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Without picking up the transponders from Site C0011, the D/V Chikyu moved to Site C0012 after the coring assembly was retrieved on board at 1930 h on 24 December 2010. Transit in dynamic positioning (DP) mode over a distance of 5 nmi at 5 kt finished at 2030 h. From 2200 h, transponders were dropped, set at four different locations, and calibrated. The location was set at 0815 h on 25 December upon completion of DP calibration.

The hydraulic piston coring system (HPCS)/extended punch coring system (EPCS)/extended shoe coring system (ESCS) coring assembly was made up and run into Hole C0012C to 3528 m drilling depth below rig floor (DRF). After tagging the seafloor at 3539.0 m DRF at 1600 h, HPCS coring began at 1630 h (Table T1). After coring the eleventh core, a hydraulic power swivel motor malfunction caused a delay from 1300 to 1500 h on 26 December. After coring the fifteenth core at 2130 h, the core wire parted when the sinker bar assembly was overloaded. Hence, the sinker bar fell to the bottom of the hole and the damaged core line was cut at ~100 m. The hole was abandoned after spotting kill mud.

The Chikyu moved to Hole C0012D while waiting on weather from 0600 to 0800 h on 27 December. Test coring was done at the seafloor at 1000 h, washed down to 20 mbsf at 1330 h, and then drilled to 118 mbsf. HPCS coring began at 1745 h and continued to 180 mbsf, where strong wind caused ship offset by ~16 m and stopped coring in this hole. We pulled out of Hole C0012D to above the seafloor at 1900 h and waited on weather.

The Chikyu moved to Hole C0012E, and the decision was made to drill down and core the sediment/basement interface with the ESCS to make the best use of a short good weather window. Hole C0012E was spudded at 1030 h on 29 December, washed down to 28.5 mbsf, and then drilled to 500 mbsf, which was reached at 1045 h on 30 December.

After preparation for coring, the first ESCS core was taken at 1415 h and coring continued to 528.5 mbsf. Coring was stopped at 2245 h because of deterioration of the weather, and the bottom-hole assembly (BHA) was pulled out of hole.

Making up the RCB coring assembly for Hole C0012F started at 0230 h on 1 January 2011 while waiting on weather. The BHA was run to 3530 m DRF, spudded at 1315 h, and drilled to 520 mbsf. RCB coring began at 1500 h on 2 January but ended at 1930 h after the second core was taken because of abnormal pressure while coring. After cleaning the outer core barrel and the hole, the center bit assembly was set for a circulation test. The test was successful, but the center bit assembly could not be retrieved because the pull bar broke, which ended coring operations in Hole C0012F.

Pulling out of the hole took place between 0730 and 1615 h on 3 January. The RCB coring assembly for Hole C0012G was made with a roller cone bit after finding that more than half of the teeth on the polycrystalline diamond compact (PDC) drill bit used in Hole C0012F were worn out. Running pipe down started at 1815 h on 3 January, and Hole C0012G was spudded at 0900 h on 4 January. We drilled to 515 mbsf and began RCB coring with full advance at 1315 h on 5 January. Full advance coring continued to 591 mbsf with medium to poor recovery. We then switched to a shorter advance to improve core recovery to 630.5 mbsf, except for one full advance core (333-C0012G-11R). Coring in Hole C0012G ended at 1545 h on 7 January, and kill mud spotting and pulling out of the hole lasted until 0330 h on 8 January.

Coring operations were disturbed twice by short intervals of low-pressure weather. In addition to weather, two incidents forced us to pull out of the hole: a parted core wire and a parted center bit at the bottom. Core quality and recovery varied depending on the formation or lithology and also the corer and drill bit types.

Core recovery was excellent for the piston cores in Holes C0012C and C0012D, with average rates of 103.3% and 104%, respectively, which presents a marked improvement in quality from Expedition 322 RCB coring. In comparison to Site C0011, cores from Site C0012 had almost constant recovery without broken cores or becoming jammed. However, Cores 333-C0012D-8H to 13H (bottom of Hole C0012D) were affected by coring disturbance (flow-in and stretching). The ESCS was used in Hole C0012E to core only at the sediment/basement interface and yielded the best quality cores compared to three other attempts with the RCB. Core 333-C0012E-3X, especially, which penetrated through red calcareous claystone/pillow basalt, has quite long (>50 cm) coherent pieces in places. Interpillow glasses of pillow basalt are well preserved at the bottom part of the same core. Average recovery was 48.6%, ranging from 11.4% to 87.9%. Holes C0012F and C0012G used RCB coring but with different bits. RCB coring with a damaged PDC bit in Hole C0012F yielded two cores with an average recovery of 48.2%. Hole C0012G was cored deep into the basaltic basement with a roller cone bit. Core recovery was 22.4% on average, varying between 9.6% and 45.8% for the full advance cores and between 4.1% and 73.2% for the half advance in the deeper part of the hole.