Carbonate diagenesis in the methane-rich sediments of the Beringian margin, IODP 323 Expedition

• Main Authors: Pierre, Catherine, Blanc-Valleron, Marie-Madeleine, März, Christian, Ravelo, Ana Christina, Takahashi, Kozo, Alvarez Zarikian, Carlos A.
• Other Authors: Paléoclimats, proxies, processus (PALEOPROXUS), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Muséum national d'Histoire naturelle (MNHN)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Muséum national d'Histoire naturelle (MNHN)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7)-École polytechnique (X)-Centre National d'Études Spatiales Toulouse (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)
• Format: Other/Unknown Material
• Language: English
• Published: HAL CCSD 2010
• Subjects: [1041] GEOCHEMISTRY; [0463] BIOGEOSCIENCES; [0454] BIOGEOSCIENCES; Microbe/mineral interactions; Isotopic composition and chemistry; Oxidation/reduction reactions; [0471] BIOGEOSCIENCES; Stable isotope geochemistry; geo; envir; Bering Sea; Bowers; Umnak Plateau
• Online Access: https://hal.archives-ouvertes.fr/hal-00908630

International audience During IODP expedition 323 in the Bering Sea (July 5- September 4, 2009) a series of drilling (down to 750 meters below sea floor) was realized at 7 sites localized on the Umnak plateau (U1339), on the Bowers Ridge (U1340, U1341, U1342) and on the Beringian margin (U1343, U1344, U1345) the oldest sediments dated at 5 Myrs were recovered at Sites U1340 and U1341. Diagenetic carbonates are present at all Sites either as nodules and cm to dm thick layers, or as isolated acicular crystals, within the diatom-rich oozes of the Bering Sea, which are also characterized by their extreme richness in methane. The mineralogical, geochemical and isotopic study of diagenetic carbonates from Sites U1343, U1344 and U1345 was realized to characterize the nature of inorganic and microbial processes responsible for this diagenesis, and to determine the composition and origin of fluids in which these carbonates were precipitated. The carbonate mineralogy is very complex it is represented by composite mixtures of magnesian calcite and dolomite of various composition. Fe-rich dolomite/siderite dominate below ~260 mbsf at Site U1343 and ~200 mbsf at Site U1344. The isotopic compositions of the diagenetic carbonates display wide ranges of variations both for calcite (+2.84 < δ18O ‰ < +6.92 -20.52 < δ13C ‰ <+4.83) and dolomite (+3.58< δ18O ‰ < +9.19; +1.28 < δ13C ‰ <+11.37). The δ13C values clearly indicate that methanogenesis was involved in the sediments during microbial fermentation of organic matter : in this reaction, the 13C-rich CO2 was converted to carbonate alkalinity via silicate weathering and the 13C-poor methane was oxidized as bicarbonate via anaerobic oxidation of methane coupled with bacterial sulfate reduction as it is shown by the association of pyrite with the diagenetic carbonates.