The Mediterranean Ridge (MedRidge) Accretionary Complex has been studied intensely over the past 40+ years in order to understand its formation and role within the Eurasian-African collision zone in the Eastern Mediterranean Sea. Since the early days of exploration, several fluid expulsion features, later identified as mud volcanoes (MVs), were discovered. Additionally, numerous hypersaline deep-water basins (i.e. brine pools) were found scattered across the MedRidge. Pore water geochemistry analyses from past studies showed that the majority of the MVs located south of Crete are influenced by diagenetic processes causing pore water freshening (e.g. clay mineral dehydration) and lead to a lower salinity compared to seawater. However, the pore water geochemistry of the brine pools as well as the Napoli MV, located in the Olimpi mud volcano field (OMVF), showed higher salinities than seawater pointing towards a source of evaporitic deposits.

During R/V SONNE cruise 278 in 2020, 25 years after the ODP Leg 160 drilling campaign in the OMVF with DV JOIDES Resolution, new sediment cores and pore water samples were accurately recovered from seepage structures, after mapping them with AUV micro-bathymetry. We will present the recently acquired data of two MVs (Gelendzhik and Heraklion) in the western OMVF, three in the eastern OMVF (Napoli, Milano and Bergamo MVs) and a brine pool located at the toe of the Bergamo MV. Pore water samples from MVs affected by clay mineral dehydration show decreasing chlorinity, increasing Na/Cl ratios and a constant depletion of SO₄^2- due to anaerobic oxidation of methane (AOM), while fluids from the MVs with an evaporitic influence show a decrease in chlorinity and Na/Cl ratios close to 1 (halite dissolution) and a downcore increase in SO₄^2-.Some of the most indicative fluid mobile elements in the case of deeply-rooted fluids (boron, lithium and strontium) measured from the highly saline samples suggest different fluid sources. An enrichment of boron and lithium in the pore waters of Napoli and Heraklion MVs point to a mixture of highly saline pore waters with a freshened fluid, whereas the unusually high Sr-concentration [2.2 mM] of Gelendzhik MV in comparison to Heraklion [0.3 mM] and Napoli MV [0.22 mM] hints towards a different source. The location of Gelendzhik MV along a major fault system suggests an influence from greater depth processes (e.g. stratigraphically deeper sediments) in contrast to the source depth of 1-2 km previously determined for the other MVs within the OMVF. These results are in agreement with the recent findings of Nikitas et al. (2021), which connected the sediment extruded at Gelendzhik and Heraklion MVs to sub-salt formations or source beds of the Messinian Evaporites.

Our findings are expanding the previous assumption that the Napoli MV represents an exception in the OMVF and illustrates the complexity of mud volcanism even at small-scales along the MedRidge Accretionary Complex.

Nikitas, A.; Triantaphyllou, M.V.; Rousakis, G.; Panagiotopoulos, I.; Pasadakis, N.; Hatzianestis, I.; Gogou, A. Pre‐Messinian Deposits of the Mediterranean Ridge: Biostratigraphic and Geochemical Evidence from the Olimpi Mud Volcano Field. Water 2021, 13, 1367. https://doi.org/10.3390/w13101367

How to cite: Behrendt, N., Menapace, W., Bohrmann, G., and Kopf, A.: The Mediterranean Ridge 25 years after ODP Leg 160 drilling: New discoveries on mud volcanism and fluid-rock interactions in the Olimpi mud volcano field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2339, https://doi.org/10.5194/egusphere-egu22-2339, 2022.

