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doi:10.2204/iodp.proc.347.110.2015

Physical properties

This section summarizes the preliminary results from Site M0066. Two holes were drilled at Site M0066. Hole M0066A was drilled to 28.00 mbsf, and Hole M0066B was drilled to 27.85 mbsf. For each hole, the uppermost 2 m was washed down because of potential contamination from hazardous materials. Despite <100% recovery, sediments recovered from Hole M0066A provide a more continuous and better record of the physical properties at Site M0066. For Hole M0066A, all physical property measurements described in “Physical properties” in the “Methods” chapter (Andrén et al., 2015) were conducted. As the thermal conductivity data and the discrete moisture and density (MAD) and P-wave measurements are few in number, the interpretations are based primarily on the shipboard multisensor core logger (MSCL) data and natural gamma ray (NGR) data.

Natural gamma radiation

High-resolution NGR exhibits relatively constant values (~10 cps) in lithostratigraphic Subunit Ia (Fig. F9). From ~5 to 8 mbsf, throughout lithostratigraphic Subunit Ib, NGR shows generally decreasing values (from ~10 to 6 cps). At the Subunit Ib/Unit II boundary, a shift to lower values (~5 cps) is observed. NGR exhibits generally low (<5 cps) and variable values in lithostratigraphic Unit II. Negative excursions potentially reflect an increase in silt or sand content, whereas positive excursions may result from an increase in clay or glauconite content (see “Lithostratigraphy”). At the Unit II/III boundary (~15.7 mbsf), NGR increases to >10 cps and, though recovery is moderate, these high values appear consistent throughout lithostratigraphic Unit III. This change could be related to an increase in clay content within lithostratigraphic Unit III (see “Lithostratigraphy”). NGR exhibits an overall decreasing trend toward the base of lithostratigraphic Unit IV (from ~13 to 5 cps), which is interpreted to result from an increased silt and sand content in lithostratigraphic Unit IV (see “Lithostratigraphy”).

Shipboard magnetic susceptibility and noncontact resistivity

Magnetic susceptibility shows low (~15 × 10^–5 SI) and constant values in lithostratigraphic Subunit Ia (Fig. F9). Near the Subunit Ia/Ib boundary, magnetic susceptibility increases to ~40 × 10^–5 SI and remains high through lithostratigraphic Subunit Ib. At the Subunit Ib/Unit II boundary, magnetic susceptibility values decrease sharply (<5 × 10^–5 SI) and maintain a low mean to ~12 mbsf, with the exception of two positive excursions. Magnetic susceptibility increases strongly from ~12 to 13.5 mbsf, and an abrupt spike that could reflect a change in lithology (~85 × 10^–5 SI) is observed at ~14 mbsf. This dramatic increase in magnetic susceptibility coincides with a small decrease in dry density at the same depth and may be characterized as a massive sand with noted clay and fine-silt interbeds (see “Lithostratigraphy”). Magnetic susceptibility shows a general decreasing trend in lithostratigraphic Unit III and in the upper interval of lithostratigraphic Unit IV (from ~19.5 to 22 mbsf). Magnetic susceptibility values are low (<20 × 10^–5 SI) and highly variable in the lower interval of lithostratigraphic Unit IV.

Noncontact resistivity (NCR) shows an overall similar trend to magnetic susceptibility (Fig. F9). NCR values are low in lithostratigraphic Unit I, increase to ~6.5 Ωm at 8.4 mbsf, and remain constant for the majority of lithostratigraphic Unit II. NCR data are difficult to interpret within lithostratigraphic Units III and IV because of poor recovery and high variability. The upper sections of cores in these units exhibit much lower values than deeper sections of the same cores.

Density

Dry density derived from moisture and density measurements is low in lithostratigraphic Subunit Ia (<1 g/cm³) and increases markedly in Subunit Ib to ~2 g/cm³ (Fig. F9). From 11.5 to 15.7 mbsf in the lower interval of lithostratigraphic Unit II, dry density decreases to ~1.6 g/cm³ before increasing to ~2.1 g/cm³ at the lithostratigraphic Unit II/III boundary. Deeper than this, density decreases toward the bottom of the hole.

Gamma density was measured at a 2 cm interval during the offshore phase of Expedition 347 (Fig. F10). Gamma density shows relatively low values (~1.6 g/cm³) through most of lithostratigraphic Subunit Ia. Gamma density exhibits a dramatic shift to higher values at the Subunit Ia/Ib boundary and remains generally high (~2 g/cm³) throughout lithostratigraphic Units II, III, and IV. Discrete bulk density measurements conducted during the OSP correlate moderately well with the shipboard measurements (r² = 0.46, Fig. F10).

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