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.
Vendian Reference Section of Southern Middle Siberia N. M. Chumakov, M. A. Semikhatov, and V. N. Sergeev Geological Institute, Russian Academy of Sciences, Pyzhevskii per. 7, Moscow, 119017 Russia e 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 uplift is 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 of the entire southern Middle Siberia. Its description is accompanied by presentation of new biostratigraphic and radioisotopic data. The section is correlated with other Vendian sections of the Baikal–Patom and some other world regions.
Keywords: Vendian, microfossils, glacial deposits, Lena River, Ura uplift DOI: 10.1134/S0869593813040023
INTRODUCTION tion of the corresponding regional stratigraphic scales In southern Middle Siberia, the most complete available for Upper Precambrian deposits of the section of Upper Precambrian (Riphean and Vendian) Baikal–Patom Highland as well as geological maps deposits is exposed in the marginal zone of the and establishment of the most complete and best dated Baikal–Patom Highland. This section comprises six Vendian reference section for the region under consid successive stratigraphic units (from the base upward): eration. The section of the Ura uplift which is almost Purpol, Medvezhii, Ballaganakh, Dal’nyaya Taiga, entirely composed of Vendian rocks was proposed to Zhuya, and “Yudoma” groups, or horizons (Dol’nik, serve as such a standard (Chumakov, 2011b). 2000). Until recently, most researchers included only The transverse Ura uplift complicates the north the Zherba and Tinnaya formations of the Patom eastern margin of the Patom fold arc. It begins near the region in the Vendian (Keller et al., 1967; Ivanov et al., Bol’shoi Patom River mouth and extends northward, 1995; Pelechaty, 1998); some of them attributed to the crossing the Lena River between mouths of the latter also the overlying Nokhtuisk Formation Dzherba (Zherba) and Malyi Patom rivers (Fig. 1). (Dol’nik, 2000). Many researchers united these for The uplift consists of four wide en echelon arranged mations into a larger unit, terming it by analogy with northeast extending anticlinal folds. In the Late Pre the Uchur–Maya region as the Yudoma complex or cambrian, the Ura uplift together with adjacent areas Yudomian (Opornye…, 1972; Khomentovskii, 2008), was a constituent of the southern passive margin of the Yudoma Horizon (Dol’nik, 2000), or Yudomian Siberian Platform. Its Vendian deposits are repre regional stratigraphic horizon (Stanevich et al., 2006, sented by nonmetamorphosed facies deposited on the 2007). shelf and upper part of the continental slope. Recently obtained biostratigraphic, chemostrati Owing to good exposition, relatively simple tec graphic, and isotopic geochronological data showed tonic structure, and easy accessibility, the Vendian sec that the Zherba and Tinnaya formations are correlative tion of the Ura uplift is well known with its stratigraphy only with the upper part of the Yudoma Group type being progressively upgraded and specified (Fig. 2). At section in the Uchur–Maya region (Semikhatov et al., present, the stratigraphic scale developed for this sec 2004) and, correspondingly, with the upper layers of tion is accepted by almost all researchers, who are the Vendian section in the East European Platform anonymous in admitting the nomenclature of defined and that the two upper groups of the Patom Complex formations and groups. At the same time, the age of its (Zhuya and Dal’nyaya Taiga) underlying the Zherba rocks has remained debatable until now. At the first Formation should also be attributed to the Vendian. stage of investigation of the region, they were attrib Such a conclusion radically changes the age interpre uted to the Upper Proterozoic (Obruchev, 1939; etc.), tation of the Upper Cambrian section in the region Lower Cambrian (Starostina, 1935), or Upper Prot and present day views on the geological history of the erozoic–Lower Cambrian (Chumakov, 1956, 1959). Baikal–Patom Highland and adjacent segments of the Subsequently, on the basis of finds of microphytolites Siberian Platform. This insistently called for correc and stromatolites (Zhuravleva et al., 1961, 1969;
359 360 CHUMAKOV et al.
116°30′ 117°00′ 117°30′ E 01020 km 1
. R
a 2 r U Le a na R. 3
b 4 60°20′ c N Bol ’ s 5 h o i P a to 6 m Chapaevo R .; 7
60°00′ 8
d L e na 9 R .
Fig. 1. The schematic geological map of the Ura uplift. (1–3) Paleozoic–Mesozoic sediments: (1) Jurassic, (2) Ordovician, (3) Cambrian; (4–7) Vendian sediments: (4) Tinnaya and Zherba formations, (5) Chenchen and Nikol’skoe formations, (6) Kalancha, Ura, and Barakun formations, (7) Bol’shoi Patom Formation; (8) Riphean sediments: Mariinskaya and Bugarikhta formations; (9) principal faults. Anticlinal folds: (a) Zherba, (b) Ura, (c) Ulakhan–Iligir, (d) Zhedai.
Dol’nuk, 1982, 2000), the two upper groups of the researchers suggested that the two upper groups of the Patom Complex (Dal’nyaya Taiga and Zhuya) were Patom Complex (Dal’nyaya Taiga and Zhuya) belong assigned to the Middle and Upper Riphean, respec to the Vendian (Sovetov, 2002). This opinion was sub tively (Resheniya…, 1963; Keller et al., 1967; Chuma stantiated by chemostratigraphic investigations of kov and Semikhatov, 1981; Chumakov, 1993; etc.). these deposits and their platform analogs (Pokrovskii Later, some geologists began correlating the Dal’nyaya et al., 2006), the find of the diverse assemblage of Per Taiga Group with the Middle and Upper Riphean tatataka type acanthomorphic acritarchs in the Ura (Ivanov et al., 1995; Dol’nik, 2000). On the basis of Formation correlated with the upper part of the historical–geological and, partly, biostratigraphic Dal’nyaya Taiga Group (Chumakov et al., 2007; data, some researchers attributed the Dal’nyaya Taiga Vorob’eva et al., 2008a; Golubkova et al., 2010), U–Pb and Zhuya groups to the upper part of the Upper isotopic dating of detrital zircons from metamor Riphean and included them in a new autonomous phosed stratigraphic analogs of this formation (Meffre Upper Precambrian unit, i.e., Baikalian (Khomen et al., 2008), and correlation with other Vendian and tovskii et al., 1998; Khomentovskii and Postnikov, Ediacaran sections (Chumakov, 2011). 2001; Khomentovskii, 2002). In fact, despite these disagreements, most researchers shared up to the beginning of the 21st century the opinion that the VENDIAN DEPOSITS OF THE URA UPLIFT Patom Complex belongs to the Riphean, while the The Upper Precambrian rocks constituting the Ura Vendian includes only the Zherba and Tinnaya forma uplift are divided into four groups (from the base tions, which are sandwiched between the Zhuya upward, Fig. 3): Ballaganakh, Dal’nyaya Taiga, Group and Lower Cambrian section. Zhuya, and Yudoma (Yudoma Horizon). The oldest, The revision of widely accepted views on age of Ballaganakh Group, underlies sequences that may be deposits under consideration started in the current attributed to the Vendian. The upper part of the Balla century. First, on the basis of paleotectonic recon ganakh Group crops out in the core of the southern structions and correlation of remote sections, some most (Zhedai) anticlinal fold. In the section exposed
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 VENDIAN REFERENCE SECTION OF SOUTHERN MIDDLE SIBERIA 361 cha Ura Kalan
patom Valyukhta Bol’shoi Barakun
Bugarikhta Mariinskaya
VERSTNYI NAKH
A’YY AG ZHUYA TAIGA DAL’NYAYA
TREKH BALLAGA
1 1
4
Reference section 1 2–3 Є V
V V
3 ? R VENDIAN n; (V) Vendian. Names of eras, n; (V) Vendian. cha Ura
kukan Zherba Zherba Tinnaya Tinnaya Valyukhta Dzhem Barakun
Nokhtuisk
Nikol’skoe Nikol’skoe Bugarikhta
Mariinskaya
NAKH
A’YY AG ZHUYA TAIGA DAL’NYAYA YUDOMA BALLAGA
1
UPPER RIPHEAN UPPER 2–3 Є VENDIAN R Stanevich et al., 2007 Ura ) Cambrian; (Sn) Sinian; (R) Riphea Є Kalancha Kalan
Barakun Nikol’skoe Valyukhta Bugarikhta Zherba
Mariinskaya Tinnaya
Dzhemkukan
Nokhtuisk Nokhtuisk
NAKH DAL’NYAYA TAIGA DAL’NYAYA
ZHUYA
BALLAGA 2001 AAINBIAINYUDOMIAN BAIKALIAN MAYANIAN
1 1
UPPER RIPHEAN UPPER Є VENDIAN to different authors. ( Khomentovskii and Postnikov, Barakun Valyukhta
Chenchen Chenchen Chenchen Chenchen Bugarikhta Zherba Nikol’skoe
Tinnaya Mariinskaya Dzhemkukan
GANAKH
A’YY AG ZHUYA TAIGA DAL’NYAYA BALLA Ura uplift area according
Ivanov et al., 1995
3 2–3 2 VENDIAN R R R Є byt Ura nakh kukan Dolgii Kulleka Ballaga Dzhem
Kalancha Maldoun Kholych;
Khalatar Shumikha Nokhtuisk Nikol’skoe
Ust Patom
Mariinskaya
3 3 2 2 2 2 KUN PATOM Sn PATOM PATOM Sn Sn Sn Sn Sn
are denoted in capital letters. AYKT HY MACHINO ZHUYA VALYUKHTA BOL’SHOI MALYI MALYI
Variegated Nokhtuisk BARA Bobrov, 1964 SINIAN (RIPHEAN) SINIAN nakh kukan Zherba Yuedei Tinnaya Alyanch Dzhem Ballaga Barakun
Kholych
Valyukhta
Nikol’skoe
Mariinskaya COMPLEX
MDL UPPER MIDDLE
ЄЄ YUDOMA 1961, 1969 Stratigraphy of Upper Proterozoic sections in the
PALEOZOIC SINIAN) (RIPHEAN, PRECAMBRIAN UPPER Zhuravleva et al., systems, groups, and horizons Fig. 2.
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 362 CHUMAKOV et al.
