Geochemical Dynamics of the Natural-Gas Hydrate System in the Sea of Marmara, Offshore Turkey

Ruffine, Livio; Fandiño, Olivia; Étoubleau, Joël; Chéron, Sandrine; Donval, Jean-Pierre; Germain, Yoan; Ponzevera, Emmanuel; Guyader, Vivien; Dennielou, Bernard; Etiope, Giuseppe; Gasperini, Luca; Bortoluzzi, Guido; Henry, Pierre; Grall, C.; Namik, Çagatay M.; Charlou, Jean-Luc; Géli, Louis

doi:10.5772/36343

Cited by 17 publications

(25 citation statements)

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“…Tectonic control of the NAF-N seems as the most significant factor for the occurrence of fluid flows (gas, oil, groundwater, brine, etc.) from shallow or deep level marine sediments to the seafloor and for gas trapping under the anticline crests in the Sea of Marmara (Armijo et al, 2005;Dupré et al, 2015;Geli et al, 2008;Kuşçu et al, 2005;Ruffine et al, 2012;Tryon et al, 2010;Tryon et al, 2012;Zitter et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Gas occurrence and shallow conduit systems in the Western Sea of Marmara: a review and new acoustic evidence

et al. 2018

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Based on 3D and 2D high-resolution multichannel seismic reflection data in the Western High-Sea of Marmara, this study reviews shallow gas occurrence and related structures and classifies gas conduit systems within the upper, few hundred meter-thick sediment layers below the seafloor. Acoustic anomalies including high amplitude-reverse polarity reflections (bright spots), low amplitude transparent zones, chaotic or discontinuous reflections, pull-down effects, and plumes in the water column are interpreted in terms of natural gas occurrence and fluid flow structures (e.g., mud volcanoes, pockmarks). The gas occurrence is thought to be mostly of thermogenic origin. Mud volcanoes are one of the primary gas conduits forming craters on the seabed due to overpressure of fluidized gassy sediment flows. Following the reach of the Northern Branch of the North Anatolian Fault (NAF-N) to the Western High, the thermogenic fluids are believed to migrate vertically and horizontally to shallow depths mainly through the faults. Natural gas most probably originates from the Thrace Basin Eocene source rock or the Eocene-Oligocene reservoir rock, which extends below the Western High. Shallow gas is distributed by minor faults and gas pipes. Gas, to some extent, emanates from the seafloor via pockmarks and mud volcanoes or is trapped by the crests of the anticlines coinciding with erosional surfaces, impermeable sediments, and gas hydrate-bearing layers. Shallow traps below the tectonized "Western High" structure are likely located in thin layers of sands imbedded with impermeable silty clay layers. However, there is no shallow reservoir in the usual sense within the upper layers imaged by the 3D seismic data (< 300 ms two-way travel time). The existence of gas is an indicator of hydrocarbonrich layers at depth and of active tectonics, and it also impacts the global climate and marine life conditions.

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Section: Introductionmentioning

confidence: 99%

Gas occurrence and shallow conduit systems in the Western Sea of Marmara: a review and new acoustic evidence

et al. 2018

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“…As the hydrocarbon Eocene Thrace Basin constitutes the basement of the Sea of Marmara [Görür and Elbek, 2013], deep-seated faults may cut hydrocarbon traps within the basement, and gas (and oil) could naturally migrate up to the surface, seep at the seafloor, and escape into the water column, as observed. The genetic relationship between the Thrace Basin gas reservoir province and the Sea of Marmara gas emissions was clearly demonstrated in the Western High, based on the geochemical gas analysis [Bourry et al, 2009;Ruffine et al, 2012] (Figure 2). Farther east, the Central High is characterized by emissions of mainly thermogenic methane but coming from a different reservoir than the gases emitted at the Western High [Bourry et al, 2009].…”

Section: Links Between Gas Emissions and (Micro)seismicitymentioning

confidence: 99%

“…Yellow dots refer to in situ gas and gas hydrates samples with indications of the gas origin [Bourry et al, 2009;Ruffine et al, 2012]. At the Western and Central highs, the biogenic methane is generated at the reservoir level, resulting from the biodegradation of oil and methanogenesis [Ruffine et al, 2012], unlike the biogenic methane at the Çınarcık Basin. The offshore extent of the Eocene Thrace Basin from Le Pichon et al [2014] is indicated (dotted yellow line).…”

