Expedition 311 synthesis; scientific findings

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doi: 10.2204/iodp.proc.311.213.2010
Author(s): Riedel, Michael; Collett, Timothy S.; Malone, Mitchell J.
Integrated Ocean Drilling Program, Expedition 311 Scientists, College Station, TX
Author Affiliation(s): Primary:
Natural Resources Canada, Geological Survey of Canada, Sidney, BC, Canada
U. S. Geological Survey, United States
Integrated Ocean Drilling Program, United States
Lamont-Doherty Earth Observatory, United States
Diatom Minilab, Japan
Museum National d'Histoire Naturelle, France
Southampton Oceanography Centre, United Kingdom
Kochi University, Japan
University of Bremen, Federal Republic of Germany
National Institute of Advanced Industrial Science and Technology, Japan
Geotek, United Kingdom
British Geological Survey, United Kingdom
Okayama University, Japan
Scripps Institution of Oceanography, United States
Korea Institute of Geoscience and Mineral Resources, South Korea
Pacific Northwest National Laboratory, United States
Virginia Institute of Marine Science, United States
Bundesanstalt fuer Geowissenschaften und Rohstoffe, Federal Republic of Germany
Oregon State University, United States
China University of Geosciences, China
University of Toronto, Canada
Volume Title: Proceedings of the Integrated Ocean Drilling Program; Cascadia margin gas hydrates; Expedition 311 of the riserless drilling platform; Balboa, Panama to Victoria, British Columbia (Canada); Sites U1325-U1329; 28 August-28 October 2005
Volume Author(s): Riedel, Michael; Collett, Timothy S.; Malone, Mitchell J.; Guèrin, Gilles; Akiba, Fumio; Blanc-Valleron, Marie-Madeleine; Ellis, Michelle; Hashimoto, Yoshitaka; Heuer, Verena; Higashi, Yosuke; Holland, Melanie; Jackson, Peter D.; Kaneko, Masanori; Kastner, Miriam; Kim, Ji-Hoon; Kitajima, Hiroko; Long, Philip E.; Malinverno, Alberto; Myers, Greg; Palekar, Leena D.; Pohlman, John; Schultheiss, Peter; Teichert, Barbara; Torres, Marta E.; Tréhu, Anne M.; Wang Jiasheng; Wortmann, Ulrich G.; Yoshioka, Hideyoshi
Source: Proceedings of the Integrated Ocean Drilling Program; Cascadia margin gas hydrates; Expedition 311 of the riserless drilling platform; Balboa, Panama to Victoria, British Columbia (Canada); Sites U1325-U1329; 28 August-28 October 2005, Michael Riedel, Timothy S. Collett, Mitchell J. Malone, Gilles Guèrin, Fumio Akiba, Marie-Madeleine Blanc-Valleron, Michelle Ellis, Yoshitaka Hashimoto, Verena Heuer, Yosuke Higashi, Melanie Holland, Peter D. Jackson, Masanori Kaneko, Miriam Kastner, Ji-Hoon Kim, Hiroko Kitajima, Philip E. Long, Alberto Malinverno, Greg Myers, Leena D. Palekar, John Pohlman, Peter Schultheiss, Barbara Teichert, Marta E. Torres, Anne M. Tréhu, Wang Jiasheng, Ulrich G. Wortmann and Hideyoshi Yoshioka; Integrated Ocean Drilling Program, Expedition 311 Scientists, College Station, TX. Proceedings of the Integrated Ocean Drilling Program, Vol.311, 4p. Publisher: IODP Management International, Washington, DC, United States. ISSN: 1930-1014
Note: In English. 62 refs.; illus., incl. sect., 1 table, geol. sketch map
Summary: Integrated Ocean Drilling Program Expedition 311 was conducted to study gas hydrate occurrences and their evolution along a transect spanning the entire northern Cascadia accretionary margin. A transect of four research sites (U1325, U1326, U1327, and U1329) was established over a distance of 32 km, extending from Site U1326 near the deformation front to Site U1329 at the eastern limit of the inferred gas hydrate occurrence zone. In addition to the transect, a fifth site (U1328) was established at a cold vent setting with active fluid and gas expulsion, which provided an opportunity to compare regional pervasive fluid-flow regimes to a site of focused fluid advection. In this synthesis, a revised gas hydrate formation model is proposed based on a combination of geophysical, geochemical, and sedimentological data acquired during and after Expedition 311 and from previous studies. The main elements of this revised model are as follows: 1. Fluid expulsion by tectonic compression of accreted sediments at nonuniform expulsion rates along the transect results in the evolution of variable pore water regimes across the margin. Sites closer to the deformation front are characterized by pore fluids enriched in dissolved salts at depth, where zeolite formation from ash diagenesis is dominant. In contrast, the landward portion of the margin shows a freshening of pore fluids with depth as a result of the progressive overprinting of diagenetic salt generation with freshwater generation from the smectite-to-illite transition at greater depth. 2. In situ methane produced by microbial CO2 reduction within the gas hydrate stability zone is the prevalent gas source for gas hydrate formation. 3. Some minor methane advection from depth is required overall to explain the occurrence of gas hydrate (and the associated downhole isotopic signatures of CH4 and CO2) within the sediments of the accretionary prism and the absence of gas hydrate within the abyssal plain sediments. In contrast, methane migrating from depth is a dominant source for gas hydrate formation at the cold vent Site U1328 (Bullseye vent). 4. Gas hydrate preferentially forms in coarser grained sandy/silt turbidites, resulting in very high local gas hydrate concentrations. Typically, gas hydrate occupies <5% of the pore space throughout the gas hydrate stability zone. Higher gas hydrate saturations were observed in intervals with abundant coarse-grained sand layers and within fault-controlled fluid and gas migration conduits at the cold vent Site U1328.
Year of Publication: 2010
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 02 Geochemistry; 07 Marine Geology and Oceanography; Aliphatic hydrocarbons; Alkali metals; Alkaline earth metals; Alkanes; Biogenic processes; Boreholes; Bottom-simulating reflectors; British Columbia; C-13/C-12; Canada; Carbon; Carbon dioxide; Cascadia subduction zone; Chlorinity; Cores; East Pacific; Expedition 311; Flows; Fluid phase; Gas hydrates; Genesis; Geochemistry; Geophysical methods; Geophysical profiles; Geophysical surveys; Hydrocarbons; Hydrochemistry; IODP Site U1325; IODP Site U1326; IODP Site U1327; IODP Site U1328; IODP Site U1329; Integrated Ocean Drilling Program; Isotope ratios; Isotopes; Lithium; Marine sediments; Metals; Methane; Migration; Models; North Pacific; Northeast Pacific; Organic compounds; Pacific Ocean; Pore water; Reduction; Resistivity; Salinity; Sediments; Seismic methods; Seismic profiles; Sr-87/Sr-86; Stability; Stable isotopes; Strontium; Surveys; Temperature; United States; Washington; Well logs; Western Canada
Coordinates: N483700 N484800 W1264000 W1270400
Record ID: 2010064295
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