–10 –5 0 5 1 Є1 Nokhtuisk 13
14
Tinnaya 15 220–340 m 16
Tirbees 17 Zherba 18 350 m
19 0.7086 Chenchen 20 400–500 m 0.7079 0.7080 0.7079 21 Nikol’skoe 150–400 m 22 <647 23 Kalancha 400 m 24
25
26 Ura 0.7077 450–500 m
upper 250–500 m 0.7073 middle 200–300 m
Barakun lower 200–400 m c d DAL’NYAYA TAIGA ZHUYA; TREKHVERSTNYI
<1850 –10 –5 0 5 1 <642 7 Bol’shoi Patom 900–1100 m 2 0.7077 8
3 0.7086 9
4 10
5 11 BALLAGANAKH >1200 m c d 6 12
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 VENDIAN REFERENCE SECTION OF SOUTHERN MIDDLE SIBERIA 363 in this area, micaceous feldspar–quartz sandstones kan Formation, Bol’shaya Chuya River) of the Patom (apparent thickness approximately 900 m) are overlain Highland. by fine grained gray limestones alternating with sand Complete sections of the Bol’shoi Patom Forma stones (approximately 300 m). By their stratigraphic tion are confined to the eastern and western limbs of position and lithology, the Ballaganakh sandstones the southern (Zhedai) anticlinal fold that complicates and limestones are correlated with the upper part of the structure of the Ura uplift. These sections are the Bugarikhta Formation and the Mariinskaya For located at the left bank of the Bol’shoi Patom River 4– mation of the Ballaganakh Group in southerly areas, 6 and 13–15 km away from its mouth, respectively. respectively. According to different estimates, the age The first of these sections, where the formation is of the Ballaganakh Group varies from Middle Riphean approximately 1000 m thick, is selected to serve as the (Keller et al., 1967; Ivanov et al., 1995; etc.) to Late reference one (Chumakov and Krasil’nikov, 1991); in Riphean (Khomentovskii and Postnikov, 2001). The the second section, the formation thickness is reduced last viewpoint is now supported by high δ13С values to 900 m. ranging from +5 to +8‰ in carbonates from the The Bol’shoi Patom Formation is largely com Mariinskaya Formation (Pokrovskii et al., 2006). Such posed of massive and bedded diamictites, gradational a high positive δ13С anomaly in the Late Precambrian to, less commonly, cross bedded sandstones, and lam is characteristic of the second half of the Late Riphean inated to rhythmically bedded siltstones locally with (Halverson and Shields Zhou, 2011). scattered rock fragments (dropstones) and tillite pel The Dal’nyaya Taiga Group in the Ura uplift con lets. The upper part of the formation contains isolated sists of four conformably occurring formations (from layers and lenses of calcarenites and dolarenites. the base upward): Bol’shoi Patom, Barakun, Ura, and Diamictites consist of a dark to locally black silty– Kalancha (Fig. 3). sandy matrix (85–97% of the rock volume) with scat tered variable rounded pebble sized to large boulder The Bol’shoi Patom Formation was defined by Sta sized rock fragments. Some of these rock fragments а rostina (1935) as a unit Сm1 and named in 1941 by exhibit subparallel variably sized striation. They are A.A. Predtechenskii in his unpublished work. The characterized by relatively uniform lithology being name “Bol’shoi Patom” was repeatedly used for this dominated both quantitatively and volumetrically by unit in different publications (Chumakov, 1959, 1993; variable gneissose granitoids (gray biotite granites and Chumakov and Semikhatov, 1981; etc.). In the unified granosyenites, 45–65% of fragments) and muscovite stratigraphic regional scale, this formation was incor and bimicaceous gneisses (20–35%). They are accom rectly termed as the Dzhemkukan Formation, which panied by subordinate dark gray limestones, dolo violated rules recommended by the Stratigraphic mites, quartzites, rare crystalline schists, and meta Code for identification of formation units. Despite morphosed basic rocks (Chumakov and Krasil’nikov, this violation, the name “Dzhemkukan Formation” is 1991; Chumakov et al., 2010). Some massive diamic widely used in the literature and in practice. The lower tites demonstrate mostly longitudinal and subordinate contact of the Bol’shoi Patom Formation in the Ura transverse orientation of elongated fragments resem uplift is unobservable. Nevertheless, there are grounds bling the glacial one (Lungershausen, 1963; Chuma to believe that it rests conformably upon the Ballaga kov and Krasil’nikov, 1991). nakh Group, since it encloses intercalations of dolo The lower half and upper fourth of the Bol’shoi mitic breccias with rock fragments litholohgically sim Patom Formation are dominated by massive and bed ilar to dolomites of marginal facies from the Mariin ded diamictites with subordinate sandstone layers and skaya Formation. Erosional contacts marked by such lenses. These sediments were likely deposited by gla breccias are also observed at the bases of stratigraphic ciers that rested on the basin bottom and by floating and facies analogs of the Bol’shoi Patom Formation shelf glaciers. The middle part of the formation exhib on both the eastern flank (Nichatka Formation, its frequent alternation of gradational–bedded diam Bogouyukhta River) and the western flank (Dzhemku 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 trisulcatus Zone 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 ~ 1 dolomite; (25) oolitic limestone; (26) stromatolitic limestone and dolomite. (C1 ) Tommotian Stage of the Lower Cambrian. Names of groups are given in capital letters.
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 364 CHUMAKOV et al. ates, which fill erosional valleys. These sediments terized by oscillations, near glacier basins accumu characterize underwater fans of glacial rivers. The lated intermittently detrital dolomites, the first pre lithology of rock fragments and the cross bedding pat cursors of distal cap dolomites. terns in sandstones suggest that detrital material was The Barakun Formation in sections of the Ura transported to the Bol’shoi Patom basin from the Sibe uplift consists of alternating members largely com rian Platform mainly owing to erosion of crystalline posed of dark limestones and black shales. Some lime rocks of the basement and partly the sedimentary Bal stone members include shale intercalations, while laganakh Formation (Chumakov and Krasil’nikov, shale members are usually intercalated by limestones. 1991). U–Pb age estimates obtained for detrital zircon Extended outcrops of the formation are relatively rare from sandstones alternating with massive diamictites and represented by limestones. In the Ura uplift, the confirm this inference (Chumakov et al., 2011b). On Barakun Formation is divisible into three subforma the curve of the relative age probability, most of these tions: lower and upper mostly limy and middle mainly zircons fall into the Archean (from 3200 to 2500 Ma shaly (Chumakov, 1959; Ivanov et al., 1995; Kokoulin, with the maximum at 2700 Ma) and Early Proterozoic 1998; etc.). Bobrov (1964) proposed to consider these (from 2400 to 1850 Ma with distinct maxima at 1850 subformations as autonomous formations (Fig. 2), and 1950 Ma) intervals. although this suggestion was disfavored. The prevalence of diamictites (including their mas The lower Barakun Subformation. The lower con sive varieties with glacial orientation of rock fragments tact of the Barakun Formation is observable in the and bedded varieties) and the presence of erratic frag western limb of the Ura anticline on the right side of ments of crystalline rocks, dropstones, tillite pellets, the Ura River downstream of the Voron Rapids. In this striated and grooved boulders—all these features indi area, the upper layer of bedded diamictites of the cate glacial and glaciomarine origin of rocks constitut Bol’shoi Patom Formation is overlain by inequigranu ing the Bol’shoi Patom Formation. Typical cap dolo lar sandstones 0.5–0.8 m thick with rare pebbles, mites resting upon the Bol’shoi Patom Formation sup which grade upward along the section into a thin layer port this conclusion. The glacial genesis of the of silty fine grained poorly consolidated sandstones formation is also confirmed by its reliable correlation (Chumakov and Krasil’nikov; Chumakov et al., 2011). with glacial sediments of the Nichatka Formation, They in turn give way to a peculiar member of dark which includes typical tillites and lacustrine and flu gray laminated and rhyrthmically bedded calcareous vioglacial sediments, in addition to glaciomarine dolomites with the apparent thickness of approxi facies (Chumakov, 1993, 2011a). The carbonate con mately 6 m. Lamination of these rocks is determined stituent of calcareous sandstones occurring among by alternation of dark and lighter micritic and pelletic diamictites in the upper part of the Bol’shoi Patom laminae from fractions of a millimeter to 1 mm thick. Formation is characterized by δ13С values ranging Dolomites include rare small quartz and feldspar clasts from –5.9 to –8.8‰ (V PDB), while carbonate boul and an admixture of clay minerals (insoluble residue ders, pebbles, and dolarenites from diamictites (nine varies from 7 to 13%). Weathered surfaces of dolomites samples) demonstrate significant scatter of δ13С values are usually light yellow. Regular lamination of dolo varying from –6.5 and –5.1 to +5‰ with prevalence mites is locally complicated by small (up to 0.5 m of small negative and positive values: from– 0.9 to across) asymmetrical intrastratal anticlinal folds with +2.2‰ (Pokrovskii et al., 2010). The presence of detachments in hinges (Fig. 4). In the literature, such three groups of carbonate rock fragments with sharply textures are called teepees. The texture and fine rhyth different δ13С values undoubtedly suggests different mical lamination of dolomites, negative isotopic car provenances during the Bol’shoi Patom glaciation. For bon composition (δ13С varies from –4.2 to –3.5‰), example, the presence of rock fragments with consid and very high 87Sr/86Sr ratios amounting to 0.71597– erable positive δ13С values indicates erosion of the 0.71690 (Pokrovskii et al., 2006, 2010) are typical of Mariinskaya Formation. The measurement of the cap dolomites, which crown many Neoproterozoic 87Sr/86Sr ratios in a single boulder of dolomitic lime glacial formations (Chumakov, 1978, 1992; Fairchild stone from the Bol’shoi Patom Formation yielded the and Hambrey, 1984; Pokrovskii et al., 2006, 2010; value of 0.70747 with the δ13С value being equal to – etc.). Small outcrops and debris of cap dolomites at 5.1‰ (Pokrovskii et al., 2010). It is conceivable that the base of the lower Barakun Subformation are also these isotopic ratios indicate sediment reworking dur recorded in the eastern limb of the Ura anticline on ing deposition of the formation. In two beds of detrital the left side of the Ura River 1 km downstream of the dolomites (dolorudites and dolarenites) occurring in Ulakhan Iligir River and along the right bank of the the upper part of the Bol’shoi Patom Formation, the Lena River in the northeastern limb of a pericline of values of the 87Sr/86Sr ratio appeared to be very high, the Zhedai anticline 3.5 km downstream of the being 0.71451 and 0.71480, respectively, which is very Chapaevo Settlement, where their apparent thickness close to the 87Sr/86Sr ratios typical of many cap dolo is approximately 10–15 m. mites, including varieties overlying this stratigraphic The wide distribution of cap dolomites and their unit (Pokrovskii et al., 2010). Such a similarity likely genesis have received much attention for a long time implies that, during deglaciation, which was charac (Fairchild and Kennedy, 2007 and references therein).
