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doi:10.2204/iodp.proc.325.106.2011

Hole M0052A

Operations

Transit to transect NOG-01B and waiting on weather

The Greatship Maya departed transect RIB-02A Site 3 (Hole M0051A) at 1645 h on 23 March 2010 and arrived at transect NOG-01B at 0910 h on 24 March.

Site 6, Hole M0052A

After going onto dynamic positioning at 0910 h, the vessel moved slowly onto station at Site 6 (Hole M0052A), completing the maneuver at 1120 h. Following an assessment of weather conditions at 1145 h, the vessel moved 500 m seaward of M0052A to wait on weather in deeper water. Operations continued to wait on weather on 25 March.

At 0655 h on 26 March the supply boat Acheron arrived alongside. Because of high winds and sea swell, it was not safe to conduct a boat-to-boat transfer of equipment. At 0745 h both vessels departed NOG-01B Site 6 to transit to calmer waters inside Flora Passage, arriving at 1100 h. Following a successful transfer, the Greatship Maya departed Flora Passage at 1120 h and arrived back at transect NOG-01B Site 6 at 1645 h, where it continued to wait on weather. At 1900 h permission was given for coring operations to start, and the seabed transponder was deployed at 1930 h. American Petroleum Institute (API) pipe was run between 2045 h and 2250 h, after which a downpipe camera survey was conducted. At 2355 h, the first extended nose corer run commenced (Table T1).

The run was halted after 1.4 m because of a very hard lithology, and the core was recovered. However, on recovery the liner was found to be crushed and the bit damaged. During recovery the API drill string came out of the hole because of vessel heave, and so Hole M0052A was terminated at 1.4 meters below seafloor (mbsf).

Sedimentology and biological assemblages

Hole M0052A consists of one lithostratigraphic unit.

Unit 1: Sections 325-M0052A-1X-1 to 1X-2, 41 cm: muddy Halimeda sand

Unit 1, spanning Sections 325-M0052A-1X-1, 0 cm, to 1X-2, 41 cm, consists of unconsolidated muddy lime sand with abundant Halimeda segments (Fig. F2). Bioclasts of mollusks, corals, and larger foraminifera are common. Halimeda segments are most abundant in interval 325-M0052A-1X-1, 0–31 cm. Well-preserved specimens of Amphistegina and Alveolinella are common in muddy very coarse sand from interval 325-M0052A-1X-2, 30–35 cm.

The corals are fragments of Seriatopora, Goniopora, Montipora, Porites, and Agariciidae (Fig. F3).

Physical properties

A total of 1.30 m of core was recovered from Hole M0052A, which was drilled to 1.40 m drilling depth below seafloor (DSF-A) (92.86% recovery). This equated to one core comprising three recovered sections. Physical property data from this hole are summarized in Table T2.

Density and porosity

In Hole M0052A, whole-core bulk density multisensor core logger (MSCL) measurements taken offshore on Core 325-M0052A-2X range from 1.85 to 2.23 g/cm³ (Fig. F4). Overall, bulk density values are relatively stable downcore. Two discrete samples obtained from this hole during the Onshore Science Party showed moderately high porosities (47% and 42%), grain densities of 2.78 g/cm³ for both samples, and bulk densities of 1.95 and 2.04 g/cm³, respectively (Fig. F5).

P-wave velocity

There are no P-wave velocity data for Hole M0052A from either the MSCL or discrete measurements.

Magnetic susceptibility

In Hole M0052A, magnetic susceptibility values obtained by offshore measurement on the MSCL range from 3.16 × 10^–5 to 6.06 × 10^–5 SI (Fig. F4). Values downcore are relatively consistent.

Electrical resistivity

Whole-core, noncontact resistivity measurements on Hole M0052A cores range from 1.12 to 1.40 Ωm (Fig. F4). Similar to the other measurements, there is no evident downhole trend.

Digital line scans and color reflectance

Cores from Hole M0052A were digitally scanned and, where appropriate, measured for color reflectance. Only 1.3 m was measured for this borehole. Color reflectance in Hole M0052A varies between 44.06% and 66.39% (Fig. F6). The values obtained show higher dispersion in areas of muddy sand with Halimeda sp. A zone at 0.7 m CSF-A shows more consistent discrete measurements. These coincide with submassive corals with a relatively homogeneous coloration. The bottommost 10 cm of the measured section corresponds to coarse lime sand, showing higher reflectance values. The values observed for a* are, in general, negative, indicating a dominance of green coloration rather than red. The values for b* are always positive, indicating the presence of the color yellow.

Paleomagnetism

Measurements of low-field and mass-specific magnetic susceptibility (χ) were performed on samples taken from the working half of the recovered core. Positive low susceptibilities occur throughout the core, ranging from 0.03 × 10^–8 to 1.13 × 10^–8 m³/kg. The arithmetic mean of the magnetic susceptibility of the core is 0.58 × 10^–8 m³/kg, indicating the presence of paramagnetic and/or ferromagnetic minerals.

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