The Dead Sea basin, the lowest and one of the saltiest places in the world, is a tectonically active 150 km long and 15–17 km wide terminal pull‐apart basin located along the southern Dead Sea plate boundary. As a result of the combined effect of climate change and anthropogenic intervention, lake levels have been dropping at an alarming rate of over 1 m per year during the last few decades. Due to this rapid decline, a number of hydrothermal springs have become exposed on land along the western shore of the lake. However, once subaerial they are typically categorized as sinkholes, despite the fact that they are a different geological feature that results from a different mechanism. Generally, hydrothermal springs within the Dead Sea are understudied. This, coupled with rapidly lowering lake levels leaves a considerable knowledge gap in how this system is changing and responding with time. Previous studies have proposed the presence of underwater springs or seeps based on temperature anomalies and acoustic blanking observed on high-resolution seismic reflection profiles. Direct observations of nearshore springs were obtained by a team of scientific divers over 10 years ago who examined water chemistry and microbiology. Their study suggested that submarine springs must be connected to a high-pressure flow system, which is able to penetrate the fresh-saline interface in the Dead Sea, probably along tectonic faults and cracks. Fractures in the sediment would force variable rates of flow depending on width of the fractures, thus possibly leading to the different chemical compositions found in the underwater springs over a short distance.  More recently, a follow up set of underwater and on land surveys were conducted in a similar, adjacent spring system, providing insight into the changes that have occurred over the past decade. This study will present a summary of past studies as well as insights gained from this most recent research. 

How to cite: Lazar, M. and Goodman-Tchernov, B.: Observations and preliminary results of hydrothermal activity on the shallowing coastlines of the Dead Sea, Israel , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4285, https://doi.org/10.5194/egusphere-egu22-4285, 2022.

The northeast sector of Java, Indonesia, is a sedimentary basin hosting several petroleum provinces. This region is characterized by distributed modern and paleo piercement structures, diffused hydrothermal systems, degassing sites and mud volcanoes. Sedimentary volcanism includes the Kalang Anyar mud volcano, one of the active piercements located along the NE-striking Watukosek fault system. This fault system extends from the volcanic arc through the sedimentary basin in the north of the island.

Kalang Anyar covers an area of approximately 1.5 km² and displays several small seeps scattered over the crater. These seeps discharge mud water, oil, and gas. Several expeditions conducted at the site allowed the acquisition of a multidisciplinary dataset including geochemical, geological and geophysical data. Seismic data highlight the occurrence of drumbeat signals marked by high central frequencies, similar to those found in other mud volcanoes.

Laboratory analyses carried out on the gas released from the seeps show a methane-dominated content with lower quantities of heavier hydrocarbons and CO₂, and a marked thermogenic origin. Moreover, CO₂ and helium isotopes suggest the presence of mantle-derived fluids that presumably migrate along the Watukosek fault system for tens of kilometers within the sedimentary basin. Water geochemistry indicates that brines are a mix of marine formations waters that interacted with illitizied units.

Carbonate blocks located on the outskirts of the crater zone have been mapped and analysed. These result to be methanogenic carbonates (carbonate cement d¹³C as low as -48.8) that formed during the microbially-mediated methane oxidation and carbonate precipitation during the offshore activity of the mud volcano. Dating of these blocks indicate that the mud volcano was recently active in sub-aqueous conditions. Kalang Anyar represents a rare example of onshore mud volcanism witnessing the offshore activity and associated precipitation of authigenic carbonates.

Dozens of new settlements have been recently constructed on the flanks and around the crater of Kalang Anyar. This exponentially growing edification represents a common example that may pose in severe danger to the settlements and the residents in case of sudden eruptive activity. The uncontrolled development of the constructions is a geo-hazard that shall not be underestimated.

How to cite: Sciarra, A., Mazzini, A., Lupi, M., Ascough, P., Husein, A., and Karyono, K.: Geochemical and geophysical characterization of Kalang Anyar mud volcano, Java, Indonesia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7389, https://doi.org/10.5194/egusphere-egu22-7389, 2022.

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.

How to cite: Akhmanov, G., Mazzini, A., Sciarra, A., Labes, A., Basova, E., Ayten, H., and Arif, H.: Characteristics and origin of macro- and mini-seepage at mud volcanoes in the Shamakhy-Gobustan region of Azerbaijan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11101, https://doi.org/10.5194/egusphere-egu22-11101, 2022.

Mud volcanism is a global phenomenon that can be found in hydrocarbon-bearing sedimentary basins that have undergone high sedimentation rates and subsidence in the past, and subsequently underwent to compressive tectonics. Due to increasing pressure at depth, Mud Volcano (MV) manifests by migration through hydrofractures, and eruption to the surface, of mix-composed fluids. Thus, they represent serious geohazards for people and infrastructures and the study of the mechanism responsible for the formation and activation of MVs is very important to assess this risk.

