Vendian Reference Section of Southern Middle Siberia · (Keller et al., 1967; Ivanov et al., 1995; etc.) to Late Riphean (Khomentovskii and Postnikov, 2001). The last viewpoint is

ISSN 0869�5938, Stratigraphy and Geological Correlation, 2013, Vol. 21, No. 4, pp. 359–382. © Pleiades Publishing, Ltd., 2013.Original Russian Text © N.M. Chumakov, M.A. Semikhatov, V.N. Sergeev, 2013, published in Stratigrafiya. Geologicheskaya Korrelyatsiya, 2013, Vol. 21, No. 4, pp. 26–51.

359

INTRODUCTION

In southern Middle Siberia, the most completesection of Upper Precambrian (Riphean and Vendian)deposits is exposed in the marginal zone of theBaikal–Patom Highland. This section comprises sixsuccessive stratigraphic units (from the base upward):Purpol, Medvezhii, Ballaganakh, Dal’nyaya Taiga,Zhuya, and “Yudoma” groups, or horizons (Dol’nik,2000). Until recently, most researchers included onlythe Zherba and Tinnaya formations of the Patomregion in the Vendian (Keller et al., 1967; Ivanov et al.,1995; Pelechaty, 1998); some of them attributed to thelatter also the overlying Nokhtuisk Formation(Dol’nik, 2000). Many researchers united these for�mations into a larger unit, terming it by analogy withthe Uchur–Maya region as the Yudoma complex orYudomian (Opornye…, 1972; Khomentovskii, 2008),Yudoma Horizon (Dol’nik, 2000), or Yudomianregional stratigraphic horizon (Stanevich et al., 2006,2007).

Recently obtained biostratigraphic, chemostrati�graphic, and isotopic geochronological data showedthat the Zherba and Tinnaya formations are correlativeonly with the upper part of the Yudoma Group typesection in the Uchur–Maya region (Semikhatov et al.,2004) and, correspondingly, with the upper layers ofthe Vendian section in the East European Platformand that the two upper groups of the Patom Complex(Zhuya and Dal’nyaya Taiga) underlying the ZherbaFormation should also be attributed to the Vendian.Such a conclusion radically changes the age interpre�tation of the Upper Cambrian section in the regionand present�day views on the geological history of theBaikal–Patom Highland and adjacent segments of theSiberian Platform. This insistently called for correc�

tion of the corresponding regional stratigraphic scalesavailable for Upper Precambrian deposits of theBaikal–Patom Highland as well as geological mapsand establishment of the most complete and best datedVendian reference section for the region under consid�eration. The section of the Ura uplift which is almostentirely composed of Vendian rocks was proposed toserve as such a standard (Chumakov, 2011b).

The transverse Ura uplift complicates the north�eastern margin of the Patom fold arc. It begins near theBol’shoi Patom River mouth and extends northward,crossing the Lena River between mouths of theDzherba (Zherba) and Malyi Patom rivers (Fig. 1).The uplift consists of four wide en echelon arrangednortheast�extending anticlinal folds. In the Late Pre�cambrian, the Ura uplift together with adjacent areaswas a constituent of the southern passive margin of theSiberian Platform. Its Vendian deposits are repre�sented by nonmetamorphosed facies deposited on theshelf and upper part of the continental slope.

Owing to good exposition, relatively simple tec�tonic structure, and easy accessibility, the Vendian sec�tion of the Ura uplift is well known with its stratigraphybeing progressively upgraded and specified (Fig. 2). Atpresent, the stratigraphic scale developed for this sec�tion is accepted by almost all researchers, who areanonymous in admitting the nomenclature of definedformations and groups. At the same time, the age of itsrocks has remained debatable until now. At the firststage of investigation of the region, they were attrib�uted to the Upper Proterozoic (Obruchev, 1939; etc.),Lower Cambrian (Starostina, 1935), or Upper Prot�erozoic–Lower Cambrian (Chumakov, 1956, 1959).Subsequently, on the basis of finds of microphytolitesand stromatolites (Zhuravleva et al., 1961, 1969;

Vendian Reference Section of Southern Middle SiberiaN. M. Chumakov, M. A. Semikhatov, and V. N. Sergeev

Geological Institute, Russian Academy of Sciences, Pyzhevskii per. 7, Moscow, 119017 Russiae�mail: [email protected]

Received August 15, 2012; in final form October 15, 2012

Abstract—Geological, chemo�, and biostratigraphic data indicate that the Vendian section of the Ura upliftis the most complete one in southern Middle Siberia and contains analogs of main units of the Vendian stra�totype. This section is well known having been investigated by several generations of geologists, well exposed,and easily accessible; therefore, it is proposed to serve as a regional reference section for Vendian deposits ofthe entire southern Middle Siberia. Its description is accompanied by presentation of new biostratigraphicand radioisotopic data. The section is correlated with other Vendian sections of the Baikal–Patom and someother world regions.

Keywords: Vendian, microfossils, glacial deposits, Lena River, Ura uplift

DOI: 10.1134/S0869593813040023

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Dol’nuk, 1982, 2000), the two upper groups of thePatom Complex (Dal’nyaya Taiga and Zhuya) wereassigned to the Middle and Upper Riphean, respec�tively (Resheniya…, 1963; Keller et al., 1967; Chuma�kov and Semikhatov, 1981; Chumakov, 1993; etc.).Later, some geologists began correlating the Dal’nyayaTaiga Group with the Middle and Upper Riphean(Ivanov et al., 1995; Dol’nik, 2000). On the basis ofhistorical–geological and, partly, biostratigraphicdata, some researchers attributed the Dal’nyaya Taigaand Zhuya groups to the upper part of the UpperRiphean and included them in a new autonomousUpper Precambrian unit, i.e., Baikalian (Khomen�tovskii et al., 1998; Khomentovskii and Postnikov,2001; Khomentovskii, 2002). In fact, despite thesedisagreements, most researchers shared up to thebeginning of the 21st century the opinion that thePatom Complex belongs to the Riphean, while theVendian includes only the Zherba and Tinnaya forma�tions, which are sandwiched between the ZhuyaGroup and Lower Cambrian section.

The revision of widely accepted views on age ofdeposits under consideration started in the currentcentury. First, on the basis of paleotectonic recon�structions and correlation of remote sections, some

researchers suggested that the two upper groups of thePatom Complex (Dal’nyaya Taiga and Zhuya) belongto the Vendian (Sovetov, 2002). This opinion was sub�stantiated by chemostratigraphic investigations ofthese deposits and their platform analogs (Pokrovskiiet al., 2006), the find of the diverse assemblage of Per�tatataka�type acanthomorphic acritarchs in the UraFormation correlated with the upper part of theDal’nyaya Taiga Group (Chumakov et al., 2007;Vorob’eva et al., 2008a; Golubkova et al., 2010), U–Pbisotopic dating of detrital zircons from metamor�phosed stratigraphic analogs of this formation (Meffreet al., 2008), and correlation with other Vendian andEdiacaran sections (Chumakov, 2011).

VENDIAN DEPOSITS OF THE URA UPLIFT

The Upper Precambrian rocks constituting the Urauplift are divided into four groups (from the baseupward, Fig. 3): Ballaganakh, Dal’nyaya Taiga,Zhuya, and Yudoma (Yudoma Horizon). The oldest,Ballaganakh Group, underlies sequences that may beattributed to the Vendian. The upper part of the Balla�ganakh Group crops out in the core of the southern�most (Zhedai) anticlinal fold. In the section exposed

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in this area, micaceous feldspar–quartz sandstones(apparent thickness approximately 900 m) are overlainby fine�grained gray limestones alternating with sand�stones (approximately 300 m). By their stratigraphicposition and lithology, the Ballaganakh sandstonesand limestones are correlated with the upper part ofthe Bugarikhta Formation and the Mariinskaya For�mation of the Ballaganakh Group in southerly areas,respectively. According to different estimates, the ageof the Ballaganakh Group varies from Middle Riphean(Keller et al., 1967; Ivanov et al., 1995; etc.) to LateRiphean (Khomentovskii and Postnikov, 2001). Thelast viewpoint is now supported by high δ13С valuesranging from +5 to +8‰ in carbonates from theMariinskaya Formation (Pokrovskii et al., 2006). Sucha high positive δ13С anomaly in the Late Precambrianis characteristic of the second half of the Late Riphean(Halverson and Shields�Zhou, 2011).

The Dal’nyaya Taiga Group in the Ura uplift con�sists of four conformably occurring formations (fromthe base upward): Bol’shoi Patom, Barakun, Ura, andKalancha (Fig. 3).

The Bol’shoi Patom Formation was defined by Sta�rostina (1935) as a unit Сm1

а and named in 1941 byA.A. Predtechenskii in his unpublished work. Thename “Bol’shoi Patom” was repeatedly used for thisunit in different publications (Chumakov, 1959, 1993;Chumakov and Semikhatov, 1981; etc.). In the unifiedstratigraphic regional scale, this formation was incor�rectly termed as the Dzhemkukan Formation, whichviolated rules recommended by the StratigraphicCode for identification of formation units. Despitethis violation, the name “Dzhemkukan Formation” iswidely used in the literature and in practice. The lowercontact of the Bol’shoi Patom Formation in the Urauplift is unobservable. Nevertheless, there are groundsto believe that it rests conformably upon the Ballaga�nakh Group, since it encloses intercalations of dolo�mitic breccias with rock fragments litholohgically sim�ilar to dolomites of marginal facies from the Mariin�skaya Formation. Erosional contacts marked by suchbreccias are also observed at the bases of stratigraphicand facies analogs of the Bol’shoi Patom Formationon both the eastern flank (Nichatka Formation,Bogouyukhta River) and the western flank (Dzhemku�

kan Formation, Bol’shaya Chuya River) of the PatomHighland.

Complete sections of the Bol’shoi Patom Forma�tion are confined to the eastern and western limbs ofthe southern (Zhedai) anticlinal fold that complicatesthe structure of the Ura uplift. These sections arelocated at the left bank of the Bol’shoi Patom River 4–6 and 13–15 km away from its mouth, respectively.The first of these sections, where the formation isapproximately 1000 m thick, is selected to serve as thereference one (Chumakov and Krasil’nikov, 1991); inthe second section, the formation thickness is reducedto 900 m.

