New data on acritarchs from the Upper Ordovician of the Tungus basin, Siberian platform

© 2014, Estonian Academy Publishers. All rights reserved. Distinctive late Ordovician acritarch assemblages have been discovered for the first time from about a 100 m sedimentary succession exposed along the Bol′shaya Nirunda River in Siberia. The studied stratigraphic interval includes the uppermost Baksian, Dolborian, Nirundian and Burian regional stages, which correspond to the Katian-?lowermost Hirnantian global stages. Acritarch assemblages from the Dolbor Regional Stage are exceptionally diverse and include aside from the longranging taxa several unique (endemic) morphotypes and a number of distinctive stratigraphically valuable species, well known outside Siberia. The occurrence of the acritarchs widespread outside Siberia is potentially important for interregional biostratigraphic correlations and might also play a significant role in biogeographic reconstructions. Having in mind that the Siberian palaeocontinent was located in a low-latitude tropical area during the entire Ordovician, the presence of taxa typical of cold-water settings along the Peri-Gondwana margin can be regarded as an additional evidence for penetration of cool-water currents into the epicontinental Tungus basin in the Upper Ordovician

Cryptospores from the Katian (Upper Ordovician) of the Tungus basin: The first evidence for early land plants from the Siberian paleocontinent

© 2015 Elsevier B.V.A diverse assemblage of cryptospores is reported for the first time from the Upper Ordovician of Siberia. It was discovered during a palynological study of a sedimentary succession of about 100 m, exposed along the Bolshaya Nirunda River, a right tributary of the Podkamennaya Tunguska River. The succession is located on the southern margin of the extensive epicontinental Tungus basin on the Siberian Platform between the Katanga and Yenisei land masses. The cryptospore assemblage was recovered from the siliciclastic-carbonate Dolbor Formation and scarcely from the overlying more carbonate Bur Formation. Both formations belong to the Katian Global Stage (Upper Ordovician). The cryptospores occur together with marine remnants (acritarchs, prasinophytes, chitinozoans, scolecodonts). It is similar to all known Upper Ordovician cryptospore assemblages in comprising naked and envelope-enclosed monads, dyads, tetrads and polyads. Although preservation is moderate to poor, the cryptospore taxa Velatitetras laevigata, Tetrahedraletes medinensis, Abditusdyadus laevigatus, Dyadospora murusdensa, Pseudodyadospora laevigata, Segestrespora laevigata and Sphaerasaccus glabellus can be identified. This report represents the first record of spores of the earliest land plants from the paleocontinent Siberia and therefore extends the global paleogeographical coverage of Late Ordovician cryptospores

Dielectric properties of 1:1 ternary Pb2B3+B5+O6 perovskite ceramics sintered from mechanochemically synthesized nanopowders

This study was supported by RFBR (project 17-03-01293_a) and by the Ministry of Education and Science of the Russian Federation (project 3.1649.2017/4.6)

Magnetic phase transitions in solid solutions of Fe-containing perovskite multiferoics

This study was supported by RFBR (project 18-52-00029_a) and by the Ministry of Education and Science of the Russian Federation (project 3.1649.2017/4.6)

Тhe effect of mechanical activation on the relaxor properties of PbMg1/3Nb2/3O3 - PbFe1/2Nb1/2O3 solid solution ceramics

This study was supported by RFBR (project 17-03-01293_a) and by the Ministry of Education and Science of the Russian Federation (project 3.1649.2017/4.6)

High potential for weathering and climate effects of non-vascular vegetation in the Late Ordovician

It has been hypothesized that predecessors of today’s bryophytes significantly increased global chemical weathering in the Late Ordovician, thus reducing atmospheric CO2 concentration and contributing to climate cooling and an interval of glaciations. Studies that try to quantify the enhancement of weathering by non-vascular vegetation, however, are usually limited to small areas and low numbers of species, which hampers extrapolating to the global scale and to past climatic conditions. Here we present a spatially explicit modelling approach to simulate global weathering by non-vascular vegetation in the Late Ordovician. We estimate a potential global weathering flux of 2.8 (km3 rock) yr−1, defined here as volume of primary minerals affected by chemical transformation. This is around three times larger than today’s global chemical weathering flux. Moreover, we find that simulated weathering is highly sensitive to atmospheric CO2 concentration. This implies a strong negative feedback between weathering by non-vascular vegetation and Ordovician climate

The piezoresponse force microscopy study of lead-free tetragonal tungsten bronze relaxor ceramics

Результаты структурных, электрофизических и СЗМ-исследований текстурированных образцов высокоплотной керамики бессвинцовых сегнетоэлектриков-релаксоров K2Sr4Nb10O30 и K4Bi2Nb10O30 со структурой типа тетрагональной вольфрамовой бронзы использованы для анализа природы их релаксорных свойств.The results of the structural, dielectric and SPM studies of the dense textured ceramics of lead-free tetragonal tungsten bronze ferroelectrics K2Sr4Nb10O30 and K4Bi2Nb10O30 were used for analysis of their relaxor properties.Работа выполнена при поддержке Проектной части Госзадания Минобрнауки № 3.1649.2017/ПЧ

Control of the degree of compositional ordering of Pb2YbМO6 (M - Nb, Ta) perovskites by means of mechanical activation

Установлено, что степень композиционного упорядочения ионов Yb3+и M5+(M-Nb, Ta) и соответственно - температуру и степень размытия сегнетоэлектрического фазового перехода в керамиках P 2Y МO6 можно изменять в широких пределах с помощью высокоэнергетической механоактивации. В частности впервые получены разупорядоченные модификации без использования каких-либо добавок.It was found out that compositional ordering degree of the Yb3+ and M5+ (M - Nb, Ta) ions in Pb2YbМO6 ceramics and correspondingly both the temperature and diffusion of ferroelectric phase transition can be varied within wide limits by means of high-energy mechanical activation. In particular, for the first time disordered modifications of Pb2YbМO6 were obtained without the use of any additives.Работа выполнена при поддержке Российского Фонда Фундаментальных Исследований (грант 17-03-01293_a) и Проектной части Госзадания Минобрнауки № 3.1649.2017/ПЧ