Although the parting of the core barrel was a surprise, the difficulty in attaining an APC mudline was not unexpected because at DSDP Site 390 a veneer of manganese nodules and sand was recovered with RCB coring; it is present throughout the Blake Nose area. Farther up the slope of Blake Nose this surface veneer is lithified and it is possible that the surface veneer partially deflected the APC attempt and snapped the barrel off. When the core barrel was pulled out of the formation, there was no indication of excessive pull-out force, so the failure was not attributed to the core barrel being stuck in the formation. We decided to offset the vessel 10 m to the east to spud-in with the XCB.
This time we apparently contacted the seafloor at 2667.3 mbrf, based on an apparent 5,000-lb reduction in drill string weight. After advancing 20.6 m and retrieving two XCB cores with no recovery, the bit appeared to advance effortlessly into soft sediments. We then initiated APC coring and obtained Cores 3H-7H. Core 7H was not able to attain a full stroke and recovered 1.5 m of nannofossil ooze aa well as large chert fragment jammed in the cutting shoe.
We then took XCB Core 8X, which appeared to penetrate the chert layer after advancing only 1.8 m. This core recovered 0.76 m of chert fragments and nannofossil ooze. Another APC core (9H) was attempted, but it did not obtain a full stroke, so we resumed XCB coring. With the exception of one additional piston core attempt (13H; which did not attain full stroke), the rest of the hole was XCB-cored. Several zones of chert were encountered between 40 and 90 mbsf.
The K/T boundary was obtained in Section 17X-2. Coring was terminated at 172.7 mbsf after meeting the objectives to recover Aptian-aged sediments. The bit cleared the mudline, and Hole 1049A was officially terminated at 0400 on 15 January 1997.
The seafloor depths for Hole 1049A determined by reduction of drill string weight are most likely incorrect as compared to those in Holes 1049B and 1049C. The depth below seafloor of a marker horizon, such as the limonitic horizon at the top of the K/T boundary, indicates that the correlative horizon in Hole 1049A (125.88 mbsf) is ~12-14 m deeper than in Holes 1049B and 1049C (111.18 and 112.99 mbsf, respectively). When comparing data from Hole 1049A to the other holes at this site, one can adjust the depth by subtracting ~12-14 m from the reported Hole 1049A meters below seafloor (mbsf) depth.
Hole 1049B
We offset the ship 10 m east of Hole 1049A and spudded Hole 1049B using an XCB core barrel with a center bit. A water depth of 2682.0 mbrf was determined by the driller gently lowering the bit until he observed a gradual reduction in drill string weight. After drilling ahead for 2 m to penetrate the surface sediments that had caused problems at Hole 1049A, we deployed an APC core barrel. APC Cores 1H-5H were taken from 2.0 to 46.5 mbsf, and Core 5H contacted the expected (based on Hole 1049A results) chert layer after advancing 6.5 m.
We drilled through the chert zone (46.5 to 90.7 mbsf) using an XCB core barrel with a center bit because of the poor core recovery at the same interval in Hole 1049A and to make up for the slower than expected penetration rates. XCB Cores 6X-7X were then taken to 109.0 mbsf. We wished to APC core the K/T boundary, and fortunately, APC Core 8H recovered a full core spanning this target horizon. XCB Cores 9X-12X where then taken from 118.5 to 156.9 mbsf. The bit was pulled out of the hole and cleared the mudline at 0030 on 16 January.
Hole 1049C
We offset the ship 10 m east of Hole 1049B and spudded Hole 1049C using the XCB with a center bit. Based on the drill string weight indicator, the water depth was found to be the same as that at Hole 1049B (2682.0 mbrf). After drilling to 2 mbsf, we took APC Cores 1H-5H (2-45 mbsf) until contact with the first chert layer at 45.0 mbsf. After the hole was drilled without coring from 45.0 to 90.0 mbsf, XCB coring advanced to 120.2 mbsf. We obtained a third copy of the K/T boundary in Core 8X. Core 10H was shot at 120.2 mbsf, and recovered a full core even though it did not achieve a full stroke, indicating the bottom part was sucked in. XCB Cores 11X 13X were taken from 129.7 to a total depth of 158.5 mbsf. We then began to retrieve the drill pipe at 1945 hr on 16 January.
After pulling out of the hole, the drill bit was inspected at the surface and we discovered that one cone and cone leg were missing; no other bit damage was observed. We suspect the large heave experienced during 16 January possibly contributed to this failure by slamming the bit into the formation. Since the drillers did not observe erratic torque while drilling, the bit failure may have occurred just before (or during) pulling out of the hole.
While the vessel was coring Hole 1049C, the operator of the dynamic positioning system observed the sudden onset of a 3.4-kt current toward the east-northeast. Concurrent with this current, a front passed through with wind gusts as high as 35 kt from the south. Because of the direction of the strong current, it was not possible for the ship to head directly into the wind-driven sea. As a result of the different angles of the wind and current, there was considerable ship motion with heaves up to 3 m and roll angles of 6°, but the front did not affect drilling operations. After securing the drilling equipment, we began the ~7-nmi transit to BN-2Alt at 0030 on 17 January.