The Bol’shoi Patom Formation is largely com�posed of massive and bedded diamictites, gradationalto, less commonly, cross�bedded sandstones, and lam�inated to rhythmically bedded siltstones locally withscattered rock fragments (dropstones) and tillite pel�lets. The upper part of the formation contains isolatedlayers and lenses of calcarenites and dolarenites.

Diamictites consist of a dark to locally black silty–sandy matrix (85–97% of the rock volume) with scat�tered variable rounded pebble�sized to large boulder�sized rock fragments. Some of these rock fragmentsexhibit subparallel variably sized striation. They arecharacterized by relatively uniform lithology beingdominated both quantitatively and volumetrically byvariable gneissose granitoids (gray biotite granites andgranosyenites, 45–65% of fragments) and muscoviteand bimicaceous gneisses (20–35%). They are accom�panied by subordinate dark gray limestones, dolo�mites, quartzites, rare crystalline schists, and meta�morphosed basic rocks (Chumakov and Krasil’nikov,1991; Chumakov et al., 2010). Some massive diamic�tites demonstrate mostly longitudinal and subordinatetransverse orientation of elongated fragments resem�bling the glacial one (Lungershausen, 1963; Chuma�kov and Krasil’nikov, 1991).

The lower half and upper fourth of the Bol’shoiPatom Formation are dominated by massive and bed�ded diamictites with subordinate sandstone layers andlenses. These sediments were likely deposited by gla�ciers that rested on the basin bottom and by floatingshelf glaciers. The middle part of the formation exhib�its frequent alternation of gradational–bedded diam�ictites, sandstones, and shales locally with conglomer�

Fig. 3. Composite Vendian section of the Ura uplift.(1) Faunal remains of the Tommotian Aldanocyathus sunnaginicus Zone of the Lower Cambrian; (2) faunal remains of the Nem�akit–Daldynian Purella antiqua Zone of the Upper Vendian; (3) faunal remains of the Namakit–Daldynian Anabarites trisulcatusZone of the Upper Vendian; (4) Ura acritarchs assemblage; (5) impressions of Beltanelloides sorichevae; (6) cap dolomite;(7) U–Pb age of detrital zircons; (8, 9) 87Sr/86Sr ratios in carbonate rocks: (8) according to (Pokrovskii et al., 2006), (9) accord�ing to (Melezhik et al., 2009); (10–12) variations of δ13С (‰) in carbonate rocks: (10) according to (Pokrovskii et al., 2006,(11) according to (Pelechaty, 1998), (12) according to (Khomentovskii et al., 2004); (13) diamictite; (14) diamictite with carbon�ate rock fragments; (15) conglomerate; (16) carbonate breccia; (17) sandstone; (18) quartzite�like sandstone; (19) marlstone;(20) siltstone and mudstone; (21) limestone; (22) horizon of anthraconite limestone; (23) dolomite; (24) sandy limestone and

dolomite; (25) oolitic limestone; (26) stromatolitic limestone and dolomite. ( ) Tommotian Stage of the Lower Cambrian.

Names of groups are given in capital letters.

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CHUMAKOV et al.

ates, which fill erosional valleys. These sedimentscharacterize underwater fans of glacial rivers. Thelithology of rock fragments and the cross�bedding pat�terns in sandstones suggest that detrital material wastransported to the Bol’shoi Patom basin from the Sibe�rian Platform mainly owing to erosion of crystallinerocks of the basement and partly the sedimentary Bal�laganakh Formation (Chumakov and Krasil’nikov,1991). U–Pb age estimates obtained for detrital zirconfrom sandstones alternating with massive diamictitesconfirm this inference (Chumakov et al., 2011b). Onthe curve of the relative age probability, most of thesezircons fall into the Archean (from 3200 to 2500 Mawith the maximum at 2700 Ma) and Early Proterozoic(from 2400 to 1850 Ma with distinct maxima at 1850and 1950 Ma) intervals.

The prevalence of diamictites (including their mas�sive varieties with glacial orientation of rock fragmentsand bedded varieties) and the presence of erratic frag�ments of crystalline rocks, dropstones, tillite pellets,striated and grooved boulders—all these features indi�cate glacial and glaciomarine origin of rocks constitut�ing the Bol’shoi Patom Formation. Typical cap dolo�mites resting upon the Bol’shoi Patom Formation sup�port this conclusion. The glacial genesis of theformation is also confirmed by its reliable correlationwith glacial sediments of the Nichatka Formation,which includes typical tillites and lacustrine and flu�vioglacial sediments, in addition to glaciomarinefacies (Chumakov, 1993, 2011a). The carbonate con�stituent of calcareous sandstones occurring amongdiamictites in the upper part of the Bol’shoi PatomFormation is characterized by δ13С values rangingfrom –5.9 to –8.8‰ (V�PDB), while carbonate boul�ders, pebbles, and dolarenites from diamictites (ninesamples) demonstrate significant scatter of δ13С valuesvarying from –6.5 and –5.1 to +5‰ with prevalenceof small negative and positive values: from– 0.9 to+2.2‰ (Pokrovskii et al., 2010). The presence ofthree groups of carbonate rock fragments with sharplydifferent δ13С values undoubtedly suggests differentprovenances during the Bol’shoi Patom glaciation. Forexample, the presence of rock fragments with consid�erable positive δ13С values indicates erosion of theMariinskaya Formation. The measurement of the87Sr/86Sr ratios in a single boulder of dolomitic lime�stone from the Bol’shoi Patom Formation yielded thevalue of 0.70747 with the δ13С value being equal to –5.1‰ (Pokrovskii et al., 2010). It is conceivable thatthese isotopic ratios indicate sediment reworking dur�ing deposition of the formation. In two beds of detritaldolomites (dolorudites and dolarenites) occurring inthe upper part of the Bol’shoi Patom Formation, thevalues of the 87Sr/86Sr ratio appeared to be very high,being 0.71451 and 0.71480, respectively, which is veryclose to the 87Sr/86Sr ratios typical of many cap dolo�mites, including varieties overlying this stratigraphicunit (Pokrovskii et al., 2010). Such a similarity likelyimplies that, during deglaciation, which was charac�

terized by oscillations, near�glacier basins accumu�lated intermittently detrital dolomites, the first pre�cursors of distal cap dolomites.

The Barakun Formation in sections of the Urauplift consists of alternating members largely com�posed of dark limestones and black shales. Some lime�stone members include shale intercalations, whileshale members are usually intercalated by limestones.Extended outcrops of the formation are relatively rareand represented by limestones. In the Ura uplift, theBarakun Formation is divisible into three subforma�tions: lower and upper mostly limy and middle mainlyshaly (Chumakov, 1959; Ivanov et al., 1995; Kokoulin,1998; etc.). Bobrov (1964) proposed to consider thesesubformations as autonomous formations (Fig. 2),although this suggestion was disfavored.

The lower Barakun Subformation. The lower con�tact of the Barakun Formation is observable in thewestern limb of the Ura anticline on the right side ofthe Ura River downstream of the Voron Rapids. In thisarea, the upper layer of bedded diamictites of theBol’shoi Patom Formation is overlain by inequigranu�lar sandstones 0.5–0.8 m thick with rare pebbles,which grade upward along the section into a thin layerof silty fine�grained poorly consolidated sandstones(Chumakov and Krasil’nikov; Chumakov et al., 2011).They in turn give way to a peculiar member of darkgray laminated and rhyrthmically bedded calcareousdolomites with the apparent thickness of approxi�mately 6 m. Lamination of these rocks is determinedby alternation of dark and lighter micritic and pelleticlaminae from fractions of a millimeter to 1 mm thick.Dolomites include rare small quartz and feldspar clastsand an admixture of clay minerals (insoluble residuevaries from 7 to 13%). Weathered surfaces of dolomitesare usually light yellow. Regular lamination of dolo�mites is locally complicated by small (up to 0.5 macross) asymmetrical intrastratal anticlinal folds withdetachments in hinges (Fig. 4). In the literature, suchtextures are called teepees. The texture and fine rhyth�mical lamination of dolomites, negative isotopic car�bon composition (δ13С varies from –4.2 to –3.5‰),and very high 87Sr/86Sr ratios amounting to 0.71597–0.71690 (Pokrovskii et al., 2006, 2010) are typical ofcap dolomites, which crown many Neoproterozoicglacial formations (Chumakov, 1978, 1992; Fairchildand Hambrey, 1984; Pokrovskii et al., 2006, 2010;etc.). Small outcrops and debris of cap dolomites atthe base of the lower Barakun Subformation are alsorecorded in the eastern limb of the Ura anticline onthe left side of the Ura River 1 km downstream of theUlakhan Iligir River and along the right bank of theLena River in the northeastern limb of a pericline ofthe Zhedai anticline 3.5 km downstream of theChapaevo Settlement, where their apparent thicknessis approximately 10–15 m.

The wide distribution of cap dolomites and theirgenesis have received much attention for a long time(Fairchild and Kennedy, 2007 and references therein).



Judging from several features, cap dolomites weredeposited in periglacial basins during postglacialtransgressions under intense continental drainagecaused by deglaciation. The detailed geochemicalcharacterization of the Barakun cap dolomite is avail�able in (Pokrovskii et al., 2010).

In the Ura River area, the cap dolomites of thelower Barakun Subformation are replaced upwardalong the section by dark clayey limestones and calcar�eous shales (several tens of meters thick) overlain inturn by dark bedded fine�grained locally pyritized cal�careous polymictic sandstones approximately 100–120 m thick with thin siltstone and mudstone mem�bers. One of these members 150 m above the base ofthe formation outcropping on the left side of the UraRiver 670 m downstream of the Ulakhan Iligir Rivermouth yielded impressions of Vendian fossils Beltanel�loides sorichevae (Leonov and Rud’ko, 2012). Theoverlying largely carbonate part of the lower subforma�tion of the Barakun Formation crops out on the leftside of the Bol’shoi Patom River 4 km downstream ofthe Dzherbedyanka River mouth. The subformation ismostly composed of dark gray to black fine�graineddolomitic laminated and platy limestones, some of

which are distinctly detrital in origin. They are fre�quently represented also by algal, microphytolitic, andoolitic varieties with siliceous concretions. Somelimestone layers exhibit underwater slumping struc�tures accompanied by carbonate breccias. The share ofshales, which form in the lower part of the formationrare thin intercalations, increases upward along thesection to constitute a uniform member up to 20 mthick at its top. The total thickness of the lower subfor�mation of the Barakun Formation is estimated torange from 200 m (Chumakov, 1959) to 400 m(Bobrov, 1964).

