The 184-nmi voyage to Site 1081 was impeded by rough seas and the northward-flowing Benguela Current. The vessel steered into 1.5-m swells generating up to 5° of pitch angle, which combined with the countercurrent, slowed the forward progress to 8 kt. By the time the JOIDES Resolution reached Site 1081, the seas had flattened, and the average speed had increased to 9.4 kt. The vessel proceeded directly to the Global Positioning System coordinates of the site, and a beacon was deployed at 0200 hr on 9 September. Hole 1081A was spudded with the APC at 0530 hr on 9 September. The seafloor depth was established at 796.1 meters below sea level (mbsl) by drill-pipe measurement (DPM). APC coring advanced without incident to 134.0 mbsf (Cores 175-1081A-1H through 15H; Table 1; also see the expanded core summary table on CD-ROM, back pocket, this volume). Core 175-1081A-16H advanced only 3 m, and coring operations were switched to the XCB system. The XCB penetrated through a 1-m-thick firm horizon and then quickly advanced into softer sediments. Operations were switched back to APC coring. Core 175-1081A-18H advanced the hole to 154.5 mbsf using advancement by recovery. Core 175-1081A-19H failed to advance because of stiffer sediments, and XCB coring was initiated again. Total penetration with the APC was 145.5 m, with 103.9% recovery (Table 1). Cores were oriented starting with Core 4H. Adara heat-flow measurements were taken at 29.5 mbsf (4H), 58.0 mbsf (7H), 86.5 mbsf (10H), 115.0 mbsf (13H), and 137.0 mbsf (16H). XCB coring advanced to 452.7 mbsf (49X), which was the revised depth objective at Site 1081. The penetration with the XCB was 307.2 m, with 78.9% recovery. The total recovery at Hole 1081A was 86.9%.
In preparation for logging, an aluminum go-devil was dropped to ensure the opening of the lockable float valve. After the hole was flushed with a high-viscosity mud, the drill string was pulled back to 403.7 mbsf, where the top drive was set back. The drill bit was then placed at the logging depth of 101.2 mbsf. Hole 1081A was logged with a full suite of sensors to continuously characterize the sedimentary changes as a proxy for the paleoclimatic record and to provide data for core-log integration. For each run, the pipe was set at 101 mbsf and pulled back to 71 mbsf during logging. The wireline logging heave compensator was started when the logging tools reached the mudline.
Logging operations began at 0200 hr on 9 September. The first log was conducted with the seismostratigraphic suite (25.8 m long). This suite was made up of the spectral gamma-ray (NGT), long-spacing sonic (LSS), phasor dual-induction (DITE), and Lamont-Doherty high-resolution temperature (TLT) sondes. This tool string was deployed in the pipe at 0245 hr and logged the hole up from 450.5 mbsf. The tool string was recovered at 0550 hr. The second log was conducted with the lithoporosity suite (19.5 m long) and included the hostile environment gamma spectrometry (HNGS), accelerator porosity (APS), lithodensity (LDS), and TLT sondes. The tool string was deployed at 0655 hr and logged the hole up from 450.5 mbsf. The third log was made with the FMS suite (12.10 m long) and included the NGT, general purpose inclinometer, and FMS sondes. This tool logged the hole up from 450.5 mbsf. The tool string was recovered at 1425 hr. The fourth and last log was made with the magnetic susceptibility suite (11.8 m long) and included the NGT, magnetic susceptibility, and the nuclear resonance magnetometer sondes. The tool string was deployed in the pipe at 1455 hr and logged the hole up from 450.5 mbsf. It was retrieved at 1740 hr. The logging equipment was rigged down by 1830 hr on 9 September. The hole was filled with heavy mud. The drill string was then pulled out of the hole with the bit clearing the seafloor at 2115 hr on 11 September, ending operations at Hole 1081A.
The vessel was offset 30 m to the south, and Hole 1081B was spudded with the APC at 2220 hr on 11 September. The seafloor depth was established at 793.1 mbsl by DPM. APC coring advanced without incident to refusal at 187.6 mbsf, with 104.4% recovery (Table 1). Cores were oriented starting with Core 175-1081B-4H. The bit cleared the seafloor at 0925 hr on 12 September, thereby ending operations at Hole 1081B.
The vessel was offset 30 m to the south, and Hole 1081C was spudded with the APC at 0955 hr. The seafloor depth was established at 793.8 mbsl by DPM. APC coring advanced routinely to refusal at 155.2 mbsf. The recovery was 103.7% (Table 1). Cores were oriented starting with Core 175-1081C-3H. The bit cleared the seafloor at 1815 hr, thereby ending operations at Site 1081.