OPERATIONS

We departed Site 1223 at 0130 hr on 23 December 2001 and arrived at waypoint 1 (27°32.787´N, 142°33.036´W), ~36 nmi southwest of the H2O junction box (27°52.916´N, 141°59.504´W), at 0000 hr on 26 December to begin a seismic and 3.5-kHz echo sounder survey. All times are reported in local ship time, which is Universal Time Coordinated (UTC) - 9 hr at Site 1224. The 766-nmi voyage took 2.9 days at an average speed of 10.9 kt. Summaries of coring results are given in Tables T2 and T3, and an operations synopsis is provided in Table T4.

At waypoint 1, the captain set the course to 56° at 6 kt to begin the survey. The water gun located at the stern of the ship was fired every 10 s during the survey as part of a seismic refraction study in which an ocean-bottom seismometer (OBS) located on the seafloor at the H2O was the receiver (see "Seismic Results from Hawaii-2 Observatory"). We had also intended to conduct a seismic reflection survey, but the single-channel streamer did not function because of an electronic failure. Fortunately, the 3.5-kHz data provided sufficient imaging of the sediment above basement to allow us to select a new primary drilling site (proposed Site H2O-5; 27°53.363´N, 141°58.758´W) that was more ideally positioned relative to the OBS than the other sites previously surveyed. Proposed Site H2O-5 was approved for drilling, subsequently becoming ODP Site 1224.

Following completion of the survey at waypoint 2 (27°54.426´N, 141°56.985´W) at ~0745 hr on 26 December, the JOIDES Resolution returned and was positioned on site with Global Positioning System navigation at 0845 hr on 26 December. Operations were then temporarily suspended while waiting on weather (WOW) because of heave, pitch, roll, and wind up to 7.7 m, 5.2°, 4.5°, and 29 kt, respectively. A total of 13.25 hr of WOW time occurred before drilling operations could proceed.

After the weather improved, the drill crew and core technician made up the advanced piston corer (APC)/extended core barrel (XCB)/motor-driven core barrel (MDCB) BHA with an 11⁷/₁₆-in Security H87F four-cone button-type drill bit. The bit was dressed with four #16 (-in) jet nozzles in preparation for a jet-in test. The pipe trip down began at 2200 hr on 26 December. When the bit was at a depth of 3778.94 m, the VIT was launched in order to conduct a camera survey of the site for debris. During the camera survey, we also conducted a survey with an echo sounder attached to the VIT frame to further delineate subsurface layers. The roll and pitch, along with the surge through the moonpool, made it very difficult to launch the VIT with the pipe moving the length of the moonpool. The VIT was fully secured with four tether ropes; the compass was oriented; and the VIT was successfully launched.

The drill string continued to be run to 4963.82 m. The top drive was then picked up, and the drill string was spaced out for performing a dynamically positioned 30-m x 30-m box survey. The survey took 2.0 hr and showed that the site was flat, undisturbed, and free of debris and cables.

First Jet-In Test

A wash barrel was dropped and the bit was lowered to 4973.47 m for a jet-in test (Fig. F3). The seafloor was tagged at 4966.1 meters below sea level (mbsl) (4977 mbrf) at 1525 hr on 27 December (see Fig. F16 in the "Explanatory Notes" chapter for a comparison of depths below rig floor and depths below seafloor). The jet-in test was performed to confirm a refusal depth for jetting in the reentry cone with 20-in casing. Operating parameters for the jet-in test included a range of 4- to 8-klb weight on bit, with a pump output of 50 strokes per minute (spm) utilizing a 6-in liner (0.123 barrels [bbl] of water per stroke) at up to 1375 psi. At 12 to 13 mbsf, a hard layer was encountered. After about an hour of jetting with pump rates increasing from 50 to 90 spm and with pressure increasing from 600 to 1375 psi, the jet-in test was stopped. Refusal depth was determined to be 4990 mbrf (13 mbsf), although the test was suspect as the ship was experiencing 4- to 5-m heave at the time of the test. The bit cleared the seafloor at 1740 hr on 27 December. The Maritime Hydraulics active heave compensator (AHC) was on during the test.

