Integrated Ocean Drilling Program Expedition 311 preliminary report; Cascadia Margin gas hydrates; 28 August-28 October 2005

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doi: 10.2204/
Author(s): Collett, Timothy S.; Riedel, Michael; 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
Integrated Ocean Drilling Program, Expedition 311 Scientists, College Station, TX
Author Affiliation(s): Primary:
U. S. Geological Survey, Denver, CO, United States
Geological Survey of Canada, Canada
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
University of California-San Diego, 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 für Geowissenschaften and Rohstoffe, Federal Republic of Germany
Oregon State University, United States
China University of Geosciences, China
University of Toronto, Canada
Source: Preliminary Report (Integrated Ocean Drilling Program), Vol.311, 104p. Publisher: IODP Management International, College Station, TX, United States. ISSN: 1932-9423
Note: In English. 54 refs.
Summary: A transect of four sites (U1325, U1326, U1327, and U1329) across the Northern Cascadia margin was cored during Integrated Ocean Drilling Program Expedition 311 to study gas hydrate occurrences and formation models for accretionary complexes. In addition to the transect sites, a fifth site (U1328), representing a cold vent with active fluid and gas flow, was visited. The four transect sites represent different stages in the evolution of gas hydrate across the margin from the earliest occurrence on the westernmost first accreted ridge (Site U1326) to its final stage at the eastward limit of gas hydrate occurrence on the margin in shallower water (Site U1329). Logging while drilling/measurement while drilling carried out at the start of the expedition prior to coring provided a set of measurements that guided subsequent coring and special tool deployments at all five sites. Additional wireline logging at each site and two vertical seismic profiles at Sites U1327 and U1328 were completed. A total of 1217.76 m of sediment core was recovered using the advanced piston corer and extended core barrel systems, interspersed with 24 (16 successful) pressure core sampler runs for onboard degassing experiments and 19 Fugro piston corer/HYACE deployments; 4 of these pressure cores were stored under in situ pressure for subsequent shore-based studies. Indirect evidence of the presence of gas hydrate included increased electrical resistivities and P-wave velocities on downhole logs and low-salinity interstitial water anomalies, numerous infrared cold spots, and decreases in void gas C1/C2 ratios, as well as gas hydrate-related sedimentological moussy/soupy textures in recovered cores. Gas hydrate was also observed directly in the recovered cores, and >30 gas hydrate samples were preserved in liquid nitrogen for shore-based studies. The combined observations show that gas hydrate mainly occurs within coarser-grained turbidite sands and silts. The occurrence of gas hydrate appears to be controlled by several key factors, and the concentration of gas hydrate changes significantly as those factors vary in the sediments along the margin. The key controlling factors are (1) local methane solubility linked with pore water salinity, (2) fluid/gas advection rates, and (3) availability of suitable host material (coarse-grained sediments). In the previous model for gas hydrate formation in an accretionary margin, the highest concentrations of gas hydrate were expected to occur localized near the base of the gas hydrate stability zone above the bottom-simulating reflector (BSR), with concentrations gradually decreasing upward as a result of pervasive fluid advection from overall tectonically driven fluid expulsion. However, the results of Expedition 311 show that this model is too simple and that there are additional overprinting factors. Although evidence for widespread gas hydrate-related BSRs was observed in the data, by far the largest concentrations of gas hydrate were observed at the top of the gas hydrate occurrence zone, at a point where the amount of methane in the pore fluid exceeds the local methane solubility threshold. This was especially observed at Sites U1326 and U1327, where gas hydrate deposits several tens of meters thick occur at a shallow depth of ∼100 meters below seafloor (mbsf) with concentrations locally exceeding 80% of the pore volume. Another site of very large gas hydrate concentrations was found at the cold vent Site U1328, where beds of massive gas hydrate occur within the top ∼40 mbsf with concentrations exceeding 80% of the pore space as a result of focused fluid/gas migration from underneath.
Year of Publication: 2005
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 29 Economic Geology, Energy Sources; Accretionary wedges; Aliphatic hydrocarbons; Alkanes; Boreholes; Bottom-simulating reflectors; British Columbia; Canada; Cascadia subduction zone; Cenozoic; Chemostratigraphy; Cores; Downhole methods; Drilling; East Pacific; Expedition 311; Fluid phase; Fluid pressure; 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; Lithostratigraphy; Marine drilling; Marine sediments; Methane; Migration; Natural gas; North Pacific; Northeast Pacific; Organic compounds; Pacific Coast; Pacific Ocean; Petroleum; Physical properties; Pore water; Sediments; Seismic methods; Seismic profiles; Seismic stratigraphy; Slope stability; Stability; Stratigraphic units; Subduction zones; Surveys; Temperature; Vancouver Island; Volatiles; Well logs; Western Canada
Coordinates: N483700 N484800 W1264000 W1270400
Record ID: 2008016939
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