Mud volcanism (also termed sedimentary volcanism) is a spectacular natural phenomenon that has attracted increasing attention for numerous onshore and offshore studies. Mud volcanoes (MVs) indeed represent open windows to explore the deep biosphere and stratigraphy and to understand the geochemical reactions that occur during fluid migration. MVs are always associated with active petroleum systems, and the current likely underestimated budgets position MVs as the second natural source of methane in the atmosphere. Ultimately, the unpredictable eruptive events make sedimentary volcanism a critical natural geohazard. For these reasons, there is growing interest to intensify the studies for these structures.Since 2018, the field course “Mud volcanism and petroleum systems” takes place annually in Azerbaijan. This summer school is organized by dedicated and enthusiastic scientists from the University of Oslo, the Lomonosov Moscow State University, and the Azerbaijan National Academy of Sciences. International experts and special guests are typically invited to share their new findings from multidisciplinary studies on fluid migrations systems, MVism and related phenomena. This intensive course has been refined throughout the years to provide the world's best training opportunity. The school prioritizes education and knowledge transfer to students and researchers interested in expanding their knowledge in fluid migration and solid transport mechanisms during MV processes. Activities start with one day of initial introductory lectures (workshop in Baku city), followed by four days of excursions and field exercises at various selected localities. The first field day explores a full migration of fluids from the source rocks, reservoir rocks and surface gas seepages visiting the most representative sites around Baku and completing field exploration and geological section logging. The second day is dedicated to Dashgil MV where the participants are involved in practical field mapping activities, shown the main surface degassing manifestations, and trained to conduct field measurements and sampling. The third day focuses on the different MV morphologies; several mud structures are visited, participants have the opportunity to distinguish and describe the main large- and small-scale features characterizing different eruption mechanisms and the resulting structures inside the carter and along the mud breccia flows. The fourth day on the field plans a visit at Lokbatan MV showing the association of MVism and petroleum systems. This is one of the most active volcanoes in Azerbaijan, with frequent eruptions reoccurring every ca. 5 years. Lokbatan is surrounded by dozens of production oil wells, highlighting the fact that MVism and hydrocarbon migration are usually connected. The location of MVs in petroleum basins, along anticline axes, strike slips, normal faults, and fault-related folds is also discussed. On the final day of the course, the school attendees provide an oral presentation, reporting on their learnings on techniques used, on field observations, and the data collected, and finally propose plans for potential future research. One moths later, the teams provide a more detailed written report that is complemented with interpretations of the data collected. All students are supervised and tutored in the field and during the report preparation and public presentation by experts from leading institutes.

High-latitude regions store large amounts of carbon trapped by ice sheets, permafrost and gas hydrates, yet joint evolution of these climate components is poorly understood. Covered by a cold-based ice-sheet during the last glaciation, the seafloor of the northeastern Barents Sea reveals one of the largest known glacitectonic provinces in the Arctic. Up to 200-m high glacitectonic landforms are cratered and overlie faults associated with 'bright spots' indicative of subsurface gas accumulations. However, sediment samples show low pore gas concentrations and no present-day gas seepage. We combine new observations and ice-sheet - hydrate modelling to propose that during the Late Weichselian, glacitectonism was caused by patchy substrate stiffening due to gradual growth of subglacial gas hydrates and permafrost. Ice decay led to rapid destabilisation and full drainage of shallow hydrate reservoirs and permafrost thaw, causing craterisation which was likely accompanied by large fluxes of carbon released into the water column. This study shows that these processes were more widespread across glaciated margins, also highlighting sensitivity and potential for abrupt changes of high-latitude carbon pools in response to complex interactions between the cryosphere, ocean, and solid earth. Seafloor craters under the Barents Sea were caused by rapid dissociation of gas hydrates following ice retreat during the last deglaciation, according to coupled ice-sheet-gas-hydrate modelling informed by bathymetric, geophysical and geological observations

The paper presents geochemical study of bottom sediments from the MSU structure located on the large Gydratny Fault in the Central Basin of Lake Baikal at a depth of 1380 m. The first detailed data on the spatial variations in the qualitative and quantitative composition of the pore waters are presented. Pioneering data were obtained on Li, B, and Sr contents in the pore water of the sediments. It has been established that fluids are actively discharged within the MSU structure, and the main pathways of their near-surface migration are confined to the tops of hills of this structure on the downthrown fault block. The fluids are highly mineralized (up to 2900 mg/L), showing the highest mineralization ever found in Lake Baikal sediments. The waters are significantly enriched in Mg, Li, B, and Sr but depleted in K. The waters are thought to be generated by the processes of authigenic formation and illitization of smectite at depths of 1 to 2.5 km in the sedimentary sequence. The maximum values of concentration gradients are recorded in the pore waters of the sediments of the western hill, which may indicate a gradual westward shift of the center of the fluid seepage activity along the fault.

