Riedel, Michael et al. (2005): Expedition 311 synthesis; scientific findings

Leg/Site/Hole:
IODP 311
IODP 311 U1325
IODP 311 U1326
IODP 311 U1327
IODP 311 U1328
IODP 311 U1329
Identifier:
2010-064295
georefid

10.2204/iodp.proc.311.213.2010
doi

Creator:
Riedel, Michael
Natural Resources Canada, Geological Survey of Canada, Sidney, BC, Canada
author

Collett, Timothy S.
U. S. Geological Survey, United States
author

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

Identification:
Expedition 311 synthesis; scientific findings
2005
In: Riedel, Michael, Collett, Timothy S., Malone, Mitchell J., Guerin, 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., Trehu, Anne M., Wang Jiasheng, Wortmann, Ulrich G., Yoshioka, Hideyoshi, 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
IODP Management International, Washington, DC, United States
311
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 CO (sub 2) 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 CH (sub 4) and CO (sub 2) ) 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.
English
Coverage:Geographic coordinates:
North:48.4800
West:-127.0400East: -126.4000
South:48.3700

Oceanography; Isotope geochemistry; 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; Integrated Ocean Drilling Program; IODP Site U1325; IODP Site U1326; IODP Site U1327; IODP Site U1328; IODP Site U1329; 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;

.