It took 6.25 hr to pull the VIT to the surface because of insufficient hydraulic fluid volume in the VIT pump. We determined later that this resulted from having two of the hydraulic lines incorrectly connected when the winch hydraulic hoses were rebuilt. The VIT was recovered at 0000 hr on 28 December. While we recovered the VIT, we pulled the bit up to 4944.57 mbrf and retrieved the wash barrel.

During deteriorating weather conditions, the upper guide horn was reinstalled; knobby joints were set across the guide horn; and the string was hung off in a 500-T elevator on the dual elevator stool, with the end of the pipe at 4953.15 mbrf. Maximum heave while WOW at this juncture was 5.8 m, with maximum pitch and roll of 3.8° and 4.1°, respectively. Total WOW before resuming operations was 13.75 hr.

Hole 1224A

At 1345 hr on 28 December, a core barrel was dropped and the drill string was spaced out to 4973.47 m. Because of a 4.6-m heave with a roll of 5°, the decision was made to core with the XCB to avoid the risk of bending the APC core barrel. The seafloor was tagged at 4966.1 mbsl (4977 mbrf), and Hole 1224A was spudded at 1455 hr on 28 December. Core 200-1224A-1X was advanced 6 m downhole with no recovery; hence, we could not establish a precise mudline (Table T2). Recovery in Core 200-1224A-2X consisted of a few gray pebbles, later interpreted to be zeolite pebbles, and recovery in Core 200-1224A-3X was little more than a smear of red clay. Thus, for the first three cores, we had advanced to ~25.2 mbsf and only recovered ~3 cm of core (0.12% recovery). On Core 200-1224A-4X, drilling progress was slow when we got to hard rock, which at the time was thought to be chert or basaltic basement. Recovery of 1.24 m of red clay and pieces of basalt confirmed that we had penetrated basement near the bottom of the 5.5-m interval cored, or at ~28 mbsf. We attempted one more XCB core (200-1224A-5X), before switching to the MDCB for one last short core. We pulled out of the hole and cleared the seafloor at 0530 hr on 29 December, ending Hole 1224A.

Overall, we cored 32.2 m and recovered 1.67 m of core (5.19% recovery), with 32 m cored and 1.45 m recovered (4.53% recovery) with the XCB and 0.2 m cored and 0.22 m recovered (110% recovery) with the MDCB (Table T2).

Hole 1224B

The bit was set at 4961.1 mbsl (4972 mbrf), and Hole 1224B was spudded with the APC at 0650 hr on 29 December. Core 200-1224A-1H appeared to have suffered from a mechanical shear due to heave, resulting in recovery of only 0.2 m, which was not considered sufficient to establish a valid mudline. The primary goal of APC coring was to establish the mudline; therefore, we offset to spud Hole 1224C. Hole 1224B officially ended at 0745 hr on 29 December after we pulled the bit up to clear the seafloor.

Hole 1224C

The bit was positioned at 4964.1 mbsl (4975 mbrf), and Hole 1224C was spudded with the APC at 0820 hr 29 December. We recovered 6.53 m of core and established the mudline at 4967.1 mbsl (mbsl) (4978.0 mbrf). Having successfully determined the mudline, the bit was pulled clear of the seafloor at 0915 hr on 29 December, marking the end of Hole 1224C.

Second Jet-In Test

Because of deteriorating weather, we pulled the bit up to 4933.6 mbsf (4944.5 mbrf) at 1000 hr on 29 December and hung the drill pipe off the dual elevator stool. Weather at the time included maximum heave, pitch, and roll of 6.3 m, 2.4°, and 8.1°, respectively, with winds up to 44 kt. Total WOW time was 16.0 hr, with operations beginning again at 0115 hr on 30 December.