The Barents Sea shelf is one of the most economically promising regions in the Arctic in terms of its resources and geographic location. However, benthic microbial communities of the northeastern Barents Sea are still barely studied. Here, we present a detailed systematic description of the structures of microbial communities located in the sediments and bottom water of the northeastern Barents Sea based on 16S rRNA profiling and a qPCR assessment of the total prokaryotic abundance in 177 samples. Beta- and alpha-diversity analyses revealed a clear difference between the microbial communities of diverse sediment layers and bottom-water fractions. We identified 101 microbial taxa whose representatives had statistically reliable distribution patterns between these ecotopes. Analysis of the correlation between microbial community structure and geological data yielded a number of important results—correlations were found between the abundance of individual microbial taxa and bottom relief, thickness of marine sediments, presence of hydrotrolite interlayers, and the values of pH and Eh. We also demonstrated that a relatively high abundance of prokaryotes in sediments can be caused by the proliferation of Deltaproteobacteria representatives, in particular, sulfate and iron reducers.

Mud volcanism is a natural phenomenon manifesting at the surface of the body with spectacular eruptions and a large variety of morphologies resulting both from explosive and effusive activity. In this study, we targeted two large (MVs) in Azerbaijan (Lokbatan and Goturdagh) characterized by different behaviors in eruptive activity. We investigated them using a multidisciplinary approach including field observation combined with drone photogrammetry, InSAR imaging, subsurface multisource survey, geotechnical analyses of mud breccia flows and numerical stability modeling in order to reveal the way the mud flows.Lokbatan most recently erupted in August 2022. Field observations in September 2022, before significant modification by rain, reveal that this most recent eruption, albeit small in terms of extruded mud breccia, triggered the disruption of huge segmented portions of the older mud flows that extend for more than 1 km. This was identified by the formation of series of fractures recording the detachment and subsequent downhill movement of the old flow. No evident ground deformations have been observed before the eruption and, repetitive field campaigns in subsequent months do not reveal any network of fresh fractures and dislocations. On the other hand, Goturdagh MV features a constant slow extrusion of compacted mud breccia from the subsurface forming an extended >1.2 km long mud flow that continuously moves. This movement is clearly visible at the top of the MV where repetitive field observations reveal an extrusion of wet and dark colored mud breccia. Along the slope, the movement creates well-developed shear zones and compressional structures typical of slope deformations. At the bottom however, the movement seem to be discontinuous and might be triggered occasionally when the force of the new material becomes critical.The field observations show that kilometer scale mass transport can extend at MVs for more than 1 km along the flank of these structures. The additional approaches will help us identify possible eruptive precursors and understand if external elements (tectonics, rainfall, …) can influence this mass movement. The same phenomenon is likely happening at many other large-scale features worldwide.

The results of subaqueous landslide studies at Krasnoyarskiy are given in this paper. The landslide were located at a subaqueous part of the delta of the Selenga River. A multidisciplinary approach was applied to the study of the landslide, including seismo-acoustic, lithological, gas-geochemical and geotechnical studies. Data from landslide and surrounding soils allowed us to propose the hypothesis that a key factor in the landslide origin was high gas saturation of soils and that the reason of landslide was an earthquake. The proposed approach to the study of bottom soils in lakes and seas can be applied both in assessing their stability and in searching for focused fluid discharge zones at the bottom in areas associated with hydrocarbon deposits in the sedimentary section. As well, the approach can be applied to mapping of permafrost melting in the Arctic region offshore, where gases often accumulate below it.

Group and molecular compositions of organic matter from bottom sediments of the northern sector of the Barents Sea were analysed. The sites where bottom sediments contain organic matter of molecular composition similar to that of oil are identified. Thermally mature hydrocarbon compounds detected in extracts from sediment samples indicates ongoing migration from deeply buried strata and fluid discharge processes on seafloor within the studied areas. Molecular compositions of extracts from bottom sediments were compared with and showed geochemical characteristics similar to some series described for the closest onshore to the study areas. That allows an assumption that the source for migrated hydrocarbons identified in studied bottom sediments can be Mid-Triassic organic-rich claystone intervals which are a part of sedimentary succession of the North Barents deep depression.

