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doi:10.2204/iodp.proc.336.106.2012

Operations

The final operations of Expedition 336 were focused on APC/XCB coring of the sediment above basement and the sediment/​basement contact in four holes. A summary of operations completed in Holes U1383D, U1383E, U1382B, and U1384A is presented in Table T1. Information about the holes and cores recovered is presented in Table T2.

Hole U1383D

The APC/XCB bottom-hole assembly (BHA) was made up with a new APC/XCB bit and lowered to 4 m above seafloor. The vessel was positioned halfway between Holes U1383B and U1383C, offset 5 m to the northwest, and Hole U1383D was spudded at 1426 h on 7 November 2011 (all times are local ship time, Universal Time Coordinated [UTC] – 3 h). Six APC cores were taken from 0 to 43.3 meters below seafloor (mbsf) (Cores 336-U1383D-1H through 6H) and recovered 47.89 m of sediment. Core 6H only penetrated 0.2 m before hitting basement, so the majority of the recovery was sucked in when pulling the barrel out of the formation. After hitting basement with the last APC core, we penetrated 1 m with Core 336-U1383D-7X and recovered 0.76 m. Hole U1383D ended at 2350 h on 7 November when the bit cleared the seafloor.

Hole U1383E

The vessel was offset 10 m to the southeast, and Hole U1383E was spudded at 0038 h on 8 November. APC Cores 336-U1383E-1H through 6H extended to 43.2 mbsf and recovered 50.38 m of sediment. Core 6H only penetrated 2.3 m before encountering basement, so the remaining 6.22 m of sediment recovered was likely sucked in when the barrel was pulled out of the formation. After the last piston core hit basement, the XCB core barrel was dropped, and the sediment/​basement interface was cored for ~1 h to 44.2 mbsf. Core 336-U1383E-7X recovered 0.3 m. Hole U1383E ended at 1000 h on 8 November when the bit cleared the seafloor.

Hole U1382B

After pulling out of Hole U1383E and raising the bit well above seafloor (4300 meters below rig floor [mbrf]), we moved in dynamic positioning (DP) mode to Site U1382. After the 3.28 nmi transit was completed at 1445 h, the bit was lowered to just above the seafloor and the top drive was picked up and spaced out for spudding. Hole U1382B was spudded at 1700 h on 8 November. APC Cores 336-U1382B-1H through 10H extended to 90.0 mbsf and recovered 83.70 m of sediment. Core 10H, the last APC core, encountered basement after penetrating ~8.5 m, so the lowermost portion of sediment recovered in this core is likely flow-in. Temperature measurements with the advanced piston corer temperature tool (APCT-3) were attempted on Cores 3H through 5H. The measurements were not good as a result of tool movement, and the measurements were discontinued because they were thought to be disturbing the sediment cores. Subsequent splitting of the cores seemed to indicate that the disturbed cores could have been caused by the lithology of the cores—coarse sediments as large as pebble size were found inside the cores. After basement was hit with the last piston core, the XCB core barrel was dropped, and the sediment/​basement interface was cored. After a few minutes of XCB coring, the formation changed, and the XCB quickly advanced to the remainder of the kelly length (4.7 m). After Core 336-U1382B-11X was pulled, another core barrel was dropped, and XCB coring continued until hard formation was encountered around 98.8 mbsf. After 30 min of coring with no advance, Core 336-U1382B-12X was pulled. The XCB cutting shoe had lost all of its carbide teeth, and only 18 cm of core was recovered. Cores 336-U1382B-11X and 12X recovered a total of 0.58 m over an 8.8 m interval. Hole U1382B ended at 1315 h on 9 November when the bit cleared the seafloor.

Hole U1384A

After raising the bit above the seafloor (4400 mbrf), we moved in DP mode to Site U1384. The 3.38 nmi transit was completed at 1815 h. We lowered the bit to just above the seafloor, picked up the top drive, and spaced out for spudding. Hole U1384A was spudded at 2130 h on 9 November. APC Cores 336-U1384A-1H through 11H extended to 94.7 mbsf and recovered 93.51 m of sediment. Core 11H was only a partial stroke, likely because basement was encountered. XCB Core 336-U1384A-12X advanced 1.5 m in ~40 min, where penetration stopped. When Core 12X was retrieved, 0.58 m of core had been recovered and the XCB cutting shoe had lost all of its carbide teeth. Hole U1384A ended at 0042 h on 11 November.

After the drill string was back on board, the BHA was disassembled and the drill floor was secured for transit. Transit to Ponta Delgada began at 0042 h on 11 November for a planned arrival time in Ponta Delgada of 0730 h on 17 November.

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