Baikal Rift Zone Research Articles

Elevated Mercury in the Water of the Angara River Source: A Response to Geodynamic Impacts and Strong Earthquakes

The mercury concentrations in the water of the Angara River Source (runoff of Lake Baikal) are compared to temporal distributions of earthquakes of various magnitudes that occurred at various distances from the water-sampling site. It is established that all significant mercury maxima in the water are preceded by strong geodynamic impacts in the Baikal Rift Zone. The predictive estimates of the average annual mercury concentration indicate a possible significant increase in its levels in local areas of fluid discharge of faults under an intense geodynamic impact. The opening of deep faults during strong movements is expected to lead to decompression with mercury degassing and rapid rise to the surface along the fault zones.

Верхняя мантия Прибайкалья и Забайкалья по данным площадных сейсмологических исследований

According to the areal interpretation of seismological data from sufficiently strong earth-quakes, new information on the velocity structure of the upper mantle of the Baikal and Trans-Baikal regions is presented. Based on the results of a tomographic interpretation of the travel times of P and S waves from the Mokhorovichich border, maps of the boundary velocities of longitudinal and transverse waves in the Baikal and Transbaikalia, the ratios of the velocities of the P and S waves (Vp/Vs), and the distribution of the Poisson's ratio (σ) are constructed. The boundary velocity in the northwestern, northern, and northeastern parts of the research area (within the Baikal rift zone) according to longitudinal and transversal waves has lower values of 7.80-7.95 km/s and 4.45-4.55 km/s, respectively. In the upper mantle of the southeastern part of the area, the mantle block is about 600x600 km in size with high longitudinal and transversal wave’s velocities of 8.40-8.45 km/s and 4.80-4.85 km/s, respectively, and increased values of Vp/Vs and σ. The assumption of its nature as a plate of eclogites (or eclogite-like rocks) in the region of the Mongol-Okhotsk orogenic belt is justified. The results were compared with materials from other research.

Эволюция палинокомплексов отложений аллювиальной формации Байкальской рифтовой зоны в неогене

Введение: В настоящее время остается не решенной проблема выделения стратонов в осадочных отложениях неогенового периода территории Байкальской рифтовой зоны. Для решения этого вопроса необходимо провести сопоставление результатов палинологических исследований отложений позднего кайнозоя Восточных Саян и южного побережья озера Байкал и их систематизацию в хронологическом ряду палеогена-неогена. Методика: Все образцы обрабатывались по сепарационному методу Гричука, который включает: обработку 10% соляной кислотой (HCl), щѐлочью (NaOH), плавиковой кислотой(HF) и тяжѐлой жидкостью (KJ+CdJ+H2O). После обогащения мацерат просматривался под микроскопом с увеличение х400-х600. Принадлежность спор и пыльцы к секциям, родам и видам определялась по признакам морфологического строения экзины, энтины, апертурного аппарата, пор и наличия борозд. Результаты и обсуждение: Описанный палинологический материал отложений озерно-аллювиальной формации южного побережья Байкала и осадочных образований, перекрытых базальтами тиссинской серии на территории Восточных Саян, сопоставлен с данными стратотипических разрезов прилегающих регионов. Это позволило обосновать соответствие полученных данных стратиграфическим рубежам региональной схемы неогена. В эоцене в общем составе пыльцы преобладают покрытосеменные. Последний этап олигоцен характеризуется преобладанием голосеменных. В нижнем миоцене также преобладает пыльца голосеменных, но в отличие от олигоцена увеличивается количество пыльцы покрытосеменных. Для среднего миоцена характерно богатое видовое разнообразие пыльцы как покрытосеменных, так и голосеменных пород. В плиоцене ведущее значение занимает пыльца голосеменных. Заключение: Детальный анализ состава палинокомплексов позволил впервые обозначить наличие на данной территории отложений палеогеновой системы и выстроить в хронологическом ряду спорово-пыльцевые комплексы неогена. На основе палинологических исследований в Байкальской рифтовой зоне, определены хронологические рубежи базальтовых покровов тиссинской серии, в рамках миоцена-нижнего плиоцена. А также возрастные границы толщ и свит озерно-аллювиальной формации южного побережья Байкала в рамках верхнего эоцена-нижнего плиоцена.