During deposition of the lower subformation of theBarakun Formation, the provenances were evidentlyslightly different as compared with their counterpartsin the Bol’shoi Patom time: mainly Archean shieldswere eroded. This is evident from U–Pb age of detritalzircons from sandstones of the lower Barakun Subfor�

mation in the Ura River section.1 On curves of the rel�

ative age probability compiled for Barakun detrital zir�

1 The data were obtained by I.N. Kapitonov and analysts from theICP–MS group of the All�Russian Institute of Geology(VSEGEI, St. Petersburg.

5 сm

Fig. 4. Cap dolomite with teepee textures in the basal layer of the Barakun Formation. Right bank of the Ura River 0.5 km down�stream of the Voron Rapids (photo by V.A. Melezhik).

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CHUMAKOV et al.

cons, its maxima are dated at 2900 and 2500 Ma, whilethe number of zircons with Early Proterozoic agesappeared to be insignificant as compared with theBol’shoi Patom Formation (Chumakov et al., 2011b).Zircons from the lower subformation of the BarakunFormation with discordance exceeding 10% form atrend, which indicates, in the opinion of I.N. Kapi�tonov, that some zircon grains were likely influenced650 ± 300 Ma ago by an event that disturbed theirU⎯Pb isotopic system. This could have been strati�form intrusion of gabbro–dolerites near the contactbetween the Bol’shoi Patom and Barakun formations.

The middle Barakun Subformation is largely com�posed of black siltstones and mudstone shales withrare thin intercalations and occasional members ofcoarse� to fine�grained black thin�bedded and platylimestones with beds of black dolomitic limestones,lenses of limestone breccias, and thin breccia hori�zons. These rocks include subordinate rare beds ofblack calcareous fine�grained sandstones. The upper170 m of the subformation are relatively well exposedon the right side of the Bol’soi Patom River in itsmouth area opposite Khatyng Aryy Island. The sub�formation thickness is estimated to range from 200–250 m (Kokoulin, 1998) to 300 m (Chumakov, 1959).

The upper Barakun Subformation. In the KhatyngAryy Island area, shales of the middle Barakun Sub�formation are overlain by a thick (approximately400 m) sequence of black limestones of the upper Bar�akun Subformation. These rocks are represented byplaty thin�bedded fine�grained varieties with interca�lations of clayey and dolomitic limestones andcoarse�grained limestones intercalated by thin lami�nae of calcareous shales. The remarkable feature ofthe subformation is intrastratal limestone conglomer�ates and 10� to 20�m�thick lenses of breccia�conglom�erate with underwater slumping structures. They con�sist of subangular deformed fragments of carbonaterocks and subrounded olistoliths of limestones anddolomites cemented by calcareous shales. The thick�ness of the subformation is estimated to be 250 m(Kokoulin, 1998) or 500 m (Chumakov, 1959).

It is difficult to determine the total thickness of theBarakun Formation in the Ura uplift because of itspoor exposition, which explains discrepancies in esti�mates obtained by different researchers. In our opin�ion, the most realistic estimate is 1100–1200 m.

The δ13C and 87Sr/86Sr values determined in theUra uplift for the Mariinskaya, Bol’shoi Patom, andBarakun formations and overlying carbonates of theDal’nyaya Taiga and Zhuya groups (Pokrovskii et al.,2006, 2010) serve as a basis for the chemostratigraphiccharacteristic of the proposed Vendian reference sec�tion and are of significance for determining the age ofthese rocks and regional correlations. As was men�tioned, the δ13C value in basal cap dolomites of thelower Barakun Subformation varies from –4.2 to⎯3.5‰; in overlying limestones, this parameter

decreases to zero values. Higher in the section, theδ13C value rapidly increases to reach +8.1‰ in themiddle part of the lower Barakun Subformation.Higher, almost to the top of the Barakun Formation,the δ13C value remains uniformly high: δ13Caver =6.5 ± 1‰ (n = 13). According to five measurements,the minimum 87Sr/86Sr value in the Barakun Forma�tion is 0.70727 (Pokrovskii et al., 2006) and that in thelower part of the formation (one measurement) is

0.70776 (Pokrovskii et al., 2010).2

The Ura Formation rests conformably upon theBaraklun Formation and is largely composed of silt�stones and mudstones with subordinate intercalationsand members of dolomites and limestones (Kolosov,1975; Kokoulin, 1998). Its most complete section isdocumented at the southern pericline of the Zherbaanticline in the lower reaches of the left Lena Rivertributary along the Ulakhan Muostakh Creek, where itwas defined as the lower Valyukhta Subformation bysome researchers (Zamaraev, 1984). In this area, thebasal part of the Ura Formation is represented by a300�m�thick sequence of siltstones and mudstoneswith intercalations of black to dark gray dolomitesoverlain by breccias of carbonate rocks 200 m thick. Aslightly different section is observed in the Ura Riverbasin. Its lower part (approximately 70 m) exposed onthe right side of the Ura River 2.5 km downstream ofthe waterfall (23 km from the Ura River mouth) is rep�resented by gray and black siltstones and calcareousshales frequently (fractions of a meter) alternatingwith limestones and their clayey varieties. Limestonesare frequently characterized by detrital texture, oolitefragments, and underwater slumping deformations.This part of the Ura Formation is underlain by a 10� to12�m�thick bed of carbonate breccia conglomeratebelonging most likely to the Barakun Formation. Theupper contact of the Ura Formation is observable on

2 The δ13C and 87Sr/86Sr values cited in this work were obtainedfor Vendian sequences of the Ura uplift by analyzing carbonatephases of samples without accounting for geochemical preserva�tion criteria of C and S isotopic systems in carbonate rocks(Mn/Sr and Fe/Sr ratios and δ18O value). The main agentsresponsible for distortion of systems in carbonates are repre�sented by meteoric water and low�temperature epigenetic fluids,which are enriched, as compared with seawater, in Mn, Fe, and12C originating from associated siliciclastic sequences and char�acterized also by an elevated 87Sr/86Sr value, decreased Sr con�centration, and reduced δ13C and δ18O values (Brand andVeizer, 1980; Derry et al., 1992; Denison et al., 1994; Knoll etal., 1995; Gorokhov et al., 1995; Kuznetsov et al., 2006, 2012).It should be emphasized that the curves of changes in the δ13Cvalue obtained by B.G. Pokrovskii and colleagues are similar intheir amplitude variations and character of changes to curvesavailable for global standard Upper Precambrian sections: in theDoushantuo and Dengying formations of South China (Zhou etal., 2007; Zhou and Xiao, 2007) and in eastern and northernOman (Brasier et al., 2000; Leather et al., 2002; Le Guerroue,2010). Moreover, the 87Sr/86Sr values obtained by Pokrovskiiand colleagues for the Zhuya Group correspond quantitativelyto ratios determined for the same rocks using the above�men�tioned geochemical preservation criteria of isotopic systems(Gorokhov et al., 1995; Pelechaty, 1998; Melezhik et al., 2009).



the right side of the Ura River and its valley slope 3.0–3.3 km from the mouth. The upper part of the UraFormation (approximately 30– 35 m thick) is com�posed of peculiar gray to greenish gray siltstones inter�calated by subordinate thin (fractions of a meter) grayand black limestones with inclusions of coarse�grainedvarieties and thin�bedded siltstones (Fig. 5). South ofthe Ura uplift, the Ura Formation is replaced by darkgray to black shales, which are attributed to the lowerpart of the Valyukhta Formation. The total thicknessof the Ura Formation in these sections is 400–500 m(Bobrov, 1964, 1979; Zamaraev, 1984; Kokoulin,1998).

In the section located on the right side of the UraRiver 3 km from its mouth, thin�bedded siltstonesoccurring 30–35 m below the top of the Ura Forma�tion yielded a diverse Ediacaran assemblage of acanth�omorphic palynoflora or assemblage of Pertatataka�type acanthomorphic acritarchs found at four levels(Faizullin, 1998; Nagovitsin et al., 2004; Chumakov etal., 2007; Vorob’eva et al., 2008a; Golubkova et al.,2010; Sergeev et al., 2011; Moczydlowska and Nago�vitsin, 2012). The analysis of all the mentioned worksreveals the following valid taxa of capriciously shapedacanthomorphic, sphaeromorphic, and netromorphicacritarchs and presumable remains of cyanobacteria inthe Ura microbiota: Ancorosphaeridium magnum Ser�geev et al., 2011; A. minor Sergeev et al., 2011;A. robustum Moczydlowska et Nagovitsin, 2012;Appendisphaera tenuis Moczydlowska et al., 1993;A. tabifica Moczydlowska et al., 1993; Archaeot�enuisphaeridium cf. fimbriatum Grey, 2005; Asseseriumfusulentum Moczydlowska et Nagovitsin, 2012;A. piramidalis Moczydlowska et Nagovitsin, 2012;Cavaspina acuminata (Kolosova, 1991); C. basiconicaMoczydlowska et al., 1993; C. uria (Nagovitsin et Fai�zullin, 2004); Ceratosphaeridium cf. glaberosum Grey,2005; Densisphaera arista Moczydlowska et Nago�vitsin, 2012; D. fistulosa Moczydlowska et Nagovitsin,2012; Eotylotopalla cf. delicata Yin, 1987; E. strobilata(Faizullin, 1998); Knollisphaeridium maximum (Yin,1987); Labruscasphaeridium sp., Multifronsphaeridiumramosum Moczydlowska et Nagovitsin, 2012; Schizo�fusa zangwenlongii Grey, 2005; ?Sinosphaera rupinaZhang et al., 1998; Tanarium anozos Willman, 2008;T. conoideum Kolosova, 1991; T. digitiformum (Nago�vitsin et Faizullin, 2004); T. muntense Grey, 2005;T. tuberosum Moczydlowska et al., 1993; Urashaeracapitalis Moczydlowska et Nagovitsin, 2012; Variom�

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Fig. 5. Section of the upper part of the Ura Formation andlower part of the Kalancha Formation. Right bank of theUra River 3 km upstream of the mouth (according toM.V. Leonov, S.V. Rud’ko, and N.M. Chumakov).(1) Gray limestone; (2) black anthraconitic limestone;(3) siltstone and mudstone; (4) underwater slumping tex�tures; (5) casts of erosion scours; (6) small�scale lenticularbedding; (7) stratiform stromatolites; (8) cone�in�conetextures; (9) finds of acritarchs of the Ura assemblage.

