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doi:10.2204/iodp.proc.303306.104.2006

Operations

Transit from Site U1303 to Site U1304

After completing operations at Site U1303, the ship departed for proposed Site LAB6A on the Eirik Drift at 1315 h on 6 October 2004. On the morning of 7 October, the daily forecast for Eirik Drift area indicated that a low-pressure system over northwestern Canada was moving eastward and was projected to affect the LAB6A area by the afternoon of 9 October. Eventual storm maximum was predicted to have winds reaching 40–50 kt with gusts to 65 kt by 11 October. After considering the possibility of 4–5 days of weather downtime waiting for the storm to pass, as well as the potential danger to the vessel presented by this system, we decided to alter course to the closest other primary site, GAR2A, at 0840 h on 7 October. We arrived at Site U1304 (GAR2A) at 0630 h on 9 October.

Hole U1304A

Hole U1304A was spudded with the advanced piston corer (APC) system at 1345 h, returning a full core barrel. Thus, we were unable to establish a seafloor depth. Piston coring continued to 239.0 meters below seafloor (mbsf), taking 26 cores with an average recovery of 105.6% (Table T1). Nonmagnetic core barrels were used for Cores 1H–19H. Core 19H was a partial stroke of the APC, which required employing the drillover procedure to free the core barrel. Consequently, subsequent cores were obtained with standard steel core barrels without running the Tensor tool to reduce the risk of a downhole hardware failure during the drilling-over process. The drillover technique was used for Cores 19H–22H and 24H–26H. Coring operations ceased when the formation became too stiff to continue and shattering of core liners became common. Operations in Hole U1304A concluded when the bit cleared the seafloor at 1945 h on 10 October 2004.

Hole U1304B

The vessel was offset 20 m southeast of Hole U1304A, and the bit was positioned 5 m shallower than for Hole U1304A (3075.0 meters below rig floor [mbrf]). Hole U1304B was spudded with the APC at 2105 h on 10 October 2004. The recovery of the initial core was 8.14 m, which suggested a seafloor depth of 3065 meters below sea level (mbsl) (3076.3 mbrf; 9.1 m shallower than the precision depth recorder depth), albeit with a nearly full core. Piston coring advanced the hole to a final depth of 242.4 mbsf with an average recovery of 104.0% (Table T1). Nonmagnetic core barrels were used through Core 19H, and subsequent cores were obtained with the standard core barrels without the Tensor tool. Cores 20H and 26H were advanced by recovery, and drillover was used to obtain Cores 20H, 21H, 24H, and 25H. Operations in Hole U1304B ended when the bit cleared the seafloor at 0215 h on 12 October.

Hole U1304C

The ship was offset 20 m southeast of Hole U1304B, and Hole U1304C was spudded with the APC at 0445 h on 12 October 2004. Based on the 4.6 m recovery in the initial core, the calculated seafloor depth is 3064.5 mbsl (3075.4 mbrf). Piston coring advanced to 69.6 mbsf, when operations had to be terminated because of deteriorating weather conditions. The passage of a cold front during the early morning hours of 12 October was accompanied by wind gusts as high as 50 kt, a steady 20–25 kt wind, and 16–18 ft seas, which caused vessel heave to exceed 4 m. These conditions made it difficult to successfully land the core barrel without prematurely parting the shear pin of the corer and compromising the quality of the cores. At 1425 h, the bit was pulled clear of the seafloor, ending operations in Hole U1304C.

Hole U1304D

From 1430 to 1745 h, the ship remained positioned at the site with the drill string suspended above the seafloor waiting for the weather to abate. At 1745 h, the vessel was offset 20 m southeast of Hole U1304C, and Hole U1304D was spudded at 1830 h on 12 October 2004. The hole was drilled with a center bit to 52.0 mbsf, where coring was initiated. The hole was APC cored from 52.0 to 243.9 mbsf with an average recovery of 97.3%, with the exception of the interval from 180.3 to 181.3 mbsf, which was drilled (i.e., not cored). Nonmagnetic core barrels were used through Core 14H, and subsequent cores were obtained with the standard steel core barrels without the deployment of the Tensor tool. Cores 14H and 20H were advanced by recovery, and drillover was used to obtain Cores 15H–17H and 19H–21H. After recovering the drill string and disassembling the bottom-hole assembly for transit, we departed for Site U1305 (LAB6A) at 1230 h on 14 October.

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