The JOIDES Resolution departed Ponta Delgada, Azores, at 1615 hr (all times are given in Universal Time Coordinated [UTC]), 28 March 1993. We steamed the 631 nmi to Site 897 in 51.25 hr. We started a single-channel seismic reflection and magnetic survey over the proposed Site IAP-4 at 2130, 30 March, to confirm its location (see "Site Geophysics" section, this chapter). During this site survey, a navigation computer program (AGCNAV) proved extremely helpful in providing a real-time display of the ship's track. The seismic survey was completed at 0052 hr, 31 March, and the ship returned to the chosen site location. A Datasonics beacon was deployed at 0145 hr at 40°50.37'N, 12°28.37'W. After the ship was in dynamic postioning (DP) mode, a backup Datasonics beacon was dropped and turned off. The site location had been offset 200 m east-northeast of the approved location to penetrate a thin layer of possible synrift sediments above basement. The precision depth recorder (PDR) indicated a water depth of 5330.2 m below rig floor (mbrf; the rig floor was approximately 11.05 m above sea level).
Beginning at 0400 hr, 31 March, a rotary core barrel (RCB) bottom-hole assembly (BHA) having a mechanical bit release (MBR) was assembled and run to the seafloor. The bit tagged the bottom at 5331.0 mbrf. Hole 897A was spudded at 1845 hr, 31 March. Cores 149-897A-1R through -6R were cut from 0.0 to 55.2 mbsf, with 17.37 m material recovered (Table 1). A WSTP was used at 55.2 mbsf.
The drawworks brakes were not holding, and several attempts to adjust them were unsuccessful. Sea conditions were causing an occasional 3-m ship's heave and ±40,000-lb fluctuations in the 580,000-lb hanging weight of the drill string. The silty/sandy top of the hole was potentially unstable, while the hole was only 55 m deep; therefore, we judged it best to terminate operations in Hole 897A. The bit was pulled above the seafloor, and the drawworks brake pads were replaced.
The ship was not moved; Hole 897B was spudded at 1320 hr, 1 April. The mud line was encountered at 5331.0 mbrf, and the hole was drilled from 0.0 to 52.0 mbsf. Erratic torque was observed in the first 30 m and was assumed to be the result of unstable seafloor sediments that had caved into the hole. A 10.0-m core was cut from 5383.0 to 5393.0 mbrf. Several attempts to retrieve the core barrel were unsuccessful. We pulled the drill pipe out of the hole and found that part of the BHA had been lost.
A new RCB BHA with a MBR was assembled, and the ship was moved 20 m north. Hole 897C was spudded at 1745 hr, 2 April. The PDR indicated a water depth of 5329.4 mbrf, and the bit encountered the seafloor at 5326.3 mbrf. Cores 149-897C-1R through -73R were cut from 49.9 through 744.9 mbsf (Table 1). A total of 695.0 m was cored with 352.8 m of material recovered. WSTP temperature measurements were taken at 117.9, 166.1, and 214.4 mbsf.
After coring Hole 897C to 744.9 mbsf, the hole appeared to be in good condition, and we judged it prudent to change the drill bit. Because a primary objective of Site 897 was significant basement penetration and the first bit was not fresh enough to complete the hole, we decided to deploy a free-fall funnel (FFF) and retrieve the pipe to replace the bit.
The bit was pulled to 74 mbsf and an FFF was deployed. The vibration-isolation tool (VIT) was deployed with a television camera and a sonar. The FFF and floats were not visible on the seafloor, but the VIT sonar indicated that the funnel was at 4 mbsf. No flow was visible exiting the crater during fluid circulation. The hole was considered to be too valuable to risk losing it on a blind reentry, and additional basement penetration and logging were considered to be important; therefore, we decided to go back to the bottom of the hole and to continue coring for the remaining life of the bit. At this point, however, the drill pipe became stuck. In the process of attempting to free it, the BHA broke off. Hole 897C was terminated, and the drill string pulled out of the hole.
We decided to drill Hole 897D to acquire additional basement and deep sediment cores and to obtain downhole logs. The ship was offset 100 m west-southwest of Hole 897C to obtain information about the lateral variability within the deep sediments and basement rocks. The PDR indicated a water depth of 5330.2 mbrf. A RCB BHA with an MBR was deployed, and the seafloor was encountered at 5327.0 mbrf. Hole 897D was spudded at 0600 hr, 10 April. We drilled from 0 to 596.0 mbsf. The core barrel was recovered at 200-m intervals as a precaution against its becoming stuck by cuttings that might circulate above it. Cores 149-897D-1R to -25R were cut from 596.0 to 837.2 mbsf, an interval of 241.2 m in which we recovered 117.94 m of material (Table 1).
After coring, the hole was flushed, the basement/sediment contact from 5982 to 6164 mbrf was reamed clear, and a short pipe trip was made to 120 mbsf. The bit was dropped at the bottom of the hole, and the pipe was pulled to 120 mbsf again for logging.
A 41-m-long geophysical combination (quad-combo) logging tool (see "Explanatory Notes" chapter, this volume) was run. The tool encountered a bridge at 228 mbsf and became stuck. The pipe also became stuck, but was freed by circulating seawater at high pressure. The open BHA was carefully washed down over the logging tool from 5447 to 5557 mbrf to recover it. The logging tool became unstuck when we had washed to within 3 m of the bottom of the tool. After recovering the logging tool, the drill string became stuck. Again, the drill string was freed by using the pumps to liquify the formation. Operations at Hole 897D and Site 897 ended at 1515 hr, 17 April, when the BHA was on deck. After a short seismic survey we then steamed to Lisbon, Portugal, to end Leg 149B.