The 21-nmi transit to Site 1265 (proposed Site WALV-9B) was accomplished in 2.3 hr at an average speed of 9.1 kt. The vessel was positioned over the site at 1415 hr on 8 April 2003. The corrected precision depth recorder seafloor depth estimate was 3079.4 meters below rig floor (mbrf). The polycrystalline diamond compact drill bit used at the previous sites was retired from service because it had sustained considerable damage to the cutting structure due to drilling through numerous chert layers. The bit was replaced with a new Rock Bit International C-3 117/16-in rotary bit.
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 1265A was initiated at 0000 hr on 9 April with the bit at 3071.0 mbrf. The seafloor depth estimated by the recovery of a full core barrel was provisionally established at 3071.0 mbrf. APC coring advanced to 285.6 mbsf, where the formation became too indurated, as APC strokes were incomplete on three consecutive cores (208-1265A-30H, 31H, and 32H), and the bit was advanced by recovery. The hole was deepened with the XCB system to the target depth of 321.0 mbsf. The active heave compensator was used while coring three of the four XCB cores (208-1265A-34X through 36X).
After flushing the hole with a 40-bbl sepiolite mud sweep, the hole was displaced with 142 bbl of 8.6-lb/gal sepiolite mud. The drill string was pulled back, and the bit was positioned at 83.8 mbsf. The triple combination (triple combo) tool string was lowered to 321.0 mbsf (bottom of hole), and the hole was logged up to the seafloor. In a separate run, the Lamont-Doherty Earth Observatory (LDEO) Multi-Sensor Gamma Ray Tool (MGT) logged the hole in acquisition mode from total depth to the drill pipe. The second tool string (Formation MicroScanner [FMS]-sonic) also reached the bottom of the hole. The third logging effort was a single-axis checkshot vertical seismic profile using the Well Seismic Tool (WST-3) with seven measurement stations. The tool could not be anchored at the top station at 139 mbsf because of the large diameter of the hole. The bit was pulled clear of the seafloor at 1045 hr on 11 April, and the vessel was offset 20 m west.
After obtaining a bottom water temperature with the APCT at 3066 mbrf, Hole 1265B was initiated at 1255 hr with the bit placed 5 m shallower than it was placed in Hole 1265A in order to obtain a stratigraphic overlap. The calculated seafloor depth from the recovery of the first core was 3070.8 mbrf. Piston coring advanced to 251.7 mbsf, where the core barrel jammed inside the bottom-hole assembly (BHA). After the core winch operator tried for nearly 3 hr to recover the core barrel and to part the shear pin in the overshot at the bottom of the sinker bar assembly, the coring line was cut above the sinker bars using the Kinley wireline cutter and the drill string and BHA were recovered. Once the BHA was on the surface, the coring line was found tangled around and jammed into the sinker bar swivel. This configuration also impeded the core winch operator's ability to jar down and part the overshot shear pin to release the coring line from the core barrel. The problem was apparently caused by slack in the coring line during or shortly after the firing of the piston corer, which snarled in the sinker bar swivel and made recovery of the core barrel impossible. The coring line was freed and reterminated, and the full core barrel was subsequently recovered. The Kinley cutter and hammers were recovered, and all BHA components were inspected. No visible hardware damage was observed.
Hole 1265C was initiated at 1130 hr on 13 April and was drilled ahead without coring with a center bit to 185.0 mbsf. The center bit was retrieved, and the first piston core was obtained from 185.0 to 194.5 mbsf. The aft coring line was utilized, running the barrel in, but the forward coring line was used to recover Core 208-1265C-1H because the aft coring line was kinked as the possible result of recoil when the corer was fired. The second piston core was obtained from 194.5 to 204.0 mbsf and also achieved a full stroke of the corer. When 70,000 lb of force could not release the core barrel, it was drilled over. When the core winch operator attempted to recover the core barrel, it appeared to move a few meters and then became firmly stuck. After working the winch for 2 hr in a vain attempt to recover the core barrel and part the shear pin, the Kinley wireline cutter was deployed again to sever the coring line just above the sinker bars at a depth of ~3260 mbrf. After the drill string was recovered once more, the coring line was found tangled around and jammed into the sinker bar swivel in the same fashion as during the previous incident on 12 April. The coring line was freed and reterminated, and the full core barrel was recovered. The Kinley cutter and hammer were recovered, and the landing seat was inspected and replaced because of a small crack in the shoulder area that was not related to this incident. The lockable float valve and bit were inspected and kept in service. It was speculated that a combination of heave (~3 m) and lithology-induced recoil (possibly augmented by chert stringers) was responsible for this incident.
Hole 1265D was initiated at 1540 hr on 14 April for a final attempt at obtaining another sample of the P/E boundary. After drilling ahead with a center bit to 248.0 mbsf, XCB coring advanced the hole from 248.0 to 270.0 mbsf. The APC was then used to obtain a partial sample of the P/E boundary from 270.0 to 274.9 mbsf.
The total cored interval for the site was 619 m, and the recovered interval was 587 m (average nominal recovery = 95%). The total interval drilled without coring was 433 m.
Four downhole temperature measurements (Hole 1265A; 38–124 mbsf) and one bottom water temperature measurement (Hole 1265B) with the APCT yielded an initial temperature gradient estimate of 4.5°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 1130 hr on 15 April.