Migrating Seismicity in the Lithosphere of the Baikal Rift Zone: Spatiotemporal and Energy Distribution of Earthquake Chains

Abstract ––Quasi-linear sequences of the epicenters of strong earthquakes, identified in many seismically active regions, are phenomenologically viewed as “migrations” of earthquake sources. Following this analogy, an earthquake chain is understood in this paper as a set of seismic events of different energies, leading to a quasi-linear one-way change in the position (“migration”) of the successive epicenters of shocks on the surface of the lithosphere zone under study. Based on this statement, a formalized method for an azimuthal analysis of seismicity is developed, which allows one to identify and isolate earthquake chains from arrays of seismological data presented in the standard format of a catalog of earthquakes. As this method is tested on a catalog of earthquakes and a catalog of simulation events, all model chains of events and a large number of earthquake chains and simulation events are identified. It is indicated by isolating chains in a random field of simulation events that some of these earthquake chains can be formed by a random spatiotemporal combination of shocks. Migrating seismicity in the lithosphere of the Baikal rift zone (BRZ) is studied by applying the method of identification and isolation of earthquake chains to materials from the “Catalog of Earthquakes of the Baikal region”. According to data on 52,700 earthquakes with a representative energy class KP ≥ 8, occurring in the Baikal region from 1964 to 2013, there are 2143 earthquake chains identified and isolated within an angular sector of azimuthal analysis q = 10° (±5° from azimuth α to the epicenter). As the angular sector of azimuthal analysis increases to q = 20° (±10°), there is an approximately twofold increase in the number of chains (M = 4245). As shown by the analysis and comparison of spatiotemporal distribution of earthquakes and earthquake chains, the spatiotemporal and energy distribution of chains of seismic events is formed by earthquake distribution in the BRZ. Beyond this zone, the chains are small in number. The established relationship between the distributions of earthquakes and earthquake chains in space, in time, and by energy indicates that in the epicentral field of seismicity of the BRZ, both “seismicity migration” chains and randomly formed chains (“pseudomigration” chains) are identified. The migrating seismicity of the BRZ is studied according to the seismicity statistics by using the criteria developed within the framework of the simulation base model of migrating seismicity to the results obtained. An index of seismicity migration activity (ISMA) that reflects a seismicity migration/pseudomigration ratio at the set level of significance is used to obtain distribution maps over the territory and graphs of changes over the years for this index. The maps show that small areas ISMA > 1 are seen in close proximity to rifting attractor structures (RASs), while seismicity migration in the rest of the BRZ is not statistically obvious. The graphs show that periods ISMA > 1 at three levels of significance are observed three to four years after the activation of RASs, which makes it possible to estimate the phase propagation velocity of a slow deformation perturbation of about 250–300 km/year. It is indicated by the results obtained that the migrating seismicity of the BRZ is directly related to the location and activations of RASs and that the RASs are the sources of local deformation perturbations in the BRZ lithosphere, which, among other things, manifest themselves in the implementation of seismicity migration chains.

Биология рыб озера Фролиха (Северный Байкал, Восточная Сибирь)

