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doi:10.2204/iodp.proc.346.109.2015

Operations

Two holes were cored at Site U1428 (proposed Site ECS-1B) and three holes were cored at Site U1429 (alternate Site ECS-1C) using the full and half advanced piston corer (APC) and the extended core barrel (XCB). At both sites, nonmagnetic core barrels were used with the APC system. Only full APC core barrels were oriented. In Hole U1428A, 26 cores extended from the seafloor to 211.5 m core depth below seafloor (CSF-A) (see the “Methods” chapter [Tada et al., 2015b]), including seven drilled intervals (totaling 37.6 m) through thick sand beds. The cored interval in Hole U1428A was 173.9 m with a recovery of 178.86 m of core (103%) (Table T1; see also Fig. F2 in the “Expedition 346 summary” chapter [Tada et al., 2015a]). After completing Hole U1428A, we moved to Site U1429, which was anticipated to have higher linear sedimentation rates and, therefore, an expanded Late Pleistocene section.

APC coring at Site U1429 was uneventful. Hole U1429A penetrated to 188.3 m CSF-A, including two drilled intervals totaling 4.1 m. Core recovery for Hole U1429A was 190.3 m (103%). Hole U1429B penetrated to 186.2 m CSF-A with a core recovery of 200.9 m (108%). Hole U1429C penetrated to 179.2 m CSF-A, including two drilled intervals totaling 4.9 m. Core recovery for Hole U1429C was 180.7 m (104%) (Table T2; see also Fig. F2 in the “Expedition 346 summary” chapter [Tada et al., 2015a]).

After completing the three holes at Site U1429, we returned to Site U1428 to drill a second, additional hole that provided material to build a complete spliced section at this site spanning at least the last ~0.3 m.y. and to provide additional material for high-resolution paleoceanographic studies. Hole U1428B was subsequently APC cored to 143.3 m CSF-A (16 cores), with a recovery of 145.85 m (102%).

Transit to Site U1428

The transit to Site U1428 from IODP Site U1427 included a short stop offshore at Kitakyushu, Japan, to evacuate a scientist suffering from kidney stones. The 248 nmi transit between Site U1427 and the evacuation rendezvous coordinates (34°30.0′N, 130°23.0′E) was covered at an average speed of 10.8 kt. The designated rendezvous time was 0800 h on the morning of 11 September 2013. Coordination of the medical evacuation was provided by the Sea Trade and Agency Yokohama and locally by Green Shipping in Moji, Japan. The R/V JOIDES Resolution was on location for the evacuation at 0736 h. The sea-going tug MusashiMaru 2 was alongside by 0752 h. The transfer was completed safely and efficiently by 0754 h. The tug was clear by 0755 h and headed back to shore. The JOIDES Resolution then resumed course for Site U1428. The remaining 228 nmi distance was covered in 21 h at an average speed of 10.9 kt. Sea passage ended at 0500 h on 12 September. The vessel was maneuvered over the location coordinates, thrusters were lowered into position, and the vessel was turned over to dynamic positioning control. By 0530 h on 12 September, the vessel was stabilized and rig floor operations began. A Falmouth Scientific positioning beacon (model BAP-547; SN1028W, 16 KHz, 206 dB) was deployed at 0614 h.

