The most recent (682-792 C.E.) volcanic eruption in the Jombolok lava field, East Sayan, Central Asia triggered exodus of Mongolian pre-Chinggis Khaan tribes (778-786 C.E.)

International audienceThis study presents new data on one of the most recent (historical) volcanic eruptions in Central Asia. The Jombolok lava field located in the East Sayan Mountains (Southern Siberia) was formed during Late Pleistocene and Holocene times. At least four phases of volcanic activity have been identified and evidences associated with the last phase have been found in the upper reaches of the Khi-Gol valley and in the Oka-Jombolok basin. The volcanic activity is represented by young basaltic lava located among older lavas. Live and dead trees have been sampled in the young lava field. Nine fragments of wood have been found embedded in lavas of the latest eruption. Dendrochronological analysis, radiocarbon dating and the analysis of historical chronicles have shown that the latest eruption occurred during the period 682-792 A.D. The volcanic activity possibly triggered the migration of Mongolian tribes out of the locality known in historical chronicles as Ergune-Kun towards the Onon River, which, 400 years later, became the place of birth and rise of Chinggis Khaan

The use of composite binders and nanomodifiers for fiber-reinforced concrete

The article presents the results of studies on the production of fiber-reinforced concrete with mineral fibers produced in a plasma reactor, composite binders and nanomodifying additives. For dispersed reinforcement of concrete, basalt mineral fibers obtained by the electrothermal method in a plasma-arc reactor were used. To reduce the negative impact of Portland cement, composite binders based on Portland cement and fly ash were used. Fly ash meets the requirements of standards and is suitable for using it as a part of building materials. The nanosilica produced at an electron accelerator was used for comparison. The introduction of nanosilica improves the mechanical properties of cement by accelerating the hydration processes of Portland cement, improving the microstructure and changing the phase composition of the cement stone. The optimal content of fly ash in the composite binder, which allows obtaining high mechanical properties, has been determined. To reduce water content in the binder super plasticizer polycarboxylate type was used

U‐PB LA‐ICP‐MS ДАТИРОВАНИЕ ЦИРКОНОВ ИЗ СУБВУЛКАНИТОВ БИМОДАЛЬНОЙ ДАЙКОВОЙ СЕРИИ ЗАПАДНОГО ЗАБАЙКАЛЬЯ: МЕТОДИКА, СВИДЕТЕЛЬСТВА ПОЗДНЕПАЛЕОЗОЙСКОГО РАСТЯЖЕНИЯ ЗЕМНОЙ КОРЫ

Our study investigates a possibility of using isotope ratios of U‐Th‐Pb system in zircon analysis by the LA‐ICP‐MS technique and monitoring of precision, convergence and accuracy. New U‐Pb isotope‐geochronological data has been obtained for the salic and mafic members of the bimodal Late Paleozoic series of subparallel dykes in the central part of the Western Transbaikalia. It is shown that a series of subparallel dykes (290–280 Ma) gives evi‐ dence of extension of the continental crust at the final stage of the Late Paleozoic granitoid magmatism. Similar ages of zircons in the salic and mafic subvolcanic rocks confirm the geological indicators of the coexistence and interactions between the magmas of contrasting compositions.Оценена возможность использования изотопных отношений U‐Th‐Pb системы при анализе цирконов методом LA‐ICP‐MS путем мониторинга прецизионности, сходимости и правильности. Получены новые U‐Pb изотопно‐геохронологические данные для салических и мафических членов бимодальной позднепалеозойской серии субпараллельных даек центральной части Западного Забайкалья. Показано, что формирование серии субпараллельных даек (290–280 млн лет назад) фиксирует условия растяжения континентальной коры на заключительном этапе позднепалеозойского гранитоидного магматизма. Близкий возраст цирконов салических и мафических субвулканитов подтверждает геологические признаки сосуществования и взаимодействия контрастных магм

Environmental drivers of biseasonal anthrax outbreak dynamics in two multihost savanna systems