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 VENDIAN REFERENCE SECTION OF SOUTHERN MIDDLE SIBERIA 365
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).
Judging from several features, cap dolomites were which are distinctly detrital in origin. They are fre deposited in periglacial basins during postglacial quently represented also by algal, microphytolitic, and transgressions under intense continental drainage oolitic varieties with siliceous concretions. Some caused by deglaciation. The detailed geochemical limestone layers exhibit underwater slumping struc characterization of the Barakun cap dolomite is avail tures accompanied by carbonate breccias. The share of able in (Pokrovskii et al., 2010). shales, which form in the lower part of the formation In the Ura River area, the cap dolomites of the rare thin intercalations, increases upward along the lower Barakun Subformation are replaced upward section to constitute a uniform member up to 20 m along the section by dark clayey limestones and calcar thick at its top. The total thickness of the lower subfor eous shales (several tens of meters thick) overlain in mation of the Barakun Formation is estimated to turn by dark bedded fine grained locally pyritized cal range from 200 m (Chumakov, 1959) to 400 m careous polymictic sandstones approximately 100– (Bobrov, 1964). 120 m thick with thin siltstone and mudstone mem During deposition of the lower subformation of the bers. One of these members 150 m above the base of Barakun Formation, the provenances were evidently the formation outcropping on the left side of the Ura slightly different as compared with their counterparts River 670 m downstream of the Ulakhan Iligir River in the Bol’shoi Patom time: mainly Archean shields mouth yielded impressions of Vendian fossils Beltanel were eroded. This is evident from U–Pb age of detrital loides sorichevae (Leonov and Rud’ko, 2012). The zircons from sandstones of the lower Barakun Subfor overlying largely carbonate part of the lower subforma 1 tion of the Barakun Formation crops out on the left mation in the Ura River section. On curves of the rel side of the Bol’shoi Patom River 4 km downstream of ative age probability compiled for Barakun detrital zir the Dzherbedyanka River mouth. The subformation is 1 The data were obtained by I.N. Kapitonov and analysts from the mostly composed of dark gray to black fine grained ICP–MS group of the All Russian Institute of Geology dolomitic laminated and platy limestones, some of (VSEGEI, St. Petersburg.
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 366 CHUMAKOV et al. cons, its maxima are dated at 2900 and 2500 Ma, while decreases to zero values. Higher in the section, the the number of zircons with Early Proterozoic ages δ13C value rapidly increases to reach +8.1‰ in the appeared to be insignificant as compared with the middle part of the lower Barakun Subformation. Bol’shoi Patom Formation (Chumakov et al., 2011b). Higher, almost to the top of the Barakun Formation, Zircons from the lower subformation of the Barakun 13 13 the δ C value remains uniformly high: δ Caver = Formation with discordance exceeding 10% form a 6.5 ± 1‰ (n = 13). According to five measurements, trend, which indicates, in the opinion of I.N. Kapi the minimum 87Sr/86Sr value in the Barakun Forma tonov, that some zircon grains were likely influenced tion is 0.70727 (Pokrovskii et al., 2006) and that in the 650 ± 300 Ma ago by an event that disturbed their lower part of the formation (one measurement) is U ⎯ Pb isotopic system. This could have been strati 2 form intrusion of gabbro–dolerites near the contact 0.70776 (Pokrovskii et al., 2010). between the Bol’shoi Patom and Barakun formations. The Ura Formation rests conformably upon the The middle Barakun Subformation is largely com Baraklun Formation and is largely composed of silt posed of black siltstones and mudstone shales with stones and mudstones with subordinate intercalations rare thin intercalations and occasional members of and members of dolomites and limestones (Kolosov, coarse to fine grained black thin bedded and platy 1975; Kokoulin, 1998). Its most complete section is limestones with beds of black dolomitic limestones, documented at the southern pericline of the Zherba lenses of limestone breccias, and thin breccia hori anticline in the lower reaches of the left Lena River zons. These rocks include subordinate rare beds of tributary along the Ulakhan Muostakh Creek, where it black calcareous fine grained sandstones. The upper was defined as the lower Valyukhta Subformation by 170 m of the subformation are relatively well exposed some researchers (Zamaraev, 1984). In this area, the on the right side of the Bol’soi Patom River in its basal part of the Ura Formation is represented by a mouth area opposite Khatyng Aryy Island. The sub 300 m thick sequence of siltstones and mudstones formation thickness is estimated to range from 200– with intercalations of black to dark gray dolomites 250 m (Kokoulin, 1998) to 300 m (Chumakov, 1959). overlain by breccias of carbonate rocks 200 m thick. A The upper Barakun Subformation. In the Khatyng slightly different section is observed in the Ura River Aryy Island area, shales of the middle Barakun Sub basin. Its lower part (approximately 70 m) exposed on formation are overlain by a thick (approximately the right side of the Ura River 2.5 km downstream of 400 m) sequence of black limestones of the upper Bar the waterfall (23 km from the Ura River mouth) is rep akun Subformation. These rocks are represented by resented by gray and black siltstones and calcareous platy thin bedded fine grained varieties with interca shales frequently (fractions of a meter) alternating lations of clayey and dolomitic limestones and with limestones and their clayey varieties. Limestones coarse grained limestones intercalated by thin lami are frequently characterized by detrital texture, oolite nae of calcareous shales. The remarkable feature of fragments, and underwater slumping deformations. the subformation is intrastratal limestone conglomer This part of the Ura Formation is underlain by a 10 to ates and 10 to 20 m thick lenses of breccia conglom 12 m thick bed of carbonate breccia conglomerate erate with underwater slumping structures. They con belonging most likely to the Barakun Formation. The sist of subangular deformed fragments of carbonate upper contact of the Ura Formation is observable on rocks and subrounded olistoliths of limestones and 2 The δ13C and 87Sr/86Sr values cited in this work were obtained dolomites cemented by calcareous shales. The thick for Vendian sequences of the Ura uplift by analyzing carbonate ness of the subformation is estimated to be 250 m phases of samples without accounting for geochemical preserva (Kokoulin, 1998) or 500 m (Chumakov, 1959). tion criteria of C and S isotopic systems in carbonate rocks (Mn/Sr and Fe/Sr ratios and δ18O value). The main agents It is difficult to determine the total thickness of the responsible for distortion of systems in carbonates are repre Barakun Formation in the Ura uplift because of its sented by meteoric water and low temperature epigenetic fluids, which are enriched, as compared with seawater, in Mn, Fe, and poor exposition, which explains discrepancies in esti 12 mates obtained by different researchers. In our opin C originating from associated siliciclastic sequences and char acterized also by an elevated 87Sr/86Sr value, decreased Sr con ion, the most realistic estimate is 1100–1200 m. centration, and reduced δ13C and δ18O values (Brand and δ13 87 86 Veizer, 1980; Derry et al., 1992; Denison et al., 1994; Knoll et The C and Sr/ Sr values determined in the al., 1995; Gorokhov et al., 1995; Kuznetsov et al., 2006, 2012). Ura uplift for the Mariinskaya, Bol’shoi Patom, and It should be emphasized that the curves of changes in the δ13C Barakun formations and overlying carbonates of the value obtained by B.G. Pokrovskii and colleagues are similar in Dal’nyaya Taiga and Zhuya groups (Pokrovskii et al., their amplitude variations and character of changes to curves 2006, 2010) serve as a basis for the chemostratigraphic available for global standard Upper Precambrian sections: in the Doushantuo and Dengying formations of South China (Zhou et characteristic of the proposed Vendian reference sec al., 2007; Zhou and Xiao, 2007) and in eastern and northern tion and are of significance for determining the age of Oman (Brasier et al., 2000; Leather et al., 2002; Le Guerroue, these rocks and regional correlations. As was men 2010). Moreover, the 87Sr/86Sr values obtained by Pokrovskii δ13 and colleagues for the Zhuya Group correspond quantitatively tioned, the C value in basal cap dolomites of the to ratios determined for the same rocks using the above men lower Barakun Subformation varies from –4.2 to tioned geochemical preservation criteria of isotopic systems ⎯ 3.5‰; in overlying limestones, this parameter (Gorokhov et al., 1995; Pelechaty, 1998; Melezhik et al., 2009).
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 VENDIAN REFERENCE SECTION OF SOUTHERN MIDDLE SIBERIA 367 the right side of the Ura River and its valley slope 3.0– m 3.3 km from the mouth. The upper part of the Ura 43 Formation (approximately 30– 35 m thick) is com 42 posed of peculiar gray to greenish gray siltstones inter calated by subordinate thin (fractions of a meter) gray 41 and black limestones with inclusions of coarse grained 40 varieties and thin bedded siltstones (Fig. 5). South of 39 the Ura uplift, the Ura Formation is replaced by dark gray to black shales, which are attributed to the lower 38 part of the Valyukhta Formation. The total thickness 37 Kalancha Formation of the Ura Formation in these sections is 400–500 m 36 (Bobrov, 1964, 1979; Zamaraev, 1984; Kokoulin, 35 1998). 1 34 In the section located on the right side of the Ura 33 2 River 3 km from its mouth, thin bedded siltstones Ura 32 occurring 30–35 m below the top of the Ura Forma Formation tion yielded a diverse Ediacaran assemblage of acanth 31 3 omorphic palynoflora or assemblage of Pertatataka type acanthomorphic acritarchs found at four levels 30 4 (Faizullin, 1998; Nagovitsin et al., 2004; Chumakov et 29 al., 2007; Vorob’eva et al., 2008a; Golubkova et al., 28 5 2010; Sergeev et al., 2011; Moczydlowska and Nago 27 vitsin, 2012). The analysis of all the mentioned works 6 reveals the following valid taxa of capriciously shaped 26 acanthomorphic, sphaeromorphic, and netromorphic 25 7 acritarchs and presumable remains of cyanobacteria in 24 the Ura microbiota: Ancorosphaeridium magnum Ser geev et al., 2011; A. minor Sergeev et al., 2011; 23 8 A. robustum Moczydlowska et Nagovitsin, 2012; 22 9 Appendisphaera tenuis Moczydlowska et al., 1993; 21 A. tabifica Moczydlowska et al., 1993; Archaeot enuisphaeridium cf. fimbriatum Grey, 2005; Asseserium 20 fusulentum Moczydlowska et Nagovitsin, 2012; 19 A. piramidalis Moczydlowska et Nagovitsin, 2012; 18 (Kolosova, 1991); Cavaspina acuminata C. basiconica 17 Moczydlowska et al., 1993; C. uria (Nagovitsin et Fai zullin, 2004); Ceratosphaeridium cf. glaberosum Grey, 16 2005; Densisphaera arista Moczydlowska et Nago 15 vitsin, 2012; D. fistulosa Moczydlowska et Nagovitsin, 14 2012; Eotylotopalla cf. delicata Yin, 1987; E. strobilata (Faizullin, 1998); Knollisphaeridium maximum (Yin, 13 1987); Labruscasphaeridium sp., Multifronsphaeridium 12 ramosum Moczydlowska et Nagovitsin, 2012; Schizo 11 fusa zangwenlongii Grey, 2005; ?Sinosphaera rupina Zhang et al., 1998; Tanarium anozos Willman, 2008; 10 T. conoideum Kolosova, 1991; T. digitiformum (Nago 9 vitsin et Faizullin, 2004); T. muntense Grey, 2005; 8 T. tuberosum Moczydlowska et al., 1993; Urashaera capitalis Moczydlowska et Nagovitsin, 2012; Variom 7 6 5 Fig. 5. Section of the upper part of the Ura Formation and 4 lower part of the Kalancha Formation. Right bank of the Ura River 3 km upstream of the mouth (according to 3 M.V. Leonov, S.V. Rud’ko, and N.M. Chumakov). 2 (1) Gray limestone; (2) black anthraconitic limestone; (3) siltstone and mudstone; (4) underwater slumping tex 1 tures; (5) casts of erosion scours; (6) small scale lenticular bedding; (7) stratiform stromatolites; (8) cone in cone textures; (9) finds of acritarchs of the Ura assemblage.
