Site 1247 (proposed Site HR4c) is located in ~835 m of water on the western flank of Hydrate Ridge ~800 m northwest of the southern summit (see Fig. F1C in the "Leg 204 Summary" chapter). The three-dimensional (3-D) seismic data indicate that the seismic stratigraphic setting is similar to that of Site 1245 (see Fig. F5 in the "Leg 204 Summary" chapter). The bottom-simulating reflector (BSR) is at a depth of ~121-124 meters below seafloor (mbsf) at this site. Horizon A is brighter and shallower (~160 mbsf) at Site 1247 than at Site 1245; Horizon Y is also shallower (~60 mbsf) at this site.
The primary objective at Site 1247 was to sample sediments and fluids from Horizon A, which lies at a location approximately halfway between Site 1245 and the summit (Site 1249), in order to determine updip variations in the physical and chemical characteristics of this horizon and, thus, understand the role it plays in fluid migration and formation of hydrate on the seafloor at the summit. A second objective was to sample Horizon A where the amplitude of this reflector changes dramatically over a short distance.
Two holes were drilled at Site 1247 (Fig. F1). Although they are only 87 m apart, the two holes sample parts of Horizon A with distinctly different seismic characteristics (Fig. F2). Hole 1247A was drilled without coring to a depth of 270 mbsf to obtain logging-while-drilling (LWD) data for this site. We returned to core Hole 1247B, which was offset from Hole 1247A by ~87 m to the west. Hole 1247B was cored to 220 mbsf using the advanced piston corer (APC) and extended core barrel (XCB).
Samples suspected of containing hydrate, based on infrared (IR) temperature anomalies, were recovered from 93 and 113 mbsf and stored temporarily in liquid nitrogen. However, on later inspection, it was discovered that, although the samples showed textures indicative of hydrate dissociation, no hydrate was actually preserved.
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-106