The 22-nmi transit to Site 1266 (proposed Site WALV-10F) was accomplished in 2.3 hr at an average speed of 9.6 kt. The vessel was positioned over the site by 1405 hr on 15 April 2003. The corrected precision depth recorder depth estimate was 3819 meters below rig floor (mbrf).
Coring intervals, times, nominal recovery rates, core barrels that required drillover to be released from the sediment, and the deployments of the Advanced Piston Corer Temperature (APCT) tool, Tensor core orientation tool, and nonmagnetic core barrel are listed in Table T1.
Hole 1266A was initiated at 2150 hr with the bit at 3811.0 mbrf. The seafloor depth, which was estimated by the recovery of a full core barrel, was provisionally established at 3811.0 mbrf. APC coring advanced to 217.1 mbsf, where the formation became too indurated to continue with the APC. The bit was advanced by recovery on the last two cores (208-1266A-24H and 25H) because of incomplete strokes. The hole was deepened with the XCB system to the target depth of 298.6 mbsf. Active heave compensation was used while coring the first XCB core (208-1266A-26X).
The bit was pulled clear of the seafloor at 1800 hr on 17 April, and the vessel was offset 20 m north. After a bottom water temperature was obtained with the APCT at 3806 mbrf, Hole 1266B was initiated with one piston core to establish a final water depth at this site. The seafloor depth calculated from the 7.65 m of recovery was 3807.9 mbrf, which was 3.1 m shallower than the provisional seafloor estimate from Hole 1266A. The center bit was lowered with the coring line, and the hole was drilled ahead without coring by 212.4 m to a depth of 220 mbsf. The hole was deepened from 220 to 248.5 mbsf with the XCB system before the piston corer was deployed in an effort to obtain an undisturbed sample of the P/E boundary. The two fully stroked cores (208-1266A-5H and 6H), spanning the interval 248.5–267.5 mbsf, contained the critical boundary interval in the bottom of Core 6H. XCB coring deepened the hole from 267.5 mbsf to the target depth of 321.0 mbsf. After the bit was pulled clear of the seafloor at 2050 hr on 18 April, the vessel was offset 20 m north.
The two objectives for Hole 1266C were to spot core and fill gaps in the sedimentary record and to obtain another sample of the critical P/E boundary. Hole 1266C was initiated after tagging the seafloor at 3807.9 mbrf. The hole was drilled with a center bit in place to 62.0 mbsf, where APC coring was initiated. APC coring advanced from 62.0 to 192.0 mbsf. The nonmagnetic core barrel was not used in this hole. The new Interstitial Water Sampler was deployed on the coring line to obtain a water sample and pore pressure and downhole temperature data at 192.0 mbsf. The data were compromised because of a leak. The center bit was lowered with the coring line, and the hole was drilled without coring from 192.0 to 245.0 mbsf (53.0 m interval). After the center bit was retrieved, one XCB core was obtained from 245.0 to 254.5 mbsf. The APC was then used to core from 254.5 to 282.7 mbsf. These three cores (208-1266C-16H, 17H, and 18H) spanned the critical P/E boundary interval and required drilling over to free the barrels from the sediment. XCB coring deepened the hole from 282.7 mbsf to the target depth of 334.2 mbsf. The 22.8-m interval from 292.2 to 315.0 mbsf was drilled without coring.
The total cored interval at Site 1266 was 604 m, and the recovered interval was 592 m (average nominal recovery = 98%). The total interval drilled without coring was 350 m.
Three downhole temperature measurements (Hole 1266A: 66–151 mbsf) and one bottom water temperature measurement (Hole 1266B) with the APCT yielded an initial temperature gradient estimate of 4.7°C/100 m.
The drill string was recovered, the hydrophones and thrusters were secured, the beacon was recalled and recovered, and the vessel left for the next site at 0445 hr on 21 April.