Displays

Since 2003 the Atacama Desert in northern Chile is well-known as Mars analog model due to its extreme aridity, high UV radiation and highly saline soils containing highly oxidizing chemical species. Is in this frame that our team and others for the past decades have described a number of sites in the Atacama and their pertinence as Mars analog. However, since 2015 a number of climatic events never reported before have affected the Atacama, thought to be caused by climate change, with effects yet to be fully understood. Given that new instruments, techniques and rovers are, and will be tested in the Atacama before to be sent to Mars, is critical to be aware of these changes in order to properly plan new explorations and testing missions in this desert. Here we present some of the evidences of the changes brought by these environmental alterations, suggesting also the regions of the Atacama that still may be less or unaffected by them.

How to cite: Azua-Bustos, A. and G. Fairén, A.: The effects of climate change on the Atacama Desert as a pertinent Mars analog model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3344, https://doi.org/10.5194/egusphere-egu2020-3344, 2020.

Winter Wonderland is an ice cave in the Uinta Mountains of northern Utah, USA. The cave, which has an entrance at 3140 m a.s.l., extends 245 m into a north facing cliff of Mississippi Madison Limestone. The cave was discovered by the U.S. Forest Service in 2014. Winter Wonderland Ice Cave likely originated in the Late Mississippian to Early Pennsylvanian when joints opened up in the vadose zone. The interior of the cave is perennially below freezing with ice covering sections of the floor to a thickness of at least 2 m. Seasonally, meltwater from the epikarst enters the cave, pools on the surface of the older ice and freezes, creating a layered ice mass containing organic matter dating back several centuries. As this water freezes, cryogenic cave carbonates (CCCs) precipitate and are incorporated in the ice. In this study, ice, water, and mineral precipitates in the cave were investigated for the presence of microorganisms adapted to this extreme environment. Samples were collected to investigate the microbial communities that may be present within the Winter Wonderland ice cave, identify what they are, and investigate whether the composition of the microbial community changes spatially within the cave and between sample types. An intact block of ice (18x10x10 cm), liquid water samples (n=8), and 13 CCC samples were collected in August 2019. The ice block was removed from a vertical exposure of ice at the back of the cave using a hand saw, water was collected from a pool on the ice surface, and the CCCs were sampled from the surface of the ice in multiple sections of the cave. The water samples were analyzed for stable isotope composition to better understand water source and freezing history. Crystallographic study of oriented slides cut from the ice revealed that the ice crystallized vertically with some variation in crystal size. All samples were also investigated with fluorescence microscopy, flow cytometry, and DNA sequencing to reveal the abundance and type of microorganisms. Preliminary fluorescence microscopy and SEM imaging reveals the presence of cocci and bacilli type microorganisms within water samples and ~10um wide eukaryotic organisms within the CCCs, suggesting that the CCCs may provide much needed nutrients for the microbes or that the CCCs themselves are products of biomineralization.

How to cite: Seixas, M., Eggleston, E., Munroe, J., and Herron, D.: A characterization of microbial diversity in the Winter Wonderland Ice Cave, Uinta Mountains, Utah, USA, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12720, https://doi.org/10.5194/egusphere-egu2020-12720, 2020.

The sabkhas of Qatar are excellent environments to examine the mechanisms of low-temperature dolomite precipitation. The detailed microbial and geochemical analysis of the dynamics in environmental conditions in two microbial mats over two years provide a unique opportunity to gain insights in low-temperature dolomite formation in modern time. The compositions of extracted exopolymeric substances (EPS)  in two microbial mats, one within the lower intertidal zone and one within the upper intertidal zone exhibit an increase in the concentration of carboxylic functional groups during periods of elevated salinity. We interpret it as an indicator for dolomite formation since carboxylic functional groups are suggested to be the primary drivers for low-temperature dolomite as nucleation sites and inhibitors of Mg complexes. Notably, the increase in the concentration of the carboxylic group is associated with an increase in salinity in sabkha which happened periodically.

These fluctuations have been accompanied by the changes in the community from cyanobacterial dominated mat to one dominated by heterotrophs. During these periodical events, when a growing microbial mat turned into degrading microbial mat, we observed low-temperature dolomite formation. Such events occur in other modern dolomite forming environments and possibly in ancient sequences. Our work observed dynamical changes both in microbial mats, exopolymeric substances composition, geochemical gradients and accompanied low-temperature dolomite formation over several seasons. Our findings proving evidence that EPS degradation within microbial mats is a key mechanism in the formation of modern and most probable, ancient low-temperature dolomite with implications for those formed in ancient sequences.

How to cite: Diloreto, Z., Dittrich, M., Bontognali, T., Al Saad Al Kuwari, H., and A. McKenzie, J.: Linking decay of microbial mats and dolomite formation in the sabkhas of Qatar, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12203, https://doi.org/10.5194/egusphere-egu2020-12203, 2020.

The geological extreme Dallol region, located around the Dallol volcano in the north-east of Danakil depression (Ethiopia), is considered as one of the harshest and hottest places on Earth. The geology is made up of years and years of evaporates accumulation. Volcanic activity generates ascending brines that may cross and mix with aquifers from inflowing meteoric water originating from the Ethiopian highlands on the east of the Danakil depression. When these mixtures reach the surface they can generate hydrothermal springs giving rise to waterbodies in the form of small ponds or lakes. During the Europlanet 2018 Danakil field expedition, ten of these saline waterbodies were extensively studied by in situ measurements and ex situ geo–physico-chemical and –microbiological analyses of collected samples, liquids as well as sediments.

The in situ physico-chemical measurements clearly indicated the extreme nature of all ten investigated lakes. Laboratory analyses of the collected batch samples of liquids and sediments confirmed the extreme character of the waterbodies and complements our geological survey of the region with valuable geo–chemical and –microbiological data.

