IODP Proceedings    Volume contents     Search


Hole M0047A


Site 12, Hole M0047A

The Greatship Maya came onto station over Hole M0047A at 1220 h on 11 March 2010 (Table T1). Retermination of the beacon transponder deployment wire delayed deployment until 1250 h. API pipe was run into just above the seabed, and a downpipe camera survey was conducted. The camera was back on deck at 1335 h, and the API tagged the seabed at 1410 h. The first standard rotary corer core was recovered at 1430 h, and coring continued until 0030 h on 12 March, when the hole was terminated at 33.2 mbsf with an average recovery of 11.4%.

The API pipe was tripped to just above the seabed by 0055 h, and a downpipe camera survey was conducted. The seabed transponder was recovered by 0145 h, and the vessel departed for Site 12, Hole M0048A, under dynamic positioning with 11 API pipes deployed.

Sedimentology and biological assemblages

Hole M0047A is divided into four lithostratigraphic units.

Unit 1: Sections 325-M0047A-2R-1 through 10R-CC: coralgal boundstone

The uppermost Unit 1, spanning Sections 325-M0047A-2R-1 through 10R-CC, consists of rock fragments that appear to be coralgal boundstone, but extensive drilling disturbance and low recovery make it difficult to determine the original lithologies. Unit 1 consists of massive and branching corals covered with coralline algae and minor microbialite crusts. The boundstone forming the uppermost part of Section 325-M0047A-2R-1 consists mainly of a framework of coralline algae and has brown and black staining (Fig. F75). Fragments of bioclastic packstone in Sections 325-M0047A-2R-CC and 3R-CC probably represent lithified internal sediment, consisting of loose fragments of coral, mollusks, bryozoans, larger foraminifera (e.g., well-preserved specimens of Amphistegina in interval 325-M0047A-3R-1, 10–15 cm), and Halimeda. Sections 325-M0047A-3R-1 through 4R-1 were probably originally richer in sediment than the rest of Unit 1.

Framework corals, mainly toward the base of Unit 1, are massive Isopora and Porites; submassive or branching Acropora (Fig. F76), Isopora, Seriatopora, Porites, and Pocilloporidae; and some ahermatypic corals (in upper parts of the interval). Diverse fragments include Acropora, Isopora, Seriatopora, Pocillopora, Stylophora, Porites, Goniopora, Tubipora musica, Stylasterina(?), Agariciidae, Faviidae, Pocilloporidae, and some highly altered Fungiidae or Mussidae.

Unit 2: Sections 325-M0047A-11R-1 through 11R-CC: lime sand

Unit 2, spanning Sections 325-M0047A-11R-1 through 11R-CC, consists of medium to coarse lime sands and pebbles rich in larger foraminifera and Halimeda, as well as fragments of mollusks, bryozoans, coral, and coralline algal crust. Abraded specimens of Calcarina, Baculogypsina, and Soritinae are abundant in very coarse sands from interval 325-M0047A-11R-1, 10–15 cm. Although there may be some degree of downhole contamination, the scarcity of fragments of overlying facies suggests that the lime sand represents the original uncontaminated deposit.

Most corals are branching Pocilloporidae (Seriatopora and Pocillopora), Acropora, and Tubipora musica, with submassive Isopora and Porites. Fragments include all of the same taxa.

Unit 3: Sections 325-M0047A-12R-1 through 13R-CC: unconsolidated sediment

Unit 3, spanning Sections 325-M0047A-12R-1 through 13R-CC, consists of unconsolidated lime granules and pebbles. Major components are coral, coralgal boundstone, and microbialite fragments, plus larger foraminifera and mollusks. Fragments of overlying boundstones indicate some downhole contamination.

The only larger corals are occasional encrusting Siderastreidae and Agariciidae (Leptoseris(?)). Common fragments are Seriatopora, Pocillopora, Acropora, Isopora, Leptoseris(?), Tubipora musica, and unidentified Pocilloporidae and Siderastreidae.

Unit 4: Sections 325-M0047A-14R-1 through 14R-CC: unconsolidated sediment rich in Halimeda

The lowermost Unit 4, spanning Sections 325-M0047A-14R-1 through 14R-CC, consists of unconsolidated lime granules and pebbles, with coarse sand containing abundant Halimeda segments. Other components are coral fragments, mollusks, and a few echinoid spines. Fragments of coralgal boundstone and microbialites are indicative of downhole contamination. Specimens of Gypsina are restricted to very coarse grained, gravelly sands from interval 325-M0047A-14R-CC, 0–5 cm.