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argosphaeridium floridum Moczydlowska et Nago�vitsin, 2012; Leiosphaeridia spp.; Gen et sp. indet.;Segmentothallus aff. S. asperus Hermann, 1989; Rug�osoopsis tenuis Timofeev et Hermann, 1979; Bul�latosphaera velata Vorob’eva et al., 2009; Aimia aff.A. gigantica Hermann; Ceratophyton sp.; Polytry�choides lineatus Hermann, 1974; Digitus fulvus Pjatile�tov, 1980; Obruchevella cf. Cucumiforma sp.; Siphono�phycus spp.; unnamed filamentous microfossils;unnamed forms 1–5.

This list includes also species from (Moczydlowskaand Nagovitsin, 2012), where these authors formallyrevised several taxa previously known from the UraFormation and described a group of new genera andspecies, which may be considered as valid until thenext revision of the Ura microbiota. At the same time,Moczydlowska and Nagovitsin (2012) regarded, with�out any explanations, some taxa described in (Sergeevet al., 2011) such as Bullatosphaera velata and Animiaaff. A. gigantica as taxonomic artifacts and identified inthe Ura Formation, also without any grounds, Miro�edichia lobata and Trachyhystrichosphaera aimica(Nagoitsin et al., 2004), which were rejected for theUra biota in (Sergeev et al., 2011) in accordance withall formal principles of the paleontological nomencla�ture. Therefore, references to the presence of Miroedi�chia and Trachyhystrichosphaera in the Ura Forma�tion cannot be accepted on the basis of either morpho�logical or purely formal criteria. As for new taxadescribed by M. Moczydlowska and K. Nagovitsin,the peculiar morphotype Urasphaera capitalisundoubtedly deserves to be identified as a new genusand species. Other taxa described in (Moczydlowskaand Nagovitsin, 2012) are questionable and reflect to aconsiderable extent subjective views of the authors onthe taxonomic significance of features in the consid�ered morphotypes. The biostratigraphic analysis of theUra microbiota is presented in the next section dedi�cated to the age assessment of lithostratigraphic unitsincluding the Dal’nyaya Taiga Group.

Most of the Ura limestones are characterized byelevated δ13С values ranging from +3.6 to +5.9‰(usually +5.1 to +5.9‰. Only a thin member at thebase of the formation yields δ13С values of approxi�mately –0.1‰ (Pokrovskii et al., 2006, 2011).According to the same authors, the minimum87Sr/86Sr value in carbonates of the Ura Formationaveraged for five samples is 0.7077.

The Kalancha Formation that crowns the section ofthe Dal’nyayaTaiga Group is mostly composed of car�bonate rocks with siltstone intercalations in the lowerpart. The formation is well exposed on the left side ofthe Lena River (Kalancha Rock and Dolgii Range)and on the left slope of the Ura River valley near itsmouth. The lower part of the formation is dominatedby dark gray to black fine�grained stromatolitic,microphytolitic, and oolitic limestones, while itsupper part, which was suggested by some geologists tobe defined as the Dolgii Formation, consists of alter�

nating gray and yellowish dolomites and black locallystromatolitic limestones.

Stromatolites observable in the Kalancha Forma�tion are represented by two taxa: (1) endemic formspecies, which was erroneously, in the opinion of oneof the authors of this work, attributed in (Dol’nik,2000) to the form genus Baicalia distributed in theMiddle and Upper Riphean sections; (2) stratiformspecies Stratifera sarmensis that occurs in southernSiberia both in the Kalancha Formation and in theupper part of the Uluntui Formation of the Baikalregion, which is attributed to the Vendian according toSr isotope chemostratigraphic data (Kuznetsov et al.,2012).

The thickness of the Kalancha Formation in theLena River section is approximately 500 m(Opornye…, 1972; Kolosov, 1975, 2000). South andsoutheast of the Ura uplift, carbonate rocks of theKalancha Formation are rapidly replaced by a shalysequence, which constitutes the upper part of the Valy�ukhta Formation and is widespread in southerly areasof the Patom Highland. Therefore, the Kalancha For�mation in sections under consideration was defined bysome researchers as the upper and middle Valyukhtasubformations (Zamaraev, 1984).

Theδ13С values in Kalancha limestones decreaseupward along the section of the formation from+5.1‰ at the base of this unit to +2.0‰ near its top(Pokrovskii et al., 2006).

The Zhuya Group is well exposed in several rockson both sides of the Lena River between the ZherbaRiver mouth and Macha Settlement. The almost com�plete section of the group crops out in the Kharchagai(Kholych) Rock between the Daban Spring and villageof Tinnaya on the left side of the Lena River. TheZhuya Group consists of two conformably occurringformations: Nikol’skoe (lower) and Chenchen(upper).

The Nikol’skoe Formation in its basal part is repre�sented in some sections by a member of gray polymic�tic medium� to fine�grained sandstones and siltstones.It is from 50 to 80 m thick and crops out on the left sideof the Lena River near the Daban Creek mouth and inthe lower reaches of the Ura River. In the latter area,the basal part of this member is composed of cross�bedded partly gravely sandstones with a thin layer ofcarbonate breccia cemented by sandy ferruginatematerial at its base that indicates an insignificant sedi�mentation break. Sandstones sampled from the UraRiver section 2 km upstream of its mouth yieldeddetrital zircons. Grains of their youngest generationform a cluster in concordia with U–Pb age of 646.9 ±3.4 Ma (Chumakov et al., 2011a).

Laterally, the member under consideration rapidlychanges its lithology and thickness. In some outcrops,for example, on the right side of the Lena River 6 kmdownstream of the Daban Creek mouth, basal sand�stones of the formation pinch out and its base is



marked only by a thin (2 cm) layer of clayey gravel�stones (Bobrov, 1979). Some researchers described thebasal sand–silty member of the Nikol’skoe Formationas the autonomous Kulleka Formation (Bobrov, 1964,1979; Kolosov, 1975).

The overlying part of the Nikol’skoe Formation iscomposed of frequently alternating variegated thin�bedded siltstones and marlstones with subordinateintercalations of pinkish and gray limestones, thequantity of which rapidly increases upward along thesection, reaching a maximum near its upper boundary.The thickness of the Nikol’skoe Formation variesfrom 120–150 m in the upper reaches of the Ura River(Kokoulin, 1998) to 220–250 m in the lower coursesof this river (Chumakov, 1959; Kokoulin, 1998) and200–360 m at the Lena River (Opornye…, 1972;Kolosov, 1975).

Limestones of the Nikol’skoe Formation demon�strate a considerable negative anomaly ofδ13С values,which decrease from –6.7‰ at the base of the forma�tion to –13.5‰ in its middle part. According to (Gor�okhov et al., 1995), the 87Sr/86Sr value derived fromeight determinations in three samples varies from0.70831 to 0.71057; the upper part of the formationyielded its minimum value averaged for six samples:87Sr/86Sr = 0.70790 (Pokrovskii et al., 2006).

The Chenchen Formation with a gradual transitionoverlies the Nikol’skoe Formation. This limestoneunit comprises two subformations. The lower subfor�mation that is assigned by some authors to the auton�omous Alyanch Formation (A.A. Predtechenskii,1941; Chumakov, 1959; Bobrov, 1979; Melezhik et al.,2009) consists largely of light gray stylolithic stroma�tolitic, micritic, detrital, and oolitic limestones. Somebeds of the last variety are composed of a gray matrixand red oolites. The thickness of the subformationincreases from 200–250 m at the Lena River (Chuma�kov, 1959; Zamaraev, 1984; Kokoulin, 1998) to 600–900 m at the Bol’shoi Patom River (Zamaraev, 1984;Melezhik et al., 2009). The upper subformation of theChenchen Formation that is assigned by someresearchers to the autonomous Kholych or KhopchaiFormation (A.A. Predtechenskii, 1941; Chumakov,1959; Bobrov, 1979; Melezhik et al., 2009) overlies thelower one with a gradual transition. It is formed byalternating gray, locally variegated (gray�red) oolitic,oncolitic, stromatolitic, silty, sandy, and detrital lime�stones. The last variety exhibits cross bedding. Theshare of sandy limestones gradually increases upwardalong the section, where they are accompanied by firstappearing intercalations of calcareous sandstones andgravelstones as well as lenses of dolomites.

In the Ura uplift, the section of the upperChenchen Subformation is crowned by a 30� to 35�m�thick member of brown fine�grained oolitic, stroma�tolitic, and sandy dolomites and sandstones. Themember contains also rare thin intercalations of mud�stones and conglomerates with a dolomitic matrix andscattered pebbles (Fig. 6). Locally, the member dem�

onstrates intraformation erosional surfaces and tex�tures of sediment dehydration (teepees; Pelechaty,1998). It is likely that deposition of the dolomiticmember of the Chenchen Formation was preceded bya sedimentation break, which is evident from distincterosional features at the base of the analogous dolo�mitic member at the Molbo and Zhuya rivers locatedbeyond the Ura uplift. These features and increase inthe grain�size composition and share of detrital rocksin the upper part of the formation distinctly indicaterapid shoaling of the Chenchen basin at its terminaldevelopment stage.

The thickness of the upper Chenchen Subforma�tion varies from 200–250 m at the Lena River (Chu�makov, 1959; Zamaraev, 1984; Kokoulin, 1998) to350–450 m at the Bol’shoi Patom River (Chumakov,1959; Melezhik et al., 2009). The total thickness of theChenchen Formation in the Ura uplift is estimated torange from 400–600 m at the Lena River (Opornye…,1972; Zamaraev, 1984; Kokoulin, 1998; Kontorovich,2005) to 800–1200 m in southerly areas (Chumakov,1959; Zamaraev, 1984; Melezhik et al., 2009).

