Petrographic and geochemical characterization of seep carbonate from Bush Hill (GC 185) gas vent and hydrate site of the Gulf of Mexico

Changing redox conditions at cold seeps as revealed by authigenic carbonates from Alaminos Canyon, northern Gulf of Mexico

“…Negative Ce anomalies have now been found in a number of modern and ancient seep carbonates, including the so-called Marmorito limestone from northern Italy and have been linked with temporarily oxic conditions (Feng et al, 2009b). Himmler et al (2010), on the other hand, proposed an alternative explanation for the origin of negative Ce anomalies in seep carbonates, suggesting that they may result from high pore water alkalinity in the presence of organic matter.…”

“…The dynamics of fluid flow, thus, provide the means to explain changing redox conditions archived in seep limestones. Resultant changes from anoxic to oxic conditions were held responsible for the contradiction of methane-derived carbonates apparently partly forming under oxic conditions (Feng et al, 2009b). Interestingly, recent studies suggested that the downward flux of oxic seawater into the otherwise anoxic sediment at some seeps is significant (Solomon et al, 2008).…”

Geochemical characteristics of the barite deposits at cold seeps from the northern Gulf of Mexico continental slope

“…The authors proposed that competition between barium and methane for sulfate controls the mineralogy of these precipitates, such that at low dissolved methane/barium molar ratios (b4-11) barite precipitation dominates, while at higher methane/barium ratios sulfate availability is limited by anaerobic oxidation of methane and calcium carbonate prevails (Aloisi et al, 2004). Aragonite, which is a common precipitate at cold seeps of the GOM and elsewhere (Feng et al, 2009;Greinert et al, 2002;Roberts et al, 2010a), is conspicuously absent from all analyzed samples. However, seep-related samples without barite from the same sites in our study contain varying amounts of aragonite (up to 58.9 wt.%; unpublished data).…”

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

“…Any seep may be composed of a single gas stream or several ones very close to each other such that they clearly define its perimeter. 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].…”