The fish fauna of Lake Frolikha comprises 12 species confirmed by our recent studies: roach Rutilus rutilus (L.), minnow Phoxinus phonixus (L.), stone loach Barbatula toni (Dyb.), spine loach Cobitis melanoleuca Nichols, pike Esox lucius L. lenok Brachymystax lenok (Pallas), Arctic charr Salvelinus alpinus (L.), Baikal black grayling Thymallus baicalensis (Dyb.), burbot Lota lota (L.), sand sculpin Leocottus kesslerii (Dyb.), stone sculpin Paracottus knerii (Dyb.) and perch Perca fluviatilis L. Biological peculiarities of these fishes are determined by unique geographical position and limnic characteristics of Lake Frolikha. Being a typical glacial lake it is located at rather low altitude a.s.l. and is adjacent to the unparalleled ecosystem of Lake Baikal. An underdeveloped shallow coastal zone with sparse aquatic vegetation, which is characteristic of glacial lakes, determines some biological traits of Lake Frolikha cyprinids. As compared with other mountain lakes of Baikal Rift Zone (BRZ), roach and minnow have lower rates of linear and weight growth as well as unusual population sex ratios. Male to female ratio in roach is 2:1 and in minnow it is 1:1 whereas in other lakes it reaches 1:4 and 1:10 respectively. The presence of native Baikal species in Lake Frolikha provided abundant food for piscivores: sand sculpins are the dominant food item of lenok, Arctic charr and perch. Lenok and perch demonstrate prominent linear and weight growth rate in the lake. In other lakes of BRZ with less abundant prey fish species Arctic charr typically diverge into several trophic forms, but in Lake Frolikha they established a monomorphic mostly piscivorous population. Charr from Lake Frolikha are relatively small and short-lived representatives of the large form of Transbaikalian charr. Their unique feature is river spawning, which is not observed in any other charr population within BRZ. Due to special protection regime of the territory, which minimizes catch losses, several fish species maintain natural unaffected structure of their populations evidenced by the abundance of old fish. The population of lenok is represented by 19 age groups, the population of roach – by 15 groups and that of burbot – by 12 groups. Alternatively, populations of small-sized prey species such as minnow and sand sculpin, which are heavily influenced by numerous predators include fewer age groups than in other mountain lakes of BRZ.

Endogenous factors for the formation and functioning of halomorphic soils in the Baikal Rift Zone (a case study of the Barguzin depression).

Endogenous factors for the formation and functioning of halomorphic soils in the Baikal Rift Zone (a case study of the Barguzin depression).

ОСОБЕННОСТИ ГЛУБИННОГО СКОРОСТНОГО СТРОЕНИЯ ЗАБАЙКАЛЬСКОГО УЧАСТКА ЦЕНТРАЛЬНО-АЗИАТСКОГО СКЛАДЧАТОГО ПОЯСА ПО ДАННЫМ СЕЙСМОЛОГИИ И ГСЗ (В СТВОРЕ ОПОРНОГО ПРОФИЛЯ 1-СБ)

The materials of deep seismic studies on the reference geophysical profile 1-SB and areal interpretation of seismological data in the Trans-Baikal part of the Central Asian folded belt are presented. It is shown that longitudinal and transverse waves from the reference boundaries in the Earth's crust and Moho surface were registered using explosions and powerful vibration sources on the 1200-km geophysical profile 1-SB in Trans-Baikal region. The inhomogeneous velocity structure (according to P - and S - waves) of the upper part of the Earth's crust to the depths of 15–20 km and Moho surface was established. The anomalous mantle with reduced values of the boundary velocity of P - and S-waves (7.8–7.95 km/s and 4.3–4.5 km/s, respectively) was reliably traced within the Baikal rift zone using GSS and seismology data. In the southeastern part of the area (in the central Mongol-Okhotsk orogenic belt and adjacent folded structures of the Trans-Baikal region), a layer of increased P-and S-wave velocity values on was detected the mantle surface at 8.4 ± 0.15 km/s and 4.9 ± 0.05 km/s, respectively. A comparison was made with the materials of other studies.

The first finding of diatoms from the Early Miocene lacustrine deposits of the Barguzin Valley (Baikal Rift Zone)

Using light and scanning electron microscopy, we studied the species composition of diatoms and their distribution in the core hole 545 of the Barguzin Valley. We determined two local diatom zones that reflected the stages of the flora development in the Barguzin Valley during the Early Miocene.

Distribution and morphology of colorless sulfur bacterium of the genus Thiothrix in water reservoirs of Baikal rift zone

The habitats of colorless sulfur bacteria of the genus Thiothrix have been investigated in 7 hot springs of the Baikal rift zone. The intensity of their development depended on the distance from the outlet of thermal water to the surface and the flow rate of water. The most massive fouling of Thiothrix was observed at the border of mixing thermal and river water (Umhei, Alla). Slight Thiothrix fouling was observed at a significant distance from the thermal water outlet of the Goryachinsk spring.

