.67 0.74

SD 1.40 0.46 0.26 0.04

Min 10.61 3.37 1.33 0.66

Max 15.60 5.34 2.14 0.83

Buton Formation

Med 18.69 4.92 1.95 0.65

SD 4.97 0.37 0.29 0.09

Min 15.66 4.81 1.82 0.56

Max 27.42 5.66 2.59 0.83

Kernos Formation

Med 11.67 4.18 1.47 0.64

SD 2.66 0.95 0.17 0.12

Min 6.82 2.63 1.18 0.41

Max 15.41 5.47 1.76 0.88

Note: Med is median value, and SD is standard deviation.

994


MASLOV et al.

1000

1Nd

100

10

Ce Pr

(c)

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

(d)

La Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

1000

1

100

10

(а) (b)

Garevka Formation

Diamictite matrix

Fig. 13. Chondrite�normalized REE patterns of fine�grained siliciclastic rocks from various formations of the Serebryanka Groupand the matrix of diamictites from the Tany Formation. Formations: (a) Tany, (b) Koiva, (c) Buton, and (d) Kernos.

4

0 40

2

10 20 30

Typical values of marinesediments

Typical values continental

freshwater sediments

V/Z

r

Zr/Cu

(a)10

0 40

2

10 20 30

Typical values of marine

sediments

Typical values of continental

freshwater sediments

Sr/

Ba

Zr/Cu

(b)

8

6

41

2

3

4

5

6

Fig. 14. Compositions of shales from various lithostratigraphic units of the Serebryanka Group in the (a) Zr/Cu–V/Zr and(b) Zr/Cu–Sr/Ba diagrams. Formations: (1) Tany, (2) Tany diamictite matrix, (3) Garevka, (4) Koiva, (5) Buton, and (6) Kernos.



0L

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UB

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of c

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MASLOV et al. T

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1.13

0.28

1.83

6.58

Ga

1.19

0.62

1.53

2.48

0.64

1.57

1.43

1.73

1.21

1.33

0.72

3.68

5.08

1.36

1.19

1.50

1.27

1.30

0.90

1.95

2.17

Ge

0.95

0.62

1.28

2.08

0.69

––

––

1.11

0.64

2.82

4.38

––

––

0.95

0.08

27.3

532

4.5

Rb

1.06

0.33

2.35

7.17

0.48

1.58

1.35

1.94

1.43

1.72

0.28

5.59

19.8

01.

480.

671.

982.

950.

970.

342.

076.

05

Sr0.

110.

050.

418.

250.

110.

240.

110.

413.

590.

140.

030.

237.

120.

220.

090.

252.

940.

130.

020.

3718

.80

Y0.

600.

131.

8313

.96

0.39

1.26

1.22

1.44

1.17

0.82

0.09

2.58

27.6

30.

980.

361.

083.

020.

400.

221.

275.

84

Zr

0.93

0.58

1.25

2.17

0.81

0.83

0.74

0.98

1.33

0.79

0.51

2.77

5.47

1.29

1.08

1.53

1.41

0.95

0.73

1.5

2.05

Nb

1.44

1.03

7.21

7.02

1.01

1.68

1.62

2.05

1.26

1.25

0.82

7.87

9.59

1.75

1.69

2.01

1.19

1.63

0.97

3.63

3.74

Mo

0.32

0.05

2.29

45.2

60.

260.

330.

240.

351.

440.

120.

020.

4730

.10

0.77

0.69

2.02

2.94

0.3

0.07

2.79

40.1

8

Cd

0.15

0.11

0.44

4.16

0.34

––

––

0.29

0.07

2.00

29.0

0–

––

–0.

640.

173

.07

700.

20

Sn1.

110.

751.

501.

980.

84–

––

–1.

140.

833.

594.

31–

––

–1.

370.

564.

477.

92

Sb0.

420.

180.

925.

210.

47–

––

–0.

760.

252.

238.

87–

––

–1.

520.

7310

.84

14.8

2

Cs

0.48

0.2

0.94

4.64

0.21

0.78

0.57

0.99

1.74

0.63

0.25

2.10

8.50

0.76

0.61

0.84

1.38

0.88

0.42

1.74

4.12

Ba

0.80

0.32

1.31

4.06

0.43

0.97

0.95

1.88

1.99

0.77

0.18

3.38

18.5

51.

070.

871.

641.

900.

710.

204.

7924

.51


LITHOGEOCHEMISTRY OF THE FINE�GRAINED SILICICLASTIC ROCKS 997 T

able

4.

(Con

td.)

Ele

�m

ent

For

mat

ion

Tan

yG

arev

kaK

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But

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os

Med

##

#H

ArM

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ed#

##

HM

ed#

##

HM

ed#

##

HM

ed#

##

H

12

34

56

78

910

1112

1314

1516

1718

1920

2122

La

0.9

0.15

2.62

17.5

30.