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 368 CHUMAKOV et al. argosphaeridium floridum Moczydlowska et Nago nating gray and yellowish dolomites and black locally vitsin, 2012; Leiosphaeridia spp.; Gen et sp. indet.; stromatolitic limestones. Segmentothallus aff. S. asperus Hermann, 1989; Rug Stromatolites observable in the Kalancha Forma osoopsis tenuis Timofeev et Hermann, 1979; Bul tion are represented by two taxa: (1) endemic form latosphaera velata Vorob’eva et al., 2009; Aimia aff. species, which was erroneously, in the opinion of one A. gigantica Hermann; Ceratophyton sp.; Polytry of the authors of this work, attributed in (Dol’nik, choides lineatus Hermann, 1974; Digitus fulvus Pjatile 2000) to the form genus Baicalia distributed in the tov, 1980; Obruchevella cf. Cucumiforma sp.; Siphono Middle and Upper Riphean sections; (2) stratiform phycus spp.; unnamed filamentous microfossils; species Stratifera sarmensis that occurs in southern unnamed forms 1–5. Siberia both in the Kalancha Formation and in the This list includes also species from (Moczydlowska upper part of the Uluntui Formation of the Baikal and Nagovitsin, 2012), where these authors formally region, which is attributed to the Vendian according to revised several taxa previously known from the Ura Sr isotope chemostratigraphic data (Kuznetsov et al., Formation and described a group of new genera and 2012). species, which may be considered as valid until the The thickness of the Kalancha Formation in the next revision of the Ura microbiota. At the same time, Lena River section is approximately 500 m Moczydlowska and Nagovitsin (2012) regarded, with (Opornye…, 1972; Kolosov, 1975, 2000). South and out any explanations, some taxa described in (Sergeev southeast of the Ura uplift, carbonate rocks of the et al., 2011) such as Bullatosphaera velata and Animia Kalancha Formation are rapidly replaced by a shaly aff. A. gigantica as taxonomic artifacts and identified in sequence, which constitutes the upper part of the Valy the Ura Formation, also without any grounds, Miro ukhta Formation and is widespread in southerly areas edichia lobata and Trachyhystrichosphaera aimica of the Patom Highland. Therefore, the Kalancha For (Nagoitsin et al., 2004), which were rejected for the mation in sections under consideration was defined by Ura biota in (Sergeev et al., 2011) in accordance with some researchers as the upper and middle Valyukhta all formal principles of the paleontological nomencla subformations (Zamaraev, 1984). ture. Therefore, references to the presence of Miroedi δ13 chia and Trachyhystrichosphaera in the Ura Forma The С values in Kalancha limestones decrease tion cannot be accepted on the basis of either morpho upward along the section of the formation from logical or purely formal criteria. As for new taxa +5.1‰ at the base of this unit to +2.0‰ near its top described by M. Moczydlowska and K. Nagovitsin, (Pokrovskii et al., 2006). the peculiar morphotype Urasphaera capitalis The Zhuya Group is well exposed in several rocks undoubtedly deserves to be identified as a new genus on both sides of the Lena River between the Zherba and species. Other taxa described in (Moczydlowska River mouth and Macha Settlement. The almost com and Nagovitsin, 2012) are questionable and reflect to a plete section of the group crops out in the Kharchagai considerable extent subjective views of the authors on (Kholych) Rock between the Daban Spring and village the taxonomic significance of features in the consid of Tinnaya on the left side of the Lena River. The ered morphotypes. The biostratigraphic analysis of the Zhuya Group consists of two conformably occurring Ura microbiota is presented in the next section dedi formations: Nikol’skoe (lower) and Chenchen cated to the age assessment of lithostratigraphic units (upper). including the Dal’nyaya Taiga Group. The Nikol’skoe Formation in its basal part is repre Most of the Ura limestones are characterized by sented in some sections by a member of gray polymic elevated δ13С values ranging from +3.6 to +5.9‰ tic medium to fine grained sandstones and siltstones. (usually +5.1 to +5.9‰. Only a thin member at the It is from 50 to 80 m thick and crops out on the left side base of the formation yields δ13С values of approxi of the Lena River near the Daban Creek mouth and in mately –0.1‰ (Pokrovskii et al., 2006, 2011). the lower reaches of the Ura River. In the latter area, According to the same authors, the minimum the basal part of this member is composed of cross 87Sr/86Sr value in carbonates of the Ura Formation bedded partly gravely sandstones with a thin layer of averaged for five samples is 0.7077. carbonate breccia cemented by sandy ferruginate The Kalancha Formation that crowns the section of material at its base that indicates an insignificant sedi the Dal’nyayaTaiga Group is mostly composed of car mentation break. Sandstones sampled from the Ura bonate rocks with siltstone intercalations in the lower River section 2 km upstream of its mouth yielded part. The formation is well exposed on the left side of detrital zircons. Grains of their youngest generation the Lena River (Kalancha Rock and Dolgii Range) form a cluster in concordia with U–Pb age of 646.9 ± and on the left slope of the Ura River valley near its 3.4 Ma (Chumakov et al., 2011a). mouth. The lower part of the formation is dominated Laterally, the member under consideration rapidly by dark gray to black fine grained stromatolitic, changes its lithology and thickness. In some outcrops, microphytolitic, and oolitic limestones, while its for example, on the right side of the Lena River 6 km upper part, which was suggested by some geologists to downstream of the Daban Creek mouth, basal sand be defined as the Dolgii Formation, consists of alter stones of the formation pinch out and its base is
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 VENDIAN REFERENCE SECTION OF SOUTHERN MIDDLE SIBERIA 369 marked only by a thin (2 cm) layer of clayey gravel onstrates intraformation erosional surfaces and tex stones (Bobrov, 1979). Some researchers described the tures of sediment dehydration (teepees; Pelechaty, basal sand–silty member of the Nikol’skoe Formation 1998). It is likely that deposition of the dolomitic as the autonomous Kulleka Formation (Bobrov, 1964, member of the Chenchen Formation was preceded by 1979; Kolosov, 1975). a sedimentation break, which is evident from distinct The overlying part of the Nikol’skoe Formation is erosional features at the base of the analogous dolo composed of frequently alternating variegated thin mitic member at the Molbo and Zhuya rivers located bedded siltstones and marlstones with subordinate beyond the Ura uplift. These features and increase in intercalations of pinkish and gray limestones, the the grain size composition and share of detrital rocks quantity of which rapidly increases upward along the in the upper part of the formation distinctly indicate section, reaching a maximum near its upper boundary. rapid shoaling of the Chenchen basin at its terminal The thickness of the Nikol’skoe Formation varies development stage. from 120–150 m in the upper reaches of the Ura River The thickness of the upper Chenchen Subforma (Kokoulin, 1998) to 220–250 m in the lower courses tion varies from 200–250 m at the Lena River (Chu of this river (Chumakov, 1959; Kokoulin, 1998) and makov, 1959; Zamaraev, 1984; Kokoulin, 1998) to 200–360 m at the Lena River (Opornye…, 1972; 350–450 m at the Bol’shoi Patom River (Chumakov, Kolosov, 1975). 1959; Melezhik et al., 2009). The total thickness of the Limestones of the Nikol’skoe Formation demon Chenchen Formation in the Ura uplift is estimated to strate a considerable negative anomaly ofδ13С values, range from 400–600 m at the Lena River (Opornye…, which decrease from –6.7‰ at the base of the forma 1972; Zamaraev, 1984; Kokoulin, 1998; Kontorovich, tion to –13.5‰ in its middle part. According to (Gor 2005) to 800–1200 m in southerly areas (Chumakov, okhov et al., 1995), the 87Sr/86Sr value derived from 1959; Zamaraev, 1984; Melezhik et al., 2009). eight determinations in three samples varies from Stromatolites contained in the Chenchen Forma 0.70831 to 0.71057; the upper part of the formation tion are represented by endemic forms attributed to yielded its minimum value averaged for six samples: form genera Katavia and Inzeria (Dol’nik, 1982, 2000) 87Sr/86Sr = 0.70790 (Pokrovskii et al., 2006). and a species of genus Gymnosolen also determined in The Chenchen Formation with a gradual transition the open nomenclature. In the South Siberian stroma overlies the Nikol’skoe Formation. This limestone tolite province, all these taxa differ from synonymous unit comprises two subformations. The lower subfor biotas developed in other similar provinces of northern mation that is assigned by some authors to the auton Eurasia (Semikhatov, 1985) by their low taxonomic omous Alyanch Formation (A.A. Predtechenskii, diversity, sharply reduced number of taxa in common 1941; Chumakov, 1959; Bobrov, 1979; Melezhik et al., with other provinces, and confinement of representa 2009) consists largely of light gray stylolithic stroma tives of form genera Katavia, Inzeria, and Gymnosolen tolitic, micritic, detrital, and oolitic limestones. Some to the Vendian section, while in the Ural, North, and beds of the last variety are composed of a gray matrix Middle Siberian provinces, these genera are charac and red oolites. The thickness of the subformation teristic of the Upper Riphean stromatolite assemblage increases from 200–250 m at the Lena River (Chuma (Krylov, 1975; Komar, 1966; Semikhatov and Serebry kov, 1959; Zamaraev, 1984; Kokoulin, 1998) to 600– akov, 1985; and references therein). 900 m at the Bol’shoi Patom River (Zamaraev, 1984; Theδ13С value in bulk samples of Chenchen car Melezhik et al., 2009). The upper subformation of the bonates increases from –9.6‰ in the middle part of Chenchen Formation that is assigned by some this unit to –7.6 and –8.4‰ in its upper part. The researchers to the autonomous Kholych or Khopchai 87Sr/86Sr ratio in limestones of the Chenchen Forma Formation (A.A. Predtechenskii, 1941; Chumakov, tion derived from six measurements varies from 1959; Bobrov, 1979; Melezhik et al., 2009) overlies the 0.70811 to 0.70870 (Gorokhov et al., 1995). Four orig lower one with a gradual transition. It is formed by inal and six published determinations of the 87Sr/86Sr alternating gray, locally variegated (gray red) oolitic, value for limestones of the Chenchen Formation are oncolitic, stromatolitic, silty, sandy, and detrital lime cited in (Pokrovskii et al., 2006). All the available mea stones. The last variety exhibits cross bedding. The surements show that this ratio varies from 0.70786 to share of sandy limestones gradually increases upward 0.70855. Among these 87Sr/86Sr values, the last authors along the section, where they are accompanied by first consider its minimum value determined for the lower appearing intercalations of calcareous sandstones and and middle part of the formation (0.7079) as the most gravelstones as well as lenses of dolomites. reliable. Similar data are presented in (Melezhik et al., In the Ura uplift, the section of the upper 2009). According to them, the 87Sr/86Sr value in lime Chenchen Subformation is crowned by a 30 to 35 m stones from the middle part of the Chenchen Forma thick member of brown fine grained oolitic, stroma tion is 0.7080 and increases to 0.7086 at its top. The tolitic, and sandy dolomites and sandstones. The last values are close to the 87Sr/86Sr ratios obtained by member contains also rare thin intercalations of mud A.B. Kuznetsov (private communication) for lime stones and conglomerates with a dolomitic matrix and stones of the Chenchen and Nikol’skoe formations at scattered pebbles (Fig. 6). Locally, the member dem the Zhuya River.
