After a brief ~10-nmi transit west from Site 1274, we arrived at Site 1275 (Fig. F1). At 0445 hr on 19 June 2003, we began a camera survey on the top of a large dome, previously surveyed during 1998 Shinkai 6500 Dive 422. During that dive, gabbro and peridotite were recovered from the southern flank of the dome (Fig. F2); our first drilling target was smooth, slabby outcrops on the north end of the dome summit.
Our camera survey for Hole 1275A required <2 hr, and we selected a target on a bare rock outcrop. We initiated coring at 0815 hr at a water depth of 1563 meters below sea level (mbsl). In an attempt to recover the uppermost surface of the outcrop, we elected to recover the core barrel after only 5 m of penetration. Since we had to lift the pipe above seafloor in order to have the proper pipe spacing at the rig floor to extract the core barrel, Core 1R (Table T1) was the only core recovered from this hole.
In an attempt to remain on or at least very near the outcrop where we cored Hole 1275A, we moved in dynamic positioning mode only 4 m south to begin Hole 1275B. Core 1R was cored to a depth of 11.0 meters below seafloor (mbsf) and required >10 hr to drill. Coring continued through Core 22R (108.7 mbsf). Because our rate of penetration early in the hole was so low and the bit had been used for nearly 80 hr of coring, we chose to terminate coring to attempt logging while coring (LWC) at a nearby location. We did not release the bit in the bottom of the hole, so we would have the option to attempt a bare hole reentry and then deepen and log Hole 1275B if time allowed. The location of Hole 1275B was marked with a glass float deployed from the subsea camera frame prior to abandonment. The average rate of penetration for the hole was only 1.4 m/hr.
Our target for the LWC operation was, in our estimation, the most optimum location for high recovery occupied during Leg 209. We selected a drilling location at the site of an outcrop where the precruise dive survey had collected serpentinized peridotite. This site was ~90 m south of Holes 1275A and 1275B. Relatively high recovery in hard rock from nearby Hole 1275B (>43%), combined with shallow water and calm seas, should have made for ideal deployment conditions. We deployed a standard eight-collar bottom-hole assembly (BHA), as memory on the LWC tool (resistivity at the bit with coring [RAB-C]) is only 70 rotating hours in its current configuration and we did not expect to penetrate more than ~70 m in that time.
After conducting a brief (1 hr) subsea camera survey, we located an outcrop near the coordinates where peridotite was sampled during the Shinkai 6500 dive. Hole 1275C was initiated at 0445 hr on June 24, with the same slow rate of penetration we experienced in Hole 1275B. After three cores and nearly 20 hr of operations we had reached only 20.8 mbsf and the three core barrels we had recovered were either empty (Core 1R) or contained only one or two small, rounded cobbles of rock. Compared to recovery of initial cores from all our previous drilling locations, recovery with the RAB-C was significantly poorer than with our conventional rotary system. Based on poor recovery, we abandoned Hole 1275C.
In an attempt to ensure the deepest penetration possible in the time we had left, we deployed a 22-collar BHA in preparation for coring Hole 1275D. We offset 4 m west from Hole 1275C and began coring Hole 1275D at 1025 hr on 25 June. Coring in the same interval with the RAB-C (Cores 1R to 3R; 0 to 17.6 mbsf) yielded 32% recovery. This was the highest rate of recovery from the first three cores from any hole drilled during Leg 209 (Fig. F3). Coring continued through Core 43R to 209 mbsf (average recovery = >50%). We terminated coring at 0915 hr on 30 June in order to leave time for wireline logging. The average rate of penetration for Hole 1275D was 2.4 m/hr. Wireline logging failed to pass an obstruction at ~103 mbsf, but two tool strings (triple combination [triple combo] and Formation MicroScanner [FMS]-sonic) were deployed over the interval from 103 to 20 mbsf. The pipe was pulled clear of the seafloor at 0515 hr on July 1, ending operations for Leg 209, and after recovering the pipe, we began our transit to Bermuda.
During the 5-day, 1410-nmi transit to Bermuda, all the cores recovered during Leg 209 were arranged throughout the upper two floors of the labstack for a postcruise research sampling party. Sample selection and resolution of the distribution of popular intervals were accomplished over 24 hr. Sample orientation and processing were completed prior to arrival in Bermuda.
Our transit speed averaged 11.6 kt. Leg 209 was completed with the first line ashore at Market Wharf, St. George, Bermuda, at 1715 hr on 6 July 2003.
1 Examples of how to reference the whole or part of this volume can be found under "Citations" in the preliminary pages of the volume.
2 Shipboard Scientific Party addresses can be found under "Shipboard Scientific Party" in the preliminary pages of the volume.
Ms 209IR-110