Hole U1428A

A three-stand APC/XCB bottom-hole assembly (BHA) was assembled, and the drill string was run to bottom. During the pipe trip, the vibration-isolated television (VIT) subsea camera was deployed. The top drive was picked up, and the drill string was spaced out to just above the seafloor. Because of the presence of submarine cables in the vicinity of this site, a camera survey of the seafloor was conducted to ensure that no holes were spudded into a submarine cable. This was considered precautionary only because the closest cables to the drill site should have been nearly 2 nmi away. A box survey was conducted radiating out from the drill site coordinates in 5 m increments. The total outside diameter of the box was 25 m. This ensured that any of the holes spudded within 15 m of Hole U1428A would be well within the preinspected area. The survey was completed at 1200 h on 12 September 2013, and after returning to zero-zero coordinates, a tag of the seafloor with the drill bit was observed on camera. This established a drill string tag depth of 735.3 meters below rig floor (mbrf), or 1.6 m shallower than the depth predicted with the precision depth recorder (PDR). The pipe was then picked up 3 m, placing the bit at 732.3 mbrf, and Hole U1428A was spudded at 1230 h. The first core barrel recovered 6.37 m of core, establishing an “official” seafloor depth of 735.4 mbrf. Oriented APC coring continued using full-length nonmagnetic core barrels through Core 346-U1428A-18H to a depth of 150.1 m CSF-A. Half APC coring continued from that point through Core 346-U1428A-32H to a total depth of 211.5 m CSF-A. Because of the large accumulation of sand in the formation, further coring at this site was abandoned. The hole was displaced with 80 bbl of 10.5 ppg weighted mud, and the drill string was pulled clear of the seafloor at 0735 h on 13 September. The bit was clear of the rotary table by 0930 h. The positioning beacon was recovered at 0811 h, and the ship was secured for transit by 0940 h. Thrusters and hydrophones were pulled, and the sea voyage to Site U1429 was initiated at 1024 h on 13 September. Total recovery for Hole U1428A was 178.86 m (103%). There were no half APC cores taken in this hole; however, there were seven drilled intervals totaling 37.6 m. Four formation temperature measurements were taken using the advanced piston corer temperature tool (APCT-3) temperature shoe at 34.9, 63.4, 91.9, and 120.4 m CSF-A.

Transit to Site U1429

The transit to Site U1429 from Site U1428 included a brief stop while en route to discharge another scientist, this one suffering from a severe case of shingles. The scientist was evacuated from the JOIDES Resolution by a Japanese Coast Guard helicopter. The transfer was completed safely and efficiently by 1100 h on 13 September 2013. The JOIDES Resolution then resumed full speed for Site U1429. The 228 nmi to Site U1429 was covered in 1.6 h at an average speed of 7.4 kt. Sea passage ended at 1200 h on 13 September. The vessel was maneuvered over the location coordinates, thrusters were lowered into position, and the vessel was turned over to dynamic positioning control. By 1215 h, the JOIDES Resolution was stabilized, and rig floor operations began.

Hole U1429A

A three-stand APC/XCB BHA was assembled, and the drill string was run to the bottom. During the pipe trip, the VIT subsea camera was deployed. The top drive was picked up, and the drill string was spaced out to just above the seafloor. As at the previous site, a camera survey of the seafloor was conducted to ensure that no holes were spudded into a submarine cable. As before, a box survey was conducted radiating out from the drill site coordinates in 5 m increments. The total outside diameter of the box was again 25 m. This ensured that any of the holes spudded within 15 m of Hole U1429A would be well within the preinspected area. The survey began at 1735 h on 13 September 2013 and was completed by 1945 h. After returning to zero-zero coordinates, a tag of the seafloor with the drill bit was observed on camera. This established a drill string tag depth of 743.6 mbrf, or 2.8 m shallower than the depth predicted with the PDR. The pipe was then picked up 3 m, placing the bit at 740.6 mbrf, and Hole U1429A was spudded at 2045 h. The first core barrel recovered 6.4 m of core, establishing an “official” seafloor depth of 743.7 mbrf. Oriented APC coring continued using full-length nonmagnetic core barrels through Core 346-U1429A-23H to 188.3 m CSF-A. As at Site U1428, large accumulations of volcanic sand in the formation prevented coring to the original deeper objectives. This led to the decision to complete three APC holes through the upper section (~200 m CSF-A) and then abandon the site. The hole was displaced with 75 bbl of 10.5 ppg weighted mud, and the drill string was pulled clear of the seafloor at 0900 h on 14 September, ending Hole U1429A and beginning Hole U1429B. Total recovery for this hole was 190.29 m (103%). No half APC cores were taken in this hole; however, there were two drilled intervals totaling 4.1 m to adjust the core breaks. Four formation temperature measurements were taken using the APCT-3 temperature shoe at 34.9, 61.1, 89.6, and 116.4 m CSF-A.