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 370 CHUMAKOV et al.
@р. Бол. Джербедянка Lena Riverо@коло устья m Molbo R. m р. Бол. Патоm m Zhuya R. m Lena River 5 km 1 upstream of Nokhtuisk 2 Apparent 20 3 4 25 5 7 52 6 15 7 28 Apparent, over 100 10 8 5 11 9
3.5 14 10 6 11 25 20 15 12 16 26 13 7.5
4 5 1.6–2.7 14 6–7 15
18 20 16
300 Apparent 18 17 4 Apparent 20
Over 18 Apparen 41 Apparent 25 100 Chenchen Formation Formation Zherba Over Apparent 20 Apparent, over 80
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 lines show correlation of some members.
The “Yudoma Group” (complex or horizon) in the with Lower Cambrian sections are coeval and belong Ura uplift and on the margin of the Patom folded zone to the Vendian (reviews in (Zuravleva and Komar, includes the Zherba and Tinnaya formations with ero 1962; Khomentovskii, 1976; Semikhatov et al., 1970, sional surfaces at the bases. They are largely represented 2004)). Now, such a correlation is rejected: the Ven by different alternating rocks with the dominant role of dian reference sections of Siberia are established to quartz sandstones and carbonate rocks in the Zherba include analogs of several units from the type section and Tinnaya formations, respectively (Fig. 3) of the Yudoma Complex located in the Uchur Maya The names “Yudoma Group” or “Yudoma Com region. Therefore, despite the fact that the names plex” were proposed for deposits of the Patom High “Yudoma Group” or “Yudoma Complex” for the land at times when most researchers who investigated Zherba and Tinnaya formations are traditional, they the Upper Precambrian sections of the Siberian Plat are conditional and, undoubtedly, invalid. These tra form and its surrounding structures believed that all ditional names under no circumstances mean that the formations of the region separated from underly these two formations are stratigraphic analogs of the ing rocks by unconformities and closely associated Aim and Ust’ Yudoma subformations in the type sec
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 VENDIAN REFERENCE SECTION OF SOUTHERN MIDDLE SIBERIA 371 tion of the Yudoma Complex (or group). As follows sented by alternating frequently calcareous black from the data mentioned above and cited below, the shales and sandstones with intercalations of bitumi analog of the Yudoma Group type section in the Ura nous limestones. The third sequence crowning the uplift is represented by all the succession of the section of the Zherba Formation is approximately 60– Dal’nyaya Taiga, Zhuya, and “Yudoma” groups. 80 m thick and known also as the Tirbees Member Therefore, to avoid confusion, we suggest renaming (Khomentovskii et al., 2004; Kochnev and Karpova, the “Yudoma Group” of the Ura uplift the “Trekhver 2010) or Tirbees Formation (Kokoulin, 1998). This stnyi Group” after the Trekhverstnyi Creek, a left trib peculiar and complex sequence was previously consid utary of the Lena River, into which it flows 2.5 km ered as the basal unit of the overlying Tinnaya Forma upstream of Nokhtuisk. The stratotype of the Trekh tion, which is also characterized by elevated rock bitu verstnyi Group comprises the Zherba and Tinnaya for minosity (Chumakov, 1959; Bobrov, 1964, 1979; mations of the Nokhtuisk section. It is reasonable to Opornye…, 1972; Kolosov, 1975; Kokoulin, 1998). attribute the Trekhverstnyi Group to the Patom Com The Tirbees Member begins with a bed (approximately plex, which included previously only the Zhuya, 20 m thick) of massive and bedded black medium to Dal’nyaya Taiga, and Ballaganakh groups (Chumakov, coarse grained highly bituminous (anthroconite) 1959). limestones with thin intercalations of calcareous The Zherba Formation rests upon the Chenchen shales. Higher in the section, the member is composed Formation with considerable hiatus, which is marked of alternating green and red marlstones and siltstones, by karst features in the upper part of the Chenchen clayey dolomites, black bituminous limestones, and Formation on the Ura uplift (Pelechaty, 1998; Kho carbonate shales. Near the top of the member, clayey mentovskii et al., 2004) and by almost complete ero dolomites enclose two thin (5 and 12 cm) intercala sion of the upper dolomitic member of the Chenchen tions of black cherts and their scattered concretions 1 Formation at the Molbo and Bol’shaya Dzherbedy (Bobrov, 1979) as well as thin layers of algal siliceous– anka rivers (Fig. 6). This hiatus follows also from wide phosphate rocks (Khomentovskii et al., 2004). regional correlations between sections of the The total thickness of the Zherba Formation is esti Chenchen and Zherba formations (Khomentovskii mated in different manners: it is 200–250 m (Kolosov, et al., 2004). At the same time, development of ero 1975; Bobrov, 1979; Kokoulin, 1998) to 500 m (Zama sional surfaces both below and above this main hiatus raev, 1984) thick without the Tirbees Member and hampers its recognition. Therefore, some authors 350 m with it (Pelechaty, 1998; Khomentovskii et al., (Chumakov, 1959; Opornye…, 1972; Bobrov, 1979; 2004). Zamaraev, 1984) took the base of a dolomitic member, The phosphate rocks of the Tirbees Member which crowns the Chenchen Formation and bears yielded a diverse assemblage of excellently preserved erosional features at its base, for the lower boundary of silicified microfossils (Yakshin, 2002; Khomentovskii the Zherba Formation. The deposition of this member et al., 2004). Yakshin described many new endemic during the Zherba time in the marginal part of the microfossil genera and species, in addition to well Patom basin was followed by drastic changes in sedi known taxa characterized by wide stratigraphic mentation patterns: mostly carbonate sediments were (Upper Riphean–Vendian–Lower Cambrian) and replaced by sandy facies. geographic distributions such as Obruchevella, Oscilla The best outcrops of the Zherba Formation are toriopsis, Glomovertella, Gloeodiniopsis, and Germino located in the eastern margin of the Ura uplift: on the sphaera. By its composition and diversity, this micro left side of the Lena River opposite the Bol’shoi Patom biota reflects an important stage in development of River mouth and opposite the Malyi Patom River microorganisms on the Siberian Platform during the mouth (Pelechaty, 1998; Khomentovskii et al., 2004). Late Precambrian. As for many endemic species In these sections, the Zherba Formation consists of described among this assemblage, the problem of three sequences. The lower sequence is over 150 m appropriateness and validity of identified new genera thick. Its basal part includes frequently encountered and species for the Precambrian microbiotas should be conglomerates composed of a sandy matrix and dolo solved by subsequent investigations and revisions, mite pebbles. These conglomerates demonstrate which still do not involve Tirbees microfossils. locally downlap relations with eroded bioherms of Determinations of the C isotope composition in stromatolitic dolomites, which imply the presence of limestones and dolomites from the terminal part of the biogenic reefs within a member (Fig. 6). The lower middle sequence of the Zherba Formation revealed sequence is mostly composed of gray cross bedded negative δ13С values and their decrease upward along glauconite quartzite like sandstones (in the lower the section from –8.0 to –2.5‰. In most associated part) with subordinate quartz gravelstones and green dolomites, the δ13С values drop to –20‰, which is ish siltstones. Most sandstone varieties are quartzose thought to be explained by limestone dolomitization in composition and only some of them contain notable and has no stratigraphic sense (Pelechaty, 1998). In the admixture of feldspars. The middle sequence of the upper sequence of the Zherba Formation (Tirbees Zherba Formation approximately 200 m thick is Member), the brief negative excursion to –5‰ is fol poorly exposed. Its exposed 40 m thick part is repre lowed by the growth of the δ13С value to 2‰ and its
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decrease gradually to zero at the top of the formation VENDIAN AGE OF THE DAL’NYAYA TAIGA, (Pelechaty, 1998). ZHUYA, AND “YUDOMA” GROUPS: ARGUMENTS IN FAVOR The Tinnaya Formation. The boundary between the Zherba and Tinnaya formations is now placed imme The lower boundary of the Vendian section in the diately below a 10 m thick bed of coarse grained Ura uplift area is distinctly definable at the base of the cross bedded sandstones and gravelstones with karst Nokhtuisk Formation on the basis of the replacement features (Pelechaty, 1998) and erosional incisions of the faunal assemblage characterizing the Purella (Khomentovskii et al., 2004) at its base. The overlying antiqua Zone of the Vendian Nemakit–Daldynian part of the Tinnaya Formation is composed of alter Stage by fossils belonging to the Aldanocyathus sun naginicus Zone of the Lower Cambrian. The lower nating members of brecciated clayey bituminous lime boundary of Vendian strata in this section is still stones and dolomites, which are separated by interca ambiguous because of insufficient available data, lations of dark gray to black carbonaceous calcareous although the distribution of organic remains in the clays, greenish siltstones, and massive limestone and Dal’yaya Taiga Group and chemostratigraphic evi dolomite beds. These rocks include a thin (15 cm) dence (Pokrovskii et al., 2006; Melezhik et al., 2009) 1 layer of black cherts 20 m below the top of the forma provide grounds for the assumption that the largest tion (Khomentovskii et al., 2004). The thickness of the upper part of this group should be attributed to the Tinnaya Formation in the Ura uplift area is estimated Vendian. This is confirmed, for example, by finds of to be 220 m (Khomentovskii et al., 2004) or 334 m diverse Pertatataka type acanthomorphic acritarchs in (Pelechaty, 1998). The upper 150 m of the formation the Ura Formation (Chumakov et al., 2007; Vorob’eva yielded small shell faunal fossils characterizing the et al., 2008a; Golubkova et al., 2010; Sergeev et al., Anabarites trisulcatus Zone of the Upper Vendian 2010, 2011) and Vendian form Beltanelloides soriche Nemakit–Daldynian Stage; higher layers contain Tik vae in the lower subformation of the Barakun