ODP Leg 175: Preliminary Report

OPERATIONS

SITE 1080
(Proposed Site SAB-2)

Hole 1080A
After a 314-nmi voyage at an average speed of 10.7 kt, the vessel proceeded directly to the GPS coordinates of the site, where a beacon was deployed at 0407 hr on 7 September. Hole 1080A was spudded at 1020 hr on 7 September. The seafloor depth was established at 2777.2 mbrf by DPM. APC coring advanced to 50.8 mbsf, which was considered APC refusal, when an attempt at the seventh piston core resulted in no advance because of contact with a very hard layer. Cores were oriented starting with 4H. The hole was then deepened with the XCB from 50.8 to 52.1 mbsf with high torque and very little penetration. After 20 min of rotation, the core barrel was recovered containing 0.12 m of dolomite, and the hole was terminated. The bit cleared the seafloor at 1730 hr on 7 September.

Hole 1080B
The vessel was offset 40 m to the south, and Hole 1080B was spudded with the APC at 1845 hr. APC coring advanced to 37.7 mbsf. When the attempt at Core 1080B-5H resulted in no advance of the core barrel because of a hard sediment layer, an XCB core barrel was dropped (5X) and advanced 0.5 m in 25 min of rotation. The decision was made to terminate the site, and the drill string was pulled back to 2767.0 m, clearing the seafloor at 0025 hr on 8 September. The hydrophones and thrusters were retracted and the drilling equipment was secured for transit by 0600 hr, thereby ending operations at Site 1080.