North-east Java is part of a large sedimentary basin containing hydrocarbon provinces that feature diffuse hy-drothermal systems, mud volcanoes, and degassing sites. Seismic profiles acquired to explore the basin reveal a broad distribution of palaeo-and modern piercement structures. The Watukosek fault system links the volcanic arc, to the south, with the Sidoarjo province, to the north. Several piercement structures, including the Kalang Anyar mud volcano, are hosted along this left-lateral strike-slip system that favors the migration of crustal fluids in this part of the basin. Here, we present a multidisciplinary geological, geophysical and geochemical study conducted at Kalang Anyar where dozens of seepage sites are active in the crater area and intermittently emit bursts oil, gas, mud, and water. The emitted gasses are methane-dominated with smaller amounts of heavier hydrocarbons and CO2. Unlike most mud volcanoes, at Kalang Anyar the mixed-thermogenic origin of the methane is coupled with geothermal anomalies, as indicated by helium and CO2 isotopic values (delta 13CCO2 as high as-4%0) that suggest the input of mantle-derived gas. Our gas flux measurements reveal that Kalang Anyar emits about 1.62 and 5.75 t yr- 1 of CO2 and CH4, respectively. The intense bubbling gives rise to a typical drumbeat seismic signal characterized by dominant frequencies around of 3-4 Hz (and up to 15 Hz). We interpret the drumbeat as fluids rising and resonating through shallow plumbing system of Kalang Anyar. Erupted clasts with different lithologies and shells are scattered across the mud volcano area, while the edges of the crater zone include cubic meter-sized carbonate-cemented blocks and ridges that contain siliciclastic sediments and abun-dant chemosymbiotic bivalves. Carbon isotope analyses of the carbonate cement (delta 13C as low as -48.8%0) identify the latter as methanogenic chemoherms. Radiocarbon (14C) dating of bivalves cemented in the blocks indicates an age of 1890-1488 BP. These results indicate that the activity of Kalang Anyar MV dates from when the area was below sea level and that the microbially-mediated precipitation of carbonates was ongoing during subaqueous methane seepage at the crater site.To the best of our knowledge, Kalang Anyar is the first example of a mud volcano that progressed from subaqueous to subaerial conditions during marine regression, displaying evidence of former marine activity (i.e. methanogenic carbonates) and current subaerial degassing at numerous seepage sites. Potentially eruptive phases represent a clear geohazard for the numerous settlements constructed inside the mud volcano. In light of this, it may be prudent to apply stricter rules for development activities, such as housing construction permits that consider the possibility of potentially catastrophic events, and apply steps to mitigate these hazards.

— High-performance sequencing of the 16S rRNA gene (V4 region) was used to reveal the most widespread groups of microorganisms in the bottom sediments of the Barents and Kara seas. In the Barents Sea, these were uncultured bacteria of the families Hyphomicrobiaceae , Anaerolineaceae , Desulfobulbaceae , and Desulfosarcinaceae (Sva0081 sediment group), actinobacteria of the genus Rhodococcus , and proteobacteria of the genus Woeseia . In the Kara Sea the most represented groups were uncultured bacteria of the order Sedimentisphaerales (the SG8-4 cluster, class Phycisphaerae , phylum Planсtomycetota ), bacteria of the family Anaerolineaceae , the family Desulfosarcinaceae (the SEEP-SRB1 cluster), the deep phylogenetic cluster NB1-j, organotrophic proteobacteria of the genera Woeseia and Pseudomonas , and sulfate reducers of the genus Desulfatiglans . The patterns of microbial distribution were analyzed depending on the depth from the bottom surface and the presence of fluid discharge zones. It was found that according to analysis of the core microbiome, uncultured bacteria of the SG8-4 cluster and uncultured bacteria of the family Anaerolineaceae predominated in the methane discharge zones in the Barents and Kara seas.