Forma sitheca sp., indicating the presence of the overlying tion in the Ura River section (Leonov and Rud’ko, 3 Purella antiqua Zone of the same stage in this section 2012). The find of Pertatataka type acanthomorphic (Khomentovskii et al., 2004; Kochnev and Karlova, acritarchs represented in the Ura Formation by the 2010). peculiar assemblage serves as a main criterion for dat ing this unit. The lower part of the Ura Formation The Tinnaya carbonate rocks from the lower part of yielded the following Pertatataka type acritarchs and the formation are characterized by δ13С values varying other fossils (Sergeev et al., 2011): Ancorosphaeridium from +2.3 to –9‰, which provide a curve with four magnum, A. minor, Appendisphaera tenuis, A. minima, negative excursions (from the base upward): –3.5, –5, Appendisphaera sp., Archaeotunisphaeridiam aff. fim –9, and –5.5‰ (Fig. 3). They are separated by nar briatum, Bullatosphaera velata, Cavaspina cf. row intervals of the section also with negative but rela C. acuminata, C. basiconica, Eotylotopalla strobilata, tively elevated δ13C values (Pelechaty, 1998). In the E. aff. delicata, Gyalosphaeridium minutum, Knol upper part of the Tinnaya Formation, the δ13C value lisphaeridium maximum, Multifronsphaeridium pelo varies from –4.8 to ⎯ 3.0‰ and decreases to –5.5‰ rium, ?Sinosphaera rupina, Tanaium conoideum, at the base of the Nokhtuisk Formation and then T. digitiformis, T. tuberosum, Variomargosphaeridium increases to zero at higher levels of this unit (Khomen litoschum, Aimia aff. gigantica, Leiosphaeridia spp., tovskii et al., 2004). Schizofusa zangwenlongii, Digitus fulvus, unnamed fil amentous microfossils, Obruchevella sp., Polytrichoides lineatus, Rugosoopsis tenuis, Segmentothallus aff. S. aspe rus, Siphonophycus spp., Ceratophyton sp. cf. Cucumi LOWER CAMBRIAN forma sp., unnamed forms 1–5. This assemblage indi The Nokhtuisk Formation rests upon the Tinnaya cates that the Ura Formation represents an analog of the second complex palynozone of Pertatataka acri Formation with insignificant hiatus (Khomentovskii tarchs established in the type section of central Austra et al., 2004). The contact between these formations lia (Grey, 2005). and the lower part of the Nokhtuisk Formation com posed of alternating variegated mudstones, marl As was mentioned, Moczydlowska and Nagovitsin stones, and stromatolitic dolomites are well exposed (2012) revised the microbiota from the Ura Formation on the left side of the Lena River 3 km upstream of the using in fact the same material analyzed by V.N. Ser geev and colleagues. In doing so, they demonstrated Nokhtuisk Settlement. In this area, the basal layers of the Nokhtuisk Formation and its lower 50 m yield 3 The find of Beltanelloides sorichevae in this section indicates that abundant small shell fossils characteristic of the Tom these fossils previously known from the upper layers of the type motian Aldanocyathus sunnaginicus Zone, the basal Vendian section in the East European Platform (Fedonkin et al., 2007) are characterized by a wider stratigraphic distribution. zonal unit of the Lower Cambrian section (Khomen Nevertheless, this fact provides no grounds for excluding this tovskii et al., 2004; Kochnev and Karlova, 2010). species from the list of characteristic Vendian taxa.
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 VENDIAN REFERENCE SECTION OF SOUTHERN MIDDLE SIBERIA 373 the subjective view on the taxonomic significance of Ishikawa et al., 2008) sections include paleontologi morphological features and defined three new genera cally substantiated analogs of the Vendian Nemakit– and nine new species, renaming the previously Daldynian Stage. described taxa. Such a procedure provided grounds for (2) Brief but significant negative δ13С anomalies them to arrive at the conclusion on the endemic char (from –5 to –13‰) are established near the base of acter of the Ura microbiota and its older age as com the member with the Nemakit–Daldynian fossils in pared with other Pertatataka biotas of Siberia and the Ura and China sections and at a close level in tuf younger age as compared with sediments of the first faceous sediments dated by the U–Pb zircon method palynozone defined in the lower part of the Lower at 542 Ma (Brasier et al, 2000; Bowring et al., 2007) in Vendian Doushantuo Formation in South China the Oman section (Fig. 7). In the Ura uplift section, (McFadden et al., 2009). In our opinion, the available the ascending shoulder of a similar anomaly (Fig. 3) is facts indicate that the Ura Formation corresponds to established in the middle part of the Zherba Forma the Grey’s second complex palynozone. tion (Pelechaty, 1998). In China, this anomaly, named The U–Pb (SHRIMP) dating of detrital zircons the Bace (Zhu et al., 2007a) or EN4 (Zhou and Xiao, from the base of the Nikol’skoe Formation cropping 2007; Zhou et al., 2011) anomaly, is documented at out near the Ura River mouth yielded important infor the base of the Zhujiaqing Formation. In Oman, a mation on age of upper layers of the Patom Complex similar situation is recorded in the lower part of the (Chumakov et al., 2011a). On the curve of the relative Fara Formation, where it is designated by the letter Z probability, several members dated at 2900, 2070, (Walter et al., 2000). Similar anomalies are also known 2500, 2000, and 1800 Ma are definable on the basis of at the bases of sedimentary sequences with fossils the 206Pb/238U and 207Pb/206Pb values, which implies characteristic of the Nemakit–Daldynian Stage in the erosion of the Archean and Lower Proterozoic base McKenzie Mountains of Canada (Walter et al., 2000) ment of the Siberian Platform. For determining the and India (Jiang et al., 2003). minimum age of upper layers of the Patom Complex, (3) In South China, the significant (≥–10‰) neg the most interesting is the youngest zircon generation ative δ13С anomaly named the Dounce (Zhu et al., extracted from the Nikol’skoe Formation. Zircons of 2007a) or EN3 (Zhou and Xiao, 2007; Zhaou et al., this generation are divisible in two groups on the basis 2011) anomaly is established in the upper part of the of both the 206Pb/238U and 232Th/238U values. The 232 238 Doushantuo Formation. In Oman, the similar event older group of grains is characterized by the Th/ U called the Shuram anomaly (up to 14‰) is registered ratios varying from 0.4 to 1.1, while in the 206Pb/238U– 207 238 in the upper part of the Nafun section (Le Guerroue, Pb/ U coordinates, the group with age of 704.3 ± 2010). By their amplitudes and stratigraphic positions, σ 4.5 Ma (1 , MSWD = 0.90) is definable around the both of these anomalies are similar to the negative concordia. The younger group of grains demonstrates 232 238 Zhuya one (Fig. 7). Correlation of the Zhuya anomaly the lowered Th/ U value ranging from 0.2 to 0.7 with its Dounce and Shuram counterparts is con and forming in the above mentioned coordinates the firmed by similarity in 87Sr/86Sr values in their consti σ concordia with age of 646.9 ± 3.4 Ma (1 , n = 48, tuting carbonate rocks. These values are estimated to MSWD = 0.900077). Thus, U–Pb (SHRIMP) ages be 0.7080–0.7084 for the Zhuya (Pokrovskii et al., obtained for detrital zircons indicate that basal sand 2006; Melezhik et al., 2009), 0.7083–0.7084 for the stones of the Nikol’skoe Formation are younger than Dounce (Jiang et al., 2007), and 0.7080–0.7088 for 646.9 ± 3.4 Ma, i.e., younger as compared with age the Shuram (Le Guerroue et al., 2006, Le Guerroue, accepted now for the lower boundary of the Vendian 2010) anomalies. Similar 87Sr/86Sr values are charac System equal to 650 Ma (Dopolneniya…, 2000). teristic of sediments aged 580–570 Ma (Halverson and The position of the Vendian lower boundary in the Shields Zhou, 2011). In the East European Platform, Ura uplift section may be derived from stratigraphi similar results are obtained for the lower part of the cally important interchangeable features characteris Vendian Redkino Horizon on the basis of U–Pb dates tic of some sections, which exhibit similarity with sec of zircons from tuffs and corresponding interpolations tions of the Dal’nyaya Taiga, Zhuya, and Trekhverst (Sokolov, 2011, 2012, Grazhdankin, 2011). These nyi groups. In this regard, the sections of the following estimates are consistent with radioisotopic data con three regions are promising: Yangtze Platform of cerning the Dounce and Shuram anomalies. U–Pb South China, eastern and northern Oman, and north TIMS dates of approximately 551 and 555 Ma are eastern margin of the East European Platform (Fig. 7). available for volcanogenic zircons from the upper part In these regions, the Vendian sections demonstrate the of the Doushantuo Formation above the Dounce succession of several chemostratigraphic, biostrati anomaly (Condon et al., 2005; Zhang et al., 2005). At graphic, and climatic events partly dated and regis the same time, according to U–Pb dating of detrital tered also in the Ura section. Let us trace these events zircons, the Shuram anomaly of Oman is younger than in the above mentioned sections (from the top down 600 Ma (Rieu et al., 2007). These measurements place ward). the upper and lower age limits for the Dounce and (1) The Ura (Khomentovskii et al., 2004; Kochnev Shuram anomalies at 550 and 600 Ma, respectively. and Karlova, 2010) and China (Steiner et al., 2007; Such values are also suitable for assessing age limits of
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 374 CHUMAKOV et al. 558 t , Blon Pinsk Glussk Lapich Pb Vychegda 555 567 ROVNO
U KOTLIN
, REDKINO
LAPLAND VCH 551 C‰ 13 δ 14 15 0.7085 0.7080 –10 0 5 0.7092 0.7088 <600 <610 0.7086 U <620 541 Oman (5, 6, 7) Eastern Europe (8, 9, 10) 544 Bay Fara Fiqa Buah
Khufai Hadash Shuram <644
Saglakh Masirah 542
ARA NAFUN t0.7086 0.7083 , 0.7084 0.7087 0.7085 Pb C‰ U 13 , δ 551 0.7078 663 656 636 South China (2, 3, 4) , 555 <620
551 621 635 Doushantuo 16 17 18 19 20 21 Nantuo Zhujiaqing Dengying Datangpo; 725 <647 0.7086 C‰ 13 δ 0.7077 0.7073 1 2 3 4 5 6 7 8 9 10 11 12 13 –10 0 10 Ura Uplift (1) Barakun Ura Kalancha Bugarikhta Chenchen Nikol’skoe Mariinskaya Zherba
El’gyan Tinnaya
Bol’shoi Patom Nokhtuisk
ZHUYA DAL’NYAYA TAIGA DAL’NYAYA BALLAGANAKH
Ma 535 542 555 635
~560 ~640
1 II–III V 1 2 3 IV V Є V R
