Glendonites and methane-derived Mg-calcites in the Sea of Okhotsk, Eastern Siberia: implications of a venting-related ikaite/glendonite formation

• Main Authors: J. Greinert A, A. Derkachev B
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Okhotsk; Sakhalin; Siberia
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.538.6338; http://users.ugent.be/~jgreiner/papers/Greinert_Derkachev_2004_Marine_Geology.pdf

Mg-calcite-cemented bioturbation traces, glendonite aggregates of idiomorphic, bi-pyramidal crystals and porous, amber-colored carbonate concretions were recovered from a methane-dominated cold vent area in 380 m water depth at the northern Sakhalin Slope, Sea of Okhotsk. Bioturbation traces consist of Mg-calcite cemented sediment with N13C values between 337 and 346x PeeDee Belemnite (PDB), which implicate methane as the carbon source. Glendonite, a calcite pseudomorphosis after ikaite (CaCO3W6H2O), and amber-colored concretions are both composed of varying amounts of calcite and Mg-calcite with N13C values between 319 and 334x PDB. Isotope analyses of an ikaite crystal recovered in the vicinity reveals N13C values between 320x and 322x PDB indicating organic matter as the carbon source. Microscopic investigations of glendonites and amber-colored concretions show a porous fabric of a primary calcite phase that is overgrown by a secondary Mg-calcite cement. As ikaite pseudomorphs to porous calcite and as carbon isotope values are the same for the ikaite and the high end member values of glendonite samples, the primary calcite phase is suggested to be a former ikaite phase. Because they share the equal color, fabric, mineral and isotopic composition with glendonites, the amber-colored concretions are also suggested to represent calcite that transformed from ikaite. A mixture of pseudomorph calcite (N13C 320x PDB), which originally formed as ikaite from degraded organic matter, and Mg-calcite (N13C 343x PDB), which crystallized due to the anaerobic oxidation