Vol 27, No 5 (2019)

ARTICLES
The mesoarchaean tonalite-trondhjemite-granodiorite associations of the Eastern Sarmatia: age and geological placement
Savko K.A., Samsonov A.V., Sal`nikova E.B., Kotov A.B., Larionov A.N., Korish E.H., Kovach V.P., Bazikov N.S.

Abstract

Two Mesoarchaean magmatism episodes (ca. 2.95 and 3.03 Ga) occurred within the Kursk domain of the Eastern Sarmatia. They formed the Saltyki complex granitoids with composition typical for Mesoarchaean cratons tonalite-trondhjemite-granodiorite associations (TTG). The mentioned episodes correlate well with the previously estimated geochronological boundaries for the Mesoarchaean Middle Dnieper and Azov domains (Ukrainian Shield) formation, which confirms the assumption that the Kursk domain was a part of the uniform Mesoarchaean Eastern Sarmatia nucleus. According to the Mesoarchaean Saltyki complex granitoids geochemical and Sm–Nd isotopic characteristics, the older TTG-gneisses seem to be the protolith for their formation.

Стратиграфия. 2019;27(5):4-18
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Early riphean billyakh group, Anabar Uplift, Northern Siberia: isotope C–O geochemistry and Pb–Pb age of dolostones
Gorokhov I.M., Kuznetsov A.B., Semikhatov M.A., Vasil`eva I.M., Rizvanova N.G., Lipenkov G.V., Dubinina E.O.

Abstract

U and Pb contents and C, O and Pb isotope composition have been determined in dolostones of the Billyakh Group (in 6 samples of the Kotuikan Formation and 15 samples of the Yusmastakh formation) which comprises the upper part of the Riphean section of the Anabar Uplift. The δ13С and δ18O values in the Billyakh dolostones vary respectively from –3.0 to +0.8‰ PDB and from 23.7 to 27.3‰ SMOW and conform with those in carbonate deposits precipitated 1600–1400 m.y. ago. In the 206Pb/204Pb–207Pb/204Pb diagram, 18 data points of all the dolostone samples of the Kotuikan and Yusmastakh formations are arranged along the straight line which corresponds to the age of 1513 ± 35 Ma. This age for the first time provides immediate geochronological description of the sedimentary rocks from the cover of the Anabar Uplift. Coupled with previously published Rb–Sr glauconite age of the subjacent Ust’-Il’ya formation, this date allows to place all the sedimentary succession of the Billyakh Group into the Early Riphean. These results are indicative of the relatively fast (within ~10 m.y.) accumulation of terrigenous-carbonate deposits of the Billyakh Group preceding injection of dolerites of the Kotui Complex and emplacement of Mesoproterozoic Kuonamka Igneous Province on Siberian Craton. The new data put a full stop in discussions about age position of the Riphean deposits exposed on the Anabar Uplift.

Стратиграфия. 2019;27(5):19-35
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Age constraints and stratigraphic significance of the microbiotes of the kaltasa formation of the lower riphean of the Volgo-Ural region
Sergeev V.N., Semikhatov M.A., Vorobyeva N.G., Sergeeva N.D., Mukund S.

Abstract

Based on previously obtained and new materials, the association of organ-walled microfossils represented by morphologically complex and large forms from the Kaltasa Formation is considered. In general, the Kaltasa microbiota resembles many associations of Neoproterozoic microfossils (late Riphean and Vendian). It was mistakenly interpreted as Late Riphean in its initial description, although the late Riphean index taxons were absent, and geological data indicated its early Riphean age. The early Riphean age of the Kaltasinskaya Formation has been confirmed in a series of studies in recent years using Re–Os, U–Pb and other modern methods of isotopic geochronology. Additionally, the low ratios of 87Sr/86Sr and almost invariant ō13C values in the surrounding sediments are comparable with the isotopic characteristics of Mesoproterozoic strata that are older than 1300 million years. The use of geochemical methods using high-reagent iron (FeHR), as well as carbon and sulfur isotopes showed the presence of aerobic conditions during the deposition of relatively deep-water sediments of the Arlan Member of the Kaltasinskaya Formation (FeHR/FeT ratio <0.38). This contradicts the general concept of the existence of an anoxic ocean in the Mesoproterozoic, but explains the presence in the microbiota composition of morphologically complex and large eukaryotic forms that are widely distributed in oxygenic environments of the Neoproterozoic.

