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doi:10.2204/iodp.proc.310.108.2007 Tiarei outer ridge: Sites M0009, M0021, and M0024–M00261Expedition 310 Scientists2OperationsHoles M0009A and M0009BFollowing coring in Hole M0008A, and in light of the results obtained, an assessment was made concerning where to drill next. It was decided to attempt to drill the pinnacle at proposed Site TAH-02A 4 on seismic Profile SISM 079 (see Fig. F5 in the “Site surveys related to Expedition 310” chapter). Acknowledging that the feature imaged on the seismic line might be the result of side-swipe and was possibly located off the seismic line, a localized search was made for a suitable drilling location using the ship’s echo sounder and tautwire to detect a shallower than expected water depth. No suitable position was located, and at 2100 h on 17 October 2005, the vessel was positioned above a flat terrace (Hole M0009A) nearby and drilling operations commenced and continued until 1915 h on 18 October. Recovery was moderate to poor (43.1%) to a total depth (TD) of 23.04 mbsf. However, promising coral material was recovered, and it was decided to attempt to recover the same section in a new hole nearby. By 2000 h, the HQ pipe had been recovered and Seacore’s drilling and reentry template (DART) lifted off the seabed, and by 2015 h, the vessel was positioned above Hole M0009B, ~5 m downslope from Hole M0009A. Coring operations commenced and continued until 1200 h on 19 October, with an improved recovery of 66.26%. Prior to logging Hole M0009B, the hole was reamed. Logging began at 1530 h on 19 October, with the resistivity and hydrochemical tools run open hole over the interval 6–21 mbsf. A hole blockage near the last deglacial/older Pleistocene sequence (lithologic Unit I/II) boundary, which resisted attempts to clear with the chisel tool, prevented the tools from being run below ~21 mbsf. Optical image logs were collected between 6 and 18.1 mbsf and acoustic image logs between 6 and 13.8 mbsf. Logging of Hole M0009B was concluded by 2320 h on 19 October. Hole M0009CJust before 0000 h on 20 October 2005, the DP Hunter moved to Hole M0009C, ~9 m west-northwest of Hole M0009B in 99.85 m water depth. Coring commenced and continued until 1935 h that day, reaching a TD of 25.66 mbsf. Coring in Hole M0009C proved very difficult, with many bit blockages and crushed liners, which were due to pieces of the formation breaking off and entering the core barrel without being properly cored. The lattice drilled was not strong enough to core, and in many cases it had to be crushed for progress to be made. Recovery improved toward the base of the hole, and total core recovery was 51.86%. At 1935 h, the hole was completed and preparations made to move over to Hole M0009D. Hole M0009DThe DP Hunter was positioned above Hole M0009D, 5.5 m east of Hole M0009B in 103.18 m water depth, and coring began at 2210 h on 20 October 2005. Coring in Hole M0009D continued until 2230 h on 21 October, to a TD of 44.59 mbsf. Progress was steady, but core runs were short and bit blocking common. After TD was reached, preparations were made to log the hole. Prior to logging the hole, the hole was reamed and flushed for 30 min. The HQ string was pulled and set with a casing shoe at 19 mbsf to run the logging tools through the open-hole section. Logging commenced at 2230 h on 21 October in very wet and windy conditions. This, combined with very poor hole conditions, led to a difficult logging period. Nevertheless, good logs were obtained in sections of open hole where it was possible to log. A hole blockage prevented the resistivity tool from reaching the base of the hole, and the chisel tool was used to clear the blockage. The resistivity, spectral gamma ray, and acoustic tools were run. However, large, meter-scale cavities in the formation created sticking points for some of the tools; thus, only some of the open bottom-hole interval was logged. The first optical image tool run was affected by power failures on the drill rig, possibly caused by heavy rainfall. Logging was temporarily interrupted while the cause of the power failures was investigated. After these runs, the casing was pulled to 5 mbsf. The top-hole section was logged with the resistivity and optical image tools, with cavities causing problems for the optical tool. While logging up, the optical image tool became stuck many times and needed to be pulled through obstructions by hand. Logging operations were completed by 1000 h on 22 October, and preparations were made to move to Hole M0010A. After logging in Hole M0009D, Sites M0010–M0014 were cored (see the “Tiarei marginal sites” chapter). Then there was a revisit to Hole M0007 (see the “Maraa western transect” chapter), followed by coring at new Sites M0015–M0018 (see the “Maraa eastern transect” chapter). After this, two sites were cored at Faaa (Sites M0019 and M0020) (see the “Faaa” chapter) before a return to the Tiarei outer ridge area to core in Hole M0021A. Hole M0021AAt Site M0021, an echo sounder survey (five profiles) was conducted over suspected drowned reefs near to the foreslope imaged on the bathymetry. Water depth was confirmed at two locations using the tautwire. After a seabed camera survey, the DART was drilled in at one of these locations, ~115 m southeast of proposed Site TAH-02A 5 in 82 m water depth. Coring operations began in Hole M0021A at 2200 h on 7 November 2005 and continued until 1640 h on 8 November. TD was 34.23 mbsf, and total recovery was 74.87%. Good core recovery confirmed that the submerged pinnacle was a drowned reef. Hole M0009EAfter coring in Hole M0021A was completed, the HQ pipe was lifted and the DART raised to 45 meters below sea level (mbsl). The vessel moved 90 m northwest to previous Site M0009, where a site for Hole M0009E was chosen in a water depth of 93 m. The DART was lowered and drilled in, and coring operations in Hole M0009E began at 2030 h on 8 November. Coring was completed at 0550 h on 9 November 2005 at a TD of 20.61 mbsf and with a total recovery of 72.73%. Prior to logging, the hole was flushed and the HQ pipe pulled and rerun with a casing shoe. From 0715 h on 9 November, Hole M0009E was logged between ~2 and 15 mbsf. The chisel tool was deployed once to clear a blockage at 6 mbsf. After logging was completed at 1440 h, the HQ pipe was tripped and the DART raised into midwater. After logging in Hole M0009E, Hole M0022A was cored (see the “Tiarei marginal sites” chapter), followed by operations at Site M0023 (see the “Tiarei inner ridge” chapter), before operations at Site M0024. Hole M0024AAfter clearing away the logging tools and lifting the DART back into the moonpool, the vessel moved to conduct an echo sounder survey in an area over a drowned reef pinnacle ~100 m east of proposed Site TAH-02A 5. From 0515 h on 12 November 2005, 14 echo sounder traverses were made (~50 m long), from which a site for Hole M0024A was chosen in 90 m water depth. Coring operations in Hole M0024A began at 1010 h on 12 November and finished at 0400 h on 13 November at a TD of 32.3 mbsf. Total recovery was 83.74%. Hole M0025AA site for Hole M0025A was chosen from the echo sounder survey conducted on 12 November 2005, 25 m north-northwest of Hole M0024A. The DART touched down in a water depth of 105.4 m, and coring began at 0530 h on 13 November and finished at 1645 h that day at a TD of 20.93 mbsf. Total recovery was 74.23%. Hole M0026AFollowing another echo sounder survey over a 50 m × 35 m area ~180 m east of proposed Site TAH-02A 4 over a drowned reef pinnacle, a site for Hole M0026A was chosen. It proved difficult to interpret the results of the echo sounder survey (three strong seabed echoes and widely differing water depths over a few meters), and it took some time before identifying a suitable site in 105 m water depth. Coring operations in Hole M0026A started at 0920 h on 14 November 2005 and were completed by 1105 h that day at a TD of 12.4 mbsf. Total recovery was 58.45%. Hole M0025BAfter lifting the DART in Hole M0026A, the DP Hunter moved to previous Site M0025 to core in Hole M0025B. After taking a tautwire depth of 95 m, the DART was lowered and coring began at 1215 h on 14 November. Coring finished at 0100 h on 15 November at a TD of 20.5 mbsf with a total recovery of 71.19%. Hole M0021BAfter raising the DART to 50 m above seabed, the vessel was moved back to Site M0021 to core in Hole M0021B (proposed Site TAH-02A 5). Once on position, the tautwire depth was taken as 80 m. The DART and drill pipe were lowered, and coring in Hole M0021B commenced at 0630 h on 15 November 2005 and continued until 2210 h that day. TD was 32.81 mbsf, and total recovery was 65.57%. Prior to logging, Hole M0021B was flushed before the HQ pipe was run back into the hole with a casing shoe. Logging in Hole M0021B commenced at 0030 h on 16 November and was competed by 0645 h that day. All tools were run to 15 mbsf. Once logging was completed, the DART was lifted onto deck and secured for the transit back to the Port of Papeete. The DP Hunter departed the last site at 0815 h on 16 November and arrived at the Port of Papeete at 1145 h. Demobilization of the vessel took place on 16 and 17 November. |
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