Iodp Expedition 311: Cascadia Margin Gas Hydrates Site U1327 Summary

Site U1327 (Scientific Prospectus Site CAS-01B) is located near ODP Site 889/890 approximately at the mid-slope of the accretionary prism over a clearly defined BSR, estimated to be at a depth of 223 mbsf. The primary research objectives for this site are linked to the transect-concept of this expedition. Site 889/890 has provided critical baseline data for the development of the objectives of this research expedition. Historical work with data from Site 889/890 has shown that the concentration of gas hydrate in sediments has been estimated by using (a) deviations in interstitial water chlorinities from measured baseline conditions, (b) electrical resistivity measurements by applying Archie’s relation, and (c) using both seismic and downhole log-derived Pand S-wave velocities. But results from Leg 146 have left many questions unanswered (Riedel et al., 2005), such as: (a) What is the geochemical reference profile for chlorinity and other geochemical gas hydrate proxies? (b) What is the electrical resistivity baseline for the sediments drilled at this site and what are the appropriate empirical Archie coefficients? (c) What is the reference profile for acoustic Pand S-wave velocities?