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SITE 1155

Transit to Site 1155
The 149-nmi transit to Site 1155 took just over 16 hr at an average speed of 9.1 kt. The reduced transit speed was a result of a course directly into a swell and against the Southern Ocean Current. At 1345 hr on 5 December, we began a SCS and 3.5-kHz survey. We interpreted these data to indicate that the sediment cover at this site was ~200 m thick.

Hole 1155A
When the survey was concluded, the vessel came about and slowly approached our prospectus site location. We deployed a positioning beacon on GPS coordinates at 1454 hr on 5 December. PDR water depth was 4986.4 meters below the rig floor (mbrf) (4975.4 meters below sea level [mbsl]). The nine-collar BHA employed on previous sites was made up with a new C-7 four-cone rotary bit.

We began washing down through the sediment column at Hole 1155A at 0215 hr on 6 December and encountered basement at 177.3 mbsf. We rotary cored from 177.3 to 203.5 mbsf with an average recovery of 9%. In an effort to increase recovery we retrieved core barrels after an average cored interval of 4.5 m. Fluorescent microsphere tracers were deployed in the core catchers of Cores 187-1155A-2R and 7R. After we recovered Core 7R, indications from drilling parameters (stalling top drive and high torque) suggested poor hole conditions. Hoping for better recovery, we decided to terminate this hole, offset 200 m west, and initiate a second hole. We determined the direction and magnitude of the offset based on a review of the precruise seismic data, as well as the SCS record obtained during our survey. The seismic data indicated slightly thinner sediment cover over a local basement high, and our intuition suggested there might be less rubble updip. The drill string cleared the seafloor at 0330 hr on 7 December.

Hole 1155B
At 0500 on 7 December, we began washing down to basement and started coring at 147.9 mbsf after we encountered a hard contact. We advanced Hole 1155B from 147.9 to 193.0 mbsf (Cores 187-1155B-2R to 9R) and averaged 50% recovery while coring 4.6- to 5-m intervals. We deployed microsphere tracers on Cores 2R and 9R. When we tried to recover Core 10R, the core barrel arrived on deck empty, with the core catcher fingers missing. As we had retrieved sufficient material to meet our objectives, rather than attempt to clean the hole, we decided to terminate operations and move to our next site. The bit cleared the seafloor at 2130 hr on 8 December, and the vessel was under way by 0700 hr on 9 December.

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