Collett, Timothy S. et al. (2005): Integrated Ocean Drilling Program Expedition 311 preliminary report; Cascadia Margin gas hydrates; 28 August-28 October 2005

Leg/Site/Hole:
IODP 311
IODP 311 U1325
IODP 311 U1326
IODP 311 U1327
IODP 311 U1328
IODP 311 U1329
Identifier:
2008-016939
georefid

1932-9423
issn

10.2204/iodp.pr.311.2005
doi

Creator:
Collett, Timothy S.
U. S. Geological Survey, Denver, CO, United States
author

Riedel, Michael
Geological Survey of Canada, Canada
author

Malone, Mitchell J.
Integrated Ocean Drilling Program, United States
author

Guerin, Gilles
Lamont-Doherty Earth Observatory, United States
author

Akiba, Fumio
Diatom Minilab, Japan
author

Blanc-Valleron, Marie-Madeleine
Museum National d'Histoire Naturelle, France
author

Ellis, Michelle
Southampton Oceanography Centre, United Kingdom
author

Hashimoto, Yoshitaka
Kochi University, Japan
author

Heuer, Verena
University of Bremen, Federal Republic of Germany
author

Higashi, Yosuke
National Institute of Advanced Industrial Science and Technology, Japan
author

Holland, Melanie
Geotek, United Kingdom
author

Jackson, Peter D.
British Geological Survey, United Kingdom
author

Kaneko, Masanori
Okayama University, Japan
author

Kastner, Miriam
University of California-San Diego, United States
author

Kim, Ji-Hoon
Korea Institute of Geoscience and Mineral Resources, South Korea
author

Kitajima, Hiroko
Pacific Northwest National Laboratory, United States
author

Long, Philip E.
Virginia Institute of Marine Science, United States
author

Malinverno, Alberto
Bundesanstalt fuer Geowissenschaften and Rohstoffe, Federal Republic of Germany
author

Myers, Greg
Oregon State University, United States
author

Palekar, Leena D.
China University of Geosciences, China
author

Pohlman, John
University of Toronto, Canada
author

Schultheiss, Peter
author

Teichert, Barbara
author

Torres, Marta E.
author

Trehu, Anne M.
author

Wang Jiasheng
author

Wortmann, Ulrich G.
author

Yoshioka, Hideyoshi
author

Identification:
Integrated Ocean Drilling Program Expedition 311 preliminary report; Cascadia Margin gas hydrates; 28 August-28 October 2005
2005
Preliminary Report (Integrated Ocean Drilling Program)
IODP Management International, College Station, TX, United States
311
104 pp.
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 approximately 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 approximately 40 mbsf with concentrations exceeding 80% of the pore space as a result of focused fluid/gas migration from underneath.
English
Coverage:Geographic coordinates:
North:48.4800
West:-127.0400East: -126.4000
South:48.3700

Economic geology, geology of energy sources; Oceanography; 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; Integrated Ocean Drilling Program; IODP Site 1325; IODP Site 1326; IODP Site 1327; IODP Site 1328; IODP Site 1329; 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;

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