TY - JOUR
T1 - Halogen systematics in the Mallik 5L-38 gas hydrate production research well, Northwest Territories, Canada
T2 - Implications for the origin of gas hydrates under terrestrial permafrost conditions
AU - Tomaru, Hitoshi
AU - Fehn, Udo
AU - Lu, Zunli
AU - Matsumoto, Ryo
N1 - Funding Information:
The authors express their thanks to the members of the Mallik 5L-38 research well drill team for successful coring. We would like to thank the members of the Mallik Science Team for sampling, Y. Chen for the Cl and SO 4 determinations, Y. Muramatsu for the Br and I measurements in the sediments and D. Elmore, X. Ma and M. Caffee for the determination of 129 I/I ratios. We also appreciate helpful comments and insights provided by G.T. Snyder, J.E. Moran, A.V. Milkov, W. Ussler, and an anonymous reviewer. This work is part of the international collaboration on the Mallik 2002 Gas Hydrate Production Research Well Program: Geological Survey of Canada (GSC), Japan National Oil Corporation (JNOC), Japan Petroleum Exploration Company (JAPEX), GeoForschungsZentrum Potsdam (GFZ), United States Geological Survey (USGS), India Ministry of Petroleum and Natural Gas (MOPNG), BP-ChevronTexaco-Burlington Joint Venture parties, and United States Department of Energy (USDOE). The program received financial support from the International Continental Science Drilling Program (ICDP). This study was supported in part by a grant-in-aid from the Japan Ministry of Education, Culture, Sports, Science and Technology, by a grant from JAPEX to RM, while the first author was at the University of Tokyo, and by grant NSF-OCE 0550122 to UF. HT also gratefully acknowledges the Japan Society for the Promotion of Science (JSPS) Postdoctoral Fellowships for Research Abroad.
PY - 2007/3
Y1 - 2007/3
N2 - The authors report here halogen concentrations in pore waters and sediments collected from the Mallik 5L-38 gas hydrate production research well, a permafrost location in the Mackenzie Delta, Northwest Territories, Canada. Iodine and Br are commonly enriched in waters associated with CH4, reflecting the close association between these halogens and source organic materials. Pore waters collected from the Mallik well show I enrichment, by one order of magnitude above that of seawater, particularly in sandy layers below the gas hydrate stability zone (GHSZ). Although Cl and Br concentrations increase with depth similar to the I profile, they remain below seawater values. The increase in I concentrations observed below the GHSZ suggests that I-rich fluids responsible for the accumulation of CH4 in gas hydrates are preferentially transported through the sandy permeable layers below the GHSZ. The Br and I concentrations and I/Br ratios in Mallik are considerably lower than those in marine gas hydrate locations, demonstrating a terrestrial nature for the organic materials responsible for the CH4 at the Mallik site. Halogen systematics in Mallik suggest that they are the result of mixing between seawater, freshwater and an I-rich source fluid. The comparison between I/Br ratios in pore waters and sediments speaks against the origin of the source fluids within the host formations of gas hydrates, a finding compatible with the results from a limited set of 129I/I ratios determined in pore waters, which gives a minimum age of 29 Ma for the source material, i.e. at the lower end of the age range of the host formations. The likely scenario for the gas hydrate formation in Mallik is the derivation of CH4 together with I from the terrestrial source materials in formations other than the host layers through sandy permeable layers into the present gas hydrate zones.
AB - The authors report here halogen concentrations in pore waters and sediments collected from the Mallik 5L-38 gas hydrate production research well, a permafrost location in the Mackenzie Delta, Northwest Territories, Canada. Iodine and Br are commonly enriched in waters associated with CH4, reflecting the close association between these halogens and source organic materials. Pore waters collected from the Mallik well show I enrichment, by one order of magnitude above that of seawater, particularly in sandy layers below the gas hydrate stability zone (GHSZ). Although Cl and Br concentrations increase with depth similar to the I profile, they remain below seawater values. The increase in I concentrations observed below the GHSZ suggests that I-rich fluids responsible for the accumulation of CH4 in gas hydrates are preferentially transported through the sandy permeable layers below the GHSZ. The Br and I concentrations and I/Br ratios in Mallik are considerably lower than those in marine gas hydrate locations, demonstrating a terrestrial nature for the organic materials responsible for the CH4 at the Mallik site. Halogen systematics in Mallik suggest that they are the result of mixing between seawater, freshwater and an I-rich source fluid. The comparison between I/Br ratios in pore waters and sediments speaks against the origin of the source fluids within the host formations of gas hydrates, a finding compatible with the results from a limited set of 129I/I ratios determined in pore waters, which gives a minimum age of 29 Ma for the source material, i.e. at the lower end of the age range of the host formations. The likely scenario for the gas hydrate formation in Mallik is the derivation of CH4 together with I from the terrestrial source materials in formations other than the host layers through sandy permeable layers into the present gas hydrate zones.
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U2 - 10.1016/j.apgeochem.2006.12.013
DO - 10.1016/j.apgeochem.2006.12.013
M3 - Article
AN - SCOPUS:33847332547
SN - 0883-2927
VL - 22
SP - 656
EP - 675
JO - Applied Geochemistry
JF - Applied Geochemistry
IS - 3
ER -