Cold seeps along the main Marmara Fault in the Sea of Marmara (Turkey)

Abstract

The main Marmara Fault exhibits numerous sites of fluid venting, observed during previous cruises and in particular with R.O.V. VICTOR during the MARMARASCARPS cruise (2002). Long CALYPSO cores were recovered near active vents and at reference sites during the MARMARA-VT cruise (2004), together with echosounder sub-bottom profiles (frequency of 3.5 kHz). We compiled R.O.V. video observations from MARMARASCARPS cruise and show that all known seeps occur in relationship with strike-slip faults, providing pathways for fluid migration. Among the main active sites, a distinction is made between gas seeps and water seeps. At gas seeps, bubble emissions at the seafloor or disturbed echofacies on sounder profiles demonstrate the presence of free methane gas at a shallow depth within the sediment. Most cores displayed gas-related expansion, most intense for cores taken within the gas plumes. On the other hand, authigenic carbonate chimneys characterize the water seeps and visible water outflow was observed at two sites (in the Tekirdağ and Central basins). The pore fluid chemistry data show that the water expelled at these sites is brackish water trapped in the sediment during lacustrine times (before 14 cal kyr BP), in relation with the paleoceanography in the Sea of Marmara. The chimney site in the Tekirdağ Basin is located at the outlet of a canyon feeding a buried fan with coarse sandy turbidites. Pore fluid composition profiles indicate that the sand layers channel the brackish fluids laterally from the basin into the fault zone at less than 20 m depth. However, a deeper gas source cannot be excluded.

Comparative metagenomics of bathypelagic plankton and bottom sediment from the Sea of Marmara

“…Finally, around 7% of Ma29 archaea belonged to the Methanosarcinales, with some sequences very closely related to members of the ANME2 group (Figure 1 and Supplementary S12). The presence of ANME sequences is not surprising, as the Marmara Sea harbors several scattered cold seep areas (Géli et al, 2008;Zitter et al, 2008) where the anaerobic oxidation of methane likely occurs. However, the relatively low proportion of archaea is consistent with the 'normal' bottom-sediment nature of the Ma29 sediment.…”

“…Sediment communities are extremely diverse, with particularly high relative abundances of Deltaproteobacteria, many of them are sulfate reducers, and planctomycetes, which are important in carbon cycling. Methanogenic and/or methanotrophic archaea were not abundant in the surface sediment sample, indicating that the transition to the methanogenesis zone is deeper and that the sediment is not actually influenced by intense seeping activity, which, in Marmara, is restricted to localized black patches along the main North Anatolian Fault (Géli et al, 2008;Zitter et al, 2008). Future comparison with metagenome sequences from those seep areas in the same location would be interesting to reveal specific adaptations to those environments.…”

“…In addition to this agitated history, the Marmara basin is highly dynamic from a geological point of view, as its Northern slope is traversed by the seismically more active branch of the North Anatolian Fault, the Main Marmara Fault. Gas seeps and water seeps have been unevenly observed in the three major basins found along this fault (from West to East: Tekirdag, the Central basin and Cinarcik) (Géli et al, 2008;Zitter et al, 2008). Gas or cold seeps are enriched in methane and can be seen directly as bubbles coming out from the sediment, or can be detected indirectly by the presence of dark patches revealing areas of strong redox activity in which sulfate reduction occurs just beneath the surface.…”

Gas Seepage along the Edge of the Aquitaine Shelf (France): Origin and Local Fluxes

“…Submarine seeps, at cold seeps, occur worldwide along the continental margins and are usually related to geological structures with either positive reliefs such as submarine pingoes [1][2][3][4][5][6][7], carbonate concretions and pavements [8][9][10][11], and mud volcanoes [9,[12][13][14][15][16][17][18] or negative reliefs like pockmarks [13,[19][20][21][22][23]. They also occur in seafloor-reaching fault areas at tectonically active regions without being associated with a specific relief [24][25][26][27][28].…”

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

“…It is a complex geological feature along the northern branch of the NAF, characterized by a mud diapir. A carbonate and a hydrate mounds as well as active cold seeps with gas bubbling to the seafloor are the major features which have been identified at this area (Tryon et al, 2010;Zitter et al, 2008).…”