Based on our analytical results, the relative small Dallol region can still be subdivided into three geological smaller areas: the outcrop zone, the volcanic base region and the distant south area. The outcrop zone is dominated by sodium, iron and potassium. Oxidation processes in the outflowing superheated ferrous and sulfidic rich brine give rise to some of the most acidic ponds on our planet. In the ponds and lakes of the volcanic base region, incredible high amounts of calcium and/or magnesium can remain in their dissolved form as the most dominant and quasi only available anion is chloride. This region is host for the most saline water body on Earth. Chemical analysis of the lakes of the distant south area show that sodium is by far the most dominant cation. It is therefore no surprise that the large Karum Lake in the south region is economically exploited for the mining of sodium chloride.

Our mineralogy analyses render results that are completely in line with the observed geochemistry of the waterbodies. Halite and sylvite are the most present minerals in the Dallol outcrop zone associated with some gypsum and in one case with anhydrite. The geology around the waterbodies of volcanic base zone are a little bit more divers. On the shores of the Gaet’ale Pond tachyhydrite, chloromagnesite, halite and sylvite is determined, while the Black Lake is surrounded by bischofite and carnalite. Logically, the mineralogy of the south area, the salt mining area, is dominated by halite and sylvite.

Apparently, the geochemistry of the outcrop zone and volcanic base region is so harsh that no extremophilic organism is able to survive in these areas. Only in the distant south area did we find indications of the presence of halophiles. Besides the bacterial genus Salinibacter, our 16S rDNA microbiological fingerprinting indicates the presence of halophilic archaea like:  Halobaculum sp., Halobellus sp., Halomicroarcula sp., Halorientalis sp. with the majority of the population being Candidatus Nanosalina sp.

How to cite: Moors, H., Honty, M., Smolders, C., Provoost, A., De Craen, M., and Leys, N.: The waterbodies of the Dallol volcano: A physico-chemical and geo-microbial survey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1581, https://doi.org/10.5194/egusphere-egu2020-1581, 2020.

A new high-resolution seismic dataset is used to investigate the distribution and influence of different phases of magmatic activity in the southeast of El Hierro, Canary Islands. The Canary Archipelago off NW-Africa has largely been formed over the past 20 Myr, but older volcanic edifices exist. One of those older edifices is Henry Seamount, an extinct 126 Ma volcano located 40 km southeast of El Hierro, the youngest (1.1 Ma) and westernmost of the Canary Islands. Hence, the area southeast of El Hierro is influenced by both older and younger magmatic activity. We also found evidence for comparatively young volcanic activity at Henry Seamount, probably contemporaneous to El Hierro. Therefore, a complex magmatic system is assumed to have resulted in the different phases of magmatic activity.

A detailed high-resolution 2D seismic reflection dataset was collected in an area between El Hierro and Henry Seamount during RV Meteor expedition M146 in 2018 to image the expressions of this magmatic system in the upper sub-surface. Several acoustic blanking zones were discovered and identified as the most prominent features in this seismic dataset. We classify these blanking zones into three different types. Type 1 blanking zones are related to volcanic edifices, which crop out at the seafloor and cut through all imaged sedimentary units. Type 2 blanking zones are characterised by upward bending of adjacent reflectors and are most likely caused by hydrothermal doming resulting from saucer-shaped sill intrusions. Type 3 blanking zones cut clearly through adjacent reflectors, and are probably related to fluids or gases that were mobilized by the sill intrusions. The type 1 and 2 blanking zones cluster in the central part of the working area, whereas the blanking zones of type 3 are located on the outskirts. This specific distribution and the occurrence of the varying blanking zone types are combined to make a conceptual model of this complex magmatic system. Our model takes sill intrusions, hydrothermal doming, as well as volcanic out-crops and mobilized fluids into account. Therefore, this study provides new insights into the magmatic evolution of the youngest Canary Island, which can help to achieve a better understanding of the whole system.

How to cite: Lenz, K.-F., Gross, F., Klügel, A., Barrett, R., Held, P., Lindhorst, K., Wintersteller, P., and Krastel, S.: New insights into the magmatic system southeast of El Hierro from high-resolution 2D seismic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15205, https://doi.org/10.5194/egusphere-egu2020-15205, 2020.

Various types of fluid expulsion features occur often at fold-and-thrust belts and subduction zones. The seepage features originate from the discharge and extrusion to the topographic surface of fluids, gases and possibly solid material, which are sourced from in-depth reservoirs. Earthquakes can occasionally trigger the eruption or increased activity of mud volcanoes and other seepage systems. The role of static and dynamic stress changes in the triggering will vary depending on the position of the seepage features with respect to the earthquake source fault. When the seepage system is controlled by faults that rupture and generate earthquakes, the role of static stress changes is likely to be influential. Subduction zones have the highest seismic potential on Earth, so large subduction earthquakes can stress massively the fault-controlled feeder systems of seepage features located above subduction thrusts. The potential role of coseismic static stress loading on fluid expulsion systems has been evaluated for accretionary and erosional subduction margins. The most significant effects occur in the epicentral area where subduction earthquakes can produce coseismic normal stress changes exceeding 20-40 bar, although these are generally restricted to relatively small regions. The magnitude of such stress changes may exceed the tensile strength of many rock anisotropies and increase crustal permeability by dilating fault-controlled conduits channeling fluids upwards. Also in fold-and-thrust belts seepage features may be associated with seismogenic faults. For instance, rupture of the Chihshang Fault (Taiwan) in 2003 produced the Mw6.8 Chengkung earthquake, which unclamped by 3 bar the feeder system of the nearby mud volcanoes that erupted shortly after the earthquake. A similar setting is also inferred for the seismogenic Pede-Apennine thrust system in northern Italy, which is also structurally controlling a number of mud volcanoes located on its hangingwall.