Стратиграфия. 2019;27(5):36-45
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The upper riphean of the Yenisei range: Sr-chemostratigraphy and Pb–Pb age of the tungusik and shirokaya groups limestone
Kuznetsov A.B., Kochnev B.B., Vasilyeva I.M., Ovchinnikova G.V.

Abstract

The Pb–Pb isotope age and the Sr isotope signature of sedimentary limestones of the Upper Riphean of the south of the Yenisei Range on the western margin of the Siberian Platform were obtained. The Pb–Pb age of carbonate sediments of the Dadykta Formation of the Tungusik Group in the Kamenka facial zone in the east of the Yenisei Range is 1020 ± 20 Ma. The Pb–Pb age of limestone of the Gorevka Formation of the Shirokaya Group in the Glushikha facies zone in the west of the region is estimated at 1020 ± 70 Ma. The 87Sr/86Sr ratio in the limestones of the Dadykta Formation lies within 0.70536–0.70590, and that of the Gorevka – 0.70552–0.70578. This coincides with a decrease in 87Sr/86Sr ratio in paleoocean immediately after the culmination of the Grenville orogeny. The correlation of the Shirokaya Group with the Oslyanka Group of the Kamenka zone with other data restricts the accumulation of the Tungusik, Shirokaya, and Oslyanka groups at 1030–950 Ma intervals. The isotope age of the Middle and Upper Riphean boundary at the base of the Tungusik Group of the Yenisei Range is estimated at 1030 Ma, which is consistent with the age of this boundary in the sections of the Turukhansk Uplift and the Uchur-Maya region of Siberia. It was revealed that most part of the Upper Riphean (Neoproterozoic) in the sedimentary record of the Yenisei Range is absent. The observed facial zonality of the Riphean sediments of the Yenisei Range represents the configuration of the ancient sedimentary basin that existed on the western margin of the Siberian Platform long before the collision, accompanied by granite intrusions and metamorphism, in the Neoproterozoic.

Стратиграфия. 2019;27(5):46-62
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Age and sources of terrigenous rocks of basal bench of the Tsagaan-Olom group of the Dzabkhan terrane: results of U–Th–Pb geochronological, Lu–Hf and Sm–Nd isotopic studies
Kovach V.P., Kozakov I.K., Wang K.L., Plotkina Y.V., Lee H.Y., Chung S.L.

Abstract

The results of the U–Th–Pb geochronological (LA-ICP-MS) and Hf-isotope (LA-MC-ICP-MS) studies of detrital zircons from sandstones as well as results of Nd-isotope studies of whole rocks from the tillite-bearing Maikhan-Uul Formation of the Tsagaan-Olom Group of the shelf cover of the southeastern part of the Dzabkhan terrane of the Central Asian Orogenic Belt are considered. The obtained data allowed to establish that the sources of sandstones of the Maikhan-Uul Formation of the Tsagaan-Olom Group were rocks of the Neoproterozoic and the early Precambrian complexes with Archean and Paleoproterozoic Hf and Nd model ages, as well as the Neoproterozoic igneous rocks formed from both juvenile and crustal sources. The age of the sandstones of the Maikhan-Uul is in the range of ca. 720–660 Ma. It is shown that a large-scale manifestation of convergence processes with the formation of the juvenile crust and the re-working of the ancient continental crust is established in the structures of the central segment of the Central Asian Orogenic Belt in the early Neoproterozoic (ca. 960–780 Ma). Most likely, these processes reflect the development of the global subduction system in the paleooceanic region of the Rodinia supercontinent margins.

Стратиграфия. 2019;27(5):63-81
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The base of the vendian in the South Urals: Rb–Sr age of glauconite of the bakeevo formation
Zaitseva T.S., Kuznetsov A.B., Gorozhanin V.M., Gorokhov I.M., Ivanovskaya T.A., Konstantinova G.V.

