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Unless otherwise noted, times are local ship time, which was Hawaii Standard Time (UTC – 10 h) for Site U1331.

Honolulu port call

Expedition 320 officially began when the first line was passed ashore to Pier 29 of Honolulu harbor at 1042 h on 5 March 2009. Following routine U.S. customs and immigration formalities, port call activities were initiated with the changing and crossover of Overseas Drilling Limited and IODP personnel. Expedition scientists boarded the ship on 6 March.

During the ~5 day port call, the usual food stocks and provisions were loaded and off-going freight disembarked. Items that were loaded in Honolulu included ~707 metric tons of marine gasoil, 147 short tons of bulk attapulgite, 7 joints of 20 inch casing, 16 joints of 16 inch casing, and 46 joints of 10¾ inch casing. Other significant items were two boxes of core liners and two reentry cone assemblies.

In accordance with the port call plan, customer service representatives came on the vessel to perform maintenance and repair on the ship's elevator and the heating, ventilation, and air conditioning (HVAC) system. A Siemens engineer also performed upgrades to the throttle system program.

A number of shipboard tours were conducted for the IODP Science and Technology Panel, several classes from the University of Hawaii (USA), and National Science Foundation visitors. A replacement refrigerated food container had to be leased at the last moment because the 10 ft auxiliary unit located on the accommodation roof could not be repaired in the time available. The U.S. Coast Guard interrupted the loading of compressed gas cylinders on 9 March for nearly an hour to address concerns relating to the handling of these items at this facility.

Following the release of the last line from the pier at 1500 h on 10 March, the JOIDES Resolution exited the harbor. Outside the harbor, a small vessel came alongside to deliver a radioactive source and two neutron tools required for the logging effort. The vessel then departed at full speed to the first site (U1331) with an expected arrival the evening of 14 March.

Transit to Site U1331

The transit to the first site of Expedition 320 was made through generally moderate seas and swell with predominantly overcast skies and occasional showers signifying that we were under the influence of the Intertropical Convergence Zone (ITCZ). We began positioning over Site U1331 at 2330 h on 14 March 2009. The 1081 nmi voyage from Honolulu was accomplished at an average speed of 10.4 kt.

During the 4 day voyage the zero-speed module, which monitors shaft speed and direction, failed 1 h out of port and the breaker supplying power to starboard shaft Motor 17A and port shaft Motor 14B tripped offline 2 h before arriving on location.

Site U1331

Hole U1331A

Once the vessel was positioning over Site U1331, an operational test of the dynamic positioning (DP) system was undertaken. Concurrent with DP testing, the making up of the bottom-hole assembly (BHA) and spacing out of the core barrel and colletted delivery system were accomplished. As the drill string was deployed, the length of each joint of pipe was measured and the internal clearance of each tubular inspected in accordance with routine practices.

Prior to spud-in, the drill string was flushed and cleaned of rust particles by pumping down a clean-out plug and two round trips of an extended core barrel (XCB) core barrel. Depths reported in this operations section are based on the measurements using the length of the drill string and are either drilling depth below rig floor (DRF) or drilling depth below seafloor (DSF).

Because the precision depth recorder was inoperative, the driller carefully extended the bit to tag the seafloor to verify the depth. Using the passive heave compensator, the bit was raised 10 m from this depth. Hole U1331A was spudded with the APC at 0750 h on 16 March 2009 (Table T1). The water depth calculated from the recovery of the first core was established as 5127.3 m DRF; the offset of the rig floor above sea level was 11.1 m, so the water depth as determined by drill string length was 5116.2 meters below sea level (mbsl).

Piston coring advanced the hole to 138.2 m DSF just above the chert layer suggested by the seismic record. We cored to 138.2 m DSF with APC Cores 1H through 15H and recovered 141.3 m of core (102%) (Table T1). Cores 1H through 11H were oriented with the FlexIt tools. Cores 12H through 15H were not oriented because the FlexIt tool was not deployed in anticipation of having to drillover stuck core barrels. The pullout force to recover the core barrels from the sediment gradually increased with depth and then decreased. We also switched to the standard, more durable steel core barrels starting with Core 12H instead of the nonmagnetic core barrels. To avoid damaging the APC, operations were then conservatively switched to the XCB corer.

XCB coring advanced from 138.2 m DSF to basement at ~190.6 m DSF. We cored a 52.4 m interval with Cores 15X through 21X and recovered 13.6 m (26%). For Cores 18X through 22X (157.3–190.6 m DSF), recovery was reduced by the presence of chert. We did manage to recover a short (0.42 m) section of the basal carbonate in the last core and bottomed out with a small sample of basalt. The total average recovery of APC/XCB coring in Hole U1331A was 81%.