A second jet-in test was deemed necessary to confirm the depth of penetration for the 20-in surface casing, which would be run with the reentry cone. A wash barrel was dropped, and the BHA was jetted in to 4996.1 mbsl (5007 mbrf; ~29 mbsf) with no obstructions encountered, unlike the first jet-in test. Jetting was done at 20 spm with a water pressure of 170 psi and no rotation of the bit. After 35 min the jet-in test was stopped at 60 spm and 600 psi with 10-klb weight on bit. The drill string was pulled out of the hole, with the bit clearing the seafloor at 0230 hr on 30 December and the rotary table at 1430 hr 30 December.

Hole 1224D

The reentry cone was positioned over the moonpool doors, and the casing string was partially assembled at 1830 hr on 30 December 2001. Poor weather conditions and the associated large heave, roll, and pitch forced us to delay operations until 1715 hr on 1 January 2002—a loss of 46.75 hr.

With weather conditions improving, the reentry cone and ~25 m of 20-in casing were assembled and lowered through the moonpool at 2335 hr on 1 January. Hole 1224D was spudded at 1220 hr on 2 January. It took only 24 min at 40 spm and 200 psi to jet the 20-in casing string down to 5003.47 mbrf (25.47 mbsf) and set the reentry cone. VIT observation of the reentry cone confirmed that it was in a satisfactory position. The bit cleared the seafloor at 1315 hr on 2 January, and the pipe was tripped back to the rig floor with the jet-in BHA and bit clearing the rotary table at 0200 hr on 3 January.

The rotary core barrel (RCB) BHA was made up and run down to 4388.89 mbrf in preparation for reentry. Hole 1224D was reentered at 1837 hr on 3 January, with coring beginning at 25.5 mbsf. Cores 200-1224D-1R and 2R were taken from standard 9.6-m-long cored intervals, with 43.2% and 50.1% recovery, respectively (Table T2). Core 200-1224D-3R penetrated only 4.6 m in an attempt to see if core recovery improved, which it did to 71.74%. Core 200-1224D-4R was to be run as another short core, which would also allow the kelly to be properly spaced out. Ship heave of 4.8 m and a 4° roll forced us, however, to pull up to 22.69 mbsf or into the casing shoe at 0500 hr on 5 January to wait out the weather after only penetrating 2 m. After 5.75 hr of WOW we returned to Core 200-1224D-5R, but again we were forced to stop coring early because of increasing seas and roll. The bit was pulled into the 20-in casing and set at 24 mbsf.

Sea state continued to increase with two major swell directions. Because of increasing dynamic positioning power requirements with no reserve for unusual loads that could force the ship off the hole, the bit was pulled to 4907.3 mbrf (70.7 m above the seafloor) at 1000 hr on 6 January. We continued WOW, with maximum heave, pitch, roll, and wind at 7.3 m, 4.3°, 10°, and 25 kt, respectively. Total WOW time was 26.0 hr total before operations resumed.

The marine forecast called for continued poor weather for our operating area, with very strong low-pressure systems to the west and north and large swells. Therefore, we decided to prepare to take advantage of any weather window by tripping the drill string and changing to the 14-in bit and BHA. This would allow us to open the cored hole when a more appropriate weather window was available and be in position to run 10-in casing. At 0045 hr on 7 January, we started to trip the pipe, with the bit clearing the rotary at 1100 hr on 7 January.

Overall, we cored 33.5 m in Hole 1224D and recovered 15.65 m of core (46.72% recovery) with the RCB coring system (Table T2).

Reaming the Hole

Taking advantage of a short interval of reduced ship motion, the crew assembled the 14-in bit and BHA, which consisted of an Atlas 14-in tricone insert bit (IADC Code 617) with three ¹⁴/₃₂-in jet nozzles. The BHA included a bit sub with float, 11-in x 8-in drill collars, one tapered drill collar, six joints of 5-in (31.5 lb/ft) drill pipe, and two crossover subs for a total BHA length of 170.03 m and a drill string weight of 510,000 lb. The bit was run down to 4790 mbrf at 2345 hr on 7 January.