Microbial community diversity in hot springs of the Baikal rift zone

The taxonomic diversity of the microbial community of the Baikal rift zone hot springs has been studied. The hot springs were characterized by different temperature (from 34 to 77 C), hydrogen sulfide concentration(from 0.02 to 12.75 mg/L), and silica (from 89 to 144 mg/L). pH values varied from 8.1 to 9.7. The dominance of distinct phyla was revealed depending on the spring water temperature. Microbial communities in bacterial mat developing at higher temperatures (53 - 58 C) were similar by taxonomic composition. The community at 34-51 C was very different from the high-temperature regions. Nitrospirae Deinococcus-Thermus dominated in the microbial mats community with temperature 65 C, but phyla Atribacteria, Nitrospirae, Chloroflexi prevailed in at 53-65 C. Proteobacteria and Cyanobacteria dominated at temperatures 34-51 C.

Первые находки пестроногого подкаменщика Cottus cf. poecilopus Heckel, 1837 в бассейне Байкала

For the first time for the Baikal Lake basin, evidence of the existence of populations of sculpin Cottus cf. poecilopus Heckel (alpine bullhead) characteristic of the adjacent Lena River basin in large northern Baikal tributaries, the Verkhnaya (Upper) Angara and the Kichera is provided. In June 2009 during the study of the lower reaches of the Kholodnaya River (Kichera-Baikal system), 8 individuals of sculpin aged from 3 to 5 years and in August 2009 5 more specimens aged from 4 to 6 were caught. All fish were fertile with the gonads in maturity stage III. In August 2010 33 individuals aged from 4 to 6 were collected in the main channel of the Upper Angara near Novy Uoyan settl.. At about the same time C.poecilopus was registered in stomachs of Arctic charr from Lake Amut (Churo-Upper Angara-Baikal system) near the divide with the Pravaya (Right) Mama (Mama-Vitim-Lena system). In August 2010 17 specimens aged from 1 to 4 were caught in the Upper Angara near the mouth of its large left tributary the Yanchui River. Sculpins from the rivers Kholodnaya, Upper Angara and Yanchui have higher growth rate as compared to the ones from mountain lakes of the upper Lena basin. About 90 % of males and females matured at the age of 3 years. Absolute fecundity of two females from the Upper Angara River was 149 and 556 (with a mean of 352,5) eggs and of two females from the Kholodnaya River, 223 and 305 (with a mean of 264) eggs. This exceeds the fecundity of sculpins from mountain lakes in the Lena part of Baikal rift zone, which averages less than 150 eggs. Sculpins spawn in the Kholodnaya River in the 1st half of June. The diet of C. cf. poecilopus all over the Baikal basin as well as in adjacent sites in the Lena basin was basically composed of larvae of amphibious insects (trichopterans, ephemeropterans, chironomids and plecopterans). The discovery of the third species from the Lena basin in the Baikal basin following the findings of Arctic charr Salvelinus alpinus and grayling Thymallus baicalolenensis evidences the absence of differences in the structure of ichthyofaunas of the upper parts of both neighboring basins. Sculpins permeate along the streams to mountain lakes more easily than other species and colonize the most elevated ones in lake cascades within the northern part of Baikal rift zone. Their dispersal across the divide could proceed in two ways: via headwater captures or via flattened passes between converging upper reaches of adjacent streams.

ИЗУЧЕНИЕ СЕЛЕВОЙ АКТИВНОСТИ В ГОЛОЦЕНЕ ПО ДАННЫМ РАДИОУГЛЕРОДНОГО ДАТИРОВАНИЯ (НА ПРИМЕРЕ ЮЖНОГО ПРИБАЙКАЛЬЯ)

For the first time for the Baikal rift zone, radiocarbon dates of humus horizons of buried Holocene soils in the profiles of debris flow fans were obtained on the right bank of the Irkut River along the Munch-Sardyk Ridge. Three stages of debris flow activity in Holocene have been identified: high (early Holocene – 10 thousand cal years ago), medium (3 thousand cal years ago – present) and low (between 10 and 3 thousand cal years ago). Apparently, the debris flow activity was determined by climatic conditions in the region and has been associated with the change of atmospheric precipitation. At the beginning of the Holocene precipitation exceeded their current level and one-time accumulation of debris flow deposits reached up to 5 m in thickness.

