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doi:10.2204/iodp.proc.347.109.2015

Physical properties

This section summarizes the preliminary physical property results from Site M0065. Three holes were drilled at this site. Hole M0065A was drilled to 73.9 mbsf, Hole M0065B to 49.3 mbsf, and Hole M0065C to 47.9 mbsf. Hole M0065C was designated as a microbiology hole and was extensively subsampled onboard (see “Microbiology”) prior to any physical properties measurements except Fast-track multisensor core logger (MSCL). For each hole, the uppermost 2 m was washed down to avoid potential chemical contamination (see “Operations”). We focused on the physical property data from Hole M0065A, which has the greatest penetration (Fig. F14), though the core recovery was very low from 46.6 mbsf because of changing coring methods from piston coring to open-hole intervals with spot hammer sampling (see “Operations”). Although all physical property measurements described in “Physical properties” in the “Methods” chapter (Andrén et al., 2015a) were conducted for Site M0065, thermal conductivity data are too sparsely distributed to exhibit any discernable downcore trend.

Natural gamma radiation

High-resolution natural gamma ray (NGR) values are relatively low (<10 cps) and increase progressively from the core top to the lower interval of lithostratigraphic Unit I (Fig. F14; see “Lithostratigraphy”), with few positive excursions observed. These generally low NGR values are interpreted as a result of high water content within organic-rich muds. At the Unit I/II boundary, NGR values decrease and then exhibit increasing values toward the base of lithostratigraphic Unit II (~15 cps). NGR exhibits relatively constant values in lithostratigraphic Subunit IIIa, with several negative excursions from the overall trend that might reflect the presence of silt intraclasts. NGR values decrease slightly (~12 cps) within lithostratigraphic Subunit IIIb. Lithostratigraphic Subunit IIIc is distinguished by gradually decreasing values toward the bottom of the hole. Variability in NGR likely reflects a coarsening-downward sequence from silty clay to medium sand through lithostratigraphic Subunit IIIc.

Shipboard magnetic susceptibility and noncontact resistivity

Magnetic susceptibility is overall generally low (<5 × 10^–5 SI) and increases slightly toward the base of lithostratigraphic Unit I (Fig. F14). Magnetic susceptibility is higher in lithostratigraphic Unit II and remains relatively constant, except for an abrupt spike (~55 × 10^–5 SI) observed at ~10 mbsf. The upper interval of lithostratigraphic Subunit IIIa is distinguished by a peak in magnetic susceptibility. However, apart from this peak, magnetic susceptibility remains constant from ~15 mbsf to the base of lithostratigraphic Subunit IIIb. Several positive excursions occurring within lithostratigraphic Subunit IIIa, approximately every 3 m, do not appear to correspond to changes in lithology. With their regular occurrence at approximately the same interval as core runs (~3.3 m), they are possibly an artifact of coring. At the Subunit IIIb/IIIc boundary, magnetic susceptibility increases and then exhibits high and variable values that reflect changes in lithology (increase in silt and sand content; see “Lithostratigraphy”).

The noncontact resistivity (NCR) data exhibit a generally similar trend to magnetic susceptibility (Fig. F14). NCR values are very low in lithostratigraphic Units I and II and progressively increase toward the base of lithostratigraphic Subunit IIIa as a normal compaction trend. Similar to magnetic susceptibility, NCR exhibits higher amplitude and more variability in lithostratigraphic Subunit IIIc.

Color reflectance

Color reflectance, in particular a*, reflects downcore changes in lithology (Fig. F14). Lithostratigraphic Units I and II are characterized by low values (more green). At the Unit II/Subunit IIIa boundary, a* values increase sharply and remain high (>4, more red) and constant through lithostratigraphic Subunit IIIa. Values decrease to a mean value of ~1 (greenish) at the Subunit IIIa/IIIb boundary and remain relatively constant in lithostratigraphic Subunits IIIb and IIIc.

Density and P-wave velocity

Gamma density was measured at 2 cm intervals during the offshore phase of Expedition 347 (Fig. F15). Gamma density increases progressively from the core top to the base of lithostratigraphic Subunit IIIb. Gamma density exhibits a shift to higher values in Subunit IIIc and remains generally high (~2 g/cm³) throughout lithostratigraphic Subunit IIIc. Discrete bulk density measurements conducted during the OSP correlate moderately well with the shipboard measurements (r² = 0.69; Fig. F16).

P-wave velocity was also measured at 2 cm intervals during the offshore phase of Expedition 347 (Fig. F15). P-wave velocity (MSCL) exhibits low and relatively constant values (~1000 m/s) from the core top to ~18 mbsf. Values are higher and highly variable in the middle interval of lithostratigraphic Subunit IIIa (~18–32 mbsf). The lower interval of lithostratigraphic Subunit IIIa, Subunit IIIb, and the upper interval of Subunit IIIc are all characterized by generally more constant values (~1500 m/s), observed in both the MSCL and discrete P-wave measurements. From ~39 mbsf to the bottom of Hole M0065A, P-wave velocity values are overall higher (>1600 m/s) than the upper section. However, there is a slight decreasing trend from ~39 to ~43 mbsf, where P-wave velocity increases again to the bottom of the hole to a high of ~1800 m/s. No significant correlation is observed between the shipboard P-wave velocity and the discrete P-wave measurements performed during the OSP.

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