Mud Flow Dynamics at Gas Seeps (Nirano Salse, Italy)

The Nirano Salse, known since the Roman Times, are one of the most beautiful and scenic mud volcanoes areas of Italy with thousands of visitors every year. In this work, we apply hydrogeological techniques to characterize mud levels in the Salse by means of GPS-RTK positioning and continuous level logging within mud conduits. Our results suggest that different mud levels in mud volcanoes clusters are due to the different gas-liquid ratio in the conduits and not necessarily exclude interconnection at depth, a hypothesis, on the other hand, that seems strengthened by mud level time series correlations. The presence of shallow aquifers at a depth of 5 to 30 m is also supported by our field data. These shallow aquifers may provide a temporary storage for the ascending gas and when fluid pressure in these aquifers exceeds the tensional strength of the sedimentary rock, leakage of fluids to the surface would occur.

A relict oasis of living deep-sea mussels Bathymodiolus and microbial-mediated seep carbonates at newly-discovered active cold seeps in the Gulf of Cádiz, NE Atlantic Ocean

Extensive beds of the deep-sea mussel Bathymodiolus mauritanicus (currently also known as Gigantidas mauritanicus) linked to active cold seeps related to fissure-like activity on Al Gacel mud volcano, Gulf of Cádiz, were filmed and sampled for the first time during the oceanographic expedition SUBVENT-2 aboard R/V Sarmiento de Gamboa. Al Gacel mud volcano is one of up to 80 fluid venting submarine structures (mud volcanoes and mud volcano/diapir complexes) identified in the Gulf of Cádiz as result of explosive venting of hydrocarbon-enriched fluids sourced from deep seated reservoirs. This mud volcano is a cone-shaped edifice, 107 m high, 944 m in diameter constituted by mud breccias and, partially covered by pavements of seep carbonates. Extensive beds of this deep-sea mussel were detected at the northern flank at 810–815 m water depth associated with bacterial mats around intermittent buoyant vertical bubble methane plumes. High methane concentrations were measured in the water column above living mussel beds. Other chemosymbiotic species (Siboglinum sp., Solemya elarraichensis, Isorropodon sp., Thyasira vulcolutre and Lucinoma asapheus) were also found in different parts of Al Gacel mud volcano. Al Gacel mud volcano may currently represent one of the most active mud volcanoes in the Gulf of Cádiz, delivering significant amounts of thermogenic hydrocarbon fluids which contribute to foster the extensive chemosynthesis-based communities detected. This finding is of paramount importance for linking extremophile bivalve populations along the North Atlantic, including cold seeps of the Gulf of México, hydrothermal vents of the Mid-Atlantic Ridge and now, detailed documented at the Gulf of Cádiz.

Characterization of Archaeal and Bacterial Communities Thriving in Methane-seeping on-land Mud Volcanoes, Niigata, Japan.

Submarine mud volcanoes (MVs) have attracted significant interest in the scientific community for obtaining clues on the subsurface biosphere. On-land MVs, which are much less focused in this context, are equally important and they may provide insights also for astrobiology of extraterrestrial mud volcanism. Hereby, we characterized microbial communities of the two active methane-seeping on-land MVs, Murono and Kamou, in central Japan. Metataxonomic 16S rRNA sequencing analysis of those sites recovered the dominant archaeal taxa affiliated with methanogens. Anaerobic methanotrophs (ANME), with the subgroups ANME-1b and ANME-3, were also recovered from the Murono site albeit a greatly reduced abundance compared to typical submarine MVs. ANME-3 was in fact identified for the first time for land-based MVs. The bacterial sequences affiliated to Atribacteria, sulfate-reducing bacteria (SRB), and Fe(III)-reducing bacteria were recovered. SRB and ANME form a syntrophic consortium, which is often found at the sulfate-methane transition zone of submarine MVs where diffused sulfate (SO42-) is constantly enriched from the ocean. Previous investigations speculate that the erupted materials from Murono are originated from the Miocene marine strata, and we hypothesize that the old sea-related juvenile water is the source of additional sulfur-related components for the SRB-ANME consortium at Murono.

Proposal for a mechanical model of mobile shales

Structural systems involving mobile shale represent one of the most difficult challenges for geoscientists dedicated to exploring the subsurface structure of continental margins. Mobile-shale structures range from surficial mud volcanoes to deeply buried shale diapirs and shale-cored folds. Where mobile shales occur, seismic imaging is typically poor, drilling is hazardous, and established principles to guide interpretation are few. The central problem leading to these issues is the poor understanding of the mechanical behaviour of mobile shales. Here we propose that mobile shales are at critical state, thus we define mobile shales as “bodies of clay-rich sediment or sedimentary rock undergoing penetrative, (visco-) plastic deformation at the critical state”. We discuss how this proposition can explain key observations associated with mobile shales. The critical-state model can explain the occurrence of both fluidized (no grain contact) shales (e.g., in mud volcanoes) and more viscous shales flowing with grain-to-grain contact (e.g., in shale diapirs), mobilization of cemented and compacted shales, and the role of overpressure in shale mobility. Our model offers new avenues for understanding complex and fascinating mobile-shale structures.

