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doi:10.2204/iodp.proc.325.105.2011

Hole M0051A

Operations

Site 3, Hole M0051A

The seabed transponder was deployed at 2315 h on 22 March 2010 with the Greatship Maya coming onto station at Site 3 (Hole M0051A) at 2320 h. API pipe started being run at 2330 h. A downpipe camera survey was conducted between 2255 and 0030 h (23 March). The first standard rotary corer core was on deck at 0105 h (Table T1). However, the second core could not be recovered because of a hydraulic failure of the elevator and mud valve at 0230 h, effectively terminating the hole at 2.5 mbsf. At 0800 h, having recovered the seabed transponder, the vessel was moved into deeper water for safety while repairs on the hydraulics continued. However, by 0900 h, the decision was taken to trip the API pipe using manual elevators. The core barrel was recovered from the bottom-hole assembly once in the slips, between 1315 and 1345 h, but minimal core remained.

Another prerequisite of the Environmental Management Plan was for a Great Barrier Reef Marine Park Authority Environmental Site Supervisor (ESS) to be onboard while Sites 1 and 2 at Ribbon Reef 3 were drilled. At 1300 h on 23 March, the ESS came alongside in the Reef Charters vessel Hurricane. However, after numerous attempts at a boat-to-boat transfer, it was decided that the sea swell and winds were too high to enable any safe transfer. The ESS and Hurricane returned to Cooktown, Australia, at 1400 h, and the Greatship Maya began waiting on weather, as conditions prohibited starting a new hole. At 1530 h, following operational discussions regarding the limited drilling options at the Ribbon Reef sites with no ESS available, the seabed transponder was recovered and the drill floor and moonpool secured for transit. The Greatship Maya came off dynamic positioning at 1645 h and departed for Noggin Pass.

Sedimentology and biological assemblages

Hole M0051A contains a single lithostratigraphic unit.

Unit 1: Sections 325-M0051A-1R-1 through 2R-CC: coralgal boundstone

The single Unit 1, spanning Sections 325-M0051A-1R-1 and 2R-CC, consists of coralgal boundstone fragments with algal nodules (rhodoliths) (Fig. F25). Thick lumpy crusts of coralline algae make up the nodules and cover coral skeletons, intergrowing with encrusting foraminifera (Homotrema). All components are slightly bioeroded, and a brownish stain covers surfaces of the coralline algal crusts. No samples were examined for larger foraminifera in this hole.

The only corals are one altered piece of Pocillopora(?) and a few unidentifiable fragments.

Physical properties

Hole M0051A was cored to a total depth of 2.50 m DSF-A, of which 0.15 m was successfully recovered (6.0% recovery). Because of the very small amount of core recovered, no physical property measurements were taken from Hole M0051A material with the exception of one color reflectance measurement, which was 58.03% L* (Table T1).

Paleomagnetism

Measurements of low-field and mass-specific magnetic susceptibility (χ) were performed on one sample taken from the working half of the recovered core. The sample recorded a positive susceptibility of 0.34 × 10^–8 m³/kg at a depth of 0.04 mbsf. This positive susceptibility value indicates the presence of paramagnetic and/or ferromagnetic minerals.

Chronology

This hole has one calibrated radiocarbon age of 10 cal y BP from Core 325-M0051A-2R (Fig. F26). There are no cores beneath this 10 cal y BP section, indicating that this hole only contains material from the last deglaciation.

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