New high-resolution geophysical data acquired from eastern Storbanken in the central Barents Sea allow reconstruction of the flow of marine-based ice dome during the final stages of ice-sheet decay. Ice-marginal and subglacial landforms show diverging and quasi-radial grounding-line retreat patterns, implying that an isolated, dynamic, shrinking ice dome was centred at ∼77° N 40° E on eastern Storbanken prior to final marine-based ice-sheet collapse. This geomorphological reconstruction contrasts with previous numerical and observational models that infer a northward-migrating ice dome or crest that extended longitudinally from Svalbard to Franz-Josef Land prior to its eventual demise. Our results provide an important past analogue for late-stage decay of marine ice domes, as well as robust empirical constraints that can be used to calibrate numerical models simulating the behaviour of marine-based ice sheets in a warming environment.

Specific composition and properties of sea bottom clayey deposits sampled during the TTR-19 cruise from the high and the depression of glaciotectonic “hill-hole pair” in the north-eastern Barents sea are discussed. The studied soils are highly disperse and polymineral deposits with high clay mineral content (36–52%). Illite and mixed-layer mineral of “illite-smectite” type with swelling interlayers predominate. Soils demonstrate low variations of index properties along studied cores as well as general trend of porosity and water content decrease and density increase with depth. Clayey silt from the depression of «hill-hole pair» appeared to be normally consolidated soil which is typical for recent marine sediments, whereas clayey silt recovered from the top of submarine hill is, on the contrary, overconsolidated. Preconsolidation stress is determined as 280–290 kPa. An overconsolidation in bottom deposits of the studied sector of the Barents Sea corresponds to their subglacial (moraine) origin. Furthermore, after the high was formed, its topmost 14–15 m might have been eroded as data evaluation suggested.

Arctic shelves represent ideal targets for research investigations since they feature numerous oil and gas provinces with high exploration potential. The Barents Sea is one of the largest prospective hydrocarbon basins in Russia, however, only few and scattered geological and geophysical surveys have been conducted. The Barents Sea region largely developed under the influence of Quaternary glaciations, as highlighted by the characteristics of the uppermost sedimentary section and, more distinctively, in the near-surface deposits. During the last deglaciation dense subglacial accumulations were deposited almost ubiquitously. These units often serve as litho-geochemical barriers, preventing the migration of fluids from deep horizons to the surface. Therefore, standard surface geochemical surveys are difficult to be applied in such a complex geological setting. This study presents new evidences of fluid saturation of near-surface sediments in the northern part of the Russian Barents Sea, especially from the poorly studied region between Novaya Zemlya and Franz Josef Land. Multibeam bathymetry, sub-bottom profiler data and high-frequency seismic data were collected during the international scientific «Training-through-Research» cruises TTR-19 and TTR-20 on the R/V «Akademik Nikolaj Strakhov» in 2020 and 2021. Acquired data reveal that bottom sediments are characterized by extremely low methane content: background concentrations are 1-5 ppm, with highest measured values not exceeding 85 ppm. Methane homologues (C2-C5) are present in trace amounts. In this regard, we focused to additional potential indirect indicators of possible fluids migration. The acquired geophysical data allowed to identify areas where bedrock and tectonic faults reach the seafloor. Here amplitude anomalies were typically observed under the base of the glacial complex suggesting recent fluid migration. Bathymetry data allowed detecting fields of pockmarks, blow-out crater and «hill-hole pair» type structures. The formation of these structures is likely associated with focused fluid discharge. In addition, «flares» were also observed on the profiler data, suggesting ongoing fluid discharge in the water column. Localities characterized by geophysical anomalies were sampled with gravity cores. Sediments cored at these sites revealed lithological indicators of fluid discharge including: core swelling, the presence of degassing channels, uneven compaction of the sediment. Further, the presence of a large amount of hydrotroilite within the sediments and methane-oxidizing Pogonophora worms, typically present at methane-degassing sites, may reflect increased concentrations of organic carbon. Compiling the fluid migration indicators collected during our multidisciplinary surveys, we created a schematic map of localities characterized by modern and palaeo fluid discharge in the northern part of the Barents Sea shelf. This scheme contains integrated probability of the connection of detected features with fluid saturation and, thus, allows us to predict the most prospected areas for fluid discharge investigations. This study highlights that combined geophysical and seafloor sampling techniques represent a valuable tool to detect hydrocarbon migration even in difficult geological settings.