Seepage features can be often trigged off by dynamic stress changes created by earthquake faults located in the intermediate- to far-field. Peak dynamic stresses related to historical and recent earthquakes that produced a response of seepage systems in the Northern Apennines fold-and-thrust belt (Italy) are calculated through PGV (measured or evaluated through GMPEs). We document response of seepage systems to some historical and recent earthquakes. Some methane vents and springs showed paroxysmal activity that was influenced by peak dynamic stress of 0.3-0.4 bar, while mud volcanoes apparently showed lower sensitivity, being influenced by dynamic stresses with amplitude ranging between 0.5 and 3.5 bar. Recently, 17 mud volcanoes erupted shortly after the main seismic events of the 2016 Central Italy seismic sequence (Mwmax6.5), showing a clear correlation with peak dynamic stresses of the order of 2-4 bar (static stress changes are instead negligible or negative).

These results collectively suggest that seepage features may respond in different ways to dynamic and static stresses depending on earthquake magnitude and epicentral distances, and that they may show different sensitivity to stress changes. Dynamic stresses are likely to exert the dominant control on the triggering, even though static stress changes can also significantly influence seepage features in the near-field.

How to cite: Bonini, M. and Maestrelli, D.: Earthquake triggering of mud volcanoes and fluid seepage systems in fold-and-thrust belts and subduction zones, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3673, https://doi.org/10.5194/egusphere-egu2020-3673, 2020.

Baikal is the largest and oldest freshwater lake on Earth. This syn-rift thick sedimentary basin hosts a large variety of present-day geological sedimentary processes, among which focused fluid seepage, mud volcanism and gas hydrate accumulation, that manifests a relationship with hydrocarbon systems in the basin. Offshore mud volcanism is well known to be one of the geological phenomena that is often associated with the presence of gas hydrates all around the World. The almost ubiquitous coupling of these processes may be a key to understand distinctive “Baikalian” mud eruption process and the resulting mud volcanic deposits. So far twenty-two mud volcanoes (MVs) have been identified in different areas of the lake, and the identification of new structures, the formation processes, and their roots depth represent challenging topics for researchers. During the last five years numerous gas hydrate-bearing features with positive circular morphology have been identified at the bottom of the lake and these represent ideal candidates to be considered as mud volcanoes.

Most mud volcanoes worldwide are characterized by the presence of mud breccia. This melange of erupted sediments consist of clayey-silty-sandy matrix mixed with clasts of different sizes and lithologies representing mainly well-lithified fragments of the different formations pierced and brecciated through the MV feeder channel. Most of the offshore MVs share these characteristics, and this criteria has been used as an unambiguous evidence to classify new MV structures. A similar approach is hardly applicable for some of the investigated structures of Lake Baikal. Seismic images reveal that the conduits of these MV candidate structures are typically shallow rooted (<0.5 km blf). The lake is a deep sedimentary basin that has been characterized by high sedimentation rates since almost 25 Ma resulting in thick deposits that are unlithified in its top part. Therefore, the recovered sediment cores are barren by the typical presence of mud breccia lithified clasts which are characteristic for “classic” mud volcanic breccia.

Here we report a set of multidisciplinary studies (including petrography, geochemistry and tomography) conducted on mud breccia cores collected from several MVs of the Baikal. Sediment core observations revealed the presence of semi-lithified clayey clast seemingly broadly distributed in the structureless sediments. Petrography studies of the individual clast reveal that they differ in mineralogical composition, and their poor lithification indicates that they originate from shallow sediments. The otherwise invisible internal structure of the cored sediments has been studied with CT-scan. Results confirm that the recovered cores contain numerous semi-lithified clasts displaying different X-ray absorption and thus mineralogical content. The absence of sedimentary structures and a completely chaotic matrix indicates a vigorous mechanism (i.e. typically ongoing in mud volcano conduits) able to amalgam different lithologies. Geochemical analyses of the sediments pore gas show the presence of prevalently microbial methane further supporting microbial reactions that commonly occur at relatively shallow depths. Results are integrated in the regional geological context and combined with geophysical data to explain the mechanisms of eruption and the peculiar sedimentary texture that differs from the traditional MVs worldwide.

How to cite: Akhmanov, G., Mazzini, A., Khlystov, O., Kudaeva, A., and Vidishcheva, O.: Peculiarities of mud volcanism in Lake Baikal, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1271, https://doi.org/10.5194/egusphere-egu2020-1271, 2020.

Pockmarks are crater-like depressions on the floor of oceans and lakes formed by the upward transport of fluids through the unconsolidated sediment column. The fluid flow through marine pockmarks is considered to enhance hydrological and biogeochemical exchanges between the sediments and the water body. While a similar relevance can be expected in lakes, the importance of lacustrine pockmarks in this regard is virtually unexplored.

Lake Thun (48.3 km² surface area), Switzerland, is an excellent system to study lacustrine pockmarks as it exhibits several sites with different geological and biogeochemical settings. One of the pockmark sites is characterized by evident methane (CH₄) ebullition and high CH₄ concentrations from ~2.4 to 8.9 mM within the sediments beneath. A large pockmark with a diameter of 110 m is located adjacent to the rock wall of a karst system and might thus be associated with groundwater discharge into the lake. Finally, spikes in electrical conductivity detected during a survey with a remotely operated vehicle (ROV) at a third pockmark site suggest a hydrogeological connection with the groundwater system in the underlying Triassic bedrock.

This third pockmark site we are studying more closely. We observed that the sediments inside the pockmark were clearly more liquified as compared to those at a reference site (outside the pockmark), providing further evidence for groundwater discharge that might presently be active. The porewater chemistry was similar at the two sites, except for the total dissolved Fe concentration which was about 2 to 5-fold lower inside the pockmark than at a reference site. Further chemical analysis of porewaters and the water column above the pockmark as well as a molecular investigation (e.g. 16S rRNA) of the sediments will be performed at two different seasons of the year (in fall and spring during the snowmelt season). All together, these results should help us to better assess the influence of groundwater discharge via this pockmark site on the hydrological balance and on the biogeochemistry of the lake, as well as to expand our limited knowledge on the mechanism of lacustrine pockmarks in general.

