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doi:10.2204/iodp.proc.325.103.2011

Hole M0030B

Operations

Site 5, Hole M0030B

By 2015 h on 13 February 2010, API pipe was being run, and the seabed was tagged at 2215 h (Table T1). The first standard rotary corer (ALN) core was recovered at 2240 h. At 0030 h on 14 February, the vessel repositioned to compensate for the strong current, bringing the API pipe back to vertical. Two more ALN cores were run, but on recovering the third at 0100 h, the barrel stuck and the wireline winch cable snapped. This again required tripping the API pipe, so Hole M0030B was terminated at 9 mbsf, with an average core recovery of 6.1%. Between 0200 and 0250 h, operations were suspended while repairs to the roughneck jaw grips were undertaken, and by 0520 h the bottom-hole assembly was at the drill floor. The barrel remained stuck until flushing with water finally released it at 0545 h, when it was discovered that the ALN bit was split. The decision was made to transit slowly to Site 6, Hole M0031A, while repairs to the wireline winch were completed. The HiPap beacon was recovered, and the vessel departed for Site 6 at 0550 h.

Sedimentology and biological assemblages

Hole M0030B had low recovery (6%) and is divided into three distinct lithostratigraphic units.

Unit 1: interval 325-M0030B-1R-1, 0–8 cm: modern lime sand

The uppermost Unit 1, consisting of interval 325-M0030B-1R-1, 0–8 cm, is composed of fine to medium lime sand. There are no visible corals.

Unit 2: interval 325-M0030B-1R-1, 8–19 cm: modern lime pebbles

Unit 2, consisting of interval 325-M0030B-1R-1, 18–19 cm, is composed of lime granules and pebbles rich in larger foraminifera, including well-preserved specimens of Cycloclypeus, Elphidiidae, Operculina, and Sphaerogypsina. Coral fragments include Seriatopora and Porites.

Unit 3: Sections 325-M0030B-2R-1 through 3R-1: coralgal boundstone

The lowermost Unit 3, spanning Sections 325-M0030B-2R-1 through 3R-1, consists of fragments of massive corals co-occurring with coralline algae, fragmented larger foraminifera Cycloclypeus and Operculina, and mollusks and probably represents a coralgal boundstone facies.

The only large corals are massive Isopora (Fig. F4) with fragments of Porites, Seriatopora, Tubipora musica, and Stylasterinidae.

Physical properties

Similar to Hole M0030A, Hole M0030B has limited core recovery (three cores with a total of ~57 cm), and consequently there were very few petrophysical measurements taken (Table T2). Cores recovered reached a total depth of ~9.00 m DSF-A, and recovery was ~6%.

Density and porosity

Bulk density (multisensor core logger) measurements vary from 1.04 to 1.89 g/cm3 in cores from Hole M0030B (Fig. F5). The cores are characterized by underfilled sections of mostly unconsolidated pebbles. These core quality issues generally result in underestimation of bulk density values. Two density measurements were taken on discrete samples during the Onshore Science Party, giving values of 1.75 and 2.06 g/cm3 (Fig. F6).

P-wave velocity

P-wave velocity measurements taken on whole cores offshore range from 1607.04 to 1613.83 m/s (Fig. F5). These velocities are very close to that of seawater (~1500 m/s) and are indicative of sediments such as silts and silty clays. The single P-wave Logger for Discrete Samples measurement taken during the Onshore Science Party on a 20 mm plug from 3.12 m core depth below seafloor (CSF-A) had a mean resaturated velocity of 2952 m/s. This velocity indicates more lithified sediment. The discrepancy between the measurements is likely a function of core quality, with the discrete sample yielding the more reliable data.

Magnetic susceptibility

Values measured using the multisensor core logger offshore on whole cores range between –11.43 × 10–5 and 2.90 × 10–5 SI (Fig. F5). This range is indicative of a mixture of diamagnetic materials and very weakly magnetic materials.

Electrical resistivity

Electrical resistivity values range from 0.87 to 18.71 Ωm over this short interval (Fig. F5). Values are primarily affected by lithology, pore fluid, and salinity, as well as core liner saturation.

Digital line scans and color reflectance

All three cores from Hole M0030B were measured using a digital line scan system with all data recorded at a resolution of 150 pixel/cm as both images and RGB values. Cores were not appropriate for measurement with the color reflectance sensor.

Paleomagnetism

For a discussion of paleomagnetism results from Hole M0030B, see “Paleomagnetism” in “Hole M0030A.”