We spudded Hole 1138A at 0445 hr on 8 January 1999. It was difficult to establish the seafloor depth because the driller did not feel a hard tag that could be identified as bottom. Based on recovery in the first core, a seafloor depth adjusted to the rig floor was established at 1153.0 m. The 3.5-kHz PDR had indicated an adjusted seafloor depth of 1158.4 m.
Continuous wireline coring proceeded in diatom clay, nannofossil clay, and nannofossil ooze through Core 28R to a depth of 266 mbsf. No chert was encountered. The formation then graded into nannofossil chalk with occasional chert layers until a hydraulic hose supplying the Varco top drive burst after recovering Core 58R from 553.6 mbsf. The ruptured hose was isolated, and a spare hose was connected within 2.25 hr. Coring continued through nannofossil chalk with thin interbeds of nannofossil claystone and into reddish brown glauconite-bearing sandy packstone and brown clayey siltstone. After recovering Core 72R from a depth of 688.5 mbsf, coring operations were halted WOW. The sea state had been deteriorating most of the day, and eventually excessive heave caused us to suspend coring in a force 8 gale. During this period, swell conditions reached 26-30 ft, seas were 8 ft, vessel heave was 12-20 ft, and the wind speed was 42 kt gusting to 46 kt. The drill string was hung off on knobby drilling joints with the bit two singles off bottom.
After WOW for 16 hr, conditions improved enough to resume operations. An additional hour was required to remove the knobbies and run the pipe back to the bottom. Total time lost because of the weather was 17.25 hr. Sediment coring was resumed and continued until Core 75R was recovered with a single hard rock jammed in the core catcher. The driller reported elevated pump pressures with the core barrel removed from the string. After four successive deployments of the bit deplugger, the last two of which were stuck briefly upon attempted recovery, coring resumed with pump pressures still abnormally high. A half core was cut and retrieved with nearly full recovery indicating that the bit throat had been cleared. Coring then continued without any additional problems. Acoustic basement was eventually contacted at 700 mbsf in Core 74R. Basaltic basement was finally reached at the base of Core 79R at an approximate depth of 745 mbsf. Recovery averaged 49.8% and ROP averaged 7.2 m/hr (ranging from 3.6 to 18.8 m/hr). Coring was terminated with the recovery of Core 89R from a depth of 842.7 mbsf. This was ~98 m into basaltic basement, or ~123 m into acoustic basement, and satisfied the scientific depth objective for this site. A total of 411.98 m of core was recovered from Hole 1138A for an overall average of 48.9%.
Further coring was suspended in the interest of conserving time for the remaining three primary drill sites. A variance was requested and received from the Ocean Drilling Program/Texas A&M University (ODP/TAMU) to forgo wireline logging at the site since logging at the remaining three primary sites was deemed more important to the scientific objectives of the leg. Because of deteriorating weather conditions, it is unlikely that logging could have been conducted in the hole without WOW until the sea state and vessel heave abated. A test of the LDEO wireline compensator confirmed this when it tripped the 5-m limit switch twice, once after operating for 5 min and again after operating for 9 min.
Leg 183 Operations - Site 1139
Leg 183 Table of Contents