OPERATIONS

The 209-nmi transit to Site 1242 (proposed Site COC-4A) required 18 hr at an average speed of 11.6 kt. The 3.5-kHz precision depth recorder (PDR) was used as a final check of site characteristics by comparison to precruise survey data. The vessel was positioning on the coordinates of Site COC-4A by 0230 hr on 26 May 2002.

Hole 1242A

After the drill string was deployed and the bit placed at 1372 meters below rig floor (mbrf), Hole 1242A was initiated with the advanced piston corer (APC) at 0710 hr on 26 May. The seafloor depth estimated by the amount of recovery of the first core was 1374.8 mbrf. This was 5.6 m shallower than the corrected PDR depth of 1380.4 mbrf. Piston coring penetrated to 176.0 mbsf before it was necessary to switch to the extended core barrel (XCB). Piston coring in the hole was terminated when the Core 19H did not achieve a full stroke of the corer. No core barrels were drilled over.

The APC cores were oriented starting with Core 3H. The only operational tensor orientation tool was removed to download data during coring of Core 12H, and no orientation data are available for that core. Downhole temperature measurements were collected with the APC temperature (APCT) tool (Table T1). The nonmagnetic core barrel was deployed on even-numbered cores up to and including Core 18H. The APC cored 176.0 m and recovered 184.09 m.

XCB coring deepened the hole from 176.0 to 250.8 mbsf (the maximum allowed depth). The XCB cored 74.8 m and recovered 76.0 m. The APC/XCB cored interval was 250.8 m (recovery = 104%). The active heave compensator was online during XCB coring.

The bit was pulled free of the seafloor at 0415 hr on 27 May.

Hole 1242B

The vessel was offset 20 m west of Hole 1242A. Prior to coring operations in Hole 1242B, a bottom water temperature measurement was obtained with the APCT tool with the bit positioned just above the seafloor. To obtain a stratigraphic overlap with the first hole, the bit was placed at 1370 mbrf and Hole 1242B was initiated with the APC at 0548 hr. The seafloor depth derived from the recovery of the first core was 1376.6 mbrf. Piston coring combined with two 2-m drilled intervals (88.4-89.4 and 98.9-103.4 mbsf) deepened the hole to 169.9 mbsf. The temperature measurements indicate a high thermal gradient of ~20°C/100 m. Cores 4H through 17H were oriented. The nonmagnetic core barrel was deployed on odd-numbered cores up to and including Core 17H. The piston cored interval was 169.9 m with 171.96 m recovered.

Nine XCB cores deepened the hole from 169.9 to 256.0 mbsf. The XCB cored 86.1 m and recovered 87.3 m. The total cored APC/XCB interval was 250.5 m with an average recovery of 104%.

The bit was pulled free of the seafloor at 2315 hr on 27 May.

Hole 1242C

The vessel was offset 20 m west of Hole 1242B. Hole 1242C was initiated with the APC at 0030 hr on 28 May. The bit was positioned at a depth of 1370 mbrf (same depth as for Hole 1242B). The seafloor depth calculated from the recovery of the mudline core was 1374.5 mbrf. Piston coring combined with drilling deepened the hole to 166.5 mbsf. Two intervals (24.0-27.5 and 46.5-48.5 mbsf) were drilled to maintain the proper overlap with the cores from the previous two holes. Cores 3H through 14H were oriented. The nonmagnetic core barrel was deployed on even-numbered cores. No core barrels were drilled over. The cored interval was 166.5 m with 171.0 m recovered (recovery = 103%).

The bit was pulled free of the seafloor at 1225 hr on 28 May.

Hole 1242D

The vessel was offset 20 m west of Hole 1242C. Hole 1242D was initiated with the APC at 1305 hr on 28 May and drilled to 13.5 mbsf, where piston coring was started. Piston coring combined with drilling deepened the hole to 91.5 mbsf. Two intervals (0-13.5 and 51.5-53.5 mbsf) were drilled to maintain the proper overlap with the cores from the previous three holes. All cores were oriented. The nonmagnetic core barrel was deployed on odd-numbered cores. No core barrels were drilled over. The cored interval was 76.0 m with 80.2 m recovered (recovery = 106%).

The vessel was secured for transit and departed for the Balboa pilot station at 2230 hr on 28 May.

NEXT