Some models have been derived to define their deep structure and dynamics at depth and closer to the surface based on local and regional processes. Such models explain mud flow pathways from deep mud chambers to shallow structures and link them to surface features and morphologies. To create such models, the results of various geophysical methods can be used. One of these is Electrical Resistivity Tomography (ERT) which has been used successfully to image fluid flow pathways in mud volcanoes.

In this work, we introduce a 2D ERT survey to investigate and image mud flow pathways on Saribokha MV (Azerbaijan). It is located on an anticline and presents a conical shape morphology characterized by active vents and multiple surface structures. The survey consisted of two ERT lines crossing each other at a 45° angle. For both lines, the 2D imaging shows a very low resistive layer (less than 2 W.m) in between two higher resistive mediums (between 2 to 5 W.m) down to 40 m depth. We interpret it as extruded mud spreading through the subsurface between the two impermeable layers of mud breccia. The impermeable surface layer acts as a kind of “rind” which prevents mudflow discharge to the surface except through mud volcanic features (gryphons, vents, and salsa lakes). The bottom impermeable layer seems to constrain transports of mud up from a deeper source only through two vertical pipes. Inside the mud flow discharge layer, we find more resistive blocks that we interpret either as artefacts due to data and inversion uncertainties or floating blocks of mud breccia between mud flow pathways that are not well resolved.

To validate these underground features and identify clearly whether two pipes feed the mud volcano, we created a synthetic model of the first profile with mud flow resistivity of 1.5 W.m and mud breccia resistivity of 3.5 W.m. Inverted synthetic result shows similar behavior to the real case and define the more resistive blocks in the mud flow discharge layer as artefacts due to inversion process. However, it does not allow to confirm the existence of two feeding pipes due to ERT limitation in high conductive areas.

These results allow us to correlate mud flow pathways and surface structures. Although, they put forth the need to improve imaging at mid-depth to determine if the driving process of Saribokha MV creation is the result of fracture appearance around the anticline axis and their following transformation into mud pipes.

How to cite: Malikov, R., Karimova, N., and Jodry, C.: Use of Electrical Resistivity Tomography to characterize fluid pathways on the Saribokha mud volcano, Azerbaijan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8922, https://doi.org/10.5194/egusphere-egu22-8922, 2022.

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.

How to cite: Bulanova, I., Solovyeva, M., Akhmanov, G., Vidischeva, O., Khlystov, O., and Mazzini, A.: The enigmatic diapir-like structures in the Elovsky area (Lake Baikal): main characteristics and formation hypothesis , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10300, https://doi.org/10.5194/egusphere-egu22-10300, 2022.

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.

How to cite: Vasilevskaya, Y., Solovyeva, M., Akhmanov, G., Mazzini, A., Khlystov, O., and Vidishcheva, O.: Correlation between seismo-acoustic anomalies and sediments gas saturation in the Southern and Central depressions of Lake Baikal. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10313, https://doi.org/10.5194/egusphere-egu22-10313, 2022.

The continent–ocean transition along the passive margin off western Svalbard is, in places, only a few kilometers away from the formerly glaciated continental shelf. Strong bottom currents in the Fram Strait have led to the deposition of several kilometers thick sedimentary ridges that extend from continental to oceanic crust all the way onto the flanks of the oblique-spreading Molloy and Knipovich mid-ocean ridges. The sedimentary ridges represent large contourite drifts and are characterized by faults that extend to the present-day seafloor. Generally, it is argued that gravitational forcing or flexure due to fast sedimentation and/or erosion is the main force leading to deformation of Quaternary sediments, and that horizontal forcing is negligible. However,  high resolution 2D and 3D seismic data along the western Svalbard margin reveal that sedimentary faults commonly propagate from the termination of rift-related faults in the oceanic crust, and are not always favorably oriented to accommodate gravitational collapse. We suggest that coupling between the slow-spreading oceanic crust and the sedimentary cover results in a transfer of stress and strain that influences near-surface sedimentary deformation. Deep crustal fluids are also transferred into the Quaternary succession utilizing faults as migration pathways. Such faults sustain shallow gas accumulations, wide-spread gas hydrate formation and cold seeps. Simultaneously, glacial isostatic rebound leads to additional lithospheric deformation and also exerts a control on fault kinematics and gas seepage. We discuss seismic examples of deep marine seepage systems and the potential implications of coupling between lithospheric deformation and sedimentation on the spatiotemporal evolution of seafloor seepage at Arctic margins.

