Methane-derived authigenic carbonates from the northern Gulf of Mexico — MD02 Cruise
Paull, Charles K.
Hart, Patrick E.
Winters, William J.
MetadataShow full item record
KeywordMethane-derived authigenic carbonates; Gulf of Mexico; High Mg-calcite; Carbon and oxygen isotope; Age of authigenic carbonates; Dissociation of gas hydrates
Authigenic carbonates were sampled in piston cores collected from both the Tunica Mound and the Mississippi Canyon area on the continental slope of the northern Gulf of Mexico during a Marion Dufresne cruise in July 2002. The carbonates are present as hardgrounds, porous crusts, concretions or nodules and shell fragments with or without carbonate cements. Carbonates occurred at gas venting sites which are likely to overlie gas hydrates bearing sediments. Electron microprobe, X-ray diffraction (XRD) and thinsection investigations show that these carbonates are high-Mg calcite (6 - 21 mol % MgCO3), with significant presence of framboidal pyrite. All carbonates are depleted in 13C (δ13C = -61.9 to -31.5 ‰ PDB) indicating that the carbon is derived mainly from anaerobic methane oxidation (AMO). Age estimates based on 14C dating of shell fragments and on regional sedimentation rates indicate that these authigenic carbonates formed within the last 1,000 yr in the Mississippi Canyon and within 5,500 yr at the Tunica Mound. The oxygen isotopic composition of carbonates ranges from +3.4 to +5.9 ‰ PDB. Oxygen isotopic compositions and Mg2+ contents of carbonates, and present in-situ temperatures of bottom seawater/sediments, show that some of these carbonates, especially from a core associated with underlying massive gas hydrates precipitated in or near equilibrium with bottom-water. On the other hand, those carbonates more enriched in 18O are interpreted to have precipitated from 18O-rich fluids which are thought to have been derived from the dissociation of gas hydrates. The dissociation of gas hydrates in the northern Gulf of Mexico within the last 5,500 yr may be caused by nearby salt movement and related brines.
Author Posting. © The Author(s), 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Geochemical Exploration 95 (2007): 1-15, doi:10.1016/j.gexplo.2007.05.011.
Showing items related by title, author, creator and subject.
Assessing sulfate reduction and methane cycling in a high salinity pore water system in the northern Gulf of Mexico Pohlman, John W.; Ruppel, Carolyn D.; Hutchinson, Deborah R.; Downer, R.; Coffin, Richard B. (Elsevier B.V., 2008-05-10)Pore waters extracted from 18 piston cores obtained on and near a salt-cored bathymetric high in Keathley Canyon lease block 151 in the northern Gulf of Mexico contain elevated concentrations of chloride (up to 838 mM) and ...
Surface and subsurface manifestations of gas movement through a N–S transect of the Gulf of Mexico Whelan, Jean K.; Eglinton, Lorraine; Cathles, Lawrence; Losh, Steven; Roberts, Harry (2004-08-31)Large volumes of gas have vented through a north-south transect of the offshore northern Gulf of Mexico. An overview of surface and subsurface manifestations of this gas venting is presented. This gas movement has caused ...
Gas and gas hydrate distribution around seafloor seeps in Mississippi Canyon, Northern Gulf of Mexico, using multi-resolution seismic imagery Wood, Warren T.; Hart, Patrick E.; Hutchinson, Deborah R.; Dutta, Nadar; Snyder, Fred; Coffin, Richard B.; Gettrust, Joseph F. (Elsevier B.V., 2008-05-10)To determine the impact of seeps and focused flow on the occurrence of shallow gas hydrates, several seafloor mounds in the Atwater Valley lease area of the Gulf of Mexico were surveyed with a wide range of seismic ...