Acanthodiaptomus tibetanus (Daday, 1908) (Calanoida, Diaptomidae) – a biogeographic relict in the water bodies of Baikal Rift Zone

A detailed morphological description of the copepod Acanthodiaptomus tibetanus and its geographic distribution on the territory of Irkutsk Region, Buryat Republic, Zabaikalsky Region and Republic of Sakha (Yakutia) within the limits of Baikal Rift Zone is presented for the first time. The authors provided information on the paleogeographic conditions of the territory these crustaceans inhabited and characterized their habitats in brief. An overview of the personal data and available literature on the geographic distribution of A. tibetanus is given. One of the major results obtained under this study was elucidation of the distribution patterns of A. tibetanus. In order to understand current distribution patterns of organisms, A. tibetanus in particular, in different basins, we carried out a historical analysis of the relief formation taking into account climatic aspects involved in these transformations.

Bituminous substances in soils of Baikal Rift zone

Parameters of hydrocarbon complex of the soils of lacustrine-alluvial plain and sandy uplands of the Baikal rift zone within the Barguzin Depression have been studied. Data were obtained on organic (non-carbonate) carbon, chloroform and hexane bitumoids, as well as on individual polycyclic aromatic hydrocarbons. The content, composition and properties of bitumoids vary depending on the intensity of endogenous activity. In soils located in the zone of active unload of hydrothermal waters and hydrocarbon fluids, atypical accumulation of organic carbon was noted; the concentrations of bitumoids do not correlate with its content. High values of the bitumoid coefficient, significant level of polycyclic aromatic compounds and their diversity, in combination with salts accumulation, indicate an additional influx of hydrocarbons and instability of the soil hydrocarbon system. The level of the indicators shifts towards background values in the soils of sandy hills with a complex combination of exogenous and endogenous factors of soil forming. Studied parameters of the soil hydrocarbon system in aggregate can serve as markers of the intensity of endogenous processes.

SOURCE PARAMETERS of STRONG EARTHQUAKES OCCURRED in the BAIKAL REGION and TRANSBAIKALIA in 2015

We calculated seismic moment tensors in a double-couple approximation (focal mechanisms, scalar seismic moments, and moment magnitudes) and hypocentral depths for twenty earthquakes with Mw≥4.2 that occurred in the Baikal region and Transbaikalia in 2015. The initial data were amplitude spectra of Rayleigh and Love waves obtained from their records at the broadband seismic stations of the IRIS and the DK networks and first-motion polarities of body waves recorded at regional distances. A combination of the normal fault and strike-slip movements dominate in the sources of the major part of the study earthquakes. For the strongest of the considered seismic events (Mw≥4.6), the subvertical compression and subhorizontal tension in the SE-NW direction prevail, i.e. the tension is perpendicular to the main structures of the Baikal rift zone. The seismic events with Mw<4.6 are characterized by a more scattered orientation of compression and tension axis that could be caused, for instance, by stress redistribution in small-scale crustal blocks after stronger earthquakes. The obtained results are of great value for issues concerned with seismic hazard assessment and the development of geodynamical models of the lithosphere evolution of the study region.

MUYAKAN EARTHQUAKE SEQUENCE in 2015 (Northern Baikal Region)

We present the results of studies of the seismic regime, focal mechanisms, and macroseismic data in the area of the largest Muyakan activation in 2015 (northern Baikal region). Due to the deployment of a network of temporary seismic stations, the number of registered earthquakes (KR≥3) increased significantly in 2015 and reached  30 thousand. Spatio-temporal development of the considered activation is characterized by stable low values of earthquake hypocenters and dividing the epicentral field into two clusters – eastern and north-western ones. Both clusters are connected with local stress-strain field (rift type and strike-slip, respectively), while the general regime of seismotectonic deformations of the crust in the activation area, calculated from the statistical analysis of 77 focal mechanisms of Muyakan earthquakes (KR≥9.2), demonstrates the predominance of submeri-dional horizontal extension. Macroseismic effects from the largest earthquakes of the Muyakan sequence were felt, predominantly, in Severomuysk settlement (=10–15 km, I=5). New data on strong motions, obtained from the records of the seismic station with the same name, have significantly complemented the database for the territory of the north-eastern flank of the Baikal rift zone. In general, the obtained results could be used to clarify the seismic hazard of the considered area and to improve the instrumental part of seismic scales.