How to cite: Cojean, A. N. Y., Bartosiewicz, M., Zimmermann, J., Lehmann, M. F., Kremer, K., and Wirth, S. B.: Different pockmark systems and their potential importance for the hydrological and biogeochemical balance of a peri-alpine lake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16565, https://doi.org/10.5194/egusphere-egu2020-16565, 2020.

Mud volcanoes (MVs) have been found in various geological settings on passive and active margins but are mostly known from collision zones on Earth. Mud volcanoes are well known to occur on land (e.g. in Azerbaijan), where at least 1000 MVs have been counted. The amount of submarine MVs is believed to be much larger and recent improvements in seafloor mapping led to the discovery of many MVs in all oceans. To contribute to the knowledge of submarine MVs, in particular the internal structure across Venere MV, we conducted a multi-geophysical imaging approach using high resolution multibeam bathymetry, (constraining seafloor expressions), multichannel, and wide-angle seismic data (constraining the internal structure and P-wave velocity distribution). Venere MV is located at the southern rim of the Crotone forearc basin of the Calabrian arc, offshore southern Italy, in a water depth of ~1500 m. The dimension of Venere MV from its bathymetric expression is ~10 km in the EW- and ~7 km in the NS-direction. Two circular cones of ~100 m elevation and ~1.5 km diameter are located in the center of Venere MV. The upper 200 m below the seafloor (bsf) consist of layers with seismic P-wave velocities gradually increasing from 1.53 to 1.7 km/s (sub-) parallel to the seafloor. A prominent reflection ~200 m bsf and a sudden increase of seismic P-wave velocities from 1.7 to 1.8 km/s mark a change with depth in the internal structure, where reflections dip, and seismic P-wave velocities laterally decrease towards the center of Venere MV. The MCS as well as seismic P-wave velocity structure indicate two separate feeder conduits of the two center cones of Venere MV. However, we do not map the roots of the MV, which are at depths beyond our data resolution. Reduced reflectivity occurs ~4 km across the center of the MV 200 m bsf and downwards. We mapped the chaotic reflections of the acoustic basement in depths varying from 500 m to 800 m bsf. Reduced reflectivity of the acoustic basement occurs beneath the center of the MV as well. Mapping of the fault system leads to the subseafloor dimension of Venere MV that exceeds its seafloor dimension by the factor of two.

How to cite: Riedel, M., Krabbenhoeft, A., Papenberg, C., Bialas, J., Bohrmann, G., and Ceramicola, S.: Internal Structure of Venere Mud Volcano in the Crotone Forearc Basin, Calabrian Arc, Italy, from Multibeam Bathymetry, Wide-Angle and Multichannel Seismic Data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4840, https://doi.org/10.5194/egusphere-egu2020-4840, 2020.

Mud volcanism is known to be strictly linked to anticlines, since these structures have the ability to trap hydrocarbons and other fluids into reservoirs placed at their core, where large overpressures may be generated. Despite mud volcanoes have been widely studied, a central and still debated theme is (i) how fluids are able to migrate upward bypassing the overburden and erupt at surface, and (ii) which role near-structures (i.e. structure directly linked to the mud volcano system, or located not far from it) and far-structures (i.e. faults located far away from the mud volcano system) may play in this process. In an effort to address these questions, we investigated the role of both types of structures in the genesis and evolution of mud volcanoes. In particular, we show six mud volcano case studies from the Emilia-Romagna and Marche pede-Apennine margin, in Italy. We integrated fieldwork data and interpretation of available seismic reflection profiles whit aerial photo analysis. Our results support the intimate link of the investigated mud volcano systems with anticline structures on top of which they are typically emplaced. We then discuss two distinct settings for fluid migration and mud volcano formation, particularly: (i) mud volcanoes emplaced on outcropping anticlines, and (ii) mud volcanoes located on top of buried structures, discerning when fluids are likely to exploit anticline-related fracture sets, or secondary structures and porosity. Finally, we speculate on how far-structures may still play a crucial role, via seismic triggering, in the occurrence of historical eruptions of some of the investigated mud volcano systems.

How to cite: Bonini, M., Maestrelli, D., and Sani, F.: Tectonic structures vs genesis and activity of mud volcanoes: examples from Emilia and Marche (Northern Apennines, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3664, https://doi.org/10.5194/egusphere-egu2020-3664, 2020.

The Island of Elba, located in the westernmost portion of the northern Cenozoic Apennine belt, is formed by metamorphic and non-metamorphic units derived from oceanic (i.e. Ligurian Domain) and continental (i.e. the Tuscan Domain) domains stacked toward NE during the Miocene.

Offshore, west of the Island of Elba, magnetic and gravimetric data suggest the occurrence of N-S trending ridges that, for the very high magnetic susceptibility, have been interpreted as serpentinites, associated with other ophiolitic rocks. Moving towards south in Tuscan domain, along N-S fault, there is clear evidence of off-shore gas seepage (mainly CH₄), which can be related to recent extensional activity.

In this contest, a cold methane seep was discovered in the sedimentary basin off Elba Island, characterized by typical mud volcanoes conditions. Generally, mud volcanoes are the shallow expression of subsurface processes characterized by movements of large masses of sediments and fluids. A marine mud volcanoes is a window into different depth levels of the submerged geosphere where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs caused by tectonic activity. Indeed, vertical migration of geogas, especially CH₄ from the reservoir strata to the sea floor occurs along focused, permeable migration pathways, often created by faults and fractures.

The sampled gas chemistry is typical of mud volcanoes, with methane as the prevalent gas component (>95 vol%) and minor gases that include carbon dioxide, nitrogen and trace amounts of helium. The combined stable C and H isotope composition of CH₄ (δ¹³C and δ²H) highlights a thermogenic origin of fluids discharged from mud volcano, contrary to likely abiotic origin gas found in the Pomonte seep and linked to serpentinized ultramafic rock systems.

