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doi:10.2204/iodp.proc.310.106.2007 Maraa eastern transect: Sites M0015–M00181Expedition 310 Scientists2OperationsHole M0015AAfter completing Hole M0007C, ~300 m to the northwest, the DP Hunter moved to Site M0015 in 72.15 m of water. After a short bathymetry traverse to locate a site for Hole M0015A, drilling operations began at 0030 h on 27 October 2005 and continued until 0325 h on 28 October. Total depth (TD) was 42.28 meters below seafloor (mbsf). There was generally good core recovery, usually with <1 m core runs between bit blocking, and 72.71% average recovery for the hole. Prior to logging, Hole M0015A was reamed and flushed for 1 h, after which the core barrel was removed and the drill string rerun with a casing shoe. Logging commenced at 0630 h on 28 October. Initially, the casing depth was set at 7 mbsf, but the logging tools would not pass downhole beyond 20 mbsf, so they were removed. The casing was run to the base of the hole and then pulled back to 20 mbsf. Logging was then possible in the bottom part of the borehole, but one tool was stuck for a while and had to be eased free with the downhole hammer. Thereafter, logging continued successfully; the casing was pulled back to 7 mbsf, and the remainder of the hole was logged, with overlap. Logging operations in Hole M0015A were completed by 1930 h on 28 October. The string was then tripped to deck, and Seacore's drilling and reentry template (DART) was lifted off the seabed. Hole M0016AAfter moving to new Site M0016, a tautwire bathymetry traverse was conducted to locate a site for Hole M0016A. By 2400 h on 28 October 2005, the DP Hunter was positioned above Hole M0016A in 80 m water depth. Shortly after midnight on 29 October, coring operations began. Throughout the day, coring continued with fairly poor recovery, and drilling indicated that the formation had many cavities. Coring in Hole M0016A was terminated at 0620 h on 30 October at a TD of 38.31 mbsf. This was because of difficulty in overcoming bit blocking, and, after a string trip to clean the whole core barrel system, the HQ inner barrel could not reenter the outer pipe because of the string bending. It is most likely that the DART had moved on the seabed, possibly through subsidence. Hole M0016BHole M0016B was located 5 m east of Hole M0016A. Initially, the noncoring insert bit was used to drill down to 17 mbsf, and then coring continued with variable but generally good core recovery. Coring operations ended at 0230 h on 31 October 2005 at a TD of 44.62 mbsf. Site M0006After moving to previous Site M0006, a tautwire site survey was conducted along a short transect. This survey was abandoned after the DART touched down on the seabed unexpectedly, indicating that the bathymetry for this area was not accurate. After running the downpipe camera to check for stinger damage and lifting the DART higher from the seabed, a new tautwire survey was conducted 10 m east of the previous transect. A suitable site was found, but when the DART was lowered it touched the seabed 2 m deeper than indicated by the tautwire. The topography of the seafloor was suspected to be very uneven at this survey location, so a new survey transect was initiated 10 m to the east. During this survey, the DART unexpectedly touched seabed again. The seabed depth at Site M0006 appeared to change rapidly, and the changes were not evident on the bathymetry data. Therefore, the search for a new site was abandoned, the DART was lifted into the moonpool, and the DP Hunter returned to previous Site M0015. Hole M0015BThe DP Hunter moved back to previous Site M0015 to start new Hole M0015B in 71.53 m water depth. Coring operations began at 1330 h on 31 October 2005 and were completed by 1730 h on 1 November at a TD of 40.12 mbsf. Because very short core runs were being achieved in the lower part of the hole and most liners were being crushed, the last four or five runs were made using the split chromed steel liners commonly used elsewhere in this type of coring. The immediate result was longer core runs before jamming, better core recovery, and improved preservation of delicate structures. Some horizons that would previously have been crushed were kept intact or in their correct cored position. Hole M0017AHole M0017A was located ~60 m north of Hole M0015B in 56.5 m water depth. Before touching down with the DART, a seabed camera survey was run to check for living corals. None were observed, and coring operations began at 2300 h on 1 November 2005. A faster penetration rate was achieved because of the use of steel split liners, which gave the drillers a much more sensitive indicator of bit blocking. As a consequence, they were able to detect bit blocking much more quickly and were sometimes able to avoid it. This meant that core runs were longer and the number of wireline trips was reduced. Core recovery also improved. No problems were encountered with the subsequent curation or science through the use of steel split liners. Coring was completed by 1600 h on 2 November at a TD of 40.56 mbsf. Prior to logging Hole M0017A, the hole was flushed. There was some difficulty with a stuck HQ pipe while trying to trip the drill string, which could be rotated but not lifted. The string eventually came free. A casing shoe was fitted for the logging operation. Logging commenced in Hole M0017A at 2130 h on 2 November and was completed by 0350 h on 3 November. Resistivity, acoustic imaging, optical imaging, hydrochemical, caliper, and sonic tools were run. Starting depth of the tools varied because of tools catching in cavities (between 31.55 and 23.23 mbsf), and the depth of the casing pipe was 13.35 mbsf. The core barrel fishing cable was used on one occasion to pull the sonic tool, which was stuck just below the casing, up to the surface. This process damaged a portion of the logging winch cable, which was cut at ~85 m. Reheading of the winch cable was completed well before the next logging operation. Hole M0018AA short echo sounder survey (30 m × 20 m grid) was conducted ~120 m south-southeast of proposed Site TAH-03A 1 to locate a suitable site for Hole M0018A. At 0915 h on 3 November 2005, the DART was lowered at the chosen site and touched the seabed 14 m deeper than suggested by the echo sounder survey. The specific site was resurveyed using the lead-line, and a new site was chosen nearby. The DART was unable to be drilled in at this site at first (a solid carbonate crust was evident on the camera survey) but was successfully drilled in on the second attempt (after the crust was broken by the stinger?). At 1640 h on 3 November, coring operations began in Hole M0018A, and they continued until 1200 h on 4 November. TD of the hole was 40.05 mbsf, with a total recovery of 61.50%. The nature and quality of the material collected indicated that most of the coreable material was being collected. A camera survey was conducted after withdrawing the drilling equipment from the hole. No undue disturbance was observed, although there was a significant mound where the DART was situated with a slight “tail” of what appeared to be cuttings coming from it and going down the presumed slope. Prior to departing the Maraa area, the tautwire was respooled and the DART was lifted onto the deck of the DP Hunter and secured. Once on deck, the stinger below the DART was found to be missing, and a new stinger was fitted. The vessel departed the Maraa area at 1750 h on 4 November and arrived at the Faaa area at 2030 h. |
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