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 VENDIAN REFERENCE SECTION OF SOUTHERN MIDDLE SIBERIA 375 the Zhuya anomaly, which is correlated with these and correlated with the Zhuya Group contains the events, which serves as additional evidence in favor of impoverished assemblage of acanthomorphic acri its Vendian age. tarchs that includes Cavaspina and some other taxa (4) The rocks immediately below the Dounce characteristic of the Pertitataka type microbiota. Pre anomaly in the Doushantuo Formation yield a diverse viously, these microfossils were erroneously attributed assemblage of acanthomorphic acritarchs (ECAP to genera and species of Upper Riphean acanthomor assemblage), which is similar in its general appearance phic acritarchs (Kolosova, 1991). The recent find to the Lower Vendian Ura and Kel’tma assemblages of indicates that final extinction of Pertatataka type the East European Platform. The Kel’tma assemblage microfossils was asynchronous with the onset of the characterizes the autonomous Vychegda Horizon, Dounce–Shuram–Zhuya negative carbon excursion, which is older as compared with the Vendian Redkino as was assumed by some researchers (Zhu et al., 2007a, Horizon of the East European Platform. In its taxo 2007b; Chumakov, 2010; etc.). nomic composition, the Kel’tma assemblage is corre (5) The lower part of the Doushantuo Formation of lated with the first ECAP zone in the stratotype sec South China and the interval of the Khufai and tion of Australia (Veis et al., 1996; Vorob’eva et al., Masirah Bay formations of Oman are dominated by 2006, 2007, 2008b, 2009a, 2009b). This provides addi considerable positive δ13С values (ranging from +5 to tional grounds for correlating the sediments sand +6‰). The middle parts of these large intervals in wiched between the Nemakit–Daldynian Stage and China and Oman exhibit brief negative δ13C excur strata with the Ura acritarch assemblage with the sions (Fig. 7). The similar interval of positive δ13С val Upper Vendian. ues (from +5 to +8‰) is also characteristic of the The largest acanthomorphic acritarchs are largest upper part of the Dal’nyaya Taiga Group, recorded near the base of the Doushantuo Formation although without a brief negative excursion in its mid 5 m above the top of cap dolomites associated with til dle part. The latter could be missed owing to the insuf lites of the underlying Nantuo Formation. Zircons ficient density of measurements in this interval of the from tuff intercalations in cap dolomites and from Ura section. tuffs sampled 5 m above the top of cap dolomites are (6) The negative peaks at bases of these wide posi dated by the U–Pb method at 635.2 ± 0.6 and 632.5 ± tive δ13C intervals under consideration corresponding 0.5 Ma, respectively (Condon et al., 2005). At the to cap dolomites of glacial horizons are well expressed same time, it is impossible to establish age relation in the Ura, China, and Oman sections (Pokrovskii ships between zonal units of the Doushantuo (McFad et al., 2006; Le Guerroue, 2010; Jiang et al., 2011). den et al., 2009) and type biozones defined in (Grey, (7) In all three compared sections, cap dolomites 2005) because of taxonomic difficulties. In their pub are underlain by glacial horizons of the Bol’shoi lications, Chinese researchers to date have used some Patom Formation on the Ura uplift, Nantuo Forma taxa names, such as Meghystrichosphaeridium and tion in South China, and Fiqa Formation in Oman. Polygonum, which were acknowledged after multiple The comparison between the Ura, South China, revisions (Grey, 2005; Moczydlowska, 2005; etc.) to and Oman sections shows that the succession of be invalid. chemostratigraphic and, partly, biotic events in the It should be emphasized that the Torgo Formation section from the base of the Cambrian to glacial hori immediately overlying stratigraphic analogs of the Ura zons is similar. Such a similarity is particularly signifi Formation on the western slope of the Aldan Shield 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 unit of 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 of the Doushantuo Formation, according to (McFadden et al., 2009); (11) Lower Vendian microfossils from the lower zone of the Doushantuo Formation, according to (McFadden et al., 2009); (12) nonskeletal Metazoa; (13) Eocholinia and Archiphasma algae; (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. (~C ) 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 2 Vendian System; (VCH) Vychegda Horizon of the Vendian System; (R3 ) 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’eva et 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.
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 376 CHUMAKOV et al. viding grounds for correlation of the glacial Bol’shoi Patom fold arc (Chumakov, 1959, 1993; Opornye…, Patom Formation with the glacial Nantuo Formation 1972), then to the Berezovo trough centroclinal and of South China. The age of the latter unit is deter farther to the western slope of the Aldan Shield mined owing to several U–Pb dates obtained for detri (Zhuravleva et al., 1959; Chumakov, 1959, 1993; tal zircons (Zhang et al., 2011). The base of the cap Opornye…, 1972). In the southwestern direction, Ven dolomite crowning the Nantuo Formation is dated at dian complexes are well traceable from the Ura uplift 635.6 ± 0.5 Ma; its lower part is dated at 636.3 ± 4.9 Ma; up to the Bol’shaya and Malaya Chuya rivers the upper part of the Datangpo Formation, which (Golovenok et al., 1963; Chumakov, 1993; Opornye…, unconformably underlies the Nantuo Formation, is 1972). Such correlations are confirmed by the condi dated at 656 ± 3 Ma. In Oman, the glacial Fiqa For tional state geological survey, scale 1 : 2000000 (Ivanov mation, the age of which is estimated by the U–Pb et al., 1995; Kokoulin, 1998; etc.). method on detrital zircons to be <644 Ma (Rieu et al., The eastern branch of the Patom arc south of the 2007), corresponds likely to the Bol’shoi Patom For Ura uplift is characterized by an elevated thickness of mation. Such a correlation allows the Bol’shoi Patom sediments under consideration and significant facies Formation to be considered as being older than changes in the Dal’nyaya Taiga Group. In the Malyi 635 Ma and younger than 644 Ma ago; i.e., it corre Patom, Zhuya, Molbo, and Bul’bukhta river basins, sponds to the basal glacial part of the Lapland Horizon glacial diamictites of the Bol’shoi Patom Formation in the Vendian stratotype (Sokolov, 1997, 2012). are replaced by black shales and sandstones, which are Thus, the available data and aforementioned corre united into the Dzhemkukan Formation, while the lations indicate that the interval of the Trekhverstnyi, Ura and Kalancha formations are replaced by the Zhuya, and Dal’nyaya Taiga groups of the Ura uplift Valyukhta Formation consisting of dark gray to black sandwiched between the top of the Nemakit–Daldy shales with subordinate sandstone and limestone nan Stage and basal Vendian Lapland Horizon corre intercalations. Southeast of these areas in the southern sponds (or is very close) by its range to the Vendian in centroclinal of the Berezovo trough in the Dzhelinda the stratotype area and represent together analogs of and Sen river basins, the basal part of the Dal’nyaya the main horizons of the Vendian stratotype: Nema Taiga Group again contains glacial sediments united kit–Daldyn, Vychegda, Kotlin, Rovno, and Lapland. into the Nichatka Formation correlated with the The completeness and exact boundaries of these hori Bol’shoi Patom Formation. In this area, the Barakun zons in the Ura Section are as yet unclear and require and Valyukhta formations are replaced by the Kumakh further investigations. Ulakh carbonate–terrigenous and Sen sandstone– dolomite formations, respectively. The latter units are traceable in the eastern direction up to the Chara and REGIONAL CORRELATIONS Tokko rivers on the western slope of the Aldan Shield. OF VENDIAN SECTIONS IN THE URA UPLIFT In the eastern part of this region, the thickness of the In regions surrounding the Baikal folded domain, Vendian section decreases. The Nikol’skoe and the lithology and structure of Vendian sections dem Chenchen formations are replaced by the Torgo For onstrate certain variations. Nevertheless, the sections mation, the Sen Formation becomes divided into the of these regions are well correlative with units of the basal Imalyk terrigenous and Tokko carbonate forma Ura type section. They are mostly correlated by trac tions, and the Kumakhulakh and Nichatka formations ing some reference formations (Fig. 8). The main role pinch out (Zhuravleva et al., 1959; Petrov, 1966). in this process belongs to the following stratigraphic In the western branch of the Patom arc and North units: (1) terrigenous Ballaganakh Group preceding Baikal Highland, the Vendian section is similar to the Vendian strata; (2) overlying glacial diamictites of the section of its eastern branch, differing only in the Bol’shoi Patom Formation and its analogs; (3) Zhuya lithology of the Dzhemkukan Formation, which is Group, which is characterized by a peculiar composi composed largely of glacial sediments in these areas. tion and bedding succession; (4) Zherba Formation. Southwest of the Malaya Chuya River head, the Balla These deposits are traced from the Ura uplift eastward ganakh Group and lower glacial part of the Dal’nyaya and southeastward along the eastern branch of the Taiga Group pinch out, while analogs of the upper part
Fig. 8. Correlation of Vendian sections of the Ura uplift, peripheral zone of the Baikal fold system, and western slope of the Aldan Shield, 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–Pb age of detrital zircon; (6)) nonskeletal Metazoa; (7) faunal assemblage of the Tommotian Aldanocyatus sunnaginicus Zone, Lower Cambrian; (8) faunal assemblage of the Purella antiqua Zone, Nemakit–Daldynian Stage, Vendian; (9) faunal assemblage of the Anabarites trisulcatus Zone, Nemakit–Daldynian Stage, Vendian; (10) sabellidites; (11) indications of stratigraphic hiatuses; 87 86 ~ 1 (12) base and top of cap dolomites; (13) Sr/ Sr ratios in carbonate rocks; (14) Pb–Pb isochron age of limestones. (C1 ) Tom motian Stage of the Lower Cambrian; (V) Vendian; (R) Riphean.