Operations were then put on hold while WOW, with a maximum heave, pitch, and roll of 7.5 m, 3.8°, and 2.3°, respectively. Total WOW time was 19.00 hr before operations officially resumed. Some of this total time includes operations that were conducted while we were WOW that were required because of changes in the operation plan caused by the weather. For example, during this time the VIT frame was launched and lowered, and Hole 1224D was reentered to return to the state we were in prior to WOW. Operations resumed at 1845 hr on 8 January after Hole 1224D was reentered.

The AHC was turned off at 1515 hr on 9 January, after we had reamed open the hole to a depth of 5021.44 mbrf (43.44 mbsf) because of problems with the AHC aft cylinder gimbal. The AHC remained off for the rest of the cruise, although the passive heave compensator was in operation.

As the hole was reamed downward, several high-viscosity sepiolite sweeps were made at depths of 5016, 5022, 5030, 5035, and 5037 mbrf to aid in cutting removal while opening the hole. There were no signs of cutting buildup. From 5037 mbrf (59 mbsf), which is the depth where RCB coring had ended, the 14-in hole was drilled to 5042.7 mbrf (64.7 mbsf). The 5.7-m-long interval took 16.5 hr of bit rotation for an average penetration rate of 0.35 m/hr. This is significantly slower than the rate of penetration for the RCB bit in the 9⁷/₈-in hole (0.66 m/hr) and significantly slower than the 14-in bit in the previously opened 9⁷/₈-in hole (0.76 m/hr). A slower drilling rate for a 14-in bit in basement is expected because the bit has to grind up a larger area relative to reaming a previously cored hole or even coring the hole.

The rig instrumentation system indicated that excessive bit torque (700 A) occurred between ~2000 and 2100 hr on 10 January at 5040.7 mbrf (62.7 mbsf), possibly because of a lithology change. This is approximately the depth reached in Hole 1224F where the lithology changed downhole from thick basalt flows to fractured basalts and pillows. A mud sweep was then circulated at 5040.7 (2000 hr on 10 January) to clean the hole of cuttings. The hole continued to show excessive torque until 64.2 mbsf, when the torque settled down to 160 A. Drilling of the 14-in hole was shut down from 2100 to 2130 hr on 10 January for replacement of a washed out saver sub in the kelly. Operations then resumed with a circulating pressure of 1950 psi. At ~2240 hr on 10 January, the circulating pressure dropped suddenly to 1100 psi. It took ~40 min for the pressure to stabilize at this lower circulating pressure, with a pressure spike occurring before it fell back to 1100 psi. This was assumed to be a jet blowing out on the bit. An additional mud sweep was pumped at 2330 hr on 10 January at 5042.7 mbrf (64.7 mbsf) to see if this would help resolve the hole problems. A third sweep was performed at 0340 hr on 11 January. Because of the ongoing hole problems, potential bit problems, and the fact that we had only planned to drill down to ~67 mbsf, we ceased drilling at 0730 hr on 11 January, for a total depth in Hole 1224D of 64.7 mbsf.

A 30-bbl sepiolite pill was circulated before making a wiper trip up to 4992.19 mbrf (14.19 mbsf) and then back down to the bottom of the hole, where 0.5 m of soft fill was tagged at 64.2 mbsf. Another 30-bbl sepiolite sweep was pumped and followed with 50 bbl of seawater. The hole was then displaced with 35 bbl of sepiolite before the string was tripped to the surface.

When the drill string was pulled to the surface, to the surprise of all, the bit had been left in the hole, thus explaining the drilling difficulties. The BHA cleared the rotary at 2025 hr 11 January.

The bit appeared to have been sheared off, with only the bit's flattened pin end (7⁵/₈-in regular threads) still engaged in the box end of the bit sub. None of the experienced drilling staff aboard the ship had ever seen this type of bit failure before, especially with a tricone drilling bit this large.

