Site 1271 is on the southern end of the inside corner high south of the 15°20´N Fracture Zone ~19 nmi northwest of Site 1270. We again chose to use a six-collar bottom-hole assembly (BHA) in order to ensure the preservation of sufficient BHA components for future drilling during this leg.
Our camera survey for Hole 1271A (Fig. F1) began at Global Positioning System coordinates between samples of gabbro and peridotite collected during Faranaut Dive 7 (Fig. F2). Our target was a smooth, sedimented slope above an outcrop of gabbro. After a 1.75-hr survey, we confirmed that our location was on a shallow, eastward-dipping slope of smooth sediment and that our depth (estimated from drill string length) was consistent with our desired drilling location.
Hole 1271A was initiated at 0545 hr on 3 June 2003 through 2.5 m of sediment. The first core required 4.75 hr to advance to 12.9 meters below seafloor (mbsf). Cores 2R and 3R (Table T1), however, were cored in a total of 50 min. After recovering Core 5R, hole conditions began to deteriorate and the driller noted the hole had begun to fill between connections. After only advancing 2.0 m on Core 6R we decided to abandon any further attempt to core deeper. The bit was pulled clear of the seafloor at 0244 hr, ending Hole 1271A. The average rate of penetration for the hole was 4.5 m/hr.
Since the shallow sedimented slope where we located Hole 1271A seemed to be our most promising drilling target (based on Faranaut Dive 7 videotapes), we decided to move southwest along the same depth contour to position Hole 1271B. Hole 1271B was spudded ~90 m from Hole 1271A.
At 0730 hr on 4 June we began coring Hole 1271B. Cores 1R to 3R were cored without incident, but while drilling Core 4R the driller suspected that a piece of rock had lodged in the bit throat or the bottom of the core barrel. High circulating pressure eventually cleared the obstruction. After cutting Core 4R the driller had difficulty getting the pipe back to the bottom of the hole through several meters of hard fill.
Coring continued through Core 20R (to 103.8 mbsf) with low recovery but little or no indication of poor hole conditions. Having achieved a depth >100 mbsf, we chose to curtail coring operations in order to collect wireline logging data. Coring was completed by 1345 hr on 6 June, and the bit was released in the bottom of Hole 1271B. As the driller attempted to pull the bottom of the pipe to logging depth (nominally 30 mbsf), the hole appeared to collapse around the pipe, shutting off circulation. With some difficulty, the pipe was freed and circulation regained.
After securing the pipe at 30 mbsf, the first logging tool was set up and run into the hole. However, the logging tool would not advance more than 6 m past the end of the pipe, indicating catastrophic hole collapse. Our logging attempt was regretfully abandoned. After the pipe was raised to 2300 meters below sea level (mbsl), we recovered the positioning beacons and began the short transit (~3.7 nmi) to our next site. Operations at Site 1271 ended at 0745 hr on 7 June. The average rate of penetration for the hole was 4.0 m/hr.
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-106