Stromatolites contained in the Chenchen Forma�tion are represented by endemic forms attributed toform genera Katavia and Inzeria (Dol’nik, 1982, 2000)and a species of genus Gymnosolen also determined inthe open nomenclature. In the South Siberian stroma�tolite province, all these taxa differ from synonymousbiotas developed in other similar provinces of northernEurasia (Semikhatov, 1985) by their low taxonomicdiversity, sharply reduced number of taxa in commonwith other provinces, and confinement of representa�tives of form genera Katavia, Inzeria, and Gymnosolento the Vendian section, while in the Ural, North, andMiddle Siberian provinces, these genera are charac�teristic of the Upper Riphean stromatolite assemblage(Krylov, 1975; Komar, 1966; Semikhatov and Serebry�akov, 1985; and references therein).

Theδ13С value in bulk samples of Chenchen car�bonates increases from –9.6‰ in the middle part ofthis unit to –7.6 and –8.4‰ in its upper part. The87Sr/86Sr ratio in limestones of the Chenchen Forma�tion derived from six measurements varies from0.70811 to 0.70870 (Gorokhov et al., 1995). Four orig�inal and six published determinations of the 87Sr/86Srvalue for limestones of the Chenchen Formation arecited in (Pokrovskii et al., 2006). All the available mea�surements show that this ratio varies from 0.70786 to0.70855. Among these 87Sr/86Sr values, the last authorsconsider its minimum value determined for the lowerand middle part of the formation (0.7079) as the mostreliable. Similar data are presented in (Melezhik et al.,2009). According to them, the 87Sr/86Sr value in lime�stones from the middle part of the Chenchen Forma�tion is 0.7080 and increases to 0.7086 at its top. Thelast values are close to the 87Sr/86Sr ratios obtained byA.B. Kuznetsov (private communication) for lime�stones of the Chenchen and Nikol’skoe formations atthe Zhuya River.

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The “Yudoma Group” (complex or horizon) in theUra uplift and on the margin of the Patom folded zoneincludes the Zherba and Tinnaya formations with ero�sional surfaces at the bases. They are largely representedby different alternating rocks with the dominant role ofquartz sandstones and carbonate rocks in the Zherbaand Tinnaya formations, respectively (Fig. 3)

The names “Yudoma Group” or “Yudoma Com�plex” were proposed for deposits of the Patom High�land at times when most researchers who investigatedthe Upper Precambrian sections of the Siberian Plat�form and its surrounding structures believed that allthe formations of the region separated from underly�ing rocks by unconformities and closely associated

with Lower Cambrian sections are coeval and belongto the Vendian (reviews in (Zuravleva and Komar,1962; Khomentovskii, 1976; Semikhatov et al., 1970,2004)). Now, such a correlation is rejected: the Ven�dian reference sections of Siberia are established toinclude analogs of several units from the type sectionof the Yudoma Complex located in the Uchur�Mayaregion. Therefore, despite the fact that the names“Yudoma Group” or “Yudoma Complex” for theZherba and Tinnaya formations are traditional, theyare conditional and, undoubtedly, invalid. These tra�ditional names under no circumstances mean thatthese two formations are stratigraphic analogs of theAim and Ust’�Yudoma subformations in the type sec�

@р. Бол.

Lena Riverо@коло устьяр. Бол. Патоm

Lena River 5 kmupstream of Nokhtuisk

Molbo R.Zhuya R.

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Джербедянка

Fig. 6. Contact between the Chenchen and Zherba formations in the central part of the Ura uplift and on its flanks.(1) Conglomerate with sandy matrix; (2) conglomerate with carbonate matrix; (3) sandstone pebbles; (4) limestone pebbles;(5) dolomite pebbles; (6) black shale pebbles; (7) gravelstone; (8) quartzite�like sandstone; (9) calcareous sandstone; (10) sand�stone; (11) siltstone; (12) mudstone; (14) dolomite; (15) sandy dolomite; (16) oolitic limestone and dolomite; (17) stromatolites;(18) glauconite. Thin continuous line designates erosional unconformity at the base of the Zherba Formation; thin dotted linesshow correlation of some members.



tion of the Yudoma Complex (or group). As followsfrom the data mentioned above and cited below, theanalog of the Yudoma Group type section in the Urauplift is represented by all the succession of theDal’nyaya Taiga, Zhuya, and “Yudoma” groups.Therefore, to avoid confusion, we suggest renamingthe “Yudoma Group” of the Ura uplift the “Trekhver�stnyi Group” after the Trekhverstnyi Creek, a left trib�utary of the Lena River, into which it flows 2.5 kmupstream of Nokhtuisk. The stratotype of the Trekh�verstnyi Group comprises the Zherba and Tinnaya for�mations of the Nokhtuisk section. It is reasonable toattribute the Trekhverstnyi Group to the Patom Com�plex, which included previously only the Zhuya,Dal’nyaya Taiga, and Ballaganakh groups (Chumakov,1959).

The Zherba Formation rests upon the ChenchenFormation with considerable hiatus, which is markedby karst features in the upper part of the ChenchenFormation on the Ura uplift (Pelechaty, 1998; Kho�mentovskii et al., 2004) and by almost complete ero�sion of the upper dolomitic member of the ChenchenFormation at the Molbo and Bol’shaya Dzherbedy�anka rivers (Fig. 6). This hiatus follows also from wideregional correlations between sections of theChenchen and Zherba formations (Khomentovskiiet al., 2004). At the same time, development of ero�sional surfaces both below and above this main hiatushampers its recognition. Therefore, some authors(Chumakov, 1959; Opornye…, 1972; Bobrov, 1979;Zamaraev, 1984) took the base of a dolomitic member,which crowns the Chenchen Formation and bearserosional features at its base, for the lower boundary ofthe Zherba Formation. The deposition of this memberduring the Zherba time in the marginal part of thePatom basin was followed by drastic changes in sedi�mentation patterns: mostly carbonate sediments werereplaced by sandy facies.

The best outcrops of the Zherba Formation arelocated in the eastern margin of the Ura uplift: on theleft side of the Lena River opposite the Bol’shoi PatomRiver mouth and opposite the Malyi Patom Rivermouth (Pelechaty, 1998; Khomentovskii et al., 2004).In these sections, the Zherba Formation consists ofthree sequences. The lower sequence is over 150 mthick. Its basal part includes frequently encounteredconglomerates composed of a sandy matrix and dolo�mite pebbles. These conglomerates demonstratelocally downlap relations with eroded bioherms ofstromatolitic dolomites, which imply the presence ofbiogenic reefs within a member (Fig. 6). The lowersequence is mostly composed of gray cross�beddedglauconite quartzite�like sandstones (in the lowerpart) with subordinate quartz gravelstones and green�ish siltstones. Most sandstone varieties are quartzosein composition and only some of them contain notableadmixture of feldspars. The middle sequence of theZherba Formation approximately 200 m thick ispoorly exposed. Its exposed 40�m�thick part is repre�

sented by alternating frequently calcareous blackshales and sandstones with intercalations of bitumi�nous limestones. The third sequence crowning thesection of the Zherba Formation is approximately 60–80 m thick and known also as the Tirbees Member(Khomentovskii et al., 2004; Kochnev and Karpova,2010) or Tirbees Formation (Kokoulin, 1998). Thispeculiar and complex sequence was previously consid�ered as the basal unit of the overlying Tinnaya Forma�tion, which is also characterized by elevated rock bitu�minosity (Chumakov, 1959; Bobrov, 1964, 1979;Opornye…, 1972; Kolosov, 1975; Kokoulin, 1998).The Tirbees Member begins with a bed (approximately20 m thick) of massive and bedded black medium� tocoarse�grained highly bituminous (anthroconite)limestones with thin intercalations of calcareousshales. Higher in the section, the member is composedof alternating green and red marlstones and siltstones,clayey dolomites, black bituminous limestones, andcarbonate shales. Near the top of the member, clayeydolomites enclose two thin (5 and 12 cm) intercala�tions of black cherts and their scattered concretions(Bobrov, 1979) as well as thin layers of algal siliceous–phosphate rocks (Khomentovskii et al., 2004).

The total thickness of the Zherba Formation is esti�mated in different manners: it is 200–250 m (Kolosov,1975; Bobrov, 1979; Kokoulin, 1998) to 500 m (Zama�raev, 1984) thick without the Tirbees Member and350 m with it (Pelechaty, 1998; Khomentovskii et al.,2004).

The phosphate rocks of the Tirbees Memberyielded a diverse assemblage of excellently preservedsilicified microfossils (Yakshin, 2002; Khomentovskiiet al., 2004). Yakshin described many new endemicmicrofossil genera and species, in addition to well�known taxa characterized by wide stratigraphic(Upper Riphean–Vendian–Lower Cambrian) andgeographic distributions such as Obruchevella, Oscilla�toriopsis, Glomovertella, Gloeodiniopsis, and Germino�sphaera. By its composition and diversity, this micro�biota reflects an important stage in development ofmicroorganisms on the Siberian Platform during theLate Precambrian. As for many endemic speciesdescribed among this assemblage, the problem ofappropriateness and validity of identified new generaand species for the Precambrian microbiotas should besolved by subsequent investigations and revisions,which still do not involve Tirbees microfossils.

Determinations of the C isotope composition inlimestones and dolomites from the terminal part of themiddle sequence of the Zherba Formation revealednegative δ13С values and their decrease upward alongthe section from –8.0 to –2.5‰. In most associateddolomites, the δ13С values drop to –20‰, which isthought to be explained by limestone dolomitizationand has no stratigraphic sense (Pelechaty, 1998). In theupper sequence of the Zherba Formation (TirbeesMember), the brief negative excursion to –5‰ is fol�lowed by the growth of the δ13С value to 2‰ and its

1

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CHUMAKOV et al.

decrease gradually to zero at the top of the formation(Pelechaty, 1998).