The only large coral is an encrusting Agariciidae (probably Leptoseris) with fragments of Acropora, Isopora, Seriatopora, and Agariciidae.

Physical properties

Hole M0047A was drilled to 33.20 m DSF-A. A total of 3.79 m of core was recovered, equating to 11.42% recovery. Petrophysical data acquired from these cores are summarized in Table T2.

Density and porosity

Bulk density values from whole-core multisensor core logger measurements range from 1.15 to 2.33 g/cm3 (Fig. F77). Because of a combination of low core recovery and short cores, it is impossible to identify trends in the data set. Ten bulk density measurements were taken on discrete samples from the hole, with values ranging from 2.04 to 2.37 g/cm3 (Fig. F78). Porosity values for the same samples range from 24% to 43%, whereas the grain density of Hole M0047A samples falls within the 2.77 to 2.81 g/cm3 range (these values are high compared to other holes in the transect). Porosity is difficult to compare with lithology because of the often disturbed or unconsolidated nature of the cores being measured. Because of the heterogeneity in the formations and/or the disturbed nature of the cored material, it is difficult to compare it with multisensor core logger data and/or stratigraphy.

Attempts to correlate data across Holes M0047A and M0043A (attempted because of the close proximity of the holes and similar water depths) were unsuccessful. This may be attributed to the high complexity and variability of fossil coral reef pore systems.

P-wave velocity

Whole-core P-wave velocity measurements on Hole M0047A cores were unsuccessful, and no samples were taken for discrete P-wave velocity measurement.

Magnetic susceptibility

Magnetic susceptibility data for Hole M0047A are sparse, owing to low core recovery. Values range from –0.83 × 10–5 to 6.38 × 10–5 SI, with highs in Sections 325-M0047A-8R-1 and 11R-1 (Fig. F77).

Electrical resistivity

Similar to the magnetic susceptibility data, the electrical resistivity data set is very small because of poor recovery. Noncontact resistivity measurements taken on whole cores yielded data ranging from 0.66 to 3.32 Ωm (Fig. F77) with no systematic changes downhole.

Digital line scans and color reflectance

Cores from Hole M0047A were digitally scanned, and, where appropriate, measured for color reflectance. Color reflectance in Hole M0047A varies between 51.53% and 78.74% L* (Fig. F79). The low values of reflectance found in the upper part of the hole are principally due to coralgal boundstones and in part due to the presence of coarse sand and pebbles in which reflectance measurements are more inaccurate. The higher values with a dispersed pattern from 7 to 22 m CSF-A correspond mainly to areas of lime pebbles with fragments of different corals. The presence of coralline algae and lime pebbles at 24 m CSF-A showed a nondispersive pattern for all color reflectance parameters. Data points at the base of the hole correspond to a disturbed area that was probably more homogeneous in color.

Thermal conductivity

For Hole M0047A, two measurements were performed with a thermal conductivity of 1.06 W/(m·K) at 18.4 m CSF-A and 0.98 W/(m·K) at 27.34 m CSF-A.


Measurements of low-field and mass-specific magnetic susceptibility (χ) were performed on samples taken from the working half of the recovered core (Fig. F80). Low negative (diamagnetic) susceptibilities were measured throughout the core, ranging from –1.48 × 10–8 to –0.04 × 10–8 m3/kg with an arithmetic mean of –0.49 × 10–8 m3/kg. Five positive values at 3.29, 6.27, 12.24, 27.31, and 31.75 mbsf recorded susceptibilities of 0.46, 0.74, 0.08, 1.18, and 0.34 × 10–8 m3/kg, respectively, indicating the presence of paramagnetic and/or ferromagnetic minerals.


Two calibrated radiocarbon ages (15 cal y BP, Core 325-M0047A-3R; 18 cal y BP, Core 7R) (Fig. F81) and one U-Th age (21 cal y BP, Core 11R) (see Table T10 in the “Methods” chapter) are consistent with their stratigraphic positions. The U-Th age is unaffected by corrections for initial 230Th, adding to the confidence in this age interpretation. Therefore, this hole recovered material from the Last Glacial Maximum and the early deglaciation to 15 cal y BP. There are three cores below the 20 cal y BP section, indicating that more Last Glacial Maximum material or even older Pleistocene deposits may be present in the hole.