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OPERATIONS (continued)

Site 1216
Transit to Site 1216 (PAT-26D)

The 534-nmi transit to proposed Site PAT-26D was accomplished in 50.3 hr at an average speed of 10.6 kt. The vessel encountered a moderate current during 5 November that reduced the daily average rate to 9.9 kt. At 1645 hr on 5 November, the vessel slowed to 6 kt, and the seismic equipment was deployed. The seismic survey utilized the 80-in3 water gun and Teledyne hydrophone streamer. The first leg of the survey was an 11 nmi north-northwest to south-southeast traverse across the prospective location. A short crossing track from east-northeast to west-southwest concluded the survey. The 24-nmi survey required 4.2 hr at an average speed of 5.7 kt. Following the retrieval of the seismic equipment, the vessel came about and returned to site, at which time the thrusters were lowered and the DPS was activated. The vessel was on the GPS coordinates of the new location by 2130 hr on 5 November. The hydrophones were then lowered, and assembly of the BHA began. A beacon was deployed at 2141 hr on 5 November.

Hole 1216A

After the drill string was deployed to a depth of 5100 mbrf, a "mudline" core was attempted from 5105.4 m and resulted in a "water core," indicating that the bit was >10 m above the seafloor. The next attempt was made at 5115.4 mbrf with the same result. A third attempt was made with the bit at 5125.4 m and a fourth from 5135.4 mbrf, both of which resulted in water cores. The driller then lowered the bit until the heave compensator appeared to activate, suggesting contact with a firm sea bottom at a bit depth of ~5167 mbrf. The sixth attempt at a mudline core was made with the bit at 5163.0 mbrf, and Hole 1216A finally was spudded with the APC at 1615 hr on 6 November. The seafloor depth that was indicated by the recovery of the first core was 5163.3 mbrf, 50 m deeper than the PDR depth. The usual suspects (misreading the PDR, miscounting the drill pipe, applying the wrong Matthew's table correction, and improper addition) were reviewed, but no culprit could be found. The uncorrected depth obtained during the initial site survey was also consistent with the PDR reading. The only viable remaining reason for this depth discrepancy appeared to reside in the possible presence of a very strong side echo that mimed a seafloor return on the bathymetric record.

A total of 10 piston cores were taken at Hole 1216A (Table T1). The cores were oriented starting with 3H. The first four piston cores were full-stroke events. All the remaining piston core attempts, however, did not achieve the fully extended 9.5-m stroke of the piston corer, probably due to the prevalence of chert stringers. Cores 5H to 10H (37.7–54.3 mbsf) were obtained using the advance-by-recovery (ABR) method. With this method, the bit position for the next piston core is advanced only to a depth equal to the recovery of the previous core. No heat flow measurements were attempted because of the high probability of damage to the Adara cutting shoe by chert. APC operations in Hole 1216A resulted in 54.3 m cored with 55.11 m recovered (101.5%).

One XCB core (11X; 54.3–62.2 mbsf) was acquired before the hole was terminated. The XCB core advanced 7.9 m and recovered 1.36 m (17.2%). The total recovery at Hole 1216A was 56.5 m, representing 90.8% of the cored interval (Table T1).

Hole 1216B

After the bit cleared the seafloor, the vessel was offset 10 m east of Hole 1216A, and Hole 1216B was spudded with the APC at 0540 hr on 7 November. This was a single-core attempt made with the bit at 5158.0 mbrf (5 m shallower than the bit position of Core 1H). The single core recovered 9.75 m or 102.6%.

After coring operations concluded at Site 1216, the drilling equipment was secured, and the beacon was successfully recovered. The 24-hr transit to the next site (PAT-19A) transit to the next site began at 1545 hr on 7 November.

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