As noted above, it was observed from the Standpipe Pressure Plot derived from the rig instrumentation system that from 2240 to ~2320 hr on 10 January there was a sustained pressure loss of ~850 psi. This 850-psi pressure loss was first interpreted as a blown jet nozzle but more likely indicated the formation of a crack at the root of the pin. In this scenario, crack propagation ultimately led to failure and loss of the entire bit.

Installation of 10-in Casing

Starting at 2030 hr on 11 January, the drill crew began assembling the 10-in casing string, which consisted of five joints of 10-in (40.5 lb/ft) casing. Because the Dril-Quip casing hanger system is not designed to land a 10-in hanger inside of the 20-in hanger, the drill crew modified the 16-in hanger by cutting off the 16-in casing extension ring. They then lifted the 16-in hanger and set it down over top of the 10-in casing sitting in the rotary table. The crew then picked up the 10-in casing hanger, which had already been made up with the casing hanger running tool, and attached it to the casing, which was sitting on the slips in the rotary table. The 10-in casing string and hanger were landed into the 16-in casing hanger and then tack welded together.

The casing string was run down starting at 2355 hr on 11 January. After we deployed and lowered the VIT frame, Hole 1224D was reentered at 1336 hr on 12 January. We noted during reentry that the reentry cone and skirt had settled by ~1.7 m below the original mudline. The casing string was run down and landed with the base at 5036.47 mbrf (58.47 mbsf) on 1515 hr on 12 January. The casing was cemented with 18.8 bbl of 15.5 ppg Class G cement. The first attempt to release from the casing hanger failed and resulted in the 10-in casing hanger being pulled up above the reentry cone. The casing hanger was landed again in the 20-in casing hanger, and this time the 10-in hanger released at 1715 hr on 12 January. The pipe was tripped up, with the running tool clearing the rotary table at 0530 hr on 13 January.

The BHA was assembled with a 9⁷/₈-in C-4 RCB bit and run down to 4388.89 mbrf in preparation for coring in Hole 1224E. The VIT camera was also lowered. Because the casing string had been lifted several meters and then relanded during the first attempt to unlatch, we wanted to reenter Hole 1224D to ensure that the casing and cement were properly installed. We tagged the base of the hole and then washed down to a depth of 5036.1 mbrf (58.1 mbsf), confirming that the reentry cone and casing were properly set for future installation of a seismometer (Fig. F5). The wash depth also indicated that the reentry cone had settled ~1.75 m below the mudline. The casing was then circulated clean, and operations at Hole 1224D were completed at 1815 on 13 January as the bit cleared seafloor.

Hole 1224E

The JOIDES Resolution was offset 15 m to the southwest and Hole 1224E was spudded at 1840 hr on 13 January at 4978 mbrf (Fig. F3). We washed down the first 8 m and then took two punch, or push, cores (200-1224E-1R and 2R), which were acquired by lowering the RCB bit through the soft sediments without rotating the bit. Both cores sustained substantial drilling disturbance, but we were able to recover 10.52 m of sediment core in a 19.2-m-long interval from 8.0 to 27.1 mbsf, whereas recovery was virtually absent in the other holes.

Coring penetrated from 27.1 to 36.7 mbsf for Core 200-1224E-3R. Basement was tagged at 27.7 mbsf during coring. Recovery consisted of basaltic basement underlying a 5-cm-thick piece of hyaloclastite into which basalt glass and clay pieces had been incorporated. This likely is the top few centimeters of the basement. After completing coring on Core 200-1224E-3R, the bit was pulled up by one stand of drill pipe to make a connection with another joint of pipe. This placed the bit above the sediment/basement contact. After making the connection, the driller was unable to reenter the basement hole. After 1 hr of attempting to find the hole at the sediment/basement contact by rotating the bit on bottom, a new hole, Hole 1224F, was started.

