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doi:10.2204/iodp.proc.342.111.2014

Physical properties

We made physical properties measurements on whole-round sections, section halves, and discrete samples from section halves. Gamma ray attenuation (GRA) bulk density, magnetic susceptibility, P-wave velocity, and NGR measurements were made on whole-round sections using the Whole-Round Multisensor Logger (WRMSL) and Natural Gamma Radiation Logger. Compressional wave velocity on section halves was also measured at a frequency of two in each section (at ~50 and 100 cm) using a P-wave caliper (PWC). For moisture and density (MAD) analyses, one discrete sample was collected in each section (typically at ~35 cm from the top of a section) from Hole U1410A. The Section Half Multisensor Logger (SHMSL) was used to measure spectral reflectance and magnetic susceptibility on archive section halves.

Magnetic susceptibility

Overall, magnetic susceptibility ranges from –2 to 291 IU (Fig. F26). In lithostratigraphic Unit I (0 to ~35 mbsf), magnetic susceptibility is high and variable (8–291 IU) and increases (from ~30 to 120 IU) downhole. Magnetic susceptibility decreases sharply to 20 IU at the Unit I/II boundary. In Unit II, magnetic susceptibility averages 30 IU, but is also characterized by many superimposed peaks that correlate among all three holes. A sharp decrease to ~5 IU is observed at the contact with underlying Unit III. Magnetic susceptibility values remain much more uniform (0–20 IU) throughout Unit III, but high-frequency variations are observed between ~70 and 120 mbsf in all three holes. In Subunits IVa and IVb, magnetic susceptibility remains constant at ~4 and 13 IU, respectively.

Density and porosity

Two methods were used to measure bulk density at Site U1410. The GRA density method provides an estimate from whole-round sections, whereas the MAD method, applied to 183 discrete samples from Hole U1410A, provides a second, independent measure of bulk density, as well as dry bulk density, grain density, water content, and porosity.

At Site U1410, bulk density ranges from 1.5 to 2.4 g/cm³ and gradually increases downhole. The downhole profile of MAD bulk density is consistent with that of GRA bulk density; however, MAD bulk density is on average ~2% lower than GRA density in the APC-cored section (Fig. F26). In lithostratigraphic Unit I, density varies from 1.6 to 1.8 g/cm³ and decreases to 1.5 g/cm³ at the Unit I/II boundary (35 mbsf). Bulk density increases downhole from 1.5 to 1.9 g/cm³ in Units II and III. Two superimposed peaks that correlate among all three holes occur within this interval, at ~50 and 160 mbsf. Bulk density values fluctuate between 1.8 and 2.1 g/cm³ in Unit IV, and increase to ~2.0 g/cm³ at the bottom of Subunit IVb.

Water content in sediment from Hole U1410A ranges from 21 to 53 wt%, and porosity varies from 43 to 76 vol%. Generally, water content and porosity decrease downhole; this trend is expected because of sediment compaction. In Unit I, both properties display high values (30–48 wt% for water content and 55–70 vol% for porosity). In Unit II, water content and porosity fluctuate from 41 to 53 wt% and from 65 to 76 vol%, respectively. These physical properties gradually decrease downhole in Unit III (from 37 to 26 wt% for water content and 61 to 50 vol% for porosity). In Subunits IVa and IVb, water content and porosity fluctuate from 23 to 35 wt% and from 44 to 59 vol%, respectively.

Grain density ranges from 2.6 to 3.3 g/cm³ in Hole U1410A. From the top of the hole to ~20 mbsf, grain density values are high (>2.8 g/cm³), whereas below this interval, grain density values remain uniform and average ~2.75 g/cm³. High values may be the result of high manganese oxide content in the sediment. Alternatively, the high values may be an artifact of measuring sandy (foraminiferal) and silty clay that may not be completely saturated.

P-wave velocity

P-wave velocity was measured using the PWL on all whole-round sections and using the PWC on undisturbed section halves from Holes U1410A–U1410C.

