Seafloor sealing, doming, and collapse associated with gas seeps and authigenic carbonate structures at Venere mud volcano, Central Mediterranean

Abstract

Methane release from the seafloor is commonly associated with chemosynthesis-based coldseep ecosystems that facilitate the precipitation of authigenic carbonates. It has been proposed that carbonate growth results in self-sealing, but little is known regarding the evolution of cold-seep structures in relation to fluid migration pathways. This study investigates structures resulting from gas seepage along ring faults peripheral to Venere mud volcano (1600 m water depth), based on multibeam bathymetry and seafloor backscatter data collected by an autonomous underwater vehicle, together with photomosaics, video observations, and samples obtained by a remotely operated vehicle. Sites of focused fluid flow are identified by gas bubble streams rising from the seafloor while anaerobic oxidation of methane over wider areas is indicated by the occurrence of chemosynthesis-based organisms (microbial mats, vesicomyid clams, vestimentiferan tube worms). At some sites, Keywords: mud volcano; cold seep; carbonate seal; photomosaic; tube worms; Calabrian Accretionary Prism Highlights  Photomosaic-and multibeam-based mapping of cold seeps at Venere mud volcano  Methane-rich fluids sustain oasis-type ecosystems and carbonate precipitation  Carbonate self-sealing, rupturing, and collapse influence morphology of the seeps  Fluid migration, accumulation, and release govern cold seep evolution

Interplay of Subduction Tectonics, Sedimentation, and Carbon Cycling

“…These authors documented highly active periods of venting that lasted 10–50 thousand years, with intervening inactive periods that spanned more than 10 thousand years. This, and other instances of episodic methane discharge described elsewhere (e.g., Teichert et al, ; Leon et al, 2007; Cremiere et al, ; Hong et al, ; Loher et al, ), have been attributed to a variety of forcing mechanisms that include localized conditions at a given fault (changes in local high permeability pathways), fluctuations in the methane reservoir (charge/recharge episodes), regional tectonics (methane release due to uplift and/or fault generation), and changes in eustatic sea level. A combination of these factors was likely at play at Site U1379, where the episodicity recorded in carbonate deposits following the initial methane pulse reveal forcing mechanisms that are not directly tied to gas hydrate changes at the site, which was above the GHSZ after 1.1 Ma (Figure a).…”

Anomalous Concentration of Methane Emissions at the Continental Shelf Edge of the Northern Cascadia Margin

“…A well‐recognized but poorly understood process that transfers mobilized carbon from the interior of continental margin sediments is through the emission of methane, both as gas bubbles and dissolved within the modified pore fluid that escapes from the seafloor (Boetius & Wenzhöfer, ; Egger et al, ; Hong et al, ; Suess, ). A minor portion of this mobilized carbon is immediately captured and returned to the sediment reservoir as solid authigenic carbonate deposits that form directly at the surface of the seafloor by anaerobic oxidation of methane, while the remaining methane is directly transferred to seawater where it is further oxidized to carbon dioxide (Sample et al, ; Torres et al, ).This study focuses on the 250‐km length of the Washington State portion of the Cascadia margin, extending from the Strait of Juan de Fuca to the Columbia River (Figure ) and uses well‐established, acoustic‐based geophysical surveys to image methane bubble streams within the water column (Loher et al, ). Recent cruises over this NE Pacific sector in the past decade have substantially increased the swath‐mapped coverage of the Cascadia accretionary wedge both across‐ and along‐strike, and now include water depths ranging from the shallow continental shelf at less than 100‐m water depth to the abyssal plain near 3,000‐m depth (Figure ).…”

Geologically controlled intermittent gas eruption and its impact on bottom water temperature and chemosynthetic communities—A case study in the “HaiMa” cold seeps, South China Sea

“…The reason that most of the fractures did not pierce the seafloor is attributed to the gas emission induced pressure decrease. However, it is inferred that continuous development of the cold seeps will lead to the formation of large amounts of gas hydrates and authigenic carbonates in the shallow sediments, decreasing the sediment permeability and plugging the original fractures (Loher et al, ). As pressure builds up, the fractures will continue developing until a new seepage point is formed.…”