Upon completion of the coring program, we conducted downhole logging, as detailed in "Downhole measurements." Downhole logging completed one run to a total depth of the borehole with the "paleo"-combo tool string (NGR, gamma ray attenuation [GRA] density, and magnetic susceptibility). These data were used to guide the coring strategy in subsequent holes at this site. The planned second run with the Formation MicroScanner (FMS)-sonic tool was aborted because of problems with the logging winch.

Hole U1331B

After the bit was pulled above seafloor at 0820 h on 18 March 2009, the vessel was offset 20 m west of Hole U1331A. Hole U1331B was spudded with the APC, and the recovery of the first core was used to calculate the seafloor depth as 5127.4 m DRF (5116.3 mbsl). The vertical offset to Hole U1331A was 5 m deeper to cover gaps between cores in the first hole. With APC Cores 1H through 17H, we advanced from 0 to 156.6 m DSF, cored 156.5 m, and recovered 163.13 m (104%). Five formation temperature measurements were made with the APCT-3 in Cores 2H, 3H, 5H, 7H, and 10H (19.6, 29.1, 48.1, 67.1, and 95.6 m DSF, respectively).

We switched to XCB coring for Core 18X (156.6–166.3 m DSF) but did not recover any core. Based on the drill, log, and core data from the first hole, we decided to drill with a center bit (without coring) through the chert interval (166.3–177.0 m DSF) and then attempt a single APC core in the sediment section below. APC Core 20H was attempted below the chert in the early Eocene basal carbonate section, but the corer was not able to penetrate the formation. We drilled ahead again without coring to 179.0 m DSF and one more XCB core was taken from 179.0–188.5 m DSF, but it did not recover any material. From 156.6 to 188.5 m DSF, we XCB cored 19.2 m but did not recover any material. An additional 12.7 m was drilled without coring. The bit was pulled free of the seafloor at 2220 h on 19 March, and the vessel was offset 20 m west of Hole U1331B.

Hole U1331C

The program for the third hole of the site was to fill in gaps in the sedimentary record from the first two holes by spot coring and to obtain any core from below the chert. Hole U1331C was spudded with the APC at 0155 h on 20 March 2009. The recovery of the first core was used to calculate the seafloor depth as 5128.0 m DRF (5116.9 mbsl). Cores 1H through 4H penetrated to 38.0 m DSF, and we recovered 39.2 m (103%). The interval from 38.0 to 59.0 m DSF was then drilled without coring, and Core 6H was taken from 59.0 to 68.5 m DSF (9.99 m recovered; 105%). We then drilled without coring from 68.5 to 92.5 m DSF and took APC Core 8H (92.5–102.0 m DSF; recovery = 9.21 m, 97%).

A short interval of 0.5 m was drilled to 102.5 m DSF, and Core 10H was taken from 102.5 to 112.0 m DSF, recovering 8.48 m (89%). The interval from 112.0 to 129.0 m DSF was drilled without coring, and Cores 2H through 14H were obtained from 129.0 to 157.5 m DSF (29.1 m recovered; 102%). Following a drilled interval of 19.5 m through a chert sequence (157.5–177.0 m DSF), a third attempt to core the short interval below the chert and above the top of basaltic oceanic crust was attempted.

This early Eocene section was one of the highest priority sections at this site and was poorly recovered in the previous two holes. This time the drillers successfully obtained this interval in APC Cores 17H and 18H (177.0–189.0 m DSF), coring 12.0 m and recovering 14.0 m (117%). Judging by the deformation of the cutting shoe and a bent 15 ft section of core barrel, it was surmised that Core 18H had more than vigorously encountered basement.

During spot coring in Hole U1331C, all piston cores up to and including Core 14H employed nonmagnetic core barrels and were oriented with the FlexIt tool. Standard steel barrels were used to obtain Cores 16H and 17H and did not use the orientation tool to avoid damaging it. We recovered 109.5 m (102%) in the cored interval of 107.0 m. An additional 82.0 m was drilled without coring. With the recovery of Core 17H, the decision was made to end coring at this site and to proceed to Site U1332.

After the drill string was pulled free of the seafloor at 1300 h on 21 March, the pipe trip was temporarily suspended for 1.5 h to accomplish the slipping and cutting of 115 ft of drilling line. Once drilling line maintenance was completed, tripping was resumed. The beacon was retrieved at 1500 h while the drill string was being recovered. At 0500 h on 22 March the drilling equipment was secured and the vessel departed for Site U1332.