The Russian portion of the Barents Sea shelf is the largest offshore zone in Russia with high petroleum potential. Numerous offshore oil and gas fields have been discovered in the southern part of the Barents Sea, however little is known about the northern and northeastern sectors. These regions were investigated during the TTR-19 and TTR-20 expeditions with the aim to characterize the gas type and content in the near-surface sediments and to identify potential fluid migration areas. Sites for seafloor coring were selected based on the acquired geophysical data, targeting seafloor morphologies of obvious interest (e.g. pockmarks, faulted zones or tunnel valleys) or subsurface acoustic anomalies observed on the seismic profiles. Lithological composition and gas extracted from the sampled sediments were analyzed using gas chromatography, pyrolysis, mass-spectrometry. Results of hydrocarbon (HC) gas molecular studies showed some differences between the northern and northeastern parts of the Barents Sea. Northeastern Barents Sea shelf sediments are characterized by low concentrations of methane up to 28 ppm, and a small amount of C2+ compounds. Northern Barents Sea shelf sediments have methane concentrations up to 69.8 ppm and the presence of C2H6, C2H4, C3H8 and C3H6 and, in a few cores, also C4H10 and C5H12. The study of the organic matter (OM) of bottom sediments (upper 2 meters) also showed a difference in the composition of its soluble part. The OM concentrations in northern part are higher than those observed in the northeastern part, and are characterized by the presence of light HC and oily compounds, which may indicate migration processes taking place in sedimentary covers. Geophysical studies conducted in the northern part, show that the complex of dense subglacial sediments is only locally distributed. These deposits are instead ubiquitous in the northeastern part and serve as a lithological barrier preventing the migration of fluids to the surface. Mass-spectrometry studies allowed the identification of the contemporary OM biomarker outlook. Hopanes and steranes with highly characteristic distributions of structural and sterochemical isomers (e.g. like in sediments with mature organic matter) were confidently identified in a few stations. In recent sediments, with poor thermal alteration, such as those studied in this research, organic matter with higher maturity can most likely be attributed to migration of thermogenic HCs. Overall the bottom sediments collected in the northern and northeastern parts of the Barents Sea showed low concentrations of OM and low amounts of methane from the headspace analyses. These observations may argue against focused active HC seepage in the study areas, nevertheless the molecular and isotopic composition indicates the presence of thermogenic gas. Therefore a fluid migration from deeper units can be inferred. We suggest that the distinct lithological variations and properties of Arctic bottom sediments are responsible for the different compositions (gases and OM) observed in the northern and northeastern parts and for the formation of background and anomalous concentrations of fluids in the near-surface sediments.

The paper presents the pore waters composition’s experimental results in the northeastern part of the Barents Sea. The pore water contains Cl–, Na+, SO4 2– and Mg2+ as dominant components and is quite similar to the Barents Seawater composition. For the first time, we measured the cation exchange capacity of (13.98-35.50 meq/100 g) and the exchanging cations composition (Na+>Mg2+>Ca2+>K+) of bottom sediments. We find that most of the sampled pore water (near 90%) have marine nature, and only near 10% is slightly transformed with sulfate reduction processes due to the diagenesis. We measure that the rare earth elements (REE) content in pore water is up to 1.589 μg/L with their content in sediments up to 144.051 mg/kg, negative cerium and positive europium anomalies are observed both in the pore waters and in bottom sediments. We calculated using PHREEQC that pore water undersaturated to gypsum and halite and supersaturated to calcite and dolomite, which may precipitate in deposits during diagenesis.

Lake Baikal (Russia) represents a unique natural laboratory for multidisciplinary studies of various geological phenomena. In particular, the diffused migration of fluids at numerous locations throughout this deep basin, manifests at the lake floor displaying a variety of degassing sites. Here we report the geophysical results collected during a dedicated marine expedition conducted in the framework of the international Training Through Research education project “Class@Baikal”. The seismo-acoustic surveys were acquired using a chirp profiler, "sparker" source, and a towed streamer. The data collected from various localities of the lake revealed the presence of acoustic anomalies. We extracted these portions of data to characterize the different types of anomalies that are inferred to be associated with fluid migration and ultimately gas saturation in the sediments. Indicators of fluid saturation are typically represented by dramatic increase or decrease in the amplitude of the signal, change in the wave pattern, inversion of the reflections, line of correlation deviation due to the velocity effect. The dimensions and dynamic characteristics of the signal were determined for each zone displaying one of these peculiarities. Three types were identified - 1) bright spots 2) sub-vertical zones of loss of correlation and 3) local morphologically positive structures. The "bright spot" (type 1) anomalies are mainly confined to faults, zones of vertical fluid migration, and mud volcanic structures. Such anomalies have high amplitude and sometimes display phase inversion. Subvertical correlation loss zones (type 2) are characterized by low amplitudes relative to the host sediments and are sometimes accompanied by "bright spot" type anomalies. Positive morphology (type 3) structures are also often found together with types 1 and 2. Using these data, we created a map of the distribution of the types of amplitude anomalies, presumably associated with the gas saturation in the sediment. Next, we compared this map with the localities of known geochemical anomalies that had been determined from the analyses of the sampled sediments. In addition, the areas of seismo-acoustic anomalies were compared with the areas of the BSR (Bottom Simulating Reflector boundary) that are generally interpreted as an indicator for the presence of gas hydrates. Gas saturation in the sediments was verified by bottom sampling several localities that displayed anomalies type 1-3. Although not all the identified anomalies were ground-truthed, the approach proposed herein represents a promising tool for future sampling campaigns aiming to map the gas composition of various sites of the lake. Conducting accurately positioned coring and measuring the gas content in the sampled sediments, we envisage calibrating these results with the acoustic signature registered in the amplitude anomalies distribution map.