561.

61.

492.

111.

421.

150.

243.

6115

.34

1.5

0.95

1.83

1.94

0.58

0.41

1.39

3.38

Ce

0.88

0.14

2.54

17.8

0.52

1.51

1.17

2.18

1.85

1.08

0.23

3.28

14.1

91.

340.

721.

732.

390.

720.

311.

354.

41

Pr

0.9

0.18

2.58

14.4

50.

571.

61.

482.

061.

391.

190.

283.

7313

.46

1.50

0.76

1.71

2.26

0.69

0.37

1.35

3.66

Nd

0.83

0.17

2.62

15.4

0.55

1.53

1.41

1.94

1.38

1.18

0.28

3.70

13.4

21.

400.

871.

581.

820.

740.

341.

283.

72

Sm0.

810.

192.

8414

.68

0.54

1.48

1.33

1.82

1.37

1.20

0.27

3.43

12.6

71.

280.

791.

341.

700.

830.

311.

484.

85

Eu

0.73

0.16

2.66

16.4

80.

511.

391.

202.

031.

701.

090.

263.

1512

.08

1.06

0.57

1.21

2.12

0.68

0.2

1.79

8.94

Gd

0.63

0.18

2.78

15.1

60.

431.

411.

311.

721.

310.

930.

232.

6311

.29

1.12

0.49

1.21

2.46

0.59

0.15

1.31

8.87

Tb

0.57

0.15

2.27

15.1

50.

351.

191.

121.

381.

230.

770.

172.

3313

.86

0.93

0.44

0.96

2.17

0.61

0.17

1.33

7.82

Dy

0.68

0.18

1.98

11.0

20.

411.

221.

141.

301.

140.

840.

182.

6915

.33

0.89

0.39

0.94

2.41

0.67

0.26

1.20

4.70

Ho

0.65

0.17

1.64

9.72

0.39

1.16

1.15

1.30

1.13

0.79

0.13

2.59

20.4

60.

880.

40.

912.

290.

650.

261.

174.

52

Er

0.66

0.18

1.48

8.06

0.4

1.13

1.12

1.31

1.17

0.81

0.12

2.73

22.0

20.

860.

320.

932.

870.

610.

291.

174.

07

Tm0.

750.

181.

478.

290.

441.

211.

191.

471.

240.

930.

173.

2318

.82

0.92

0.35

1.01

2.86

0.77

0.31

1.76

5.73

Yb

0.76

0.21

1.37

6.65

0.43

1.18

1.15

1.41

1.23

0.9

0.22

3.21

14.3

10.

940.

391.

032.

60.

750.

311.

294.

16

Lu

0.74

0.21

1.25

6.07

0.44

1.14

1.11

1.40

1.26

0.88

0.23

3.11

13.7

70.

920.

351.

012.

920.

770.

312.

578.

32

Hf

0.91

0.6

1.2

2.01

0.78

0.85

0.71

0.97

1.37

0.87

0.58

3.08

5.28

1.22

1.01

1.39

1.37

1.07

0.67

1.43

2.15

Ta1.

510.

972.

913.

000.

831.

431.

271.

631.

281.

130.

679.

4914

.08

1.43

1.24

1.57

1.27

1.65

1.09

6.83

6.24

Tl

0.69

0.17

1.07

6.32

0.27

1.42

1.00

1.78

1.78

0.77

0.48

2.09

4.34

0.83

0.76

2.21

2.89

0.79

0.30

1.25

4.14

Pb

0.36

0.14

1.04

7.45

0.29

0.88

0.4

2.04

5.07

0.42

0.1

1.17

11.2

10.

880.

671.

812.

680.

620.

131.

8313

.9

Bi

0.95

0.26

2.08

7.91

0.34

1.32

1.05

2.41

2.30

1.11

0.27

13.3

749

.77

0.73

0.63

1.38

2.19

1.31

0.21

7.74

37.4

Th

0.86

0.20

1.45

7.13

0.42

1.37

1.25

1.78

1.42

1.15

0.24

3.63

15.1

61.

290.

581.

602.

750.

660.

331.

273.

83

U0.

640.

391.

132.

900.

420.

700.

580.

811.

390.

580.

292.

267.

760.

720.

471.

453.

070.

810.

341.

724.

99

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24

265

16

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998


MASLOV et al.