How to cite: Plaza-Faverola, A., Cooke, F., Vachon, R., Waghorn, K., Koehl, J. B., Beaussier, S., and Bünz, S.: Coupling between rifted oceanic crust and sedimentary deformation in the Fram Strait: implications for seafloor seepage and gas hydrates dynamics., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11917, https://doi.org/10.5194/egusphere-egu22-11917, 2022.

The Barents Sea region is an area of extensive erosion that occurred during the Cenozoic due to a tectonic uplift followed by several Quaternary glaciations. Several hydrocarbon fields have been discovered in the region where gas leakage through the seafloor is widespread. One of the promising regions of hydrocarbon occurrence is the north-western sector of the Russian Barents Sea. This poorly studied region has been recently targeted for scientific studies by several expeditions conducted in the framework of the Training Through Research program (TTR). The obtained geophysical and geological data revealed the presence of numerous acoustic and bathymetry anomalies (e.g., gas chimneys, bright spots, pockmarks) that are associated with higher gas content in the sampled sediments.

Here we combine (i) a set of shallow seismic data acquired during recent TTR expeditions (sparker seismic and sub-bottom profiling sections) with (ii) conventional deep seismic sections and (iii) a database of geochemical surveys of cored sediments. These merged data are used to compile a comprehensive database for the north-western sector of the Russian Barents Sea providing information on:

• the area of the potential Mesozoic reservoirs reaching the seafloor
• distribution of the seismically interpreted fluid pathways reaching the surface
• the position of the known or inferred seafloor seepage sites

One of the major goals is to correlate the geology of the outcropping strata with the variations of gas and water geochemistry, and ultimately to link the mapped/inferred fluid migration pathways to the Triassic-Jurassic reservoirs which are known to have high hydrocarbon potential in this region. Finally, the compiled database may represent a useful tool to geochemically characterize so far undiscovered hydrocarbon fields.

How to cite: Kishankov, A., Mazzini, A., Akhmanov, G., Solovyeva, M., Vidishcheva, O., Piatilova, A., and Krylova, M.: Gas leakage in the NW Russian Barents Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10970, https://doi.org/10.5194/egusphere-egu22-10970, 2022.

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.

How to cite: Solovyeva, M., Akhmanov, G., Mazzini, A., Vasilevskaya, Y., Piatilova, A., Vidishcheva, O., Basova, E., and Montelli, A.: Evidences of fluid-saturation in near-surface sediments in northern Barents Sea shelf, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10227, https://doi.org/10.5194/egusphere-egu22-10227, 2022.

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. 

How to cite: Vidischeva, O., Poludetkina, E., Basova, E., Dralina, E., Bogdanov, A., Bakay, E., Man’ko, I., Akhmanov, G., and Mazzini, A.: Hydrocarbons investigations from near-surface sediments of the north and northeastern Barents Sea shelfs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10172, https://doi.org/10.5194/egusphere-egu22-10172, 2022.

Bazhenov formation is the richest and principal oil shale formation in Russia, which covers the majority of the West Siberian oil fields.

Reservoirs within upper part of Abalak and Bazhenov formations are often associated with secondary altered rocks. According to the results of lithological, mineralogical, isotopic studies of cores, hydrothermal reworking of the deposits took place in past, leading to the precipitation of specific mineral associations, changes in porosity and permeability, organic matter thermal alterations. Two main phases of hydrothermal activity can be distinguished. The first one – sedimentary, took place when the deposits were not consolidated - the analogue of modern methane seeps on the Sea floor. This phase is characterized by precipitation of authigenic carbonates, as well as precipitation of barite, framboidal pyrite. The second phase took place when the rocks were already consolidated – high-temperature deep fluids migrated from underneath strata along weak zones (faults), reached different levels within the Abalak-Bazhenov complex and reworked the rocks with change of its mineral composition, porosity and organic matter maturity. 

As a result of the various deep fluid systems impact two main mechanisms take place: a) formation of secondary reservoirs due to the leaching processes b) zones of secondary hydrothermal mineralization with signs of seal. The latter have an inhomogeneous and patchy character of distribution vertically and laterally. And when they are exposed to later aggressive fluids, their reservoir properties may be improved.

