Site 1159 | Table of Contents
SITE 1158

Transit to Site 1158
Because of high winds and heavy seas the 42-nmi transit from Site 1157 to Site 1158 took nearly 7 hr, and we could not deploy the geophysical gear. We dropped a positioning beacon on the prospectus site GPS coordinates at 1715 hr on 15 December. Water depth as measured by the PDR at this site is 5178.4 m. The nine-collar BHA employed on the earlier sites was made up with a new C-7 four-cone rotary bit.

Hole 1158A
We began operations by washing down through the sediment column until we contacted basement at 198.9 mbsf. The wash barrel was retrieved, and we deepened the hole by rotary coring to 213.3 mbsf. We deployed fluorescent microspheres as a tracer for microbiological infiltration analysis on Core 187-1158A-2R. Rapid penetration, high and erratic torque during drilling, and poor recovery (~6%) in the two core barrels we retrieved led to our abandoning this hole. The drill string cleared the seafloor at 1330 hr on 16 December, and we offset 200 m north, where our precruise site survey indicated thinner sediment cover.

Hole 1158B
After washing through the sediment column to 126.2 mbsf and recovering the wash barrel, we rotary cored in basement to 141.2 mbsf before unstable hole conditions forced us to abandon Hole 1158B. Microbiological tracers (microspheres) were deployed on Core 187 1158B-3R. The bit cleared the seafloor at 0545 hr on 17 December; we offset another 200 m north to attempt a third hole at this site.

Hole 1158C
We contacted basement at 108.0 mbsf in Hole 1158C and recovered the wash barrel and a single rotary core barrel (108.0-117.4 mbsf, 17% recovery) before poor hole conditions again precluded continuing operations. Microsphere tracers were deployed on Core 187-1158C-2R. Based on our experience thus far and on the recovery of sufficient material to meet our primary objectives, we chose to end operations at this site. The drill bit cleared the seafloor at 1420 hr and the rotary table at 2315 hr on 17 December.

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