Velocity models fitting for the seismic events location within the Baikal rift zone

Whereas the defined velocity model plays a key role in the process of seismic events localization, so selection of the model as much as possible corresponding to the real velocity conditions of the investigated area becomes a crucial task. Basing on the analyses of published results of the Lake Baikal area seismic study a layered P-waves models for two situations defined: For the high velocity consolidated rock on the lake banks and low velocity sediments up to 10 km thick under the lake bottom.

An integrated information environment to support geophysical research of the Baikal Rift Zone

In this paper it is proposed to organize information support for geophysical research of the Baikal Rift Zone by organizing an integrated system available on the Internet. The system provides access to experimental data and their computational analysis, and also provides systematization of information objects of the subject area based on the ontology of the subject area.

Strong motion record processing of the Baikal rift zone

The work is devoted to the adaptation of the earthquake record processing algorithm of the Pacific Earthquake Engineering Research Center to the peculiarities of seismic monitoring of the Baikal region. A tool for forming a database for building a regional seismic attenuation model is presented.

Taxonomical and functional diversity of microbial communities in two hot springs of the Baikal rift zone

The Baikal Rift Zone hosts many hot springs with a wide range of temperature and physical-chemical conditions, which may harbour different niches for the distribution of microbial communities. We investigated microbial community composition and their functional activity in two alkaline hot springs with a temperature range of 34.4 to 73.6°C. Comparative analysis of the composition of the dominant taxa showed significant differences depending on the collection sites. In the community of high-temperature zones with a water temperature of 55-64°C, a high proportion of thermophilic bacteria Acetothermia (up to 57.9%), Deinococcus-Thermus (up to 50%), and Aquificae (up to 10.8%). Proteobacteria (29-77%) and Firmicutes (15-26%) dominate in the sulphide-free Garga spring (73-75°C). The functional analysis of the microbial community showed that the primary producers are cyanobacteria, anoxygenic phototrophs, and chemolithotrophic bacteria. At the terminal stages of the mineralization of organic matter, sulphate-reducing bacteria are the main destructors in the microbial communities in hot springs. The cyano-bacterial and sulfidogenic microbial communities play an important role in the formation of geochemical barriers and mineral formation.

Taxonomic composition and proteolytic potential in the microbial mat of the Uro hot spring (the Baikal rift zone)

We studied the taxonomic diversity of microbial mat in the Uro hot spring (the Baikal rift zone, BRZ) with temperatures of 62°C (Ur-3) and 56°C (Ur-4). According to the results of high-throughput sequencing, the composition of the community is represented by various phylogenetic groups Cyanobacteria, Proteobacteria, Deinococcus-Thermus, Chloroflexi, Firmicutes, and Bacteroidetes involved in different stages of organic matter production and degradation in microbial mats. According to metagenomic analysis, there is a wide variety of natural peptidases, enhancing the potential of their specialised functions of energy and substance conversion in microbial mats.

Diversity and Ecology of Diatoms in Pliocene Deposits of the Tunka Valley (Baikal Rift Zone)

Fossil diatoms are an excellent tool for reconstructing the palaeoenvironmental and palaeogeographic changes involving lacustrine systems. In this work, the diatom content of Pliocene sediments recovered from a core extracted in the Tunka Basin (Baikal Rift Zone, Russia) is described. Revealed by light and scanning electron microscopy, 170 species of diatoms were found. Benthic, alkaliphilic, indifferent, cosmopolitan, and oligosaprobe species predominated. Ecological, geographical, and stratigraphic analysis of diatoms showed two ecozones, differing in taxonomic diversity of species. From the data obtained, palaeoenvironmental conditions of these zone formations have been reconstructed. It was shown that during the period corresponding to sedimentation in Ecozone II, the reservoir was cooler, as suggested by the increase of arctic-alpine taxa. The absence of Baikal Pliocene endemics and the presence of local endemics in the Tunka core indicate that there was no geographical connection between the palaeolake of the Tunka Valley and Lake Baikal during the Pliocene.