The Tinnaya Formation. The boundary between theZherba and Tinnaya formations is now placed imme�diately below a 10�m�thick bed of coarse�grainedcross�bedded sandstones and gravelstones with karstfeatures (Pelechaty, 1998) and erosional incisions(Khomentovskii et al., 2004) at its base. The overlyingpart of the Tinnaya Formation is composed of alter�nating members of brecciated clayey bituminous lime�stones and dolomites, which are separated by interca�lations of dark gray to black carbonaceous calcareousclays, greenish siltstones, and massive limestone anddolomite beds. These rocks include a thin (15 cm)layer of black cherts 20 m below the top of the forma�tion (Khomentovskii et al., 2004). The thickness of theTinnaya Formation in the Ura uplift area is estimatedto be 220 m (Khomentovskii et al., 2004) or 334 m(Pelechaty, 1998). The upper 150 m of the formationyielded small�shell faunal fossils characterizing theAnabarites trisulcatus Zone of the Upper VendianNemakit–Daldynian Stage; higher layers contain Tik�sitheca sp., indicating the presence of the overlyingPurella antiqua Zone of the same stage in this section(Khomentovskii et al., 2004; Kochnev and Karlova,2010).

The Tinnaya carbonate rocks from the lower part ofthe formation are characterized by δ13С values varyingfrom +2.3 to –9‰, which provide a curve with fournegative excursions (from the base upward): –3.5, –5,–9, and –5.5‰ (Fig. 3). They are separated by nar�row intervals of the section also with negative but rela�tively elevated δ13C values (Pelechaty, 1998). In theupper part of the Tinnaya Formation, the δ13C valuevaries from –4.8 to ⎯3.0‰ and decreases to –5.5‰at the base of the Nokhtuisk Formation and thenincreases to zero at higher levels of this unit (Khomen�tovskii et al., 2004).

LOWER CAMBRIAN

The Nokhtuisk Formation rests upon the TinnayaFormation with insignificant hiatus (Khomentovskiiet al., 2004). The contact between these formationsand the lower part of the Nokhtuisk Formation com�posed of alternating variegated mudstones, marl�stones, and stromatolitic dolomites are well exposedon the left side of the Lena River 3 km upstream of theNokhtuisk Settlement. In this area, the basal layers ofthe Nokhtuisk Formation and its lower 50 m yieldabundant small�shell fossils characteristic of the Tom�motian Aldanocyathus sunnaginicus Zone, the basalzonal unit of the Lower Cambrian section (Khomen�tovskii et al., 2004; Kochnev and Karlova, 2010).

1

VENDIAN AGE OF THE DAL’NYAYA TAIGA, ZHUYA, AND “YUDOMA” GROUPS:

ARGUMENTS IN FAVOR

The lower boundary of the Vendian section in theUra uplift area is distinctly definable at the base of theNokhtuisk Formation on the basis of the replacementof the faunal assemblage characterizing the Purellaantiqua Zone of the Vendian Nemakit–DaldynianStage by fossils belonging to the Aldanocyathus sun�naginicus Zone of the Lower Cambrian. The lowerboundary of Vendian strata in this section is stillambiguous because of insufficient available data,although the distribution of organic remains in theDal’yaya Taiga Group and chemostratigraphic evi�dence (Pokrovskii et al., 2006; Melezhik et al., 2009)provide grounds for the assumption that the largestupper part of this group should be attributed to theVendian. This is confirmed, for example, by finds ofdiverse Pertatataka�type acanthomorphic acritarchs inthe Ura Formation (Chumakov et al., 2007; Vorob’evaet al., 2008a; Golubkova et al., 2010; Sergeev et al.,2010, 2011) and Vendian form Beltanelloides soriche�vae in the lower subformation of the Barakun Forma�tion in the Ura River section (Leonov and Rud’ko,

2012).3 The find of Pertatataka�type acanthomorphic

acritarchs represented in the Ura Formation by thepeculiar assemblage serves as a main criterion for dat�ing this unit. The lower part of the Ura Formationyielded the following Pertatataka�type acritarchs andother fossils (Sergeev et al., 2011): Ancorosphaeridiummagnum, A. minor, Appendisphaera tenuis, A. minima,Appendisphaera sp., Archaeotunisphaeridiam aff. fim�briatum, Bullatosphaera velata, Cavaspina cf.C. acuminata, C. basiconica, Eotylotopalla strobilata,E. aff. delicata, Gyalosphaeridium minutum, Knol�lisphaeridium maximum, Multifronsphaeridium pelo�rium, ?Sinosphaera rupina, Tanaium conoideum,T. digitiformis, T. tuberosum, Variomargosphaeridiumlitoschum, Aimia aff. gigantica, Leiosphaeridia spp.,Schizofusa zangwenlongii, Digitus fulvus, unnamed fil�amentous microfossils, Obruchevella sp., Polytrichoideslineatus, Rugosoopsis tenuis, Segmentothallus aff. S. aspe�rus, Siphonophycus spp., Ceratophyton sp. cf. Cucumi�forma sp., unnamed forms 1–5. This assemblage indi�cates that the Ura Formation represents an analog ofthe second complex palynozone of Pertatataka acri�tarchs established in the type section of central Austra�lia (Grey, 2005).

As was mentioned, Moczydlowska and Nagovitsin(2012) revised the microbiota from the Ura Formationusing in fact the same material analyzed by V.N. Ser�geev and colleagues. In doing so, they demonstrated

3 The find of Beltanelloides sorichevae in this section indicates thatthese fossils previously known from the upper layers of the typeVendian section in the East European Platform (Fedonkin et al.,2007) are characterized by a wider stratigraphic distribution.Nevertheless, this fact provides no grounds for excluding thisspecies from the list of characteristic Vendian taxa.



the subjective view on the taxonomic significance ofmorphological features and defined three new generaand nine new species, renaming the previouslydescribed taxa. Such a procedure provided grounds forthem to arrive at the conclusion on the endemic char�acter of the Ura microbiota and its older age as com�pared with other Pertatataka biotas of Siberia andyounger age as compared with sediments of the firstpalynozone defined in the lower part of the LowerVendian Doushantuo Formation in South China(McFadden et al., 2009). In our opinion, the availablefacts indicate that the Ura Formation corresponds tothe Grey’s second complex palynozone.

The U–Pb (SHRIMP) dating of detrital zirconsfrom the base of the Nikol’skoe Formation croppingout near the Ura River mouth yielded important infor�mation on age of upper layers of the Patom Complex(Chumakov et al., 2011a). On the curve of the relativeprobability, several members dated at 2900, 2070,2500, 2000, and 1800 Ma are definable on the basis ofthe 206Pb/238U and 207Pb/206Pb values, which implieserosion of the Archean and Lower Proterozoic base�ment of the Siberian Platform. For determining theminimum age of upper layers of the Patom Complex,the most interesting is the youngest zircon generationextracted from the Nikol’skoe Formation. Zircons ofthis generation are divisible in two groups on the basisof both the 206Pb/238U and 232Th/238U values. Theolder group of grains is characterized by the 232Th/238Uratios varying from 0.4 to 1.1, while in the 206Pb/238U–207Pb/238U coordinates, the group with age of 704.3 ±4.5 Ma (1σ, MSWD = 0.90) is definable around theconcordia. The younger group of grains demonstratesthe lowered 232Th/238U value ranging from 0.2 to 0.7and forming in the above�mentioned coordinates theconcordia with age of 646.9 ± 3.4 Ma (1σ, n = 48,MSWD = 0.900077). Thus, U–Pb (SHRIMP) agesobtained for detrital zircons indicate that basal sand�stones of the Nikol’skoe Formation are younger than646.9 ± 3.4 Ma, i.e., younger as compared with ageaccepted now for the lower boundary of the VendianSystem equal to 650 Ma (Dopolneniya…, 2000).

The position of the Vendian lower boundary in theUra uplift section may be derived from stratigraphi�cally important interchangeable features characteris�tic of some sections, which exhibit similarity with sec�tions of the Dal’nyaya Taiga, Zhuya, and Trekhverst�nyi groups. In this regard, the sections of the followingthree regions are promising: Yangtze Platform ofSouth China, eastern and northern Oman, and north�eastern margin of the East European Platform (Fig. 7).In these regions, the Vendian sections demonstrate thesuccession of several chemostratigraphic, biostrati�graphic, and climatic events partly dated and regis�tered also in the Ura section. Let us trace these eventsin the above�mentioned sections (from the top down�ward).

(1) The Ura (Khomentovskii et al., 2004; Kochnevand Karlova, 2010) and China (Steiner et al., 2007;

Ishikawa et al., 2008) sections include paleontologi�cally substantiated analogs of the Vendian Nemakit–Daldynian Stage.

(2) Brief but significant negative δ13С anomalies(from –5 to –13‰) are established near the base ofthe member with the Nemakit–Daldynian fossils inthe Ura and China sections and at a close level in tuf�faceous sediments dated by the U–Pb zircon methodat 542 Ma (Brasier et al, 2000; Bowring et al., 2007) inthe Oman section (Fig. 7). In the Ura uplift section,the ascending shoulder of a similar anomaly (Fig. 3) isestablished in the middle part of the Zherba Forma�tion (Pelechaty, 1998). In China, this anomaly, namedthe Bace (Zhu et al., 2007a) or EN4 (Zhou and Xiao,2007; Zhou et al., 2011) anomaly, is documented atthe base of the Zhujiaqing Formation. In Oman, asimilar situation is recorded in the lower part of theFara Formation, where it is designated by the letter Z(Walter et al., 2000). Similar anomalies are also knownat the bases of sedimentary sequences with fossilscharacteristic of the Nemakit–Daldynian Stage in theMcKenzie Mountains of Canada (Walter et al., 2000)and India (Jiang et al., 2003).

