Site 1246 (proposed Site HR1b) is located in 850 m of water ~3 km north of the southern Hydrate Ridge summit (see Fig. F1C in the "Leg 204 Summary" chapter). The three-dimensional (3-D) seismic data show that the bottom-simulating reflector (BSR) is at ~114 meters below seafloor (mbsf) at this site. This site also samples a pair of bright regional seismic reflectors, referred to as Horizons B and B´, at depths of ~60 and 100 mbsf, respectively. At this site, the temperature and pressure at the seafloor are well within the gas hydrate stability zone (GHSZ), indicating that gas hydrates can exist within the entire stratigraphic section above the BSR if hydrate-forming gases are available in concentrations that exceed their in situ solubility.
The primary objective at Site 1246 was to sample Horizons B and B´ where they are within the GHSZ. By comparing Site 1246 to Site 1244, where Horizons B and B´ are below the GHSZ, we hope to constrain lithologic and hydrologic explanations for the strong reflectivity of these seismic horizons, obtain insights into the processes that transport fluids into and through the GHSZ, and develop more effective strategies to predict the presence of hydrate from seismic and other remote-sensing data.
Two holes were drilled at Site 1246 (Fig. F1). Hole 1246A was drilled to a depth of 180 mbsf without coring to obtain the initial logging-while-drilling (LWD) data for this site. At Hole 1246B, we obtained 16 advanced piston corer (APC) cores, sampling to a depth of 136.7 mbsf with 99% recovery. Only basic sampling was conducted on these cores.
1Examples of how to reference the whole or part of this volume can be found under "Citations" in the preliminary pages of the volume.
2Shipboard Scientific Party addresses can be found under "Shipboard Scientific Party" in the preliminary pages of the volume.
Ms 204IR-105