Soils of unique phosphorites’ landscapes of lake Khovsgol’ depression (Mongolia) of Baikal rift zone: ecological features of functioning and necessity for their conservation

A comprehensive study of ecological functioning features of the soils, formed on outputs of phosphorites’ layers of Ongolignur deposit of Khovsgol phosphorite basin of South-Western branch of Baikal rift zone was conducted. The understanding of the soil-ecological potential of the soil cover of the studied area both in the conditions of natural development of geosystems and under the influence of destabilizing anthropogenic factor was expanded. The possible consequences of the technogenic pressure to the unique natural ecosystem of lake Khovsgol have been studied in aspect of potential mining of the phosphorite deposit. Within the study, it was found that the soil formation, soil chemistry and biogeochemical migration of phosphorus and other elements, the humus state of soils and biological productivity of biocenosises (that is the natural-resource potential) of the study area is strongly determined by the influence of lithogenic basis (matrix) of soil, intrazonal factors and cryogenesis.

Прибайкалье и Забайкалье

The seismicity of Pribaikalye and Transbaikalia in 2013 is reviewed. 6706 earthquakes with КР≥5.6 were recorded there during that year. Most of them (92 %) are located in the Baikal rift zone. The high degree of clustering of seismic events is observed in South Baikal and Baikal-Muja areas. The largest earthquake with Mw=4.3 was in the Baikal-Muja area. Focal mechanisms of 47 earthquakes (КР9.6) were determined in 2013. Most of them correspond to normal faults, with strike-slip component contribution in some cases. Overall, the rate of seismic activity observed in Pribaikalye and Transbaikalia in 2013 was low.

The “Mercury breathing” of the Baikal rift zone according to the study of tree annual rings (on the example of Tunkinskaya depression)

The work evaluates the general distribution of mercury in the rings of trees of the Tunkinskaya depression (the Republic of Buryatia, the national park “Tunkinsky”).The used methods of dendrochronology and dendrogeochemistry allow us to estimate the contribution of different factors affecting the quality of the environment and ascertain the history of natural components pollution. In this research, the phenomenon of natural degassing of mercury in the Baikal Rift Zone (BRZ) according to the study of annual tree rings is considered. The BRZ covers 13 large parallel lobes separated from each other by high mountain ridges and bridges. Geodynamic activity of the zone is shown by contrast relief transformation and high seismicity. High tectonic and seismic activity causes the “output” of mercury to the surface. The dynamics of Hg concentration changes in the Tunkinskaya lobe for more then half a century was observed. The average mercury content in the sample was 7 ng/g, the max – 35ng/g. The max concentration is detected in areas of the territory associated with free tectonic faults. The connection between the peaks of high mercury concentration in wood and periods of major earthquakes was detected.

Microbial Community of Umkhei Thermal Lake (Baikal Rift Zone) in the Groundwater Discharge Zone

The diversity and functional activity of the microbial community of the bottom sediments and water of the thermal alkaline Umkhei Lake (Baikal Rift Zone), which was formed as a result of groundwater discharge, has been studied. The lake water is shown to be thermal hydrocarbonate–sulphate–sodium water of the Kuldur type. Lake sediments are characterized by higher temperatures and greater saturation with microelements. A comparative analysis of the species abundance of the microbial community of water and bottom sediments shows high indices of diversity in all layers of sediments, while the diversity in water is low. An analysis of taxonomic diversity reveals the predominance of the members of Proteobacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Chloroflexi phyla in the community of water and bottom sediments. The presence of bacteria with various metabolic pathways of substance and energy transformation in both production and destruction processes is determined. The sequences belonging to the genus Hydrogenophaga (class β-Proteobacteria, phylum Proteobacteria), which is an indicator of the deep geochemical processes of hydrogen production, are found in the bottom layers of sediments. The rates of microbial processes of photosynthesis, dark assimilation of CO2, sulfate reduction, and methanogenesis are determined to characterize the functional activity. The main part of the organic-matter production in water is found to be formed as a result of the activity of chemolithoautotrophic prokaryotes. In the microbial community, the producers synthesize organic matter using volcanogenic carbon dioxide enriched in the heavy isotope (δ13C). An analysis of the rates of terminal processes indicates that sulfate reduction is the main process.

