Methane, ethane and total inorganic carbon in fluid samples taken during the 1989 Kaiko-Nankai Project

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doi: 10.1016/0012-821X(92)90100-A
Author(s): Gamo, Toshitaka; Sakai, Hitoshi; Ishibashi, Jun-ichiro; Shitashima, Kiminori; Boulègue, Jacques
Author Affiliation(s): Primary:
Univ. Tokyo, Ocean Res. Inst., Tokyo, Japan
Ec. Norm. Supér., France
Univ. Pierre et Marie Curie, France
Volume Title: Fluids in convergent margins
Volume Author(s): Kastner, M., editor; Le Pichon, Xavier
Source: Earth and Planetary Science Letters, 109(3-4), p.383-390; Fluids in subduction zones, Paris, France, Nov. 5-6, 1991, edited by M. Kastner and Xavier Le Pichon. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. 20 refs.; illus. incl. 2 tables, sect., sketch map
Summary: Water samples collected by the French submersible Nautile from macrofauna flourishing in cold seepage zones of the eastern Nankai Trough accretionary prism were analysed for major chemical components on board Nadir and in shore-based laboratories in order to characterize pore fluid chemistries. Extremely high CH4 concentrations of >= 4.01 mu M confirmed the active supply of CH4-rich fluids from the bottom. The CH4/C2H6 ratio ranged from 113 to 3875, suggesting a biogenic rather than a thermogenic origin for the hydrocarbons. It is inferred that the oxidation of biogenic CH4 occurs in surface sediments at a rate that is approximately twice as fast as that of C2H6, based on the positive correlation between CH4 concentrations and CH4/C2H6 ratios. The existence of NH+4 (10-50 mu M) and high alkalinity values (< 3 mM) in some water samples were indicative of microbial organic matter decomposition (sulphate reduction and/or methane generation in the sediments). By extrapolating the SIGMACO2- delta13C(SIGMACO2) relationship, delta13C(SIGMACO2) of an unknown fluid end- member was estimated to range from -30 to -47 per mille, indicating a contribution of CH4-derived CO2 with low delta13C values. [Authors' abstract]
Year of Publication: 1992
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 07 Marine Geology and Oceanography; Accretionary wedges; Aliphatic hydrocarbons; Alkanes; Carbon; Chemical composition; Composition; Dehydration; Ethane; Fluid phase; Geochemistry; Hydrocarbons; Inorganic carbon; Leg 131; Marine sediments; Methane; Nankai Trough; North Pacific; Northwest Pacific; Ocean Drilling Program; Ocean floors; Oceanography; Organic compounds; Organic materials; Pacific Ocean; Pore water; Sea water; Sediments; Troughs; West Pacific
Coordinates: N333500 N335200 E1380500 E1374500
Record ID: 1992024691
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom