Proc. IODP, 311, Gas hydrate on the northern Cascadia margin: regional geophysics and structural framework

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Chapter contents Abstract Introduction General plate tectonic regime and structure of accretionary prism Evidence of gas hydrate Conceptual model of gas hydrate formation Thermal regime of the accretionary prism Gas hydrate concentration estimates and no-hydrate, no-gas baselines Electrical resistivity Pore water chlorinity/salinity Seismic P-wave velocity Free gas concentrations Cold vents Summary of vent structure seismic observations Summary of piston coring Seafloor video observations New alternative surveying techniques Drilling objectives Post-Expedition 311 outlook References Figures F1. Coring transect. F2. Heat flow data. F3. Seismic profiles. F4. Gas hydrate cycle. F5. Heat probe measurements. F6. BSR-derived heat flow. F7. Pore water salinity. F8. Core porosities. F9. Vent field and core locations. F10. Seismic sections. F11. SCS time slice. F12. Magnetic suseptibility. F13. Normalized compliance. F14. CSEM resistivities. PDF file		Previous \| Next doi:10.2204/iodp.proc.311.109.2006 Gas hydrate on the northern Cascadia margin: regional geophysics and structural framework¹ M. Riedel,² E.C. Willoughby,³ M.A. Chen,³ T. He,⁴ I. Novosel,⁵ K. Schwalenberg,⁶ R.D. Hyndman,³ G.D. Spence,⁴ N.R. Chapman,⁴ and R.N. Edwards⁷ Abstract Integrated Ocean Drilling Program Expedition 311 is based on extensive site survey data and historic research at the northern Cascadia margin since 1985. This research includes various regional geophysical surveys using a broad spectrum of seismic techniques, coring and logging by the Ocean Drilling Program Leg 146, heat flow measurements, shallow piston coring, and bottom video observations across a cold-vent field, as well as novel controlled-source electromagnetic and seafloor compliance surveying techniques. The wealth of data available allowed construction of structural cross-sections of the margin, development of models for the formation of gas hydrate in an accretionary prism, and estimation of gas hydrate and free gas concentrations. Expedition 311 established for the first time a transect of drill sites across the northern Cascadia margin to study the evolution of gas hydrate formation over the entire gas hydrate stability field of the accretionary complex. This paper reviews the tectonic framework at the northern Cascadia margin and summarizes the scientific studies that led to the drilling objectives of Expedition 311 Cascadia gas hydrate. ¹Riedel, M., Willoughby, E.C., Chen, M.A., He, T., Novosel, I., Schwalenberg, K., Hyndman, R.D., Spence, G.D., Chapman, N.R., and Edwards, R.N., 2006. Gas hydrate on the northern Cascadia margin: regional geophysics and structural framework. In Riedel, M., Collett, T.S., Malone, M.J., and the Expedition 311 Scientists. Proc. IODP, 311: Washington, DC (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.311.109.2006 ²Expedition 311 Scientists' addresses. Correspondence author: mriedel@eps.mcgill.ca ³Pacific Geoscience Centre, Geological Survey of Canada, 9860 West Saanich Road, PO Box 6000, Sidney BC VSL 4B2, Canada. ⁴Earth and Ocean Sciences, University of Victoria, Victoria BC V8W 2Y2, Canada. ⁵Hydrocarbon Systems—EP Solutions, Shell International Exploration and Production, Inc., 200 North Dairy Ashford Street, Houston TX 77079, USA. ⁶Federal Institute for Geosciences and Natural Resources (BGR), Geozentrum Hannover, Hannover D-30655, Germany. ⁷Department of Physics, University of Toronto, Toronto ON M5S 1A7, Canada. Publication: 28 October 2006 MS 311-109 Top of page \| Previous \| Next