The objective of present research is to find integrated lithological, mineralogical, isotopic evidence of deep hydrothermal fluids influence on the rocks of Bazhen-Abalak complex and characterize development history of these processes. These studies allow to predict both prospecting intervals of oil and gas generation and secondary porous reservoirs for industrial exploration.

How to cite: Gafurova, D., Yurchenko, A., Khotylev, A., Karpova, E., Balushkina, N., Kalmykov, G., Kalmykov, A., and Mazzini, A.: Hydrothermal fluid system geological history and its influence on oil and gas rock complex, West Siberia, Russia., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11820, https://doi.org/10.5194/egusphere-egu22-11820, 2022.

Characterization of Fluid Connectivity in Sedimentary Sequences using Strontium Isotopes

Johansen¹ I., Polteau¹ S., Schöpke¹ C.A.

• Institute for Energy Technology (IFE), Instituttveien 18, 2007 Kjeller, Norway, stephane.polteau@ife.no

Sedimentary basins typically contain complex internal heterogeneities that can segregate fluids into a series of isolated compartments. The permeability of these heterogeneities is often dynamic and time dependent: they can form impermeable barriers that prevent porous flow in timescales of a few years, while allow mixing of fluids by advection and/or diffusion on geological timescales. In general, the isotope composition of formation waters forms trends reflecting mixing by advection or slow equilibration controlled by diffusion during isotope exchange. In nature, when two systems (rocks, minerals, water/rock mixtures) are in chemical equilibrium but have different isotope compositions, both systems exchange their atoms to tend towards isotopic homogeneity while being chemically heterogeneous. Hence, the trends in isotope data enable the identification of a dynamic residual signal that would otherwise not be noticeable by other data that equilibrate faster. For example, pressure differences between sedimentary units equilibrate rapidly within a few thousand years, while millions of years are necessary to homogenize the isotopic composition of formation waters across low-permeability boundaries. Interpretation of these geochemical patterns provides information about the flow properties of the system and help to predict fluid connectivity and migration between different units. As such, Strontium Residual Salt Analysis (SrRSA) can help pinpoint important flow barriers and identify fluid connectivity in sedimentary basins.

How to cite: Johansen, I., Polteau, S., and Schöpke, C. A.: Characterization of Fluid Connectivity in Sedimentary Sequences using Strontium Isotopes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9674, https://doi.org/10.5194/egusphere-egu22-9674, 2022.

Gas chimneys, fluid escape pipes, and diffused gas clouds are common geohazards above or below most petroleum reservoirs and in some CO2 storage sites. However, the processes driving the formation of such structures are poorly understood, as are the timescales associated with their growth or their role as long-term preferential fluid migration pathways in sedimentary basins. Here we present results from high-resolution simulations of geological processes leading to the formation of focused fluid flow structures. Our analyses indicate that time-dependent rock (de)compaction yields ascending solitary porosity waves forming high-porosity and high-permeability vertical chimneys that will reach the surface. The size and location of chimneys depend on the reservoir topology and compaction length. Our simulation results suggest that chimneys could have been formed and lost their connection to the reservoir on a time scale of a few months. We compare our modeling results with seismic data from the Ringhorne Oil Field, located in the central part of the North Sea over the Heimdal Terrace and the Utsira High [1].

[1] Yarushina, V.M., Wang, L.H., Connolly, D., Kocsis, G., Fæstø, I., Polteau, S., Lakhlifi, A., 2021. Focused fluid-flow structures potentially caused by solitary porosity waves. Geology.

How to cite: Polteau, S., Wang, L. H., and Yarushina, V.: Coupled hydromechanical modeling of focused fluid flow structures, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2769, https://doi.org/10.5194/egusphere-egu22-2769, 2022.

