OPERATIONS

The 124-nmi transit to Site 1154 took 11.5 hr at an average speed of 11 kt. At 0115 hr on 2 December, the vessel slowed to 6 kt for a single-channel seismic and 3.5-kHz survey over the site. These data indicated a similar sediment thickness to that penetrated at Site 1153 (~200 m).

Hole 1154A

After the survey we deployed a beacon on Global Positioning System (GPS) coordinates ~450 m southwest of our prospectus coordinates, closer to the center of a localized sediment pond. Water depth at this site obtained by precision depth recorder (PDR) was 5747.4 m. A nine-collar bottom-hole assembly was made up of a C-7 four-cone rotary bit, a mechanical bit release, a head sub, an outer core barrel, a top sub, another head sub, seven 8-in drill collars, one tapered drill collar, six 5-in drill pipes, and one crossover sub.

We spudded Hole 1154A with the rotary core barrel at 1235 hr on 2 December. We washed ahead to 233.2 mbsf before we encountered a hard contact, presumed to be igneous basement. Rotary coring advanced the hole from 233.2 to 267.6 mbsf, with an average recovery of 27% (Table T1). In an effort to increase recovery, we retrieved core barrels after advancing an average of 4.5 m. Whirl-Pak plastic bags containing fluorescent microspheres used as microbiological tracers were deployed on Cores 187-1154A-3R, 6R, and 9R.

Coring was terminated 34.4 m into basement. The total drill string length at this depth was 6015 m, representing a static hook load of 675,000 lb. While advancing Core 187-1154A-9R, the driller noted evidence of deteriorating hole conditions. Since we had recovered adequate material to meet our scientific objectives, we decided to abandon Site 1154. On 4 December the bit cleared the seafloor at 1215 hr and cleared the rotary table at 1445 hr. The vessel was under way to the next site by 2130 hr.