Multidisciplinary investigation on cold seeps with vigorous gas emissions in the Sea of Marmara (MarsiteCruise): Strategy for site detection and sampling and first scientific outcome

MarsiteCruise was undertaken in October/November 2014 in the Sea of Marmara to gain detailed insight into the fate of fluids migrating within the sedimentary column and partially released into the water column. The overall objective of the project was to achieve a more global understanding of cold-seep dynamics in the context of a major active strike-slip fault. Five remotely operated vehicle (ROV) dives were performed at selected areas along the North Anatolian Fault and inherited faults. To efficiently detect, select and sample the gas seeps, we applied an original procedure. It combines sequentially (1) the acquisition of ship-borne multibeam acoustic data from the water column prior to each dive to detect gas emission sites and to design the tracks of the ROV dives, (2) in situ and real-time Raman spectroscopy analysis of the gas stream, and (3) onboard determination of molecular and isotopic compositions of the collected gas bubbles. The in situ Raman spectroscopy was used as a decision-making tool to evaluate the need for continuing with the sampling of gases from the discovered seep, or to move to another one. Push cores were gathered to study buried carbonates and pore waters at the surficial sediment, while CTD-Rosette allowed collecting samples to measure dissolved-methane concentration within the water column followed by a comparison with measurements from samples collected with the submersible Nautile during the Marnaut cruise in 2007. Overall, the visited sites were characterized by a wide diversity of seeps. CO2- and oil-rich seeps were found at the westernmost part of the sea in the Tekirdag Basin, while amphipods, anemones and coral populated the sites visited at the easternmost part in the Cinarcik Basin. Methane-derived authigenic carbonates and bacterial mats were widespread on the seafloor at all sites with variable size and distributions. The measured methane concentrations in the water column were up to 377 μmol, and the dissolved pore-water profiles indicated the occurrence of sulfate depleting processes accompanied with carbonate precipitation. The pore-water profiles display evidence of biogeochemical transformations leading to the fast depletion of seawater sulfate within the first 25-cm depth of the sediment. These results show that the North Anatolian Fault and inherited faults are important migration paths for fluids for which a significant part is discharged into the water column, contributing to the increase of methane concentration at the bottom seawater and favoring the development of specific ecosystems

Bioaccumulation des radiolaires et des diatomées à l’Eocène moyen en Atlantique équatorial (Plateau de Demerara, Leg ODP 207). Possibles relations avec des changements climatiques et paléocéanographiques

L’enrichissement en silice est dû au pullulement des radiolaires et débute juste au-dessus du passage Éocène inférieur–moyen (environ 49 Ma). Il reflète une modification majeure du zooplancton de l’Atlantique équatorial, dominé jusque là par des foraminifères planctoniques. Les diatomées, qui constituent une composante mineure de la silice biogène, sont essentiellement représentées par des espèces planctoniques robustes, typiques des environnements néritiques. Des espèces indicatrices d’upwelling sont présentes. L’absence d’influence continentale est à noter. Le début d’accumulation de la silice biogène est probablement dû à la mise en place d’une intense circulation de courants profonds et à une plus forte productivité. Il coïncide avec un changement majeur d’un océan Éocène inférieur stagnant à un autre plus dynamique à l’Éocène moyen, à la suite d’un changement climatique global encore mal compris.Middle Eocene siliceous bioaccumulation on Demerara Rise is explored using taphonomic and palaeoecological studies of radiolaria and diatoms, respectively. Enrichment and improved preservation of silica began just above the Lower to Middle Eocene transition (ca. 49 Ma) and was mainly due to radiolarian productivity. It reflects a profound change in the zooplankton communities of the western Equatorial Atlantic, dominated previously by planktic foraminifera. Diatoms are a minor siliceous component of the Middle Eocene chalk. This microflora is dominated by robust planktic species, typical of neritic environments, and includes some upwelling indicators. Benthic species are absent. No continental taxa were recorded. Onset of biogenic silica accumulation was probably due to the establishment of a vigorous bottom current circulation and higher levels of productivity. It coincides with a major palaeoceanographic shift from a Lower Eocene stagnant to a more vigorous Middle Eocene ocean, following some as yet poorly understood global climatic change.</p

Mud volcanism and authigenic carbonates related to methane-rich fluids migration in the Tortonian-Messinian marls of the Huercal Overa basin (S.E. Spain)

