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doi:10.2204/iodp.proc.310.109.2007 Tiarei marginal sites: Sites M0008, M0010–M0014, and M00221Expedition 310 Scientists2OperationsHole M0008AAt 1700 h on 16 October 2005, the DP Hunter departed Site M0007 and headed for Site M0008, located on transect TAH-02A off the northeast coast of Tahiti. Shortly after arrival at 2400 h, a seabed survey using the downpipe camera was conducted. At 0400 h on 17 October, coring operations began in Hole M0008A. This hole was to serve as a reference hole for the other holes on the transect. However, recovered material consisted of river deposits of unconsolidated basalt gravels and pebbles mixed with volcaniclastic sediments. As a result, recovery was poor throughout (24.5%). Total depth (TD) was reached at 40.2 meters below seafloor (mbsf), and operations ended in Hole M0008A at 1720 h on 17 October. Before continuing operations at Tiarei marginal sites, operations were conducted at Site M0009 (see the “Tiarei outer ridge” chapter). Hole M0010AThe DP Hunter was positioned above Hole M0010A by 1400 h on 22 October 2005, ~140 m east-southeast of proposed Site TAH-02A 4, in 89.53 m water depth. Seacore's drilling and reentry template (DART) was drilled into the seabed, and coring operations began at 1635 h. Coring continued until 1000 h on 23 October, to a TD of 34.6 mbsf. During the coring period, an HQ string trip was made to clear a continually blocking bit. Hole M0011AHole M0011A was located ~140 m east of proposed Site TAH-02A 4, in 101.34 m water depth. After running the American Petroleum Institute (API) pipe, drilling the DART into the seabed, and running the HQ pipe, coring operations began at 1330 h on 23 October 2005. Coring commenced in very soft silts with poor recovery, but recovery improved when the river deposits gave way to a carbonate framework. At 0030 h on 24 October, coring operations were completed in Hole M0011A at a depth of 17.65 mbsf. Hole M0012AHole M0012A was the first of three holes to be located within the new Environmental Protection and Safety Panel (EPSP)–approved zone southeast of proposed Site TAH-02A 4. Before the DART was lowered onto the seabed, a downpipe camera survey was run; it showed a live coral colony at the first location. The ship was repositioned 25 m downslope in 77.05 m water depth, and the DART was drilled in. Coring operations began in Hole M0012A at 0900 h on 24 October 2005. Recovery was generally poor, although it improved in the more competent material at the base of the hole. Coring was completed at 2040 h on 24 October at a TD of 34.1 mbsf. Hole M0013AHole M0013A was located 30 m downslope from Hole M0012A, in 90.95 m water depth. The DP Hunter was in position to start drilling at 2300 h on 24 October 2005. After the API pipe and DART were lowered to the seabed, a downpipe camera survey was conducted. Coring operations began at 0100 h on 25 October. At 0415 h, coring was abandoned because of the lack of suitable coral material. TD was 11.7 mbsf. Hole M0014AHole M0014A was spudded ~70 m north-northwest of Hole M0013A, in 99.25 m water depth. Coring operations began at 0610 h on 25 October 2005 and were completed at 1615 h at a TD of 15.43 mbsf. The HQ string, API pipe, and DART were lifted onto deck and secured for the transit to previous Site M0007 at the south end of the island. Poor weather was forecast for north of the island, and so the decision was made to revisit promising sites in the south. The transit commenced at 1930 h, and Site M0007 was reached at 0200 h on 26 October. Operations recommenced at Site M0007 (see the “Maraa western transect” chapter), followed by operations at Sites M0015–M0018 (see the “Maraa eastern transect” chapter). After operations in the Maraa area were completed, operations were conducted at Sites M0019 and M0020 (see the “Faaa” chapter). On returning to the Tiarei area, operations were conducted at new Site M0021 and previous Site M0009 (see the “Tiarei outer ridge” chapter). Operations at new Site M0022 followed. Hole M0022AThe DP Hunter was positioned above Hole M0022A, ~175 m north-northwest of proposed Site TAH-02A 4, in 115 m water depth. After checking the depth with the tautwire, the DART was drilled in and coring commenced at 1750 h on 9 November 2005. It was hoped that the hole would penetrate a Pleistocene gully that may have been subsequently accreted by last deglacial corals. Basalt gravel and volcaniclastic sand of Pleistocene affinity were recovered from a shallow depth, so Hole M0022A was abandoned after 8.8 m penetration at 2310 h on 9 November. By midnight, preparations were being made to trip the API pipe and DART. At 0000 h on 10 November, the DART was raised to the moonpool after abandoning coring in Hole M0022A, and the vessel was moved to previous Site M0023 (see the “Tiarei inner ridge” chapter). |
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