Landscape and climatic conditions of the depressions of the southwestern part of the Baikal rift zone

The article presents data on continuous monitoring of the characteristics of the climate system with high spatial-temporal resolution. The study area is the Tunkinskaya rift system of depressions, in particular, the Tunkinskaya and the Mondinskaya depressions. Five cross sections characterizing the typical conditions of mountain-depression landscapes of the South Baikal region were selected. At each point of a cross section, a description of the landscape, laying of the soil section, its description, sampling for subsequent laboratory analyses to clarify the genesis and name were carried out. Meteorological parameters were monitored using stand-alone programmable thermographs. It was shown that the influence of individual and contrasting morphometric characteristics of depressions on the climate is reflected in the characteristics of the temperature and humidity regime as a whole, as well as in the features of the cold and warm period. There is a high spatial heterogeneity of temperatures and precipitation with a noticeable gradient between the peripheral and central parts of depressions. It is also shown that the territory is characterized by the high contrast of geological, geomorphological, phytocenotic and soil conditions, which creates a unique landscape diversity both between different depressions and within each depression.

Spatio-temporal heterogeneity of soil cover in Baikal area and its impact on the development of agriculture in the region

The soil cover of the territory of Baikal region is characterized by a significant variety, and the structure of soil cover – by a high complexity due to complex geological history of the region, to the influence of tectonic processes of the Baikal rift zone, to the wide spread of young mountain systems, island permafrost and other factors. Distribution of loess rocks at the territory of the forest-steppe zone of Baikal region contributes to the genesis of fertile soils, but increases the heterogeneity of soil cover, which should be considered in agricultural land use.

Investigation of migratory seismicity in the lithosphere of the Baikal rift zone

The study of migrating seismicity was carried out according to data on 52700 earthquakes of representative energy classes KР ≥ 8, which occurred in the lithosphere of the Baikal Rift Zone (BRZ) from 1964 to 2013. M = 2143 quasilinear chains of earthquakes are distinguished and the basic laws of the space-time and energy distribution are established. In the epicentral field of the BRZ seismicity, there are chains of “seismic migration” and chains formed by chance (“pseudo-migration”). To identify the migrating seismicity, the seismic migration activity index (ISMA) was used, which characterizes the seismic migration / pseudo-migration ratio at a given level of significance, obtained maps of the distribution of the index over the territory and graphs of changes over years. The results of the study indicate a direct link between the migrating BRZ seismicity and the location and activation of rifting attractor structures (RAS).

Integration of the GPR and radio-impedance techniques in studies of the Baikal rift zone

R adio wave propagation techniques have been very rarely applied to investigate tectonic fault zones and geoelectric profiles of the Baikal rift zone. In our study, we used a combination of g round-penetrating radar (GPR) and radio impedance techniques in order to identify and investigate tectonic crustal fault zones in the study area. Using soundings in the super-long, long and ultra short radio wave ranges (from tens of KHz to few GHz ) , we detected the tectonic fault zones in t he seismically active Baikal rift zone , specifically in the Tunk a depression and the areas of South ern Baikal and Kotokel lake s. Faults and fault zones were identified from impedance variations and changes in the geoelectric profiles by analyzing the radio impedance profiles and soundings in the super-long and long radio wave ranges . The georadi o location of fault structures in the ultra-short wave range made it possible to differentiate the patterns of tectonic disturbances up to individual seismic dislocations in sedimentary and crystalline rocks and to determine the kinematics of movements in the fault zone s . The techniques used in this study complement each other and ensure obtaining adequate quantitative descri ptions of the study object s . By i ntegrati ng various techniques of radio wave diagnostics , it is possible to obtain more detailed information on the structure s of the tectonic fault zones . The results obtained in this study and the radio impedance and GPR sounding and profiling techniques developed to investigate a heterogeneous underlying medium can be used in seismological and geological engineering surveys of the eastern and northern regions of Russia.