Abstract

The mineralogical, crystallochemical and geochronological study of globular phyllosilicates (GPS) of glauconite–illite series from the Bakeevo Formation was performed. This formation is the basal member of the Vendian Asha Group in the South Urals. Monomineral GPS-fractions representing the globules of varied size and density are composed of Al-glauconite and illite. Rb–Sr dating of the GPS of the Bakeevo Formation in combination with modeling of cation distribution in their structure and comparison of the model data with Mössbauer and IR spectroscopy data was carried out for the first time. Rb–Sr age of the Bakeevo glauconite is 642 ± 9 Ma. Mineralogical and geochemical characteristics in combination with theoretical calculations show that the stratigraphic significance of this age is quite reasonable. The initial ratio 87Sr/86Sr in the glauconitization environment is 0.7080 ± 0.0009 and within the experimental error is consistent with this ratio in Vendian sea water. Hence the lower boundary of the Vendian in the South Urals has an age of about 640 Ma.

Стратиграфия. 2019;27(5):82-96
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C- and Sr-isotope chemostratigraphy and Pb–Pb age of carbonaceous sediments of the vorogovka group (neoproterozoic), northwestern Yenisei ridge
Kochnev B.B., Kuznetsov A.B., Pokrovsky B.G., Sitkina D.R., Smirnova Z.B.

Abstract

C- and Sr-isotope record is received and Pb–Pb age is determined from carbonaceous sedimentary rocks of Vorogovka Group in the type section at Vorogovka River, northwestern Yenisei Ridge. The sequence of the group consists of the Severnaya Rechka, Mutnina and Sukhaya Rechka Formations that fill a large trough, and lithological and textural features indicate the rapid sedimentation. Most carbonaceous rocks are presented by limestones with low Fe/Sr and Mn/Sr relations and average δ18O value –6.0 ± 1.6‰ V-PDB indicating the well-preserved isotope systems of the rocks. 87Sr/86Sr relations and δ13С values vary within narrow limits as 0.70816–0.70826 and –1.4…+0.8‰ for upper Severnaya Rechka limestones and as 0.708180.70829 and +1.0…+2.0‰ for Sukhaya Rechka limestones, respectively. Pb–Pb isochronous age of carbonaceous rocks of the Severnaya Rechka Formation is 580 ± 40 Ma (MSWD = 1.4), and of Sukhaya Rechka Formation is 565 ± 90 Ma (MSWD = 1.1). Judging from chemostratigraphical and isotope-geochronological data, the forming of limestone sediments of Vorogovka Group could occur at 580–550 Ma ago, that corresponds to the Late Vendian or the Late Ediacaran. The endurance of accumulation of Vorogovka Group likely not exceeded 10–15 Myr. Vorogovka Trough differed in the type of sedimentation from other Late Vendian marginal troughs at the southwestern Siberian Platform, and formed independently from them.

Стратиграфия. 2019;27(5):97-112
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Paleobiogeographic analysis of the assemblages of late vendian macrofossils
Zakrevskaya M.A.

Abstract

The similarity analysis of the taxonomic composition of the 13 main localities of the Vendian macrofossils worldwide was performed according to the Ohai coefficient. There are two distinct subgroups among shallow-marine localities. The first subgroup consists of the following localities: Australia, the southeastern White Sea area, Podolia, India, and the Urals (degree of similarity 0.16–0.38). The second subgroup includes the localities of Siberia, Northwest Canada, Southern China, South America, Southern Namibia, and the USA (degree of similarity is up to 0.58). Such a division of the shallow-marine localities corresponds to the spread of carbonate sediments and the distribution of the tubular problematical species Cloudina. It can be assumed that this difference occurs due to the association of the localities of the second subgroup to warm-water climatic conditions (precipitation of carbonates, distribution of problematical remains with a carbonate skeleton), while the localities of the first subgroup are confined to cold-water conditions. Thus, the performed analysis indicates the location of the cratons of Australia, Baltica, and India at high latitudes (which differs from the results demonstrated in some paleotectonic reconstructions based on paleomagnetic studies) and confirms the hypothesis of the location of the Siberian platform at tropical and subtropical latitudes. Based on the conducted analysis, two paleobiogeographical areas were identified for the Late Vendian: the Subpolar area (Australia, Baltica, India) and the Equatorial area (Siberia, Laurentia, Kalahari, South China, Rio de la Plata).

Стратиграфия. 2019;27(5):113-122
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