The samples collected on this mud volcano are extremely depleted in ³He and their ³He/⁴He ratios are typical for a geological setting in which radiogenic crustal helium is strongly predominant. On the contrary, the Pomonte ophiolitic gas seeps show a mantle-derived ³He-rich component estimated in the range between 10 and 15%.

Petrological data highlight the presence of siltites and marly mudstones characterized by different origin than those found on neighboring islets (shallow marine organogenic limestones); therefore, the possibility that the fragments of rock blocks, found in the mud volcano area, derive form erosional processes of the islet is discarded. The conical shapes highlighted by the multibeam echosounder are very similar to the typical backscatter signature of other mud volcanoes, thus confirming the possibilities of classify this site as mud volcano. Indeed, already during the scuba diving survey that allowed sampling gas and sediment, it was clearly observed and documented as a mud volcano.

How to cite: Sciarra, A., Saroni, A., Grassa, F., Ivaldi, R., Demarte, M., Lott, C., Weber, M., Eich, A., Cimenti, E., Mazzarini, F., and Coltorti, M.: A shallow mud volcano in the sedimentary basin off the Island of Elba, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1336, https://doi.org/10.5194/egusphere-egu2020-1336, 2020.

Azerbaijan hosts the highest concentration of mud volcanoes (MVs) on Earth with structures that may reach several kilometres in diameter and the height up to 600 m. Many of these structures alternate between periods of dormancy with vigorous eruptions. The frequency of the eruptive activity varies between MVs, and is typically related to the time required to build sufficient overpressure able to drive the extrusion of fluids and mud breccia at the surface.

Lokbatan is possibly the most active MV on Earth exhibiting powerful eruptions occurring every 3-5 years. These phenomena manifest with spectacular gas flares that reach several tens of meters in height and the bursting of thousands of m³ of mud breccia resulting in spectacular mud flows that extend for more than 1.5 kilometres. Unlike other active MVs, Lokbatan does not show any visual evidence of diffuse degassing (e.g. active pools of gryphons) in the crater zone. Gas flux measurements completed with closed-chamber technique sensitive to ppmv, reveal extremely low values throughout the structure around the crater with average CH₄=0.13 g/m²day and CO₂₌4.53 g/m²day. We suggest that after eruptive events, the mud breccia is able to seal the structure preventing the gas release and therefore promoting the overpressure build-up in the subsurface. This self-sealing mechanism allows a fast recharge of the MV resulting in more frequent and powerful eruptions. These spectacular phenomena are able to release in short time intervals massive amounts of gas, erupted mud breccia and energy due to the sudden overpressure release. Our field observations reveal the presence of large (up to ~50,000 m³) stratified blocks that were originally part of a large crater cone. These blocks were rafted > 1 km from the vent on top of mud breccia flows. We use a lubrication theory model to show that it is reasonable to transport blocks this large and this far provided the underlying mud flow was thick enough. The presence of large rafted blocks is not a unique phenomena observed at Lokbatan MV and is documented also at other large-scale structures.

How to cite: Mazzini, A., Akhmanov, G., Michael, M., Sciarra, A., Khasayeva, A., and Guliyev, I.: Explosive mud volcano eruptions and rafting of mud breccia blocks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1315, https://doi.org/10.5194/egusphere-egu2020-1315, 2020.

The Class@Baikal 2019 expedition led by UNESCO-Moscow State University Educational-Scientific Center for Marine Geology and Geophysics (the Department of Geology, Moscow State University Lomonosov) sailed several transects between the southern and central part of the Lake Baikal, Russia. Seismic profiles were made to map the lake bottom sediments and structures as well as several short piston cores were drilled. The drilling sites were located a) following a nearshore to offshore transect to study the sedimentary processes and b) in areas where mud volcanoes were located in the geophysical data. Intriguingly, the sediments retrieved from the cores contained a high amount of plant debris, such as wood and conifer needles. The present palynological study has been started with the goal to better understand the sedimentological processes resulting in these distinct horizons of plant fossil rich sediments. Another goal is to obtain a stratigraphic age for the mud clasts and the surrounding matrix sediments of the presumed mud volcano structures. The first sediment samples appear to be rich in pollen and spores which allows to establish a palynostratigraphic framework for the studied cores.

How to cite: Labes, A., Mazzini, A., Akhmanov, G. G., and Kürschner, W. M.: Palynology of Holocene Lake Baikal sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5213, https://doi.org/10.5194/egusphere-egu2020-5213, 2020.

Lake Baikal is a part of large intracontinental rift zone. Baikal sedimentary infill is more than 7 km thick and was developed under predominantly extensional tectonics. Large number of faults of different geometry is imaged by several seismic surveys carried out in the region. The fault systems serve as fluid discharge pathways from deep sources to surface. A number of active seepage structures were mapped and studied during the Class@Baikal expeditions along the major fault system of the Central Baikal basin, which extends in SW-NE direction over 40 km and was named recently as the Gydratny Fault. Irregular distribution of these seeps, differences in their morphology and activity rate imply a variable permeability of the fault and different characteristics of migration pathways along its segments.

High-resolution seismic sections were acquired across the Gydratny Fault during the Class@Baikal cruises. The survey was followed by extensive bottom sediments and gases sampling. Hydrocarbon gases and isotopic characteristics as well as sediment pore water composition were analysed. Methane was detected in sediments along the whole fault extend in concentrations of more than 100 ml/l, exceeding background values (<15 ml/l), suggesting that the fault plane acts as regional fluid migration path. The highest methane content (>275 ml/l) and the presence of its homologues were observed at several local sites situated along the fault and associated with mud volcanoes and gas hydrate bearing seeps. The carbon isotopic composition varies from -72 to -57‰ VPDB for methane and from -21 to -31 ‰ VPDB for ethane, suggesting that these are thermogenic gases that migrate from deep layers of sedimentary infill of the basin.

