The 432-nmi voyage to Site 1237 (proposed Site NAZCA-17A) was accomplished in 39.0 hr at an average speed of 11.1 kt. At 0340 hr on the morning of 26 April 2002, the vessel left Chilean waters and entered the territorial waters of Peru. During the evening of 26 April, the vessel received permission to operate in the national waters of Peru (Peruvian Navigation Permit 067-2002). On approach to site, the 3.5-kHz precision depth recorder (PDR) was used as a final check of site characteristics by comparison to precruise survey data. The vessel was positioning on the coordinates of Site 1237 by 2020 hr.
After the drill string was deployed to a depth of 3203 meters below rig floor (mbrf), the top drive was picked up and spaced out to a depth of 3225 mbrf. Hole 1237A was initiated with the APC at 0355 hr on 27 April. The core barrel was full (i.e., the mudline was not recovered), and the hole was terminated.
Hole 1237B was initiated with the APC at 0505 hr. The bit was positioned 5 m shallower than in Hole 1237A (3220 mbrf), and the mudline was recovered. The seafloor depth estimated by the amount of recovery was 3224.0 mbrf, 9.4 m shallower than the corrected PDR estimate. Piston coring advanced until the wireline parted at the rope socket while we attempted to recover Core 13H (110.0-119.5 meters below seafloor [mbsf]). An extra wireline trip was made with a core barrel fishing tool, and the tensor tool and sinker bars were retrieved. The shear pin on the sinker bars had also parted and an additional wireline run was needed to recover the barrel containing Core 13H.
APC coring resumed and deepened Hole 1237B to 317.4 mbsf, where Core 34H failed to achieve a full stroke with the APC (Table T1). During coring operations in this hole, permission was granted from Ocean Drilling Program/Texas A&M University (ODP/TAMU) headquarters to deepen the hole by as much as 30 m beyond the mandated 300 mbsf maximum depth prescribed by the Pollution Prevention and Safety Panel (PPSP), as long as it could be accomplished with fully stroked piston cores. The core barrels containing Cores 20H through 34H were drilled over when they could not be pulled free of the sediment with a force of 60 klb. The nonmagnetic core barrel was deployed on even-numbered cores up to and including Core 20H (Table T1). The nonmagnetic core barrel was not used after this to prevent potential damage to the barrel as a result of the drilling-over process. The cores were oriented starting with Core 3H. Downhole temperature measurements were taken with the APC temperature (APCT) tool at various depths (Table T1). A total of 317.4 m was cored and 331.4 was recovered (Table T1). This represented the deepest penetration with the APC since Leg 162. To our knowledge, only four other piston-cored holes in ODP history had exceeded a penetration of 300 m: Leg 162, Hole 981A (320.0 mbsf); Leg 145, Hole 882A (398.3 m); and Leg 130, Holes 806B and 806C (320.0 and 309.6 mbsf, respectively).
The vessel was moved 10 m west. Prior to coring, a bottom water temperature measurement was obtained with the APCT tool with the bit positioned just above the seafloor. To obtain the desired stratigraphic overlap with the first hole, the bit was then positioned at 3223 mbrf and Hole 1237C was initiated with the APC at 0941 hr on 29 April. The seafloor depth inferred by the recovery of the initial core was 3223.2 mbrf. Piston coring deepened the hole to 315.3 mbsf, where Core 33H failed to achieve a full stroke. A total of 313.3 m was cored and 323.7 m recovered (recovery = 103%) (Table T1) in Hole 1237C.
The core barrels containing Cores 17H through 19H and 21H through 33H were drilled over. The nonmagnetic core barrel was deployed on odd-numbered cores up to and including Core 17H (Table T1). To maintain a stratigraphic overlap with the previous data, the interval from 113.8 to 115.8 mbsf was drilled. The cores were oriented starting with Core 3H. Downhole temperature measurements were taken with the APCT tool (Table T1). The thermal gradient at Site 1237, estimated from the temperature measurements in Holes 1237B and 1237C, was ~3.1°C/100 m. The bit was pulled free of the seafloor at 0325 hr on 1 May.
After the vessel was moved 10 m west, Hole 1237D was initiated with the APC at 0445 hr on 1 May. The objective for this hole was to spot-core intervals to cover coring gaps left in the previous holes. Another 11 piston cores were obtained, representing a cored interval of 104.5 m with 106.1 m recovered (Table T1). Cores were oriented starting with Core 3H. Four intervals were drilled in this hole: 0-2.8, 40.8-69.8, 79.3-80.3, and 108.8-224.5 mbsf. The total drilled interval amounted to 148.5 m. The nonmagnetic core barrel was deployed on Cores 2H, 4H, 6H, and 8H. The core barrels containing Core 9H through 11H (224.5-253.0 mbsf) were drilled over.
The vessel was secured for transit and left location at 0300 hr on 2 May.