At present time several dozen hydrocarbon fields are known in the Vendian-Cambrian complex of the Lena-Tunguska basin, which clearly does not exhaust its potential. The significant stratigraphic interval of the complex, its thickness (up to 3000 m), favorable properties laid down in sedimentogenesis, namely the presence of source, reservoir and seal deposits, allow us to hope for the discovery of new oil and gas deposits. Sedimentological studies of the Vendian-Cambrian complex, carried out using a network of key lithological sections and outcrops, made it possible to create a series of schematic maps of sedimentation environments on a scale of 1:5000000 for six time intervals (Nepa, Tira, Danilovo, Tommotian-Early Atdabanian, Botomian-Amgaian and Late Cambrian). The evolution of sedimentation of the Vendian-Cambrian complex is considered, as well as an assessment of its oil and gas properties, which are primarily associated with various sedimentation environments.

The paper presents results of gas-geochemical studies of bottom sediments and petroleum potential assessment of Baikal Rift Basin. During the expeditions of the Class@Baikal project in 2014–2019, gases from the Lake Baikal bottom sediments were analyzed. The results showed a clear difference in chemical and isotopic composition of the seeping gases collected in the northwestern and southeastern parts of the lake. The seepage released from northwest part were relatively enriched by methane and had a low concentration of C2+ compounds. The seepage gases had relatively lighter carbon isotopes composition of CH4 (from -72,7 to -50,1 ‰ VPDB) and the high variability of δ13C in C2H6 (from -65 to -22 ‰ VPDB). The gases released from southeastern part of the lake had an increase in C2+ compounds and had relatively lighter carbon isotopes composition of methane (from –57,2 to –41,0 ‰ VPDB). The carbon isotopes composition of ethane varies from -32 to -25 ‰ VPDB. Asymmetric structure of the Baikal rift basin and various processes of gas migration within it might cause the variations. Diffusive process led to the lighter carbon isotopes composition of the seepage gases from the northwestern part of lake and the gas molecular composition enrichment by methane. Such molecular and isotopic fractionations caused by geochemical processes helps to understand the migration of gas from source rocks to the earth’s surface. Similar geochemical indicators of fractionation should be taken into consideration when assessing oil and gas source rocks and basin potential from gas geochemical studies data.