Search for hydrogeochemical indicators of the genetic relation between mud volcanism and oil and gas fields

The paper reports the results of a comparative analysis of the chemical and isotope composition (δ180 and δD) of mud volcanic waters and formation waters from oil and gas fields. Studies show that the waters discharged by mud volcanoes in most cases are very similar to formation waters. The most characteristic geochemical traits of both waters are elevated concentrations of hydrocarbonate ions, iodine, boron, bromine, and a low content of sulfate ions.

Mud volcanism as a dangerous phenomenon for oil and gas facilities

The research dwells on the danger of mud volcanism for human economic activity, namely, oil and gas production. We performed quantitative assessment of mud volcanoes activities, using Azerbaijan and Kerch-Taman region as examples. Average annual number of mud volcanoes eruptions is 3–4 for Azerbaijan and 1–2 for Kerch-Taman region. We estimate the catalogues of mud volcanic eruptions for those areas to be 52 % and 39 % complete, respectively. Mud volcanoes eruptions are quite frequent. In both regions, over 50 % of all recorded eruptions occur within ten years of the latest eruption. Analysis of mud volcanic eruptions catalogues shows that the volume of breccia ejected during an eruption is practically not related to how long the mud volcano was quiescent. Analysis of potential impact of seismicity on mud volcanic activity shows that the probability of mud volcanoes responding to an earthquake is 6 % and 10 % for Azerbaijan and Kerch-Taman region, respectively.

Sea bottom characteristics and geochemistry of oil and gas seeps in the Gulf of Mexico

From 2015 to 2018, TGS conducted a comprehensive multiclient oil and gas seep hunting survey in the Gulf of Mexico. The basis for identifying seeps on the sea bottom was a high-resolution Multi-Beam Echo Sounder survey, mapping approximately 880,000 km2 of the sea bottom deeper than 750 m water depth, at a bathymetric resolution of 15 m and a backscatter resolution of 5 m. We have identified more than 5000 potential oil and/or gas seeps, and of those, we cored approximately 1500 for hydrocarbon geochemical analysis. The sea bottom features best related to hydrocarbon seepage in the GoM are high backscatter circular features with or without bathymetric expression, high backscatter features with “flow” appearance, mud volcanoes, pock marks, brine pools, “popcorn” texture, faults, and anticlinal crests. We also tracked gas plumes in the water column back to the sea bottom to provide an additional criterion for hydrocarbon seepage. Cores from sea bottom targets recovered liquid oil, tar, and gas hydrates. Oil extract and gas analyses of samples from most target types produced values substantially higher than background in oil and gas.

The mud volcanoes at Santa Barbara and Aragona (Sicily, Italy): a contribution to risk assessment

The Santa Barbara and Aragona areas are affected by mud volcanism (MV) phenomena, consisting of continuous or intermittent emission of mud, water, and gases. This activity could be interrupted by paroxysmal events, with an eruptive column composed mainly of clay material, water, and gases. They are the most hazardous phenomena, and today it is impossible to define the potential parameters for modelling the phenomenon. In 2017, two digital surface models (DSMs) were performed by drone in both areas, thus allowing the mapping of the emission zones and the covered areas by the previous events. Detailed information about past paroxysms was obtained from historical sources, and, with the analysis of the 2017 DSMs, a preliminary hazard assessment was carried out for the first time at two sites. Two potentially hazardous paroxysm surfaces of 0.12 and 0.20 km2 for Santa Barbara and Aragona respectively were defined. In May 2020, at Aragona, a new paroxysm covered a surface of 8721 m2. After this, a new detailed DSM was collected with the aim to make a comparison with the 2017 one. Since 2017, a seismic station was installed in Santa Barbara. From preliminary results, both seismic events and ambient noise showed a frequency of 5–10 Hz.

Biologically-oriented mud volcano database: muddy_db

Mud volcanoes (MVs) are naturally occurring hydrocarbon hotbeds with continuous methane discharge, contributing to global warming. They host microbial communities adapted to hydrocarbon oxidation. Given their research value, MVs still represent a niche topic in microbiology and are neglected by hydrocarbon-oriented research. All the data regarding MVs is sporadic and decentralized. To mitigate this problem, we built a custom Natural Language Processing pipeline (muddy_mine), and collected all the available MV data from open-access articles. Based on this data, we built the muddy_db database. The muddy_db represents the first biologically oriented database rendered as a user-friendly web app. This database includes all the relevant MV data, ranging from microbial taxonomy to hydrocarbon occurrence and geology. The muddy_mine and muddy_db tools are licensed under the GPLv3. muddy_db R Shiny web app: https://muddy-db.shinyapps.io/muddy_db/ muddy_db R package: https://github.com/TracyRage/muddy_db muddy_mine Conda package: https://github.com/TracyRage/muddy_mine.