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doi:10.2204/iodp.proc.325.103.2011

Hole M0030A

Operations

Transit to transect HYD-01C

The Greatship Maya departed for IODP Hole M0030A on transect HYD-01C at 2100 h on 11 February 2010 after spending 53 h in port. For the first 16 h, transit speed was a maximum of 5 kt because of water coming up through the moonpool door and ingressing into the engine room via a faulty hatch. Once the hatch was repaired, the transit speed was slowly increased to 12 kt from 1300 h onward. There was also a problem with the vessel’s air conditioning system for 24 h after departing Townsville, Australia, which was rectified by the engineering crew onboard.

Site 5, Hole M0030A

The Greatship Maya arrived on station over Hole M0030A at 2315 h on 12 February 2010 (Table T1) and proceeded to begin tests on the dynamic positioning system. The initial spin test revealed an offset of 12 m, as the center of the vessel had not been correctly set to rotate around the drillstring in the moonpool. Corrections were made and further spin tests conducted until 0200 h on 13 February. The HiPap seabed transponder was deployed, and at 0223 h the bridge gave the go-ahead to commence coring operations. By 0520 h, the American Petroleum Institute (API) pipe had been run to 5 m above the seabed, and the downpipe camera was deployed for a precoring seabed survey to make sure the position was devoid of live coral. It was noted that there were very strong currents pushing the end of the API pipe.

At 0610 h, the camera became stuck on recovery when the cable wrapped around the camera frame inside the API pipe. By 0625 h, the camera was at the top of the string but again caught, so the cable was cut and the camera recovered. By 0700 h, API pipe was being run to tag the seabed, and the first core was on deck at 0945 h. Runs 1 and 2 were conducted using the standard rotary corer (ALN) barrel and Run 3 using the extended nose corer. However, during the extended nose corer run the shoe became blocked with loose carbonate sand, so the coring strategy was altered, pumping the ALN barrel back down with seawater and coring with seawater flushing. However, at 1345 h, the overshot wire became slack and entangled when deployed to recover the ALN barrel and had to be cut. By 1700 h, the wireline had been recovered, but the overshot had been left inside the API pipe, as the shackle had broken. This required tripping of the string to recover the barrel and overshot, thereby terminating the hole at 6 meters below seafloor (mbsf) with an average recovery of 4%. Recovery of the barrel and overshot was completed by 1730 h, and the chaser on the overshot was found to have jammed in the first API pipe. Repairs were conducted on the overshot chaser and the wireline between 1730 and 2005 h. It was decided to core the same location (Hole M0030B).

Sedimentology and biological assemblages

Hole M0030A had low recovery (4%) and is divided into two distinct lithostratigraphic units.

Unit 1: Section 325-M0030A-1R-CC: living coralline crusts

The uppermost Unit 1, consisting of the 6 cm recovered in Section 325-M0030A-1R-CC, is composed largely of recently live coralline algae “bindstone” (Fig. F2). There are no visible corals.

Unit 2: Section 325-M0030A-2R-CC: unconsolidated sediment

The lowermost Unit 2, consisting of the 18 cm of Section 325-M0030A-2R-CC, is composed of fine to coarse lime sand containing bioclasts of mollusks, echinoids, and abundant larger foraminifera, including well-preserved specimens of Cycloclypeus and Operculina. There are no visible corals.

Physical properties

Because of limited recovery (4%) from Hole M0030A (0.24 m total recovery from 6 m drilling depth below seafloor [DSF-A]), very few petrophysical measurements were taken (Table T2). This section summarizes the petrophysical data acquired both offshore and at the Onshore Science Party in Bremen.

Digital line scans and color reflectance

Two cores were measured from Hole M0030A using a digital line scan system with all data recorded at a resolution of 150 pixel/cm as both images and red-green-blue (RGB) values. Both cores were also scanned for color reflectance (Fig. F3). Color reflectance L* in Hole M0030A varies between 54.71% and 68.08%. The shallowest core measured (Section 325-M0030A-1R-1) is composed mainly of a coralline algae bindstone and has lower reflectance and higher a* and b* values than Section 325-M0030A-2X-1, which is composed of lime sand. Because of the low recovery in this hole, no obvious trends are observed with depth.

Paleomagnetism

Measurements of low-field and mass-specific magnetic susceptibility (χ) were performed on samples taken from the working half of the recovered core (Table T3). Low positive susceptibilities occur throughout the cores, ranging from 0.23 × 10^–8 to 1.72 × 10^–8 m³/kg. A negative value of –0.63 × 10^–8 m³/kg was recorded for the sample taken at 3.03 mbsf in Hole M0030B.

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