Environmental factors are common forces driving infectious disease dynamics. We compared interannual and seasonal patterns of anthrax infections in two multihost systems in southern Africa: Etosha National Park, Namibia, and Kruger National Park, South Africa. Using several decades of mortality data from each system, we assessed possible transmission mechanisms behind anthrax dynamics, examining (1) within- and between-species temporal case correlations and (2) associations between anthrax mortalities and environmental factors, specifically rainfall and the Normalized Difference Vegetation Index (NDVI), with empirical dynamic modeling. Anthrax cases in Kruger had wide interannual variation in case numbers, and large outbreaks seemed to follow a roughly decadal cycle. In contrast, outbreaks in Etosha were smaller in magnitude and occurred annually. In Etosha, the host species commonly affected remained consistent over several decades, although plains zebra (Equus quagga) became relatively more dominant. In Kruger, turnover of the main host species occurred after the 1990s, where the previously dominant host species, greater kudu (Tragelaphus strepsiceros), was replaced by impala (Aepyceros melampus). In both parks, anthrax infections showed two seasonal peaks, with each species having only one peak in a year. Zebra, springbok (Antidorcas marsupialis), wildebeest (Connochaetes taurinus), and impala cases peaked in wet seasons, while elephant (Loxodonta africana), kudu, and buffalo (Syncerus caffer) cases peaked in dry seasons. For common host species shared between the two parks, anthrax mortalities peaked in the same season in both systems. Among host species with cases peaking in the same season, anthrax mortalities were mostly synchronized, which implies similar transmission mechanisms or shared sources of exposure. Between seasons, outbreaks in one species may contribute to more cases in another species in the following season. Higher vegetation greenness was associated with more zebra and springbok anthrax mortalities in Etosha but fewer elephant cases in Kruger. These results suggest that host behavioral responses to changing environmental conditions may affect anthrax transmission risk, with differences in transmission mechanisms leading to multihost biseasonal outbreaks. This study reveals the dynamics and potential environmental drivers of anthrax in two savanna systems, providing a better understanding of factors driving biseasonal dynamics and outbreak variation among locations.The National Science Foundation of South Africa.https://onlinelibrary.wiley.com/r/ecmam2023Veterinary Tropical Disease

УСЛОВИЯ ПЛАВЛЕНИЯ ГРАНИТОИДНЫХ КСЕНОЛИТОВ В КОНТАКТЕ СО ЩЕЛОЧНО‐БАЗИТОВОЙ МАГМОЙ (ГУСИНООЗЕРСКАЯ ДАЙКА, ЗАПАДНОЕ ЗАБАЙКАЛЬЕ): К ПРОБЛЕМЕ ПРОИСХОЖДЕНИЯ УЛЬТРАКАЛИЕВЫХ КИСЛЫХ РАСПЛАВОВ

The alkaline mafic (lamprophyric) Gusinoozerskaya dyke in West Transbaikalia is composed of partially melted granite xenoliths. Among the xenoliths, two melted substrates are observed: (1) plagioclase and quartz, and (2) alkaline feldspar and quartz. Few millimeters thick microfelsite and microgranophiric rims are the products of melting around the granite xenoliths. Ultra‐acid glass is observed in the inner parts of the xenoliths at the boundary of quartz and feldspars. A distinctive feature of the fresh melts (regardless of the composition of the protolithic sub‐ strate) is an increased content of potassium with K2O/Na2O≥2. Having compared the compositions of the products of contact melting with the experimental data, we conclude that melting took place in the presence of alkaline‐chloride and/or alkaline‐carbonic fluid released from the crystallizing host alkaline‐basic magma. The probable geotectonic conditions for the occurrence of ultrapotassic acid magmas are estimated.Щелочно‐мафическая (лампрофировая) Гусиноозерская дайка (Западное Забайкалье) содержит гранитные ксенолиты, испытавшие частичное плавление. Среди ксенолитов выявлено два субстрата, претерпевших плавление: 1) плагиоклаз и кварц и 2) щелочной полевой шпат и кварц. Продукты плавления представляют собой микрофельзитовые и микрогранофировые оторочки вокруг гранитных ксенолитов мощностью в первые миллиметры. Во внутренних частях ксенолитов на границе кварца и полевых шпатов наблюдается ультракислое стекло. Отличительной особенностью новообразованных расплавов, независимо от состава протолитового субстрата, является их повышенная калиевость с отношением K2O/Na2O≥2. На основе сопоставления составов производных контактового плавления с экспериментальными данными показано, что плавление происходило в присутствии щелочно‐хлоридного и/или щелочно‐углекислого флюида, выделявшегося из кристаллизующейся вмещающей щелочно‐основной магмы. Оценены вероятные геотектонические условия возникновения ультракалиевых кислых магм