International audienceMethane-rich fluids that are generated at depth in organic-rich deposits migrate within the sediments to the seafloor where they are expelled to form mud volcanoes or pockmarks. These migrating fluids are generally involved in diagenetic processes as authigenic carbonate formation that is mediated by microbial activity and they may participate to gas hydrate formation. These features are well-known in the present-day continental margins but their fossil records are relatively scarce. In the Huercal Overa basin (South East Spain), there are chaotic to roughly layered structures intruding the Tortonian-Messinian marls that are interpreted as due to mud volcanism. Moreover, the surrounding marls contain abundant authigenic dolomite nodules. The oxygen and carbon isotopic compositions of these dolomites exhibit wide ranges (-1.4 < δ18O <+3.9 ; -35.5 < δ13C <+5.1). They indicate that authigenic carbonate precipitation occurred within the marly sediments due to circulation of deep fluids that might be relatively warm as shown by the low δ18O values and where anaerobic oxidation of methane (low δ13C values) and methanogenesis (high δ13C values) were active. These two features, methane derived authigenic dolomites and mud volcanism, are testifying of the intense methane-rich fluid migration in the marly deposits of the western Mediterranean basins during the late Neogene, which was the time of major paleoenvironmental changes in the Mediterranean sea climaxing during the Messinian salinity crisis

Les assemblages de diatomées des niveaux infra-gypseux du Messinien de Méditerranée (Espagne, Sicile, Chypre)

Pestrea, Simona, Blanc-Valleron, Marie-Madeleine, Rouchy, Jean-Marie (2002): Les assemblages de diatomées des niveaux infra-gypseux du Messinien de Méditerranée (Espagne, Sicile, Chypre). Geodiversitas 24 (3): 543-583, DOI: 10.5281/zenodo.537695

Methane derived authigenic carbonates from the upper continental margin of the Bay of Biscay (France)

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La matière organique des alternances sel-marne du salar d'Uyuni (Altiplano, Bolivie). Etudes géochimiques et palynologiques. / The organic matter of the salt-marl alternating layers of the salar of Uyuni (Altiplano, Bolivia). Geochemical and palynological studies

The organic matter of the salt-marl alternating layers of the salar of Uyuni (Altiplano, Bolivia). Geochemical and palynological studies The salar of Uyuni, in the central Bolivian Altiplano, is the largest salt pan in the world. The UA deep well sediments (121 m in depth) correspond to 12 salt crusts separated by 11 parting muds. Geochemical, palynological, petrographical and mineralogical studies have been performed to study the organic matter of the argillaceous facies interstratified with halite. OM is scarce (mean TOC = 0,4%), as compared to other salt-marl alternating layers. Palynofaciès shows a large abundance of planktonic lacustrine algae ; but, from IH -10 parameters, OM is comparable to type II marine OM of planktonic origin rather than lacustrine type I OM.Le sondage UA, au centre du salar d'Uyuni, a traversé une alternance de sédiments halitiques et «lacustres» sur plus de 120 m de profondeur. Diverses analyses, géochimiques, palynologiques, pétrographiques et minéralogiques, ont été effectuées afin d'étudier la matière organique présente. Cette MO est peu abondante (COT = 0,4 % en moyenne) par rapport à celle des alternances «sel-marne » d'autres séries. Le palvnofaciès montre une grande richesse relative en algues planctoniques lacustres, bien que cette MO ne se comporte pas comme un type I : les paramètres de pyrolyse Rock-Eval la rapprochent d'une MO de type II (classiquement observée dans les faciès sapropéliques en domaine marin).Schuler Monique, Blanc-Valleron Marie-Madeleine, Risacher François. La matière organique des alternances sel-marne du salar d'Uyuni (Altiplano, Bolivie). Etudes géochimiques et palynologiques. / The organic matter of the salt-marl alternating layers of the salar of Uyuni (Altiplano, Bolivia). Geochemical and palynological studies. In: Sciences Géologiques. Bulletin, tome 48, n°4, 1995. Palynologie. pp. 211-247

Carbonate deposition and diagenesis in evaporitic environments: The evaporative and sulphur-bearing limestones during the settlement of the Messinian Salinity Crisis in Sicily and Calabria

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Reply to the comment on “Carbonate deposition and diagenesis in evaporitic environments: The evaporative and sulphur-bearing limestones during the settlement of the Messinian Salinity Crisis in Sicily and Calabria” by Caruso et al., 2015. Palaeo3, 429, 136–162

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