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Petrogenesis and geodynamics of volcanic rocks late precambrian the northwest Pay-Khoy
T. A. Kaneva
Mineral and chemical composition of the Late Precambrian igneous rocks of northwestern Pay-Khoy, their evolution and paleogeodynamic position to date have been insufficiently studied. The results of the study of the Late Precambrian igneous rocks of northwestern Pay-Khoy are given in the publication. We used the methods of optical and electron microscopy, chemical and isotopic analysis. It was found that the Late Precambrian igneous rocks of northwestern Pay-Khoy were formed in the island-suprasubduction environment and back-arc spreading environment. Geological, petrographic and petrogeochemical data suggested the existence of two spatially separated island arcs. The rocks of morozovskaya suite recorded as early stage of island arc magmatism, and situation back-arc spreading, and sokolninskaya suite - developed stage. Fractional crystallization was the main mechanism of evolution of the melts from which Late Precambrian igneous rocks of northwestern Pay-Khoy were formed.
Keywords: subduction zone, island arc, volcanic rocks, clinopyroxene, fractional crystallization, Late Precambrian igneous rocks, northwestern Pay-Khoy.
DOI: 10.19110/2221-1381-2016-12-3-15
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Late holocene small mammals from localities of Sharyu river valley (Chernyshev’s ridge)
I. V. Kryazheva, D. V. Ponomarev, T. van Kolfschoten, J. van der Plicht
The Holocene history of small mammal fauna is of interest as an example of transformation of communities under the natural changes of climate. Study object were 2720 molars of small mammals from localities in Sharyu River valley (left tributary of Usa River). Molars were studied by standard palaeontological techniques. 14C AMS method was used for dating of fossil assemblages. All localities are zoogenic sites with abundant fossil remains of vertebrates. In the result, two phases of micromammalian fauna development in the Chernyshev’s Ridge are described: Subatlantic and modern periods. It was revealed that typical taiga forest assemblages of small mammals inhabited the Chernyshev’s Ridge during Subatlantic time. This fauna was nearly identical to micromammalian communities of the same interval in the Subpolar Urals but contrasted to tundra assemblages of the eastern slope of the Polar Urals. Species composition differences between Sharyu—2 and Sharyu—3 were caused by the hunting activity of different species of avian predators (diurnal raptors and owls). Alternations between recent micromammalian assemblages of the Chernyshev’s Ridge and communities of adjacent territories are linked to differences in taphonomy.
Keywords: small mammals, Late Holocene, Chernyshev’s ridge, northeastern part of European Russia.
DOI:10.19110/2221-1381-2016-12-16-22
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Petrographical features of Upper Frasnian volcaniclastic graywackes in Jalangaskul region
(West-Magnitogorsk zone of South Ural)
A. M. Fazliakhmetov, M. J. Arzhavitina, A. A. Gilyazov
The Frasnian deposits of the West Magnitogorsk Zone of the Southern Urals have been studied for several decades. Despite this, the authors discovered sequence of high-silica volcaniclastic graywackes and chert in Yalangaskul Lake region. Our study revealed previously unknown features of the geological development of the territory at the end of the Frasnian. The detected sequence was traced along by route observations and airborn photographs. As a result, it was found that the sequence is a lens with length of 30—35 km and a maximum thickness of 350 meters.
The petrographic study of sandstones allowed determining them as greywacke and feldspar greywacke. Clasts of high-silica vulcanites, quartz and feldspars are dominated, fragments of medium and basic volcanites, cherts and quartzites are found in smaller amounts. Four genetic groups of fragments were identified: pyroclastic, volkanoterrigenous, intraclastic and quartzites with unclear genesis. Mortar texture in sandstones was described. The presence of interbedding, cyclicality and association sandstones with cherts points out the deep-sea environment and supply sediments by means of turbidity current. The source area was region of volcanic activity, where explosion material, products of erosion of lithified volcanic rocks and soft siliceous fine-clastic sediments were involved in sedimentary process.
On the base of high-silica volcaniclastic greywackes position they can be attributed presumably to the bottom of the Biyagodinskaya suite, which corresponds to the upper horizons of the Frasnian.
Keywords: graywackes, mortar texture, tephraturbidities, deepwater deposits, the Biyagodinskaya suite, the Frasnian, South Ural.
DOI: 10.19110/2221-1381-2016-12-23-30
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In-situ burials of benthic communities in Wenlock storm sediments of the Chernov Swell
T. M. Beznosova, V. Yu. Lukin, V. A. Matveev
The represented data suggest storm mode of sedimentation with predominance of wave turbulence in the Wenlock. We found unique in-situ burials of benthic communities and remains of mineralized biota in stromatolites, replaced by pyrite, which formation had been caused by anoxic conditions after the organism death. The obtained results support reconstruction of evolution of the Early Silurian ecosystems.
Keywords: storm sediments, taphonomy, brachiopods, tabulate corals, stromatolites.
DOI:10.19110/2221-1381-2016-12-31-36
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Temperature survey of zircon from the granitoids of the Subpolar Urals
Yu. V. Denisova
Now significant experience of use of zircon as geothermometer was accumulated. This allows applying different methodologies to determine a more accurate temperature mode of formation of the given rocks. The study results of accessory granitoids zircon of the Subpolar Urals (the Badjaju, Yarot, Kozhim and Nikolaihsor massifs) are presented in this paper. The temperatures of crystallization of the mineral using thermometry of zircon saturation and the classic evolutionary — morphological analysis were determined. The comparison of data, obtained in different ways, was carriedout. The temperatures of formation of the studied massifs of the Subpolar Urals were specified.
Keywords: accessory zircon, granitoid, the Badjaju massif, the Yarot massif, the Kozhim massif, the Nikolaihsor massif, the Subpolar Urals, Pupin, Watson.
DOI: 10.19110/2221-1381-2016-12-37-44
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| Chronicle, events, facts |
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Rafting the Volonga River down to the Devonian delta
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Geological heritage of Komi Republic. All about quartz
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21st century crystallography outlines at the First Russian Crystallography Congress
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Biostratigraphist, paleontologist and paleoecologist
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Media mirror
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The rarest element (Kozyreva's Jubilee)
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