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Tectonic and sedimentary controls on widespread gas emissions in the Sea of Marmara: Results from systematic, shipborne multibeam echo sounder water column imaging

et al. 2015

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Understanding of the evolution of fluid-fault interactions during earthquake cycles is a challenge that acoustic gas emission studies can contribute. A survey of the Sea of Marmara using a shipborne, multibeam echo sounder, with water column records, provided an accurate spatial distribution of offshore seeps. Gas emissions are spatially controlled by a combination of factors, including fault and fracture networks in connection to the Main Marmara Fault system and inherited faults, the nature and thickness of sediments (e.g., occurrence of impermeable or gas-bearing sediments and landslides), and the connectivity between the seafloor and gas sources, particularly in relation to the Eocene Thrace Basin. The relationship between seepage and fault activity is not linear, as active faults do not necessarily conduct gas, and scarps corresponding to deactivated fault strands may continue to channel fluids. Within sedimentary basins, gas is not expelled at the seafloor unless faulting, deformation, or erosional processes affect the sediments. On topographic highs, gas flares occur along the main fault scarps but are also associated with sediment deformation. The occurrence of gas emissions appears to be correlated with the distribution of microseismicity. The relative absence of earthquake-induced ground shaking along parts of the Istanbul-Silivri and Princes Islands segments is likely the primary factor responsible for the comparative lack of gas emissions along these fault segments. The spatiotemporal distribution of gas seeps may thus provide a complementary way to constrain earthquake geohazards by focusing the study on some key fault segments, e.g., the northern part of the locked Princes Islands segment.

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“…The Sea of Marmara is also characterized by a large number of widespread gas expulsion sites at the seafloor, bubbling up to several tens to hundreds of meters into the water column [ Burnard et al ., ; Dupré et al ., ; Gasperini et al ., ; Géli et al ., ; Kuscu et al ., ; Tary et al ., ; Zitter et al ., ]. Such gases are primarily of thermogenic origin in the western Marmara, which is geologically connected to the hydrocarbon reservoirs of the Thrace basin, while mainly biogenic gases, i.e., generated by microbial activity, have been collected from the seafloor of the Cinarcik Basin and the Gulf of Izmit (Figure ) [ Bourry et al ., ; Gasperini et al ., ; Kuscu et al ., ; Ruffine et al ., ]. The chemical composition of pore waters is also very heterogeneous from one site to another [ Burnard et al ., ; Cagatay et al ., ; Halbach et al ., ; Tryon et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Pore water geochemistry at two seismogenic areas in the Sea of Marmara

Ruffine

Germain

Polonia

et al. 2015

Geochem Geophys Geosyst

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Within the Sea of Marmara, the highly active North Anatolian Fault (NAF) is responsible for major earthquakes (Mw 7), and acts as a pathway for fluid migration from deep sources to the seafloor. This work reports on pore water geochemistry from three sediment cores collected in the Gulfs of Izmit and Gemlik, along the Northern and the Middle strands of the NAF, respectively. The resulting data set shows that anaerobic oxidation of methane (AOM) is the major process responsible for sulfate depletion in the shallow sediment. In the Gulf of Gemlik, depth concentration profiles of both sulfate and alkalinity exhibit a kink-type profile. The Sulfate Methane Transition Zone (SMTZ) is located at moderate depth in the area. In the Gulf of Izmit, the low concentrations observed near the seawater-sediment interface for sulfate, calcium, strontium, and magnesium result from rapid geochemical processes, AOM, and carbonate precipitation, occurring in the uppermost part of the sedimentary column and sustained by free methane accumulation. Barite dissolution and carbonate recrystallization have also been identified at deeper depth at the easternmost basin of the Gulf of Izmit. This is supported by the profile of the strontium isotope ratios ( 87 Sr/ 86 Sr) as a function of depth which exhibits negative anomalies compared to the modern seawater value. The strontium isotopic signature also shows that these carbonates had precipitated during the reconnection of the Sea of Marmara with the Mediterranean Sea. Finally, a first attempt to interpret the sulfate profiles observed in the light of the seismic activity at both sites is presented. We propose the hypothesis that seismic activity in the areas is responsible for the transient sulfate profile, and that the very shallow SMTZ depths observed in the Gulf of Izmit is likely due to episodic release of significant amount of methane.

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Geochemical Dynamics of the Natural-Gas Hydrate System in the Sea of Marmara, Offshore Turkey

Cited by 17 publications

References 75 publications

Gas occurrence and shallow conduit systems in the Western Sea of Marmara: a review and new acoustic evidence

Gas occurrence and shallow conduit systems in the Western Sea of Marmara: a review and new acoustic evidence

Tectonic and sedimentary controls on widespread gas emissions in the Sea of Marmara: Results from systematic, shipborne multibeam echo sounder water column imaging

Pore water geochemistry at two seismogenic areas in the Sea of Marmara

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