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Hole M0040A


Transit to transect HYD-02A

The Greatship Maya transited to the survey transect under guidance from the pilot. The vessel crossed Hydrogr Passage in a southeast direction and reached Site 10, Hole M0040A, at 1830 h on 5 March 2010.

Site 10, Hole M0040A

By 1925 h on 5 March 2010, the seabed transponder had been deployed and the Greatship Maya had settled on station over Hole M0040A (Table T1). American Petroleum Institute (API) pipe was run to just above the seabed by 2125 h, when the downpipe camera was deployed. The camera survey was completed by 2220 h, and API pipe was run until the seabed was tagged at 2235 h. The first core was on deck at 2250 h, and coring continued until the end of Run 3, when repairs to the driller’s shack electrics halted operations between 0030 and 0155 h on 6 March. Operations then restarted for another nine runs until the hole was terminated at 0825 h at 21.5 meters below seafloor (mbsf), with an average recovery of 54.6%.

Three API pipes were tripped to bring the drill string to ~4 m above the seabed. A downpipe camera survey was then conducted between 0850 and 0910 h, prior to the vessel moving 10 m to starboard to the next hole.

Sedimentology and biological assemblages

Hole M0040A is divided into six lithostratigraphic units.

Unit 1: Sections 325-M0040A-1R-1 through 1R-CC: unconsolidated mud

The uppermost Unit 1, spanning Sections 325-M0040A-1R-1 through 1R-CC, consists of unconsolidated mud with a small amount of lime sand. Interval 325-M0040A-1R-1, 0–10 cm, is rich in pebble-sized or smaller bioclasts of Halimeda, mollusks, foraminifera, and echinoids (spines). Below this interval, bioclasts are rare, except for a few small benthic foraminifera. There are no larger foraminifera or planktonic foraminifera. There are no corals in Unit 1.

Unit 2: Section 325-M0040A-2R-1: unconsolidated fine lime sand and pebbles

Unit 2, consisting only of Section 325-M0040A-2R-1, is composed of 17 cm of pebble-sized or smaller bioclasts of mollusks, larger foraminifera (including Homotrema), corals, Halimeda, and serpulids, associated with calcareous fine sand. There are a few fragments of Seriatopora.

Unit 3: Section 325-M0040A-3R-1: fragments of coralgal-microbialite boundstone

Unit 3, consisting only of Section 325-M0040A-3R-1, contains 23 cm of fragments of coralgal-microbialite boundstone. The boundstone is buff colored and composed of bryozoans, nongeniculate coralline algae, and microbialites. Because the material was fragmented by the drilling process, the succession of lithologies in the unit cannot be determined. There are no corals in Unit 3.

Unit 4: Sections 325-M0040A-4R-1 through 4R-CC: unconsolidated bioclasts and lithoclasts

Unit 4, spanning Sections 325-M0040A-4R-1 through 4R-CC, consists of pebble-sized and smaller bioclasts of mollusks, corals (hermatypic and solitary corals), foraminifera, and lithoclasts of microbialite boundstone (and packstone). Corals are associated with microbialites.

There are a few Seriatopora fragments throughout Unit 4, with some larger Seriatopora fragments and a piece of massive Goniopora(?) in Section 325-M0040A-4R-CC.

Unit 5: Sections 325-M0040A-5R-1 through 9R-1: microbialite boundstone

Unit 5, spanning Sections 325-M0040A-5R-1 to 9R-1, 36 cm, consists mainly of microbialite with an interlayer of bioclastic packstone/rudstone in interval 7R-1, 9–40 cm (Fig. F2). Coralgal boundstone in interval 325-M0040A-9R-1, 0–14 cm (Fig. F3) and bioclastic rudstone in interval 9R-1, 14–37 cm (Fig. F4) occur at the base of Unit 5. Microbialites have a range of different fabrics, from massive and laminated to thrombolitic. Corals are common, but nongeniculate coralline algae are rare. Cavities of uncertain origin are partly filled with consolidated and unconsolidated fine-grained (silt-sized) internal sediment (Fig. F5). The packstone/rudstone and rudstone intervals are rich in bioclasts of mollusks, echinoids, corals, Halimeda, and, to a lesser extent, bryozoans.

The main corals are thin encrusting to submassive layers of Porites, Montipora(?), and Agariciidae (Figs. F6, F7). Associated corals include massive Goniopora(?), Acroporidae, and Faviidae, as well as encrusting to branching Seriatopora, Goniopora, Porites, Tubipora musica, Pocilloporidae, and Acroporidae. Fragments include Seriatopora, Porites, Tubipora musica, Montipora(?), Acroporidae, Agariciidae, and Poritidae.

Unit 6: Sections 325-M0040A-9R-CC through 12R-CC: unconsolidated sediment

The lowermost Unit 6, spanning Sections 325-M0040A-9R-CC through 12R-CC, consists mainly of unconsolidated fine- to medium-grained lime sand that contains molluscan shell fragments and a few bryozoans. Very coarse sands from interval 325-M0040A-10R-1, 20–25 cm, contain fragmented specimens of Operculina and Soritinae, as well as abraded specimens of Rotallidae (Amphistegina?). Well-preserved or fragmented specimens of Operculina and Soritinae are common in fine to medium sands from interval 325-M0040A-11R-1, 70–75 cm, whereas similar fine to medium sands from interval 12R-1, 70–75 cm, contain sparse but well-preserved specimens of Operculina, Miliolidae, Amphistegina, and Soritinae. A few well-preserved specimens of Operculina and Miliolidae also exist in fine to medium sands from interval 325-M0040A-12R-2, 50–55 cm. There are no corals in Unit 6.