Azerbaijan hosts the largest concentration of mud volcanoes (MVs) on Earth. Here, high sedimentation rates and deposition of thick organic-rich series resulted in petroleum basin formation and, in turn, created the ideal setting and conditions to generate widespread sedimentary volcanism. Some of the regions hosting these piercements have been broadly studied, while others (e.g. the Shamakhy-Gobustan region) are less explored. In this seismically more active part of the country, the tectonic control plays a stronger role for the emplacement of diapirs and fluid migration. Here we report a multidisciplinary study conducted on a set of six MVs (Kichik Maraza, Gizmeydan, Gushchu, Malikchobanly, Madrasa and Shikhzairli) located in the Gobustan-Shamakhy region and combine satellite image interpretation with field observations, gas sampling, CH4 and CO2 flux measurements. The studied MVs are generally hosted by anticline axes intersected by fault structures that facilitate the migration of fluids. The resulting surface morphologies include elongated (Kichik Maraza, Malikchobanly MVs) or pie-shaped (Gizmeydan, Gushchu, Shikhzairli MVs). One MV does not show an edifice and is positioned along a laterally extensive fault wall (Madrasa). Morphologies vary depending on the setting, the type of erupted mud breccia and/or the diameter of the conduit. Some of these MVs are characterized by scattered pools and gryphons where gas, water, mud and oil are released. These focused emissions are typically concentrated in the crater area (Little Kichik Maraza, Gizmeydan, Malikchobanly MVs). MVs that recently erupted can display limited or no visual gas release features (like pools or developed gryphons) since these were destroyed by erupted mud breccia flows (Big Kichik Maraza, Gushchu, Shikhzairli MVs). Copious amount of dense oil was observed at numerous gryphons of Madrasa MV. Gas analyses revealed that all the sampled seeps release methane-dominated gas that has a thermogenic origin. Molecular fractionation of this gas occurs during the vertical migration from the reservoirs. Evidence of secondary microbial methane and biodegradation is also observed at some of the seepage sites. The conducted flux measurements were carried out over the crater and the flanks of the MVs targeting the diffused miniseepage (the invisible degassing that typically occurs over vast areas at and around MV craters) and individual seepage sites (e.g. pools or gryphons). Significant degassing was detected at all the investigated structures, also at those that did not display obvious visual seepage. Results show that these MVs release in average similar CH4 Tg yr-1 like most of the other structures in Azerbaijan and one order of magnitude higher than many MV on Earth. CH4 emissions reach up to 64 tonnes yr-1 (Kichik Maraza MV) and CO2 up to 20 tonnes yr-1 (Gizmeydan MV). In more seismically active Shamakhy-Gobustan region the tectonic control plays a stronger role for the resulting morphologies of MVs, fluid migration pathways and composition.

This paper presents a schematic summary of comprehensive analysis of seismic, reflection profiling, and hydroacoustic data on faults which caused sediment deformation in the central segment of the Central Baikal basin. According to the tectonophysical analysis results, the fault pattern within sediment fill has been recognized as zone-block, i.e., it represents a network of high-density fracture zones limiting weakly deformed blocks. The structure of large NE-trending fault zones (Olkhon, Beregovoy, Gydratny, and Svyatoy Nos) is controlled by main fault planes (or their segments) bounded by subsidiary faults. Geomorphic expression of NW cross faults in the sedimentary cover as broad zones of smaller-scale fractures accounts for early stages of the evolution of basement faults. In a longitudinal direction, they divide the basin into large fragments. The zone-block structure of the sedimentary strata was developed in different stress regimes: strike-slip and extension at the early and late orogenic rifting stages, respectively. At the modern stage of tectogenesis, the established network of fault zones controls the gaseous (including hydrate formation) and seismic activity expression in the subsurface. Hydrate-bearing mud volcanoes and seeps are confined to major faults, while earthquake epicenters are confined to fault zones and form clusters at junctions of large NE-trending faults with NW-oriented extension zones and E-W left-lateral strike-slip faults.

Lake Baikal is the largest fresh water lake on Earth and has been target of numerous expeditions to investigate the mechanisms of diffused fluid migration that characterize large part of this basin. Among the numerous areas that have been investigated during the Training Through Research Class@Baikal program, here we report the findings from the Elovsky area located in in the northern part of the southern basin of the lake. Initial surveys in the area conducted geophysical investigations that revealed the presence of acoustic anomalies and enigmatic positive structures scattered on the lake floor. These are characterized by low-amplitude parabolic reflection over the bottom and sub-circular landforms with width of 200-300 meters and height of 10 to 25 meters. Seismic data also detected a buried lenticular semi-transparent sedimentary body (thickness of 30-90 meters) spread over most of the study area at a depth of 20-60 meters in average. This unit can be clearly distinguished from the parallel-layered seismic record of the host sediments, and is interpreted as a large landslide or a vast high-density gravity flow deposit. The structures described above are spatially confined to the area of spreading of the lenticular body, in connection with which we can assume their genetic relationship. Bottom sampling targeted the topmost part of these positive structures and recovered layers of clayey silt and silty clayey silt and in some instances were retried very dense and compacted dry silt-clay, which is an unusual texture for the bottom sediments of Baikal. Gas extracted from these sediments revealed higher concentrations of methane, in particular at the topmost localities. Based on the collected data we propose that the genesis of the Elovsky features is associated to clay diapir-like mechanism, somehow similar to that observed at mud volcanoes. The roots of this system reach the transparent landslide deposits. We argue that these deposits are likely gas saturated and triggered the slow extrusion of these compacted sediments.