Overall, we cored 28.7 m in Hole 1224E and recovered 14.91 m of core (51.95% recovery) with the RCB coring system (Table T2).

Hole 1224F

The start of Hole 1224 F is somewhat of an anomaly in the ODP nomenclature, because the bit never pulled totally out of Hole 1224E, but it did pull out of the hard rock portion of Hole 1224E. The distance between Holes 1224E and 1224F is likely no more than ~1 m. In any case, we began penetrating basement again at 1630 hr on 14 January in Hole 1224F.

For all the bad weather we had previously, we were due a good spell. Thus, coring proceeded without interruption except for the occasional wiper trip and one trip to replace the knobby joints with drill pipe. During the latter trip, which started at 2315 hr on 17 January after recovery of Core 200-1224F-11R, the bit was inadvertently pulled above the basement/sediment contact. The driller worked the drill string up and down with rotation in an attempt to reenter Hole 1224F. Instead, Hole 1224E was reentered five times before the bit finally went back into Hole 1224F. RCB coring proceeded after washing ~11 m of soft fill from the bottom of the hole. Cores continued to be cut at a rate of ~6-8 hr/core, which was roughly twice as fast as cores cut from near the top of the basement. No core was recovered in Core 200-1224F-16R. The bit deplugger was run to remove potential obstructions, but Core 200-1224F-17R also had no recovery. Owing to time limitations, coring in Hole 1224F ended and preparations for logging began.

Overall, in Hole 1224F we penetrated 174.5 m, cored 146.8 m, and recovered 37.7 m of core (25.68% recovery) with the RCB coring system (Table T2).

Logging

The bit was released in the bottom of Hole 1224F at 2320 hr on 19 January. The hole was then displaced with 75 bbl of sepiolite. A FFF was launched at 0442 hr on 20 January to facilitate reentries into Hole 1224F on future scientific experiments.

At 0730 hr on 20 January, the triple combination (triple combo) logging tool (see "Downhole Measurements") was prepared to run downhole. The tool reached 5152 mbrf, which is only 0.5 m off the bottom of the hole. The first logging run was completed, and the tool was through the rotary table at 1520 hr on 20 January. Because a new logging cable had been installed during Leg 199 and was not fully stretched, the winch speed was relatively slow, which added ~3 hr to each logging run. For each logging run, the base of the pipe was lowered to 49.9 mbsf initially. As each run was made uphole, the pipe was pulled up from 49.9 mbsf to 34.5 mbsf to increase the open hole interval for logging.

The second logging run was with the FMS/DSI tool. An electrical problem required the tool to be pulled back to surface for repairs. After the tool was checked and it went into the hole ~1000 m, the tool started having power problems. It was brought back to surface, and it was determined that the telemetry cartridge was at fault. The cartridge was changed. The tool was then lowered to bottom with no further problem. Three passes of this string were run uphole at 275 m/hr from the bottom of the hole to the basement contact (27.7 mbsf). The third logging run was completed, and the tool cleared the rotary table at 0525 on 21 January.

We had planned to test the three-component well seismic tool (WST-3) if time and weather conditions permitted. A 4.92-L (300 in³) Bolt air gun aboard the JOIDES Resolution was used as the source. The gun was suspended from a buoy and tethered to the aft port crane with the gun depth at 5.5 m below the sea surface. When the WST-3 tool was in the drill pipe at a depth of 1057 mbrf, it was clamped to the pipe to conduct a test. The shot time was supposed to be detected by the blast hydrophone suspended 3 m beneath the gun. However, the seismic acquisition tool (SAT) detected no source signals from either the blast hydrophone or the WST-3. Subsequently, three problems were found: a circuit was faulty in the blast hydrophone of the air gun; there was an air leak from the air gun; and the WST-3 telemetry worked intermittently. The experiment was thus terminated because there was insufficient time to attempt to fix these problems and complete the planned shooting and logging program for the WST-3. The time constraint on the logging program was determined by the departure time required to make the San Diego port call. The WST-3 was back through the rotary table at 0945 hr on 21 January.