Physical properties

Hole M0040A was cored to a total depth of 21.50 m drilling depth below seafloor (DSF-A), of which 11.73 m was successfully recovered (54.56% recovery). Physical property data for this hole are summarized in Table T2.

Density and porosity

Gamma density varies from 1.01 to 2.44 g/cm3 in cores from Hole M0040A (Fig. F8). The cores are characterized by sections dominated by fracturing and by the fact that the cores are undersaturated. This is particularly evident in the fluctuating gamma bulk density values in Sections 325-M0040A-5R-1 through 9R-2. Fourteen discrete samples from Hole M0040A (Fig. F9) yield bulk density measurements in the range 1.83 to 2.33 g/cm3. Between 0 and 1.5 m core depth below seafloor (CSF-A), sandy lime mud and lime sand samples exhibit high porosity (49%–53%). From 3.5 to 12.69 m CSF-A, fragments of numerous lithologies include, but are not limited to, coralgal microbialite boundstone and bioclastic packstone with mollusks. The porosity of these sediments is lower, with a mean value of 26%. Below 12.69 m CSF-A to total depth, the lime sand has a higher porosity (37%–48%).

P-wave velocity

P-wave velocity measurements taken on whole cores offshore range from 1522 to 1829 m/s (Fig. F8). However, cores were frequently undersaturated and underfilled, which implies these values may be an underestimate of the in situ values (see “Physical properties” in the “Methods” chapter). P-wave velocity is at its highest at ~16 m CSF-A (Sections 325-M0040A-11R-1 and 11R-2), where fine sediments with some shell fragments are present. Whole-core velocities were not obtained between 2 and 14 m CSF-A in areas mainly composed of coralgal-microbialite and microbialite boundstones. Six core plug samples were taken from Hole M0040A and measured using the discrete P-wave logger. Velocities (mean resaturated values) measured on these samples range from 3727.67 to 4073.00 m/s (Fig. F10A), which are appropriate values for well-lithified porous formations such as these. In the discrete samples measured from Hole M0040A, P-wave velocity mostly increases with increasing bulk density (Fig. F10B).

Magnetic susceptibility

Recovered core from Hole M0040A exhibits a range of magnetic susceptibility values, from –1.69 × 10–5 to 34.44 × 10–5 SI (Fig. F8). Values are dominantly in the –1.69 × 10–5 to 2 × 10–5 SI range. Intervals of higher magnetic susceptibility include the uppermost 1 m of the hole, which has values in the region of 16 × 10–5 SI, which decreases stepwise to the dominant hole value (note that the stepwise nature of this change may be indicative of a sporadic sensor [80 mm loop] issue (see “Physical properties” in the “Methods” chapter). The two other highs occur in Sections 325-M0040A-10R-1 (14.06 m CSF-A) and 12R-2 (20.19 m CSF-A).

Electrical resistivity

Electrical resistivity measured on whole cores is highly variable and ranges from 0.56 to 26.54 Ωm (Fig. F8). Values are primarily affected by lithology, pore fluid, and salinity, as well as core liner saturation. Resistivity values are most reliable in the upper and lower portions of the borehole where the values are the lowest (~0–2 m CSF-A and between ~15.60 m CSF-A and the base of the hole). The recovered cores are fractured and undersaturated where they are dominated by microbialite (Sections 325-M0040A-5R-1 through 9R-2), so resistivity values must therefore be considered with caution.

Digital line scans and color reflectance

All cores from Hole M0040A were measured 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. Appropriate cores were also scanned for color reflectance (Fig. F11). Color reflectance in this hole varies between 50.27% and 72.73%. Measurements from shallower lithologies, which correspond to units mostly composed of fine sands and mud, have lower reflectance than coarser sediments such as coral fragments. Reflectance increases from 5 m CSF-A and remains high (53.71%–72.73%) to 10 m CSF-A. When fine sediments are present, the signal for a* is negative, indicating green coloration. Larger grain size gives higher values close to or within the red scale. Values for b* remain in the same range, with high variations within sections. The a*/b* ratio is a good indicator of changes in lithology in this hole, as it captures the trends in a* and b* simultaneously.

Thermal conductivity

Four thermal conductivity measurements were taken in Hole M0040A, and values range from 1.04 to 1.18 W/(m·K) (Fig. F12). No particular trend is visible in this small data set.


Measurements of low-field and mass-specific magnetic susceptibility (χ) were performed on samples taken from the working half of the recovered core using both 1 cm3 and paleomagnetic standard samples (Fig. F13). Very low to low negative (diamagnetic) susceptibilities occurred throughout the core, ranging from –0.07 × 10–8 to –5.0 × 10–8 m3/kg with an arithmetic mean value of –1.29 × 10–8 m3/kg. In addition, positive susceptibilities ranging from 0.00 to 131.58 × 10–8 with an arithmetic mean value of 5.45 × 10–8 m3/kg were recorded. The positive susceptibility peaks indicate the presence of ferromagnetic minerals.


Two calibrated radiocarbon ages (10 calibrated years before present [cal y BP; years before 1950 AD], Core 325-M0040A-2R; 15 cal y BP, Core 4R) (Fig. F14) and one U-Th age (25 cal y BP, Core 8R) (see Table T10 in the “Methods” chapter) are consistent with their stratigraphic positions. The U-Th age is unaffected by corrections for initial 230Th (the seawater correction makes the age 0.6 k.y. younger), adding to the confidence in this age interpretation. Therefore, this hole recovered material from the Last Glacial Maximum interval and has captured the early portion of the deglaciation to 10 cal y BP.