P-wave velocity ranges from 1500 to 1650 m/s in PWL data and from 1490 to 1960 m/s in PWC data in all three holes. PWC values are consistently lower than the PWL values by ~20 m/s in the APC-cored section (Fig. F27). P-wave velocity gradually increases downhole and maximum velocities are recorded at the bottom of the hole. PWL measurements were not performed in the lower part of lithostratigraphic Unit III and Subunits IVb and IVc in Holes U1410A and U1410C (from ~160 mbsf to the bottom of each hole). PWC measurements show higher variations within this interval; we attribute this variability to the change in coring methods from APC to XCB.

Natural gamma radiation

NGR was measured on whole-round sections from Holes U1410A–U1410C. Overall, values range from 2 to 47 cps. Through lithostratigraphic Unit I, NGR increases downhole from 13 to 42 cps (Fig. F27), a trend that is in step with a decrease in carbonate content (see “Geochemistry”). In Unit II, NGR decreases to a minimum of <20 cps at ~48 mbsf in Hole U1410A, ~50 mbsf in Hole U1410B, and ~45 mbsf in Hole U1410C. NGR values increase to 40 cps downhole through the rest of Unit II but abruptly decrease to 30 cps at the Unit II/III boundary. Carbonate content increases abruptly across the Unit II/III boundary. In Unit III, NGR values remain relatively constant and fluctuate between 13 and 30 cps. Three shifts at ~82, 110, and 160 mbsf can be correlated among all three holes. All of these peaks correspond to alternations between greenish clay and whitish carbonate-rich clay layers (see “Lithostratigraphy”). The shift observed at ~160 mbsf coincides with a slight increase in carbonate content. NGR values rapidly decrease from 27 to 10 cps at the Unit III/IV boundary at ~215 mbsf; this shift corresponds to the transition from gray-green carbonate-poor sediment of Unit III to carbonate-rich white chalk of Unit IV. In the carbonate-rich Subunits IVa and IVb, NGR remains uniformly low (~10 cps).

Color reflectance

Color reflectance was measured on archive section halves from all three holes. The standard operating resolution of data acquisition was decreased from 2.5 to 5 cm in all three holes because the rate of core recovery required faster processing. Changes in color reflectance parameters a* and b* are consistent among all three holes (Fig. F28). In lithostratigraphic Unit I, values average ~1 for a* and ~0 for b*. In Unit II, a* and b* values show more variations (a* and b* range from –4 to 8.5 and from –5.5 to 16, respectively); this variability is associated with the large changes in sediment color (from light olive-gray to dark greenish gray) of this unit (see “Lithostratigraphy”). Through Unit III, a* and b* remain relatively constant, and a* averages 0 whereas b* averages –1. From the Unit III/IV boundary (~210 mbsf) to the base of Subunit IVb, a* and b* increase from –2 to 12 and from –3 to 8, respectively. The increase in a* and b* corresponds to the change from greenish to pinkish white sediment. In Subunit IVb, a* and b* remain constant, with a* ranging from 4 to 8 and b* ranging from 5 to 10).

L* exhibits the same downhole trend in all three holes. From the top of the hole to ~40 mbsf, L* decreases downhole from ~55 to 40. A shift to higher values, with a peak of 60, occurs at ~42 mbsf. Below this level, L* values continue to increase slightly (from 50 to 65) to the bottom of Unit III. Two broad peaks occur at ~115 and ~150 mbsf within this interval. At the contact with the underlying Subunit IVa (at ~215 mbsf), L* values increase sharply from 65 to 90, a shift that correlates with the transition from gray-green nannofossil clay to white nannofossil chalk. L* values remain high and constant, with an average value of 85, throughout Subunits IVa and IVb. The major variations in L* recorded at Site U1410 occur at the same levels as changes in the NGR data series (Fig. F28). This pattern correlates to changes in calcium carbonate content (see “Geochemistry”).

Thermal conductivity

Twenty-eight measurements were completed on whole-round sections from Hole U1410A (Table T21). Overall, thermal conductivity ranges from 0.9 to 1.5 W/(m·K) (Fig. F29). In lithostratigraphic Unit I, thermal conductivity ranges from 0.9 to 1.4 W/(m·K). From the top of Unit II to the bottom of the hole, thermal conductivity values increase gradually downhole from ~1.1 to 1.5 W/(m·K). Thermal conductivity measurements approximately correlate to GRA bulk density values (R² = ~0.58) (Fig. F30).

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