Seismic data show well-established segmented nature of the Gydratny Fault system, which is believed to be a reason for observed variations of fluid discharge rates. Integrated analysis of the collected geophysical and geochemical data allowed evaluating contributions of different structural elements of the Gydratny Fault to fluid migration pattern in the area. NE segment of the fault system is a well expressed normal fault propagating to the lake bottom which is associated with higher methane concentrations (150-200 ml/l), elevated methane homologues content of up to 40 ml/l and heavier carbon isotopic composition in gas samples. The SW segments is either faintly expressed in the bottom relief or does not reach the surface at all. The methane concentrations in sediment samples collected from the segment are 100-150 ml/l and its carbon isotopic composition is normally lighter. We suggest that deeper parts of the SW fault segment are still highly conductive and concentrated hydrocarbon fluids migrate from the source upwards but some near-surface dispersal of migrated fluids occurs at places where the fault does not reach the lake bottom. The Gydratny master fault is accompanied by numerous subsidiary faults developed within hanging wall while footwall is less faulted. The associated faults are believed to enhance the main fluid migration system and this interpretation is supported by observations of normally higher methane concentrations in bottom sediments of the hanging block.

This study was funded by RFBR Grant № 18-35-00363.

How to cite: Vidischeva, O., Solovyeva, M., Egoshina, E., Vasilevskaya, Y., Poludetkina, E., Akhmanov, G., Khlystov, O., and Mazzini, A.: Integrated analysis of geophysical and geochemical data from cold fluid seepage system along the Gydratny Fault (Lake Baikal), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20934, https://doi.org/10.5194/egusphere-egu2020-20934, 2020.

Baikal is a Cenozoic syn-rift sedimentary basin with many surficial manifestations of distinct hydrocarbon system. Focused gas seeps, gas-hydrate accumulations, and various mud volcanoes are abundant all over the lake bottom and were recently studied in order to characterize an upward fluid migration from deeper strata. Highly concentrated oil seeps which can provide detailed information on basin fluid migration pathway configurations are mostly developed at the east coast and rift flank of Lake Baikal.

Herewith, we report results of detailed geochemical studies (gases, organic matter, bitumen, pore waters, and sediments) completed on samples collected from an area of active oil and gas seepage, asphalt/tar edifices and subbottom gas-hydrates occurrences located 18 km offshore the Gorevoy Utes cape (the eastern coast of the lake) at the depth of 850-950 m.

As a part of the Class@Baikal-2018 expedition, two high-resolution seismic profiles (total length of about 10 km) crossing the fluid discharge zone in transverse directions were acquired to locate 22 bottom sampling stations and to retrieve samples. Four more seismic lines and 12 sampling cores were collected during the follow up Class@Baikal-2019 cruise.

The highest concentrations of all gases and a fresh crude oil in sediments are characteristic for a spot of only about 500 m in diametre, marking a probable centre of the most intense deep fluid migration to the surface. The elemental composition characteristic of sampled oil was determined as follow: C=83.84%, H=10.67%, N=0.37%, and S<0.08% by wt. And its molecular compounds are 15% asphaltenes, 20% resins, 35% aromatic hydrocarbons, and 30% saturates.

High concentration of methane was also detected in samples at the distance from this central spot all around the studied field. According to isotopic analyses, this indicates lateral redistribution of thermogenic methane ongoing together with enhanced bacterial methane generation in surrounding sediments. δ13С of methane from the peripheries varies from -70.98 ‰ to -88.46 ‰, whereas the δ13С of methane from the central spot is heavier (up to -41.00 ‰). The high content of methane homologues (ethane and propane) and carbon dioxide is characteristic and indicative for all samples taken from the central spot. A few samples collected outside of the central zone demonstrated the high thermogenic methane concentration, carbon dioxide content and presence of some methane homologues as well. Most likely this points out at existence of locally permeable segments aside of main conduit, probably some fractures accompanying the central pathway. Interestingly, no fresh oil was found in those samples.

Rock-Eval pyrolysis, isotopic analyses and biomarker studies revealed that the source rocks for both hydrocarbon gases and oil are terrigeneous and contain predominant humic organic matter components (kerogen type III). These strata belong to different maturation stages, ranging from low-mature to peak-mature, which is well explained by the complex structure of the rift sedimentary infill and documented presence of local thermal anomalies in the region.

Results of geochemical studies are incorporated into an integrated model of source-to-surface fluid migration to explain the observed peculiarities of the Gorevoy Utes seepage area.

How to cite: Egoshina, E., Delengov, M., Vidishcheva, O., Bakay, E., Fadeeva, N., Akhmanov, G., Mazzini, A., and Khlystov, O.: Geochemistry of oil-and-gas seepage in Lake Baikal: towards understanding fluid migration system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1741, https://doi.org/10.5194/egusphere-egu2020-1741, 2020.

REEs concentrations in mud volcanic waters were normalized to RPSC (Russian Platform of Shale Composite). On the Yuzhno-Sakhalinsky mud volcano (Sakhalin Island, Russia), along with the sampling for analysis of REEs concentrations, hydrogeochemical monitoring was also conducted.

How to cite: Sobisevich, A., Ershov, V., Elovskiy, E., Baloglanov, E., and Puzich, I.: Concentrations and behavior of rare earth elements in mud volcanic waters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4413, https://doi.org/10.5194/egusphere-egu2020-4413, 2020.

Mud volcanism (MV) is an efficient dewatering mechanism common to collisional settings which provides transport of major and trace elements from deep sedimentary reservoirs to the surface. Boron is the chief geochemical fingerprinting tracer of MV activity. Numerous MVs of the Kerch Peninsula emit water and mud with extreme boron enrichment. Boron content correlates with the burial depth of the source Oligo-Miocene mudrocks yielding the highest boron contents in illite-dominated mud (up to 1500 ppm B) in the Bulganak MV, which represent the deepest endmember (up to 3.5 km) in the Kerch Peninsula. Smectite-dominated mud from shallow depths (1-1.5 km) at small MVs are poorer in both illite and boron (up to 250 ppm). B-enrichment of the parent shale and diagenetically-driven smectite illitization and dewatering are considered as the main prerequisites for boron enrichment in MVs.

