Hole 1157A
We deployed a positioning beacon about 1.6 km east of the prospectus
GPS coordinates where our survey indicated a 200-m sediment thickness.
Water depth at this site is 5080.4 mbrf, determined by the PDR. A new C-7
four-cone rotary bit was installed on the same nine-collar BHA used at
our previous sites. We started washing through the sediment column at
Hole 1157A at 2300 hr on 12 December and continued to 200.0 mbsf,
where drilling conditions indicated we had reached basement. A single
wash barrel was recovered, and we cored from 200.0 to 216.4 mbsf before
we decided, based on poor drilling conditions and recovery, to abandon the
hole. We deployed fluorescent microspheres as a tracer for
microbiological infiltration analysis on Core 187-1157A-2R. The drill
string cleared the seafloor at 1300 hr on 13 December; we offset 200 m
west to drill Hole 1157B.
Hole 1157B
We initiated Hole 1157B by washing down to 136.6 mbsf before hitting
basement. Coring continued from 136.6 to 171.0 mbsf with an average
recovery of 29%. Microbiological tracers were deployed on Cores 187
1157B-2R and 9R. After ~34 m of penetration and 10 m of recovered
basalt, we concluded operations at this site. The bit cleared the seafloor
at 0225 hr and the rotary table at 1045 hr on 15 December.