Hole U1429B

Because a massive sand horizon was also present at this site, the operations plan was revised to eliminate any deep penetration attempt. Instead, the focus was on obtaining two additional ~200 m holes to thoroughly recover the upper section. Hole U1429B began as the drill string cleared the seafloor. The ship was offset 15 m north of Hole U1429A. The bit was positioned at 736.6 mbrf. An APC core barrel was deployed, and Hole U1429B was spudded at 0935 h on 14 September 2013. The 2.93 m of core recovered established a seafloor depth of 743.2 mbrf. APC coring with full-length core barrels continued through Core 346-U1429B-22H to 186.2 m CSF-A. Partial strokes were experienced on Cores 6H, 18H, and 22H; however, all others were full stroke. Hole U1429B was once again terminated just into the volcanic sand. The hole was displaced with 75 bbl of 10.5 ppg mud, and the drill string was pulled clear of the seafloor at 2210 h on 14 September, ending Hole U1429B. Total recovery for this hole was 200.92 m (108%). Of the 22 cores recovered, all were full-barrel cores. There were no attempted half APC cores.

Hole U1429C

Hole U1429C began as the drill string cleared the seafloor. The ship was offset 15 m south of Hole U1429A. The bit was positioned at 738.6 mbrf. An APC core barrel was deployed, and Hole U1429C was spudded at 2235 h on 14 September 2013. The 4.16 m of core recovered established a seafloor depth of 744.0 mbrf. APC coring with full-length core barrels continued through Core 346-U1429C-24H to 179.2 m CSF-A. Partial strokes were experienced on Cores 6H, 16H, 20H, and 24H; however, all others were full stroke. The hole was once again terminated just into the volcanic sand. Total recovery for Hole U1429C was 180.70 m (103.7%). Of the 22 cores recovered, all were full-barrel cores. There were no attempted half APC cores.

Hole U1429C was displaced with 75 bbl of 10.5 ppg mud, the top drive was set back, and the drill string was pulled clear of the seafloor at 1055 h on 15 September. The pipe was tripped back to the surface, and the BHA racked back in the derrick. Because the move back to Site U1428 was only 4 nmi, the last stand with the bit and outer core barrel components was left hanging on the hook through the rotary table. This saved time and allowed the ship to get under way faster. The positioning beacon was recovered back aboard during the pipe trip at 1142 h. The ship was secured for transit by 1225 h. Thrusters and hydrophones were pulled, and the brief sea voyage to Site U1428 was initiated at 1242 h on 15 September.

Return to Site U1428

The transit back to Site U1428 was quickly accomplished. The 4.0 nmi distance was covered in only 0.75 h at an average speed of 5.3 kt. Sea passage ended at 1330 h on 15 September 2013. The vessel was maneuvered over the location coordinates, thrusters were lowered into position, and the vessel was turned over to dynamic positioning control. By 1345 h, the JOIDES Resolution was stabilized, and rig floor operations began.

Hole U1428B

Because of the shallow nature of the single hole and short duration on site, a positioning beacon was not deployed to the seabed. The APC/XCB BHA was quickly assembled, and the drill string was run to bottom. The ship was offset 15 m north of Hole U1428A. The top drive was picked up, and the pipe was spaced out, positioning the bit at 728.8 mbrf. Hole U1428B was spudded at 1635 h on 15 September 2013. The first core barrel recovered 2.49 m of core, establishing a seafloor depth of 735.8 mbrf. APC coring continued using full-length nonmagnetic core barrels through Core 346-U1428B-16H to 143.3 m CSF-A. Hole U1428B was displaced with 55 bbl of 10.5 ppg weighted mud, the top drive was set back, and the drill string was pulled clear of the seafloor at 0130 h on 16 September. The bit was clear of the rotary table by 0330 h. The bit and bit sub were removed, and the ship was secured for transit by 0345 h. Thrusters and hydrophones were pulled, and the sea voyage to Site U1430 was initiated at 0418 h on 16 September. Total recovery for this hole was 145.85 m (102%). Of the 16 cores recovered, all were full-barrel cores. There were no attempted half APC cores.

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