CONCLUSIONS

The data presented in this paper allow us to drawsome conclusions on the characteristics of the EarlyVendian sedimentation environment. First, despite thepresence of at least three levels of tillite�like conglomer�ates (diamictites) in the Serebryanka section, theindexes of chemical alteration in most of our samples offine�grained siliciclastic rocks are rather high in almostall formations (65–77), which indicates the input ofmature, most likely repeatedly redeposited/recycledmaterials into the sedimentation basin. In this case, weundoubtedly observe a paleoclimatic signal, which issuggested by the absence of correlation between CIAand such indicators of the composition of catchmentrocks as Th/Cr, La/Sc, and Th/Sc. The previous com�parison of the compositions of the Serebryanka shaleswith PAAS [85] showed that even the matrix of diamic�tites from the Tany Formation is similar in compositionto the post�Archean average Australian shale, i.e., to therock with a significant fraction of lithogenic compo�nents [45], whereas the shales of this level are signifi�cantly depleted in CaO and enriched in Na2O relative toPAAS. Low PAAS�normalized CaO contents were alsoobserved in the shales of the Koiva Formation. Thesame is characteristic of the Kernos shales, althoughthey display also some Na2O enrichment. In general,the climate of Serebryanka time can be estimated assemiarid–semihumid, similar to that dominating in theLate Vendian paleocatchments [13].

The median Mo/Mn values of the fine�grainedsiliciclastic materials of most lithostratigraphic units ofthe Serebryanka Group indicate that they were accu�mulated in a well aerated basin. An exception is the car�bon�poor shales of the Buton Formation, which show amedian Mo/Mn value of 0.016 (minimum 0.011 andmaximum 0.024).

The systematics of the trace elements Sr, Ba, Zr, Cu,and V in the shales of the Serebryanka Group allow usto suggest, with some additional assumptions, that sed�iments were accumulated in a fresh�water basin duringthe almost whole period of the formation of the Sere�bryanka Group. This conclusion is consistent with Srisotopic data for the carbonate rocks of the Koiva For�mation.

The shales of most lithostratigraphic units of theSerebryanka Group show a weak or moderategeochemical enrichment in a limited number of traceelements. For instance, the fine�grained rocks of theTany Formation are weakly enriched in Li and Ta, therocks of the Kernos Formation of the same grain sizeare slightly enriched in Nb and Ta, and the shales of theKoiva Formation are moderately enriched in Li andslightly enriched in Rb. Only the initially clay�domi�nated rocks of the Garevka Formation show slightenrichments in a wider range of elements: Co, Ni, Zn,Ga, Rb, and Nb.

The indicator trace element ratios (Th/Sc, La/Sc,Th/Cr, and others) in the fine�grained siliciclastic rocksof the Serebryanka Group suggest that the Early Ven�dian paleocatchments comprised a variety of rocksranging from granitoids to basites. The latter were prob�ably most extensively eroded at the end of Serebryankatime. The distribution of trace element contents (Th,La, Ni, Cr, and Sc) and ratios (Th/Sc, Co/Hf, andCe/Cr) in the shales of various lithostratigraphic unitsof the Serebryanka Group suggest that primitiveArchean complexes did not play a significant role in theEarly Vendian plaeocatchments. This inference is inagreement with our previous estimates of the Nd modelage of the fine�grained terrigenous rocks of the Serebry�anka Group [8]. According to these results, the shales ofthe Tany and Koiva formations have TNd(DM) values of~2.0 Ga, whereas clay rocks with TNd(DM) ~ 1.77–1.73 Ga are most common in the upper part of thegroup.

Based on the Ce/Ce* values characteristic of theshales of the whole Serebryanka section, it was con�cluded that submarine volcanism exerted little influ�ence on sedimentation in the Early Vendian basin.Exceptions are Koiva and Kernos times, when hema�tite�bearing shales in association with pillow basaltswere accumulated in some zones of the basin. However,even the fine�grained siliciclastic rocks of the KernosFormation show Ce anomalies ranging from 0.7 to 1.3;according to widely accepted interpretations, theserocks were probably formed under the conditions of lowcrustal permeability for deep fluids. In our opinion, thissuggestion is supported by the distribution of the com�positions of fine�grained siliciclastic rocks in variousdiscrimination diagrams: in most cases, the composi�tions of shales from various formations of the Serebry�anka Group fall in the fields of passive geodynamic set�tings.

The data presented in this paper provide a generaloverview of the environments of the formation of theEarly Vendian sedimentary sequences in the westernslope of the Central Urals. They must be extended inthe future by the analysis of variations in the aforemen�tioned and other lithogeochemical parameters in thesections of all lithostratigraphic units of the Serebry�anka Group (similar to that done for the Koiva Forma�tion), which will result in a more realistic and compre�hensive model for the Early Vendian paleoenvironmentfor one of the most complete sections of the final systemof the Precambrian in Northern Eurasia.

ACKNOWLEDGMENTS

This study was financially supported by IntegrationProject no. 09�C�5�1013 of the Ural, Siberian, and FarEast branches of the Russian Academy of Sciences“Reconstruction of Provenances for the SedimentaryBasins of Northern Eurasia: Sedimentation Environ�



ments and Potential Ore Mineralization” and theRussian Foundation for Basic Research, projectno. 09�05�00279.

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Lithogeochemistry of the Fine-Grained Siliciclastic Rocks of the Vendian Serebryanka Group of the Central Urals

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