| 1. |
- Bibikova, E. V., et al.
(author)
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Sarmatia-Volgo-Uralia junction zone: Isotopic-geochronologic characteristic of supracrustal rocks and granitoids
- 2009
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In: Stratigraphy and Geological Correlation. - 0869-5938. ; 17:6, s. 561-573
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Journal article (peer-reviewed)abstract
- The geochronologic (U-Pb isotopic system of zircons) and isotopic-geochemical (Sm-Nd isotopic system of the bulk rock) studies were performed along the profile extending from the eastern Sarmatia (in the west) to the Middle Volga megablock of Volgo-Uralia (in the east), i.e., across the entire junction zone for dating the integration of Sarmatia and Volgo-Uralia, representing two segments of the East European Craton. It is established that the examined rocks are characterized by the Paleoproterozoic Nd isotopic model age, which varies from 2.1 and 2.4 Ga, except for some samples indicating a similar age of the crust through the entire Sarmatia-Volgo-Uralia junction zone. The highly metamorphosed complexes of the granulite and amphibolite facies constituting the southwestern margin of Volgo-Uralia are Paleoproterozoic, not Archean, in age, contrary to previous views. Two Early Paleoproterozoic lithotectonic complexes are defined in Volgo-Uralia: South Volga metasedimentary and Tersa metasedimentary-volcanogenic. The obtained data confirm the asynchronous integration of individual segments into the East European Craton: the integration of Sarmatia and Volgo-Uralia approximately 2100-2000 Ma ago was followed by the conjunction of this newly-formed continent with Fennoscandia ca. 1800 Ma ago.
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| 2. |
- Bibikova, E. V., et al.
(author)
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The early crust of the Volgo-Uralian segment of the East European Craton: Isotope-geochronological zirconology of metasedimentary rocks of the Bolshecheremshanskaya Formation and their Sm-Nd model ages
- 2015
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In: Stratigraphy and Geological Correlation. - 0869-5938. ; 23:1, s. 1-23
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Journal article (peer-reviewed)abstract
- We present the results of isotope-geochronological study of metasedimentary rocks of the Bolshecheremshanskaya Formation of the Volgo-Uralian segment of the East European Craton carried out to identify their protoliths. 16 samples of high-alumina gneisses from well cores were studied using the Sm-Nd isotope method and T-Nd(DM) model ages. Accessory zircons were selected from rocks with the most ancient model ages (more 3.2 Ga) in three wells: Minnibaevskaya 20000, Novo-Elkhovskaya 20009, and Zai-Karatayskaya 12930 in South Tatarstan. The isotope U-Pb dating of 200 zircon grains was performed on a Cameca 1280 NORDSIM secondary ion mass spectrometer at the Natural History Museum (Stockholm, Sweden). The most applicable sites for analysis of zircon crystals were pre-selected based on cathodoluminescence images. The analytical results demonstrate the diversity of zircon groups in age from 3.8 to 2.6 Ga and together with geochemical features of metasedimentary rocks of the Bolshecheremshanskaya Formation suggest the heterogeneous composition and age of provenance areas under denudation. Occurrence of Eoarchean and Paleoarchean zircons in the clastic material of the protolith of the Bolshecheremshanskaya gneisses indicates the existence of Early Archean crustal terrains in Volgo-Uralia.
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| 3. |
- Bogdanova, Svetlana, et al.
(author)
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Assembly and Breakup of Rodinia (Some results of IGCP project 440)
- 2009
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In: Stratigraphy and Geological Correlation. - 0869-5938. ; 17:3, s. 259-274
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Research review (peer-reviewed)abstract
- The principal results of project 440 "Assembly and Breakup of Rodinia" of the International Geological Correlation Programme (IGCP) are reviewed in this work. A map of that supercontinent compiled using geological and paleomagnetic data describes global paleogeography 900 Ma ago. The assembly of Rodinia, which comprised most of Precambrian continental blocks, lasted ca. 400 m.y. (from 1300 to 900 Ma). Its breakup presumably triggered by mantle superplume took place between 830 and 650 Ma. The correlation between tectonic events in different continental blocks is considered. Some problems concerning the Rodinia reconstruction and history, e.g., the slow growth of juvenile crust and effects of mantle-plume events during the amalgamation period and of glaciations at the breakup time, are discussed. The latter caused changes in the biosphere and climate, whereas postglacial periods stimulated progress in biota evolution.
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| 4. |
- Herman, AB, et al.
(author)
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Maastrichtian-Paleocene floras of Northeastern Russia and north Alaska and floral changes at the Cretaceous-Paleogene boundary
- 2004
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In: Stratigraphy and Geological Correlation. - 0869-5938. ; 12:5, s. 485-494
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Journal article (peer-reviewed)abstract
- Taphofloras of the Koryak Upland and the Sagwon Locality of North Alaska are described in terms of their taxonomic composition, stratigraphic ranges, and comparison with coeval floras of Northeastern Russia and Alaska. Causes and amplitude of changes in Arctic floras across the Cretaceous-Paleogene boundary are considered. In its aspect and taxonomic composition, the Late Maastrichtian flora of the Amaam Lagoon (the Koryak Upland) is very close to the early Paleocene Sagwon flora of North Alaska. This is inconsistent with a hypothesis of the global ecological crisis at the Cretaceous-Paleogene boundary. Development of floras was controlled by long-term climatic fluctuations and by evolution and migration of plants.
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