The Paleocene Eocene Thermal Maximum (PETM, ~56 Ma) was a rapid global warming of 5-6 ºC resulting from massive (>2000 Gigatons) carbon emissions. A potential release mechanism is thermogenic gas from contact metamorphism of carbon-bearing sediments due to magma intrusions into sedimentary basins. Here, we present seismic data and borehole information from the North Atlantic Igneous Province. They show that even in the center of the rift system, water depths were sufficiently shallow to allow most gas released from hydrothermal vent systems to bypass the water column. The shape of the vent craters and stratified infill suggest vigorous explosive gas release during the initial phase of vent formation and rapid shallow marine and largely undisturbed infill thereafter. The recorded negative carbon isotope excursion and occurrence of the index taxon Apectodinium augustum in the crater-infill support assignment to a latest Paleocene to earliest Eocene vent formation. The data support a scenario where magmatic sill emplacement and resulting hydrothermal activity rapidly injected thermogenic greenhouse gas into the atmosphere.

How to cite: Berndt, C., Planke, S., Alvarez Zarikian, C., Bünz, S., Karstens, J., Svensen, H., and Manton, B. and the IODP Expedition 396 Scientific Party: Shallow-water hydrothermal venting in the North Atlantic during the Paleocene Eocene Thermal Maximum , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2359, https://doi.org/10.5194/egusphere-egu22-2359, 2022.

Lusi is the nickname of the largest sub-aerial erupting clastic system on Earth. This sediment-hosted geothermal system relentlessly erupts since May 2006 in the East Java back-arc sedimentary basin. This spectacular system features two main active craters (~100 m in diameter each) surrounded by thousands of satellite active seeps that extend over a region of 7km². Previous multidisciplinary studies revealed that Lusi is connected at depth with the neighboring Arjuno-Welirang volcanic complex through a system of faults (Watukosek Fault System) that extend from the volcano towards the north in the sedimentary basin. The migration of these mantle-derived fluids feeds the long-lasting activity of the eruption. Vigorous convection fuels the system and leads to geyser-like eruptive activity.

To investigate the morphology and the effect that pre-existing geological structures may have on the development of the shallow plumbing system of Lusi, we deployed a pool of 25 IRIS V-Fullwavers to conduct a 3D deep electrical resistivity tomography extending over 15 km² around the eruption site. The inverted data reveal the structure of the subsided area hosting the region where a mix of groundwater, mud breccia, hydrocarbons and boiling hydrothermal fluids are stored. We estimate that after 12 years of Lusi's inception, a collapse region of 0.6km² developed around the active vents. Combining the flow rate data with our geoelectrical data, we estimate a total budget of 0.47km³ of mud breccia (i.e., including the erupted volume and that trapped in the collapse zone around the carter). Our investigation also points out the link between the well-developed Watukosek Fault System and the upwelling of the deep-sourced fluids that initiated, and still drive, the development of the new-born Lusi eruption. Lusi provides the unprecedented opportunity to study the development of the early phases of a piercement structure and its impact on society. Our study highlights how fully 3D geoloectrical methods may represent a key tool to investigate and possibly mitigate geohazards.

How to cite: Mazzini, A., Carrier, A., Sciarra, A., Fischanger, F., Winarto-Putro, A., and Lupi, M.: 3D Deep Electrical Resistivity Tomography of the Lusi Eruption Site in East Java, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5960, https://doi.org/10.5194/egusphere-egu22-5960, 2022.

East Java features a transition from magmatic to sedimentary volcanism. In addition, the back arc basins are characterised by the presence of surface piercements structures that reveal the migration of mantle derived fluids. Despite a clear connection between the local tectonics and the distribution of the eruptive centrs, the mechanisms of driving fluid migration in East Java remain unclear. In 2006 a large sediment hosted geothermal system named Lusi, pierced the Kendeng basin in East Java and since then it continues to erupt relentlessly. This large-scale eruption represent the most recent manifestation of hydrothermal and mantle derived fluids in the sedimentary basin. We deployed a temporary seismic network from 2015 to 2016 to investigate the velocity structure of a large portion of the East Java region. Specifically, we studied the spatial and structural relationships between the volcanic arc and the back-arc domains, by performing a local earthquake tomography. We inverted the phase arrivals released by regional earthquakes to show sharp V_p and V_p/V_s transitions. We observe a marked reduction of P-wave velocities and a high V_p/V_s ratio in the back-arc basins. Our study point out a clear connection between the plumbing system of the volcanic arc and the back arc basins. By combining geochemical, geological and geophysical data we propose a conceptual model suggesting that magmas and hydrothermal fluids may migrate from the middle to the upper crust into the sedimentary basins capitalising on existing thrust faults. According to our proposed model, Lusi is located at the intersection of low-angle thrust faults and steep-dip strike slip faults, in region where the hydraulic transmissivity of the upper crust is enhanced.