(3) In South China, the significant (≥–10‰) neg�ative δ13С anomaly named the Dounce (Zhu et al.,2007a) or EN3 (Zhou and Xiao, 2007; Zhaou et al.,2011) anomaly is established in the upper part of theDoushantuo Formation. In Oman, the similar eventcalled the Shuram anomaly (up to 14‰) is registeredin the upper part of the Nafun section (Le Guerroue,2010). By their amplitudes and stratigraphic positions,both of these anomalies are similar to the negativeZhuya one (Fig. 7). Correlation of the Zhuya anomalywith its Dounce and Shuram counterparts is con�firmed by similarity in 87Sr/86Sr values in their consti�tuting carbonate rocks. These values are estimated tobe 0.7080–0.7084 for the Zhuya (Pokrovskii et al.,2006; Melezhik et al., 2009), 0.7083–0.7084 for theDounce (Jiang et al., 2007), and 0.7080–0.7088 forthe Shuram (Le Guerroue et al., 2006, Le Guerroue,2010) anomalies. Similar 87Sr/86Sr values are charac�teristic of sediments aged 580–570 Ma (Halverson andShields�Zhou, 2011). In the East European Platform,similar results are obtained for the lower part of theVendian Redkino Horizon on the basis of U–Pb datesof zircons from tuffs and corresponding interpolations(Sokolov, 2011, 2012, Grazhdankin, 2011). Theseestimates are consistent with radioisotopic data con�cerning the Dounce and Shuram anomalies. U–PbTIMS dates of approximately 551 and 555 Ma areavailable for volcanogenic zircons from the upper partof the Doushantuo Formation above the Dounceanomaly (Condon et al., 2005; Zhang et al., 2005). Atthe same time, according to U–Pb dating of detritalzircons, the Shuram anomaly of Oman is younger than600 Ma (Rieu et al., 2007). These measurements placethe upper and lower age limits for the Dounce andShuram anomalies at 550 and 600 Ma, respectively.Such values are also suitable for assessing age limits of

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the Zhuya anomaly, which is correlated with theseevents, which serves as additional evidence in favor ofits Vendian age.

(4) The rocks immediately below the Dounceanomaly in the Doushantuo Formation yield a diverseassemblage of acanthomorphic acritarchs (ECAPassemblage), which is similar in its general appearanceto the Lower Vendian Ura and Kel’tma assemblages ofthe East European Platform. The Kel’tma assemblagecharacterizes the autonomous Vychegda Horizon,which is older as compared with the Vendian RedkinoHorizon of the East European Platform. In its taxo�nomic composition, the Kel’tma assemblage is corre�lated with the first ECAP zone in the stratotype sec�tion of Australia (Veis et al., 1996; Vorob’eva et al.,2006, 2007, 2008b, 2009a, 2009b). This provides addi�tional grounds for correlating the sediments sand�wiched between the Nemakit–Daldynian Stage andstrata with the Ura acritarch assemblage with theUpper Vendian.

The largest acanthomorphic acritarchs arerecorded near the base of the Doushantuo Formation5 m above the top of cap dolomites associated with til�lites of the underlying Nantuo Formation. Zirconsfrom tuff intercalations in cap dolomites and fromtuffs sampled 5 m above the top of cap dolomites aredated by the U–Pb method at 635.2 ± 0.6 and 632.5 ±0.5 Ma, respectively (Condon et al., 2005). At thesame time, it is impossible to establish age relation�ships between zonal units of the Doushantuo (McFad�den et al., 2009) and type biozones defined in (Grey,2005) because of taxonomic difficulties. In their pub�lications, Chinese researchers to date have used sometaxa names, such as Meghystrichosphaeridium andPolygonum, which were acknowledged after multiplerevisions (Grey, 2005; Moczydlowska, 2005; etc.) tobe invalid.

It should be emphasized that the Torgo Formationimmediately overlying stratigraphic analogs of the UraFormation on the western slope of the Aldan Shield

and correlated with the Zhuya Group contains theimpoverished assemblage of acanthomorphic acri�tarchs that includes Cavaspina and some other taxacharacteristic of the Pertitataka�type microbiota. Pre�viously, these microfossils were erroneously attributedto genera and species of Upper Riphean acanthomor�phic acritarchs (Kolosova, 1991). The recent findindicates that final extinction of Pertatataka�typemicrofossils was asynchronous with the onset of theDounce–Shuram–Zhuya negative carbon excursion,as was assumed by some researchers (Zhu et al., 2007a,2007b; Chumakov, 2010; etc.).

(5) The lower part of the Doushantuo Formation ofSouth China and the interval of the Khufai andMasirah Bay formations of Oman are dominated byconsiderable positive δ13С values (ranging from +5 to+6‰). The middle parts of these large intervals inChina and Oman exhibit brief negative δ13C excur�sions (Fig. 7). The similar interval of positive δ13С val�ues (from +5 to +8‰) is also characteristic of thelargest upper part of the Dal’nyaya Taiga Group,although without a brief negative excursion in its mid�dle part. The latter could be missed owing to the insuf�ficient density of measurements in this interval of theUra section.

(6) The negative peaks at bases of these wide posi�tive δ13C intervals under consideration correspondingto cap dolomites of glacial horizons are well expressedin the Ura, China, and Oman sections (Pokrovskiiet al., 2006; Le Guerroue, 2010; Jiang et al., 2011).

(7) In all three compared sections, cap dolomitesare underlain by glacial horizons of the Bol’shoiPatom Formation on the Ura uplift, Nantuo Forma�tion in South China, and Fiqa Formation in Oman.

The comparison between the Ura, South China,and Oman sections shows that the succession ofchemostratigraphic and, partly, biotic events in thesection from the base of the Cambrian to glacial hori�zons is similar. Such a similarity is particularly signifi�cant between the Ura and South China sections, pro�

Fig. 7. Correlation of Vendian sections of the Ura uplift with sections of South China, Oman, and Eastern Europe.(1) Glacial sediments; (2) cap carbonates; (3) trilobites; (4) faunal assemblage of the Aldanocyatus sunnaginicus Zone, lower unitof the Tommotian Stage; (5) faunal assemblage of the Purella antiqua Zone, Nemakit–Daldynian Stage, Upper Vendian; (6) fau�nal assemblage of the Anabarites trisulcatus Zone, Nemakit–Daldynian Stage, Upper Vendian; (7) sabelliditids; (8) claudinids;(9) Upper Vendian microfossils; (10) Lower Vendian ECAP�type microfossils, including the assemblage from the upper zone ofthe Doushantuo Formation, according to (McFadden et al., 2009); (11) Lower Vendian microfossils from the lower zone of theDoushantuo Formation, according to (McFadden et al., 2009); (12) nonskeletal Metazoa; (13) Eocholinia and Archiphasmaalgae; (14) vendotenids; (15) Beltanelloides sorichevae. Dates (Ma): (16) U–Pb SHRIMP/TIMS on volcanogenic zircons,(17) U–Pb SHRIMP/TIMS on detrital zircons; (18) U–Pb SHRIMP/TIMS on zircons from volcanics (t); (19) 87Sr/86Sr ratios

in carbonates; (20) indications of stratigraphic hiatuses; (21) stratigraphic unconformities. ( ) Cambrian; (VIV) Nemakit–Dal�dynian Stage of the Vendian System; (VII–III) Kotlin and Redkino horizons of the Vendian System; (VI) Lapland Horizon of the

Vendian System; (VCH) Vychegda Horizon of the Vendian System; (R32) upper part of the Upper Riphean. Main sources:

(1) Chumakov, 1959, Bobrov, 1964; Khomentovskii et al., 2004; Pokrovskii et al., 2006; Chumakov et al., 2007, 2011a; Vorob’evaet al., 2008a; Melezhik et al., 2009); Kochnev and Karlova, 2010; Leonov and Rud’ko, 2012; (2) Zhou and Xiao, 2007; Zhu et al.,2007a, 2007b; (3) McFadden et al., 2009; Jiang et al., 2011; (4) Zhang et al., 2011; etc.); (5) Le Guerroue et al., 2006;(6) Le Guerroue, 2010; (7) Rieu et al., 2007; etc.; (8) Sokolov, 1997, 2011, 2012; (9) Veis et al., 1996; Vorob’eva et. al., 2006,2008a, 2009a, 2009b; (10) Chumakov, 1978, 1992, 2009; etc. Names of groups and horizons are given in capital letters. (VCH)Vychegda Horizon.

C~

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CHUMAKOV et al.

Fig. 8. Correlation of Vendian sections of the Ura uplift, peripheral zone of the Baikal fold system, and western slope of the AldanShield, according to (Zhuravleva et al., 1959, 1961, 1969; Opornye…, 1972; Chumakov, 1993; Ivanov et al., 1995; Khomentovskii,2008; Khomentovskii et al., 2004; Sovetov and Komlev, 2005; Kochnev and Karlova, 2010; Kuznetsov et al., 2012; etc.).(1) Glacial sediments; (2) cap carbonates; (3) Beltanelloides sorichevae; (4) Lower Vendian acanthomorphic microfossils; (5) U–Pbage of detrital zircon; (6)) nonskeletal Metazoa; (7) faunal assemblage of the Tommotian Aldanocyatus sunnaginicus Zone, LowerCambrian; (8) faunal assemblage of the Purella antiqua Zone, Nemakit–Daldynian Stage, Vendian; (9) faunal assemblage of theAnabarites trisulcatus Zone, Nemakit–Daldynian Stage, Vendian; (10) sabellidites; (11) indications of stratigraphic hiatuses;

(12) base and top of cap dolomites; (13) 87Sr/86Sr ratios in carbonate rocks; (14) Pb–Pb isochron age of limestones. ( ) Tom�

motian Stage of the Lower Cambrian; (V) Vendian; (R) Riphean.

C11~

viding grounds for correlation of the glacial Bol’shoiPatom Formation with the glacial Nantuo Formationof South China. The age of the latter unit is deter�mined owing to several U–Pb dates obtained for detri�tal zircons (Zhang et al., 2011). The base of the capdolomite crowning the Nantuo Formation is dated at635.6 ± 0.5 Ma; its lower part is dated at 636.3 ± 4.9 Ma;the upper part of the Datangpo Formation, whichunconformably underlies the Nantuo Formation, isdated at 656 ± 3 Ma. In Oman, the glacial Fiqa For�mation, the age of which is estimated by the U–Pbmethod on detrital zircons to be <644 Ma (Rieu et al.,2007), corresponds likely to the Bol’shoi Patom For�mation. Such a correlation allows the Bol’shoi PatomFormation to be considered as being older than635 Ma and younger than 644 Ma ago; i.e., it corre�sponds to the basal glacial part of the Lapland Horizonin the Vendian stratotype (Sokolov, 1997, 2012).