MV waters are mainly related to diagenetically altered basinal water diluted by ¹⁸O- and B-enriched dehydration water released during smectite illitization. The range of boron contents in the Kerch MV waters is as large as 14 to 1640 ppm (470 ppm on average), and the B_MV/B_SW ratios are from 3.0 to 354. Waters of small MVs show lower B enrichment (14-73 ppm; B_MV/B_SW = 3.0-15.8). The majority of Cl-HCO₃/Na and HCO₃-Cl/Na highly evolved saline MV waters sampled in large MVs are also enriched in ¹⁸O (δ¹⁸O = +9.8 to +14.5 ‰ VSMOW) and D (δD = -30 to -4 ‰ VSMOW) isotopes being also rich in boron (average 650 ppm). Waters of small MVs are poorer in ¹⁸О (δ¹⁸O = +3.6 to + 6.1 ‰) and B (average 130 ppm). The fluid generation temperatures inferred to be Т_Mg/Li = 34 to 117°С. In the hot season, MV waters reach a salinity of 40-70 g/L TDS and precipitate halite, Na and Na-Ca borates. At the Bulganak MV field, there is a unique accumulation of MV-related borates, which contain predominant tincalconite and ulexite, minor borax and traces of probertite. The broad occurrence of ulexite in the Kerch MVs is due to the B (460– 630 ppm) and Ca (>30 ppm) ranges of NaCl-dominated brines, which are known to be optimal for ulexite crystallization in modern playas and salars. MV-related borate deposits can form at the following essential conditions: venting of B-rich MV waters; environment akin to playa lake; long dry and hot seasons; evaporation and ensuing increased boron concentration in shallow close MV pools; pH of MV water between 8.5 and 9.5; low permeability of clayey mud cover. The study was supported by the Russian Science Foundation, grant 17-17-01056.

How to cite: Sokol, E., Kokh, S., Kozmenko, O., and Lavrushin, V.: Borate accumulations related to onshore mud volcanism: Case study from the Kerch Peninsula, the Caucasus collision zone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3307, https://doi.org/10.5194/egusphere-egu2020-3307, 2020.

Terrestrial detection of biomarkers in various mineral matrices using Raman spectrometers including field deploying of miniature instrumentation in Mars-analogue sites can be seen as a training for next Martian missions. In fact, both the European Space Agency (Exomars) and North American Space Agency (Mars 2020) robotic rovers will include Raman spectrometers. Feasibility of detecting biomarkers of extremophilic cyanobacteria and algae (pigments, osmotic solutes and lipids) using Raman microspectrometry was reviewed previously. Here the idea is to show - firstly how portable Raman instrumentation permits to detect carotenoids fast and onsite under field conditions. Secondly, laboratory microspectrometric investigations allow to obtain more detailed information about spatial distribution of pigments originating from microorganisms.

Macrocrystalline gypsum layers and aggregates are well-known from Tertiary series in Sicily and Eastern Poland. In Southern Sicily gypsum sediments accumulated during Messinian crisis (Late Miocene) are outcroping and were investigated near Scala dei Turchi, Torre Salsa and Siculiana Marina. Polish Tertiary (Badenian, Middle Miocene) examples of gypsum colonisations of decimetre long outcropping crystals were studied near Chotel Czerwony, Skorocice and Chwalowice. Miniature portable Raman spectrometers equipped with green lasers allowing recording of resonance Raman signals of carotenoids are evaluated here. Possibilities of collecting spectra of carotenoids under non-resonant conditions using a portable sequentially shifted Raman spectrometer (785 and 853nm lasers) are shown as well. Observed shifts of positions of Raman features of carotenoids between gypsum samples (and sites) are discussed and critically evaluated. In addition, acquired data are compared to data obtained through laboratory Raman microspectrometric investigations. Selected zones of microbial colonisations of few types of gypsum are described from the point of view of the presence of algae and cyanobacteria. Pigments are detected through conventional Raman microspectrometric measurements. Carotenoids were documented in major part of samples (common Raman bands at around 1525, 1157, and 1004 cm⁻¹). Additionally, Raman spectra of other pigments were recorded in several zones using near infrared excitation (785 nm): chlorophyll (1151, 1327, 1287, 1184, 917, and 745 cm⁻¹), scytonemin (1593, 1152, 1438, and 1173 cm⁻¹) and phycobiliproteins (1633, 1584, 1371, 1236, 813, and 667 cm⁻¹).

Portable instrumentation permits detection of carotenoids in gypsum fast and onsite under field conditions. Raman microspectrometric investigations of colonisations allow to gather detailed information about pigment distribution in micrometric zones of gypsum samples.

How to cite: Jehlicka, J., Němečková, K., and Culka, A.: Detecting microbial pigments from gypsum using Raman spectroscopy: from field prospection to laboratory studies , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3003, https://doi.org/10.5194/egusphere-egu2020-3003, 2020.