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 VENDIAN REFERENCE SECTION OF SOUTHERN MIDDLE SIBERIA 377 0.7083 0.7080 0.7073 Sen Torgo Yuedei Kumakhulak Pb 560 ± 30 Pb Yuedei Valyukhta Dzhemkukan Nichatka 0.7086 <647 0.7086 0.7077 0.7073 Ura Kalancha Tinnaya Tinnay Tinnay Barakun Barakun Ura Uplift Zhuya River Chaya Rive Nokhtuisk Bugarikhta Bugarikhta
Mariinskaya Mariinskaya
Bol’shoi Patom Valyukhta Zherba Zherba Zherba Zherba Tinnaya Barakun Valyukhta Chenchen Chenchen Chenchen Nokhtuisk Nikol’skoe Nikol’skoe Nikol’skoe Bugarikhta Mariinskaya Dzhemkukan Bol’shaya Chuya River Peripheral zone of the Baikal fold region Aldan Shield <647 c d c d c d c d Min Zherba Uluntui Usatovo Chenchen Nikol’skoe Chaya Rive Goloustnaya c d 1234 5678910111213 14 0.7084 0.7087 Pb 560 ± 30 c d Pb Ussol’e Uluntui Ayankan Ayankan Kachergat Ushakovo Member Goloustnaya Bugul’deika South Baikal region ? 1 1 3 V R Є
STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 21 No. 4 2013 378 CHUMAKOV et al. of the Dal’nyaya Taiga Group and Zhuya Group are The available data on correlation of the well recognizable in sections along the Chaya River Bugul’deika Member and Goloustnaya and Uluntui and the head area of the Malaya Chuya River formations of the Baikal Complex with the Dal’nyaya (Opornye…, 1972). Taiga Group of the Patom Highland disprove the tra The Chaya section is transitional between the ditional opinion in the Russian geological literature Patom and near Baikal sections; therefore, the Kalan that this complex should be attributed either to the cha Formation at the Chaya River was called by some upper part of the Middle Riphean and lower part of the researchers also both the Kalancha and Goloustnaya Upper Riphean (Dol’nik, 1982, 2000; Stanevich et al., or Uluntui formations (Opornye…, 1972). The analog 2007) or to the Baikalian, a unit dating back to 850– of the Chenchen Formation at the Chaya River is over 600 Ma (Opornye…, 1972; Khomentovskii et al., 1998; lain by sediments, which are correlated by their lithol Khomentovskii and Postnikov, 2001, Khomentovskii, ogy and position in the section with the Trekhverstnyi 2002). The new data show that the Baikal Complex in Group of the Ura uplift. From the Chaya River, these the range of the Bugul’deika Member and Goloust sediments are traced as the Goloustnaya and Uluntui naya, Uluntui, and Kachergas formations should be formations and “Yudoma Group” or “Yudomian” in correlated with the Vendian System (Kuznetsov and the southwestern directions along the western margin Letnikova, 2005; Kuznetsov et al., 2012). of the North Baikal Highland and Baikal Range up to the southern Baikal region (Opornye…, 1972). In the Kurgun River basin, located in the southern part of the CONCLUSIONS last region, the Goloustnaya Formation is built up by a The recent chemostratigraphic, paleontological, member of glacial sediments (diamictites, conglomer and radioisotopic data indicate that the Dal’nyaya ates, and sandstones), which is named the Bugul’deika Taiga, Zhuya, and Trekhverstnyi groups of the Ura Member (Sovetov and Komlev, 2005). uplift are the Vendian in age. Correlations of these The traditional correlation of Near Baikal sections units with well studied Upper Proterozoic sections of with the Patom section based on geological (biostrati other regions support this inference. The upper graphic and event) criteria is confirmed by recent Sr boundary of the Vendian System in the Ura uplift sec and C isotopic chemostratigraphic methods and tion is established at the base of the Nokhtuisk Forma Pb ⎯ Pb isochron dating of the least altered limestones tion on the basis of biostratigraphic data (Khomen from the upper part of the Uluntui Formation: 560 ± tovskii et al., 2004; Kochnev and Karlova, 2010). Its 30 Ma (Kuznetsov et al., 2012). lower boundary in this section is placed with high con The δ13C values in a thin dolomite member occur fidence at the base of the glacial Bol’shoi Patom For ring in the upper part the Goloustnaya Formation mation on the basis of finds of diverse Vendian acanth (basal unit of the Baikal Complex) in the type section omorphic acritarchs (ECAP) in the Ura Formation of the complex increases from –2.6‰ at the base of and Beltanelloides sorichevae in the lower part of the the member to +2.8‰ at its top. Taking into consid Barakun Formation and also on the basis of the corre eration the occurrence of the Goloustnaya Formation lation of the Bol’shoi Patom Formation with glacial on diamictites of the Bugul’deika Member, these val sediments of the Nantuo and Fiqa formations of ues can be correlated with the above mentioned δ13C China and Oman, respectively, and with the Lapland values obtained for the basal part of the lower Barakun Horizon of Eastern Europe. Consequently, sediments Subformation. In the 600 m thick member of lime sandwiched between the base of the Nokhtuisk For stones occurring at the top of the Uluntui Formation mation and the base of the Bol’shoi Patom Formation in the same section of the Baikal Complex, the values should be attributed to the Vendian System. vary around +4.7‰, deviating from this value usually (2) Correlation of the Ura Formation with East by 0.8–0.9‰ (Kuznetsov et al., 2012). Variations of European, China, and Oman Vendian sections with δ13C in the upper part of the Uluntui Formation are reliable radioisotopic dates and some biostratigraphic comparable with their changes in sections of the reference levels provide grounds for the assumption Dal’nyaya Taiga Group in the interval from the upper that the Vendian section of the Ura uplift includes the part of the lower Barakun Subformation to the lower Kotlin, Redkino, and Lapland sediments, i.e., main part of the Kalancha Formation. units of the Vendian System, in addition to the Nema Recent measurements in samples which met very kit–Daldyn Horizon. The position of boundaries and strict requirements on geochemical preservation of stratigraphic ranges in the Ura section need further carbonate rocks (Mg/Ca < 0.05, Mn/Sr < 0.03, investigations. Fe/Sr < 0.4, δ13O > –8‰) yielded information of (3) Correlation of the Ura section with Vendian 87Sr/86Sr values in them, which were from 0.70842 to sequences in surrounding structures of the Baikal 0.70874 (Kuznetsov et al., 2012). In terms of Sr chro folded region and on the western slope of the Aldan nostratigraphy, this implies that early diagenesis of the Shield shows that the Vendian section in the Ura uplift analyzed upper Uluntui rocks corresponds within the area represents the most complete succession of these error limits with their Pb–Pb age. sediments in the spacious region under consideration.
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(4) As compared with these sections, the Vendian Chumakov, N. M., Riphean Middle Siberian glaciohorizon, succession on the Ura uplift is better substantiated by Stratigr. Geol. Correlation, 1993, vol. 1, no. 1, pp. 21–34. paleontological and chemostratigraphic data and less Chumakov, N. M., Neoproterozoic glacial events in Eur altered by secondary processes, well exposed, and eas asia, Developments in Precambrian Geology, 2009, vol. 16, ily accessible for investigation. pp. 389–403. All these properties allow the Vendian section of Chumakov, N. M., Precambrian glaciations and associated biospheric events, Stratigr. Geol. Correlation, 2010, vol. 18, the Ura uplift to be recommended as a regional refer no. 5, pp. 3–15. ence section of the Vendian System for the southern Chumakov, N. M., Late Proterozoic African glacial era, part of Middle Siberia. Stratigr. Geol. Correlation, 2011, vol. 19, no. 1, pp. 3–23. Chumakov, N. M., Glacial deposits of the Nichatka Forma ACKNOWLEDGMENTS tion, Chara River basin and review of Upper Precambrian diamictites of Central Siberia, Mem. Geol. Soc. London, We are grateful to M.V. Leonov, S.V. Rud’ko, and 2011a, no. 36, pp. 297–302. A.B. Kuznetsov for the permission to use their unpub Chumakov, N. M. and Krasil’nikov, S. S., Lithological fea lished materials; Yu.K. Sovetov for valuable recom tures of Riphean tilloides of the Ura Uplift, Litol. Polezn. mendations; and O.A. Petrovichev for his help in pre Iskop., 1991, no. 3, pp. 58–78. paring the manuscript. This work was supported by the Chumakov, N. M., Kapitonov, I. N., Semikhatov, M. A., Russian Foundation for Basic Research (project et al., Vendian age of the upper part of the patom complex nos. 11 05 00232, 10 05 00294, 11 05 92692 IND) in Middle Siberia: U/Pb LA ICPMS dates of detrital zir cons from the Nikol’skoe and Zherba Formations, Stratigr. and Program no. 28 of the Presidium of the Russian Geol. 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