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doi:10.2204/iodp.proc.346.107.2015

Operations

Four holes were cored at Site U1426 (proposed Site YB-2) using the full and half advanced piston corer (APC) and the extended core barrel (XCB) (Table T1; see also Fig. F2 in the “Expedition 346 summary” chapter [Tada et al., 2015a]). Holes U1426A, U1426B, U1426C, and U1426D were cored to 396.7, 34.7, 204.0, and 99.4 m CSF-A (see the “Methods” chapter [Tada et al., 2015b]) and recovered 418.78, 35.82, 211.89, 103.71 m of core, respectively. A total of 95 APC and 2 XCB cores obtained 770.2 m of sediment (104.8% recovery). The advanced piston corer temperature tool (APCT-3) was deployed four times.

Transit from Site U1425

The 148 nmi transit to Site U1426 was covered in 13.4 h at an average speed of 11 kt. Sea passage ended at 0636 h on 3 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 0715 h, the vessel was stabilized for rig floor operations to begin. A Falmouth Scientific positioning beacon (model BAP-547; SN1028W, 16 KHz, 206 dB) was deployed at 0822 h.

Hole U1426A

A three-stand APC/XCB bottom-hole assembly was assembled, and the drill string was run to the seafloor. After picking up the top drive and spacing out the drill string to 907.4 meters below rig floor (mbrf), which was 6.0 m deeper than the depth provided by the precision depth recorder, an APC core barrel was deployed. The first core barrel recovered 2.47 m of core, establishing a seafloor depth of 914.4 mbrf. Oriented APC coring continued using full-length nonmagnetic core barrels through Core 346-U1426A-28H at 256.2 m CSF-A. At this depth, the APC was switched to the half APC (4.7 m) system, and coring continued through Core 37H (297.0 m CSF-A), where a solid dolomite layer was encountered. The XCB was picked up and used to cut a 1.0 m core (38X) until breaking through the layer of resistance. Half APC coring resumed from that point and continued through Core 59H (396.7 m CSF-A). The hole was displaced with 160 bbl of 10.5 ppg mud. The top drive was set back, and the drill string was pulled clear of the seafloor at 2330 h on 4 September 2013, ending Hole U1426A. Total recovery for this hole was 418.78 m (105.6%). A total of 29 half APC cores were recovered. Four successful temperature measurements were taken using the APCT-3 temperature shoe at 31.0, 59.5, 88.0, and 116.5 m CSF-A, respectively.

Hole U1426B

The ship was offset 15 m north of Hole U1426A, and the bit was positioned 3 m lower at 910.4 mbrf. Hole U1426B was spudded at 0045 h on 5 September 2013. Recovery from the first core established a seafloor depth of 913.7 mbrf. APC coring continued with four cores recovered for intensive geochemistry sampling to 34.7 m CSF-A. By 0215 h, the last core barrel had been laid out and the rig floor prepared for tripping pipe. Because the hole was shallow, the pipe was tripped out of the hole with the top drive in place. The bit cleared the seafloor at 0230 h, officially ending Hole U1426B. Recovered core totaled 35.82 m (103%).

Hole U1426C

The ship was offset 15 m south of Hole U1426A. The top drive was picked up, the bit was positioned at 911.4 mbrf, and Hole U1426C was spudded at 0250 h on 5 September 2013. The mudline core established a seafloor depth of 914.4 mbrf. APC coring continued through Core 346-U1426C-15H to 128.3 m CSF-A. XCB Core 16X cut through a hard dolomite layer, allowing the continuation of APC coring. Full-length core barrels were used through Core 24H to 206 m CSF-A. The hole was plugged and abandoned with 80 bbl of 10.5 ppg mud. The drill string was pulled with the top drive to 895 mbrf, clearing the seafloor at 1425 h. This ended Hole U1426C. Total recovery for this hole was 211.9 m (103.9%). There were no half APC cores from this hole.

Hole U1426D

The ship was offset 15 m west of Hole U1426A. The top drive was picked up, and the bit was positioned at 909.4 mbrf. Hole U1426D was spudded at 1500 h on 5 September 2013. The sediment/water interface was recovered in Core 1H, establishing a seafloor depth of 914.4 mbrf. APC coring continued with 11 full-length cores recovered to 99.4 m CSF-A. The hole was plugged and abandoned with 40 bbl of 10.5 ppg mud. The top drive was set back, and the drill string was pulled clear of the seafloor at 2030 h. The bit subsequently cleared the rotary table at 2235 h. The rig floor was secured for transit, thrusters were raised, and sea passage to IODP Site U1427 began at 2342 h. Total recovery for this hole was 103.71 m (104.3%). There were no half APC cores taken from this hole.

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