The shallow marine depositional and early diagenetic conditions in the predominantly anoxic oceans that followed the Great Oxygenation Event (GOE) remain to be fully understood. In post-GOE coastlines, ferruginous seawater was locally admixed with oxidised freshwater carrying products from the enhanced weathering of sulfides on land, to form coastal aquifers likely exhibiting sulfate concentrations significantly higher than those generally estimated for Proterozoic open oceans; e.g., < 400 μM¹. Also, there is mounting petrographic evidence for pseudomorphs after gypsum (or anhydrite) in Paleoproterozoic shallow marine facies, indicating that the penecontemporaneous oxidised sulfur levels in peritidal to intertidal settings were high enough to allow for the formation of primary sulfate minerals. The study of such ancient coastal depositional/early diagenetic conditions throughout modern systems is not straightforward since most of the purposed analogues to Precambrian ferruginous oceans lack environmentally relevant sulfate levels. A combination of spectroscopic and physicochemical measurements of the bottom waters of a meromictic, post-mining lake featuring a dysoxic hypolimnion and an anoxic monimolimnion reveals relatively high concentrations of sulfate ([SO₄^2-]= 19 ± 2 mM) and dissolved iron ([Fe(II)]= 127 ± 17 μM), with redox gradients marked by changes in Fe and N speciation². The oligotrophic artificial lake—known as Lake Medard (Czech Republic)—also features a depth-dependent co-variation in the abundance of volatile fatty acids, pH and alkalinity, together with a lack of dissolved sulfide, which can only be detected (at near quantification limits) in the 60 m depth sediment-water interface (SWI). Within the hypolimnion, changes in the relative abundance of bacterioplankton taxa point to prokaryotes (mostly Proteobacteria) being important for the co-recycling of dissolved C, N, and Fe stocks, but exerting limited sulfate reduction. In the clayey anoxic sediments there is no accumulation of authigenic sulfides but gypsum, and early diagenetic siderite acts as a significant Fe(II) sink. Preservation of P-bearing FeOOH polymorphs were also observed by using a combination of high-resolution synchrotron-based in situ XRF and XRD analyses. In the sediment pile accessory amounts of pyrite (≤ 0.5 wt. %) can be detected as depth increase, suggesting that a high turnover rate of reduced sulfur occurs towards the SWI. Such effect could be tied to sulfur disproportionation. The meromictic, oligotrophic, ferruginous and sulfate-rich study site exhibits chemical conditions that, via extrapolation, could provide insight int the microbial and abiotic pathways that controlled the coupled iron and sulfur geochemistry of shallow marine Paleoproterozoic coastal zones. A study of dissolved sulfate-bound oxygen and sulfur, and iron isotope ratios of the bottom water column is currently underway to constrain iron- vs. sulfate-reducing activity and ongoing re-oxidation processes.

¹Fakhraee, M., Hancisse, O., Canfield, D.E. et al. Proterozoic seawater sulfate scarcity and the evolution of ocean–atmosphere chemistry. Nat. Geosci. 12, 375–380 (2019).

²Petrash, D.A., Jan, J., Sirová, D., et al. Iron and nitrogen cycling, bacterioplankton community composition and mineral transformations involving phosphorus stabilisation in the ferruginous hypolimnion of a post-mining lake. Environ. Sci. Process. Impacts 20, 1414–1426 (2018).

How to cite: Petráš, D., Thomazo, C., and Lalonde, S.: The ferruginous, sulfate-rich hypolimnion of a post-mining lake as an analogue to disentangle redox cycling in Paleoproterozoic coastal zones, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-667, https://doi.org/10.5194/egusphere-egu2020-667, 2020.

In situ identification of life signatures on Solar System bodies other than Earth is extremely challenging and demands for sophisticated and sensitive instrumentation for their detection. Life signatures can be grouped into six different categories, ranging from biomolecules (e.g., lipids and amino acids), to microstructures (such as microfossils) [1]. Sulphur fractionated element isotopes belong to another important category and are of high interest to current astrobiology. In this contribution, we report on a novel measurement protocol, which is dedicated to measure accurately fractionated sulphur isotopes in different Mars analogue materials with an accuracy at the ³⁴δ level using our miniature and sensitive Laser Ablation Ionisation Mass Spectrometer (LIMS) that was designed for space exploration missions.

The applied LIMS instrument in this study consists of a miniature reflectron-type time-of-flight mass analyser (160 mm x Ø 60 mm) and a femtosecond laser system (λ = 775 nm, τ ~190 fs) used as ablation and ionization source [2-3]. By means of irradiance studies performed on the Mars analogues, optimal measurement conditions could be elaborated, which allowed to measure sulphur fractionation with an accuracy at the ³⁴δ level.

All measurements presented here were conducted on five very different Mars analogues that were collected at different extreme field sites on Earth, including Rio Tinto in Spain and Movile and Sulphur caves in Romania. The analogues differ strongly in their total sulphur weight abundance, which range from ~5 to ~95 %, and in their fractionation degree of sulphur (³⁴δ from about +8 to -7). In comparison to the state-of-the-art sulphur isotope measurements the LIMS measurements showed an accuracy of ~1.5 ³⁴δ. The measurement protocol is simple and sufficiently accurate for in situ application. It will provide valuable information of e.g., geochemical processes occurred on Solar System body surfaces, and will enable the identification of sulphuric-based life in case the fractionation is above fractionation induced by geochemical processes.

References

1) E. Hays, H.V. Graham, D.J. Des Marais, E.M. Hausrath, B. Horgan, T.M. McCollom, M. Niki Parenteau, S.L. Potter-McIntyre, A.J. Williams and K.L. Lynch, "Biosignature Preservation and Detection in Mars Analog Environments", Astrobiol., 17, 2017, 363 – 400.

2) Riedo, M. Neuland, S. Meyer, M. Tulej and P. Wurz, "Coupling of LMS with a fs-laser ablation ion source: elemental and isotope composition measurements", J. Anal. At. Spectrom., 28, 2013, 1256 – 1269.

3) Tulej, A. Neubeck, M. Ivarsson, A. Riedo, M.B. Neuland, S. Meyer and P. Wurz, "Chemical composition of micrometer-sized filaments in an aragonite host by a miniature laser ablation/ionization mass spectrometer", Astrobiol., 15, 2015, 669 - 682.

How to cite: Riedo, A., Grimaudo, V., Aerts, J. W., Cedeño López, A., Tulej, M., Ehrenfreund, P., and Wurz, P.: Detection of sulphuric life in Mars analogue material using a miniature LIMS system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20279, https://doi.org/10.5194/egusphere-egu2020-20279, 2020.