Thus, the available data and aforementioned corre�lations indicate that the interval of the Trekhverstnyi,Zhuya, and Dal’nyaya Taiga groups of the Ura upliftsandwiched between the top of the Nemakit–Daldy�nan Stage and basal Vendian Lapland Horizon corre�sponds (or is very close) by its range to the Vendian inthe stratotype area and represent together analogs ofthe main horizons of the Vendian stratotype: Nema�kit–Daldyn, Vychegda, Kotlin, Rovno, and Lapland.The completeness and exact boundaries of these hori�zons in the Ura Section are as yet unclear and requirefurther investigations.

REGIONAL CORRELATIONS OF VENDIAN SECTIONS IN THE URA UPLIFT

In regions surrounding the Baikal folded domain,the lithology and structure of Vendian sections dem�onstrate certain variations. Nevertheless, the sectionsof these regions are well correlative with units of theUra type section. They are mostly correlated by trac�ing some reference formations (Fig. 8). The main rolein this process belongs to the following stratigraphicunits: (1) terrigenous Ballaganakh Group precedingVendian strata; (2) overlying glacial diamictites of theBol’shoi Patom Formation and its analogs; (3) ZhuyaGroup, which is characterized by a peculiar composi�tion and bedding succession; (4) Zherba Formation.These deposits are traced from the Ura uplift eastwardand southeastward along the eastern branch of the

Patom fold arc (Chumakov, 1959, 1993; Opornye…,1972), then to the Berezovo trough centroclinal andfarther to the western slope of the Aldan Shield(Zhuravleva et al., 1959; Chumakov, 1959, 1993;Opornye…, 1972). In the southwestern direction, Ven�dian complexes are well traceable from the Ura upliftup to the Bol’shaya and Malaya Chuya rivers(Golovenok et al., 1963; Chumakov, 1993; Opornye…,1972). Such correlations are confirmed by the condi�tional state geological survey, scale 1 : 2000000 (Ivanovet al., 1995; Kokoulin, 1998; etc.).

The eastern branch of the Patom arc south of theUra uplift is characterized by an elevated thickness ofsediments under consideration and significant facieschanges in the Dal’nyaya Taiga Group. In the MalyiPatom, Zhuya, Molbo, and Bul’bukhta river basins,glacial diamictites of the Bol’shoi Patom Formationare replaced by black shales and sandstones, which areunited into the Dzhemkukan Formation, while theUra and Kalancha formations are replaced by theValyukhta Formation consisting of dark gray to blackshales with subordinate sandstone and limestoneintercalations. Southeast of these areas in the southerncentroclinal of the Berezovo trough in the Dzhelindaand Sen river basins, the basal part of the Dal’nyayaTaiga Group again contains glacial sediments unitedinto the Nichatka Formation correlated with theBol’shoi Patom Formation. In this area, the Barakunand Valyukhta formations are replaced by the KumakhUlakh carbonate–terrigenous and Sen sandstone–dolomite formations, respectively. The latter units aretraceable in the eastern direction up to the Chara andTokko rivers on the western slope of the Aldan Shield.In the eastern part of this region, the thickness of theVendian section decreases. The Nikol’skoe andChenchen formations are replaced by the Torgo For�mation, the Sen Formation becomes divided into thebasal Imalyk terrigenous and Tokko carbonate forma�tions, and the Kumakhulakh and Nichatka formationspinch out (Zhuravleva et al., 1959; Petrov, 1966).

In the western branch of the Patom arc and NorthBaikal Highland, the Vendian section is similar to thesection of its eastern branch, differing only in thelithology of the Dzhemkukan Formation, which iscomposed largely of glacial sediments in these areas.Southwest of the Malaya Chuya River head, the Balla�ganakh Group and lower glacial part of the Dal’nyayaTaiga Group pinch out, while analogs of the upper part



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CHUMAKOV et al.

of the Dal’nyaya Taiga Group and Zhuya Group arewell recognizable in sections along the Chaya Riverand the head area of the Malaya Chuya River(Opornye…, 1972).

The Chaya section is transitional between thePatom and near�Baikal sections; therefore, the Kalan�cha Formation at the Chaya River was called by someresearchers also both the Kalancha and Goloustnayaor Uluntui formations (Opornye…, 1972). The analogof the Chenchen Formation at the Chaya River is over�lain by sediments, which are correlated by their lithol�ogy and position in the section with the TrekhverstnyiGroup of the Ura uplift. From the Chaya River, thesesediments are traced as the Goloustnaya and Uluntuiformations and “Yudoma Group” or “Yudomian” inthe southwestern directions along the western marginof the North Baikal Highland and Baikal Range up tothe southern Baikal region (Opornye…, 1972). In theKurgun River basin, located in the southern part of thelast region, the Goloustnaya Formation is built up by amember of glacial sediments (diamictites, conglomer�ates, and sandstones), which is named the Bugul’deikaMember (Sovetov and Komlev, 2005).

The traditional correlation of Near�Baikal sectionswith the Patom section based on geological (biostrati�graphic and event) criteria is confirmed by recent Srand C isotopic chemostratigraphic methods andPb⎯Pb isochron dating of the least altered limestonesfrom the upper part of the Uluntui Formation: 560 ±30 Ma (Kuznetsov et al., 2012).

The δ13C values in a thin dolomite member occur�ring in the upper part the Goloustnaya Formation(basal unit of the Baikal Complex) in the type sectionof the complex increases from –2.6‰ at the base ofthe member to +2.8‰ at its top. Taking into consid�eration the occurrence of the Goloustnaya Formationon diamictites of the Bugul’deika Member, these val�ues can be correlated with the above�mentioned δ13Cvalues obtained for the basal part of the lower BarakunSubformation. In the 600�m�thick member of lime�stones occurring at the top of the Uluntui Formationin the same section of the Baikal Complex, the valuesvary around +4.7‰, deviating from this value usuallyby 0.8–0.9‰ (Kuznetsov et al., 2012). Variations ofδ13C in the upper part of the Uluntui Formation arecomparable with their changes in sections of theDal’nyaya Taiga Group in the interval from the upperpart of the lower Barakun Subformation to the lowerpart of the Kalancha Formation.

Recent measurements in samples which met verystrict requirements on geochemical preservation ofcarbonate rocks (Mg/Ca < 0.05, Mn/Sr < 0.03,Fe/Sr < 0.4, δ13O > –8‰) yielded information of87Sr/86Sr values in them, which were from 0.70842 to0.70874 (Kuznetsov et al., 2012). In terms of Sr chro�nostratigraphy, this implies that early diagenesis of theanalyzed upper Uluntui rocks corresponds within theerror limits with their Pb–Pb age.

The available data on correlation of theBugul’deika Member and Goloustnaya and Uluntuiformations of the Baikal Complex with the Dal’nyayaTaiga Group of the Patom Highland disprove the tra�ditional opinion in the Russian geological literaturethat this complex should be attributed either to theupper part of the Middle Riphean and lower part of theUpper Riphean (Dol’nik, 1982, 2000; Stanevich et al.,2007) or to the Baikalian, a unit dating back to 850–600 Ma (Opornye…, 1972; Khomentovskii et al., 1998;Khomentovskii and Postnikov, 2001, Khomentovskii,2002). The new data show that the Baikal Complex inthe range of the Bugul’deika Member and Goloust�naya, Uluntui, and Kachergas formations should becorrelated with the Vendian System (Kuznetsov andLetnikova, 2005; Kuznetsov et al., 2012).

CONCLUSIONS

The recent chemostratigraphic, paleontological,and radioisotopic data indicate that the Dal’nyayaTaiga, Zhuya, and Trekhverstnyi groups of the Urauplift are the Vendian in age. Correlations of theseunits with well�studied Upper Proterozoic sections ofother regions support this inference. The upperboundary of the Vendian System in the Ura uplift sec�tion is established at the base of the Nokhtuisk Forma�tion on the basis of biostratigraphic data (Khomen�tovskii et al., 2004; Kochnev and Karlova, 2010). Itslower boundary in this section is placed with high con�fidence at the base of the glacial Bol’shoi Patom For�mation on the basis of finds of diverse Vendian acanth�omorphic acritarchs (ECAP) in the Ura Formationand Beltanelloides sorichevae in the lower part of theBarakun Formation and also on the basis of the corre�lation of the Bol’shoi Patom Formation with glacialsediments of the Nantuo and Fiqa formations ofChina and Oman, respectively, and with the LaplandHorizon of Eastern Europe. Consequently, sedimentssandwiched between the base of the Nokhtuisk For�mation and the base of the Bol’shoi Patom Formationshould be attributed to the Vendian System.

(2) Correlation of the Ura Formation with EastEuropean, China, and Oman Vendian sections withreliable radioisotopic dates and some biostratigraphicreference levels provide grounds for the assumptionthat the Vendian section of the Ura uplift includes theKotlin, Redkino, and Lapland sediments, i.e., mainunits of the Vendian System, in addition to the Nema�kit–Daldyn Horizon. The position of boundaries andstratigraphic ranges in the Ura section need furtherinvestigations.

(3) Correlation of the Ura section with Vendiansequences in surrounding structures of the Baikalfolded region and on the western slope of the AldanShield shows that the Vendian section in the Ura upliftarea represents the most complete succession of thesesediments in the spacious region under consideration.



(4) As compared with these sections, the Vendiansuccession on the Ura uplift is better substantiated bypaleontological and chemostratigraphic data and lessaltered by secondary processes, well exposed, and eas�ily accessible for investigation.

All these properties allow the Vendian section ofthe Ura uplift to be recommended as a regional refer�ence section of the Vendian System for the southernpart of Middle Siberia.

ACKNOWLEDGMENTS

We are grateful to M.V. Leonov, S.V. Rud’ko, andA.B. Kuznetsov for the permission to use their unpub�lished materials; Yu.K. Sovetov for valuable recom�mendations; and O.A. Petrovichev for his help in pre�paring the manuscript. This work was supported by theRussian Foundation for Basic Research (projectnos. 11�05�00232, 10�05�00294, 11�05�92692�IND)and Program no. 28 of the Presidium of the RussianAcademy of Sciences.

Reviewer M.A. Fedonkin

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Translated by I. Basov

SPELL: 1. cherts

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Vendian Reference Section of Southern Middle Siberia · (Keller et al., 1967; Ivanov et al., 1995; etc.) to Late Riphean (Khomentovskii and Postnikov, 2001). The last viewpoint is