The VIT was launched starting at 1030 hr 21 January to observe the FFF at the top of Hole 1224F (Fig. F7). A large hole was observed in the seafloor from circulating the cuttings out of the hole. As a result, the top of the FFF was observed at ~4980.5 mbrf (2.5 mbsf) with the three buoys just below the mudline, secured to the FFF by ⁵/₃₂-in steel cable. The end of the casing on the FFF is estimated to be at 6.2 mbsf.

The open end of the drill pipe cleared the seafloor and FFF at 1238 hr on 21 January. The VIT was recovered at 1445 hr, and the BHA cleared the rotary table at 2355 hr on 21 January, completing activity at Site 1224.

The vessel was secured to commence a sea voyage by 0030 hr on 22 January. A test of the SCS system was conducted from 0030 hr to 0145 on 22 January prior to leaving the site. Although the system was demonstrated to be working, there was insufficient time to conduct a seismic survey. Pie charts of the time spent on various classes of activities are given in Figure F7 in the "Leg 200 Summary" chapter.

Because a complete sedimentary section was not recovered above basement, we use the drill pipe measurements from the holes and jet-in tests at Site 1224 to estimate the thickness. Undulations in bathymetry and the basement/sediment interface can add to the uncertainty, but these are likely small (±1 m) over the small area encompassed by the six drill holes (see Fig. F3), which is roughly 20 m x 20 m. The drill pipe measurement also has an uncertainty of about ±1 m. The constraints are as follows:

1. In Hole 1224A, basaltic basement was encountered in the core catcher of Core 200-1224A-4X, where a ~6-cm chunk of basalt was recovered. The cored interval is from 25.2 to 30.7 mbsf. We also recovered ~117 cm of sediment above this, which places the basement contact somewhere between 25.2 + 1.17 mbsf and 30.7 - 0.06 mbsf, or between 26.37 and 30.64 mbsf. The driller noted a hard contact, as determined by a change in the weight on bit, at 28.9 mbsf. At this point, we did not have an accurate mudline, so this estimate has a greater uncertainty than those below.
2. The second jet-in test penetrated down to 29 mbsf, which was taken to be the depth to basement. A mudline had been established in Core 200-1224C-1H prior to this test, so basement should be 29 mbsf or deeper in the jet-in hole.
3. In Hole 1224D, the 20-in casing was set at 25.5 mbsf and the first core, which was basalt, was cored from 25.5 to 35.1 mbsf, with 4.15 m of recovery. Thus, the basement is between 25.5 and 35.1 - 4.15 mbsf, or between 25.5 and 30.95 mbsf. A better estimate comes from the driller, who noted a change in the weight on bit at 29.5 mbsf.
4. In Hole 1224E, sediment was recovered in the push, or punch, core that extended to 27.1 mbsf. The next core (Core 200-1224E-3R) recovered 4.39 m of basalt in the interval from 27.1 to 36.7 mbsf. Basement is thus between 27.1 and 36.7 - 4.39 mbsf, or between 27.1 and 32.31 mbsf. In addition, the driller noted that he felt basement from weight on bit at 27.7 mbsf.

We consider the best estimates as 29, 29.5, and 27.7 mbsf, where basement was felt. All three estimates are consistent with the ranges obtained from coring. Basement may thus vary in depth below seafloor by ~2 m or average ~28 or 29 mbsf over the area of operations with the variation related to uncertainties in the drill pipe measurement.

The vessel settled onto a bearing of 78° for San Diego. Weather conditions were excellent aiding in a rapid transit to San Diego. The 1320-nmi trip took 125.26 hr, for an average transit speed of >11 kt. The harbor pilot came on board at 0700 hr on 27 January, and the vessel was tied up at port with the first line ashore at 0820 hr on 27 January, officially ending Leg 200.