Patterns of mega-forest fires in east Siberia will become less predictable with climate warming

Very large fires covering tens to hundreds of hectares, termed mega-fires, have become a prominent feature of fire regime in taiga forests worldwide, and in Siberia in particular. Here, we applied an array of machine learning algorithms and statistical methods to estimate the relative importance of various factors in observed patterns of Eastern Siberian fires mapped with satellite data. More specifically, we tested linkages of “hot spot” ignitions with 42 variables representing landscape characteristics, climatic, and anthropogenic factors, such as human population density, locations of settlements and road networks. Analysis of data spanning seventeen years (2001–2017) showed that during low or moderately high fire seasons, models with full set of variables predict locations of fires with a very high probability (AUC = 95%). Sensitivity, or the ratio of correctly predicted fire pixels to the total number of pixels analyzed, declined to 30–40% during warm and dry years of increased fire activity, especially in models driven by anthropogenic variables only. This analysis demonstrates that if warming in Eastern Siberia continues, forest fires will become not only more frequent but also less predictable. We explain this by examining model performance as a function of either temperature or precipitation. This effect from climate makes it nearly impossible to segregate ignition points from locations, which were burnt several hours or even several days earlier. An increase in secondary burnt locations makes it difficult for machine learning algorithms to establish causality links with anthropogenic and other groups of variables

U‐PB LA‐ICP‐MS DATING OF ZIRCONS FROM SUBVOLCANICS OF THE BIMODAL DYKE SERIES OF THE WESTERN TRANSBAIKALIA: TECHNIQUE, AND EVIDENCE OF THE LATE PALEOZOIC EXTENSION OF THE CRUST

Our study investigates a possibility of using isotope ratios of U‐Th‐Pb system in zircon analysis by the LA‐ICP‐MS technique and monitoring of precision, convergence and accuracy. New U‐Pb isotope‐geochronological data has been obtained for the salic and mafic members of the bimodal Late Paleozoic series of subparallel dykes in the central part of the Western Transbaikalia. It is shown that a series of subparallel dykes (290–280 Ma) gives evi‐ dence of extension of the continental crust at the final stage of the Late Paleozoic granitoid magmatism. Similar ages of zircons in the salic and mafic subvolcanic rocks confirm the geological indicators of the coexistence and interactions between the magmas of contrasting compositions

Trends in dynamics of forest upper boundary in high mountains of northern Baikal area

Studies of spatial-temporal variability of the upper boundary of the forest on the north-western coast of Lake Baikal (Baikal and Upper Angara Ridges) are performed on the base of the analysis of forests renewal processes and of the dynamics of larch radial increment in the ecotone of the forest upper boundary and out of it. The presence of a large amount of well-developed uplands and circuses with considerable heights drops in the structure of mountain system favours formation of interrupted boundary between forest and subgoltsy belt. The timber stand of the upper forest boundary in the studied area is represented by Daurian larch. Three tree-ring chronologies of larch are obtained. The longest chronology is obtained for mountain taiga belt of Baikal Ridge and is as long as 460 years. Since 1980ies, a sustainable trend of increase of radial trees growth is observed. It is observed the most distinctly in trees of the upper forest boundary on the Baikal Ridge. There is advancing of trees species into subgoltsy belt and into mountain tundra, which depends, respectively, on slopes heights, exposition and tilting, on sites of growth of concrete cenoses. Modern peculiarity of the vegetation of the studied area is presence of abundant viable larch undergrowth (from 2–3 to 25 y.o.) and fir in the ecotone of upper forest boundary and in subgoltsy belt, as well as appearing of single specimens of spruce. Main undergrowth mass (2/3) is presented by trees aged in average 15–25 y.o., i.e., they appeared in late 1980ies. Due to increase of snow cover thickness in winter, the trees young growth obtained great protection from freezing resulting in the increase of ability of young growth to live up to elder age