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doi:10.2204/iodp.proc.346.110.2015

Operations

Three holes were cored at Site U1430 using the full and half advanced piston corer (APC) and the extended core barrel (XCB). Oriented, nonmagnetic core barrels were used with the full APC system in Hole U1430A. Half APC cores in Hole U1430A were not oriented but used nonmagnetic barrels. A total of 29 APC cores and 3 XCB cores penetrated to 274.4 m core depth below seafloor (CSF-A) (see the “Methods” chapter [Tada et al., 2015b]) in Hole U1430A, recovering 258.24 m (94%). In Hole U1430B, 29 APC cores and 8 XCB cores extended from the seafloor to 275 m CSF-A, recovering 259.71 m (94%). In Hole U1430C, 33 APC cores and 1 XCB core penetrated to 250 m CSF-A, recovering 257.02 m (103%). Total core recovery for Site U1430 was 775 m (Table T1; see also Fig. F2 in the “Expedition 346 summary” chapter [Tada et al., 2015a]).

Transit to Site U1430

The transit from Site U1428 to Site U1430 was slowed somewhat by the effects of tropical storm Man-yi, which passed ~300 nmi to the east of the R/V JOIDES Resolution off the eastern side of Japan. Strong winds (sustained at 36 kt and gusting to 48 kt) caused some heavy seas and reduced our transit speed to 9.0 kt. The 430.5 nmi total distance was ultimately covered in 44.0 h at an average speed of 9.8 kt. The sea passage ended at 0018 h on 18 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 0100 h, the ship was stabilized, and rig floor operations began.

Hole U1430A

A Falmouth Scientific positioning beacon (model BAP-547; SN1028W, 16 kHz, 206 dB) was deployed at 0123 h on 18 September 2013. A three-stand APC/XCB bottom-hole assembly was assembled, and the drill string was run to the bottom. The top drive was picked up, and the bit was positioned at 1077.7 meters below rig floor (mbrf), 3.0 m shallower than the precision depth recorder depth. Hole U1430A was spudded at 0445 h on 18 September. The first core barrel recovered 3.58 m of sediment, establishing a seafloor depth of 1083.6 mbrf. Oriented APC coring continued using full-length nonmagnetic core barrels through Core 346-U1430A-25H to 230.7 m CSF-A. Half APC coring with nonmagnetic core barrels continued through Core 29H to 249.5 m CSF-A, where refusal was reached in acoustic basement. The XCB was then used to advance the hole to 274.5 m CSF-A (Cores 30X through 32X). XCB coring was problematic because of the nature of the interbedded hard/soft layering of the formation. Based on poor recovery and slow penetration rates with the XCB, the decision was made to stop coring in this hole. Hole U1430A was circulated and displaced with 114 bbl of 10.5 ppg heavy mud, and the drill string was pulled clear of the seafloor at 0220 h on 19 September, ending the hole. Total recovery for Hole U1430A was 258.24 m (94%); however, core recovery with the XCB system was only 1.12 m of the 24.9 m advanced (4.5%). Four successful formation temperature measurements were taken using the advanced piston corer temperature tool (APCT-3) temperature shoe at 32.1, 60.6, 89.1, and 117.6 m CSF-A.

Hole U1430B

The ship was offset 15 m north of Hole U1430A. The bit was positioned at 1081.7 mbrf. An APC core barrel was deployed, and Hole U1430B was spudded at 0330 h on 19 September 2013. The 8.27 m of core recovered established a seafloor depth of 1082.9 mbrf. APC coring with full-length core barrels continued through Core 346-U1430B-25H to 234.6 m CSF-A. This was followed by the half APC system for Cores 26H through 28H to 246.0 m CSF-A. At that point, we switched to XCB and recovered Cores 29X through 36X to 274.1 m CSF-A. One final half APC core (37H) advanced the hole to a total depth of 275.0 m CSF-A. The hole was displaced with 114 bbl of 10.5 ppg mud, the top drive was set back, and the drill string was pulled up to a logging depth of 79.1 m WSF (see the “Methods” chapter [Tada et al., 2015b]).

Rig-up for wireline logging began at 0215 h on 20 September. Because of the shallow hole depth and to maximize the logging data acquired, the paleo combo tool string was split into two shorter tool strings. All logging runs reached within a few meters of total hole depth, and all wireline logging runs were considered successful. By 1530 h, the rig floor was rigged down from logging, and the drill string was pulled clear of the seafloor at 1550 h on 20 September, ending Hole U1430B. Total recovery for Hole U1430B was 259.71 m (94%). A total of 25 full APC cores and 4 half APC cores were recovered. As in Hole U1430A, recovery with the XCB remained poor. Eight XCB cores were attempted, penetrating 28.1 m and recovering only 5.94 m (21%).

Hole U1430C

Hole U1430C began as the drill string cleared the seafloor. The ship was offset 15 m south of Hole U1430A. The bit was positioned at 1079.7 mbrf. An APC core barrel was deployed, and Hole U1430C was spudded at 1645 h on 20 September 2013. The 4.78 m of core recovered established a seafloor depth of 1084.4 mbrf. Oriented APC coring continued using full-length nonmagnetic core barrels through Core 346-U1430C-26H to 227.3 m CSF-A. A single XCB barrel (Core 27X) was deployed to drill through a hard layer, penetrating 1.5 m. This core recovered 0.05 m of dolomite fragments. Half APC coring with nonmagnetic core barrels continued, recovering Cores 28H through 34H to 250.0 m CSF-A. The hole was displaced with 100 bbl of 10.5 ppg weighted mud, the top drive was set back, and the drill string was pulled clear of the seafloor at 1215 h on 21 September. The bit was clear of the rotary table, the bit and bit sub were removed, and the rig floor was secured for transit by 1500 h. Thrusters and hydrophones were pulled, and the sea voyage to the next site (a return to Site U1427) was initiated at 1518 h on 21 September. Total recovery for Hole U1430C was 257.02 m (103%). Of the 34 cores recovered, 26 were full APC cores, 7 were half APC cores, and 1 was an XCB core.

Although Site U1430 was the last newly occupied site during this expedition, because of the overall excellent coring and logistical successes to this point of the expedition additional operations time was available to enable returning to Site U1427 and then to Site U1425, as described in each of their site chapters.

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