How to cite: Lupi, M., De Gori, P., Valoroso, L., Baccheschi, P., Minetto, R., and Mazzini, A.: Magmatic and mud volcanism in East Java investigated with passive seismic methods., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10443, https://doi.org/10.5194/egusphere-egu22-10443, 2022.

Geysers, hot springs erupting water and vapour intermittently, have fascinated scientists for several centuries. However, many aspects such as interconnection between geysers or heat transfer in the plumbing system remain poorly understood. We monitored the temperature inside the active Strokkur and the nearby yearly-erupting Great Geysir geysers (Iceland) at different depths within the conduits. In June 2018, Strokkur was producing explosions at an average frequency of 3.6 minutes, emitting jets for 1 to 4 seconds up to 30 m high. Eruptions consist of 1 to 4 bursts of water at speeds ranging from 2 to 30 m/s.  Eruptions corresponds to temperature peaks in the conduit.  Analysis of the cooling and subsequent warming phases following eruptions within each eruptive cycle confirms a constant recharge of the system and highlights different heat transfer dynamics between the lower and upper part of the Strokkur conduit, as clearly marked by a distinct shape of the temperature oscillations. Our analysis suggests that a bubble trap geometry may play a key role in modulating the eruptions. The spectrogram of temperature oscillations in Strokkur has a main peak at a frequency of 4 mHz, corresponding to the average eruption frequency and a secondary peak at 1-2 mHz, which reflects the occurrence of multiple eruptions (i.e. sequences of 2-3 explosions separated by a few seconds each). A 1-2 mHz frequency peak is also observed on the spectrograms of Great Geysir records, although their intensities are not temporally correlated with those of Strokkur records. Finally, the lowest frequency peak between 0.1 and 0.5 mHz is observed on all Great Geysir records but only on the shallowest Strokkur record. These data do not only suggest that an oscillatory behaviour of the system is driving eruptions but also point out connections, possibly to the same aquifer at depth, however, because of the lack of  synchronicity of the oscillations within the two conduits, we tend to exclude any direct connection among the upper conduits of the two geysers. 

How to cite: Pioli, L., Collignon, M., Lupi, M., Trippanera, D., Carrier, A., and Fischanger, F.: Conduit dynamics and interaction in geyser systems: insights from the Haukadalur system (Iceland), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11639, https://doi.org/10.5194/egusphere-egu22-11639, 2022.

The gradual shift over time of the spectral lines of harmonic seismic and/or acoustic tremor, that is commonly known as spectral gliding, has been largely observed at different volcanoes. Despite the clear advantage of the experimental approach in providing direct observation of degassing processes and of the related elastic radiation, experimental studies on gliding tremor are lacking. To fill this gap, we investigated different episodes of gliding of acoustic and seismic tremor observed during analogue degassing experiments performed under different experimental conditions, by systematically changing: 1) analogue magma viscosity (10-1,000 Pa s), 2) gas flux (5-180x10^-3 l/s) and 3) conduit surface roughness (fractal dimension of 2-2.99). The occurrence of gliding experimental seismic and acoustic tremor was linked to high gas flux rates and viscosities and generally associated with an increasing trend and often preceding a major burst. In a few cases we observed decreasing secondary sets of harmonic spectral lines. Results suggest that gliding episodes are mainly related to the progressive volume variation of shallow interconnected gas pockets. Spectral analyses performed on acoustic signals provided the theoretical length of the resonator. The latter was compared against the temporal evolution of the gas pockets, quantified from video analyses. The similarities between the observed degassing regime and churn-annular flow in high viscous fluids encourages further studies on churn dynamics in volcanic environments.

How to cite: Spina, L., Cannata, A., Morgavi, D., Privitera, E., and Perugini, D.: An experimental investigation of seismic and acoustic harmonic tremor gliding and implication for churn-like flow, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13256, https://doi.org/10.5194/egusphere-egu22-13256, 2022.