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doi:10.2204/iodp.proc.342.104.2014

Physical properties

We measured physical properties 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 NGR Logger. Thermal conductivity measurements could not be performed on Site U1403 samples because of technical problems. Compressional wave velocity was measured on section halves at a frequency of two in each section (at ~50 and 100 cm). For moisture and density (MAD) analyses, one discrete sample was collected in each section (at ~¼ of the section length). Lastly, the Section Half Multisensor Logger (SHMSL) was used to measure spectral reflectance and magnetic susceptibility on archive section halves.

Magnetic susceptibility

Magnetic susceptibility values in lithostratigraphic Unit I vary from 60 to 100 IU and then show a prominent drop downhole to ~20 IU around 20 mbsf (Fig. F29). This decrease probably reflects the transition between the nannofossil ooze of Unit I and clay of the upper part of Unit II. Magnetic susceptibility shows a subsequent downhole increase to relatively constant values (~35 IU) in the lower part of Unit II. Magnetic susceptibility values in Unit III average ~20 IU. In the upper part of Unit IV, values decrease to ~5 IU and show a downhole step increase to ~30 IU at 130 mbsf that is maintained to the base of this unit. Magnetic susceptibility is higher and more variable in Unit V. This last unit is characterized by four large magnetic susceptibility peaks (Fig. F29), which are tentatively associated with

• The C16 event at ~110 mbsf,

• The ETM2 transition at ~160 mbsf,

• The PETM at 183 mbsf in Hole U1403A and 177 mbsf in Hole U1403B, and

• The K/Pg boundary at ~220 mbsf.

Density and porosity

Two methods were used to evaluate bulk density at Site U1403. The GRA method provided a bulk density estimate from whole-round sections. The MAD method on discrete samples provided a second, independent measure of bulk density, as well as dry density, grain density, water content, and porosity. MAD and GRA bulk density measurements display the same trends and are also similar in absolute values through the entire section (Fig. F29). In both Holes U1403A and U1403B, MAD bulk density values are lower (~0.05 g/cm³) than GRA bulk density from the top of the holes to ~150 mbsf. From ~150 mbsf to the bottom of the hole, which was cored with the XCB, these two data sets are largely comparable in value. We speculate that the GRA densities are overestimated because of a calibration problem. Generally, changes in bulk density correspond to changes in lithology. Bulk density is ~1.5 g/cm³ immediately below the seafloor in the nannofossil ooze with clay and varies between 1.3 and 1.65 g/cm³ through lithostratigraphic Units I, II, and III (see “Lithostratigraphy”). A slight step toward lower values (1.2 g/cm³) between 120 and 145 mbsf corresponds to the appearance of nannofossil ooze (Unit IV). The transition between Units IV and V at ~150 mbsf correlates with an increase in carbonate content (see “Geochemistry”) and bulk density in the middle of Unit IV. Wet bulk density in the upper half of Unit V (155–210 mbsf) is relatively uniform, with low-amplitude variations around ~1.60 g/cm³, whereas the lower half of the unit is marked by an increase to 2.0 g/cm³.

Porosity averages 70 vol% in Units I, II, and III, increases to 85 vol% in Unit IV, decreases to 60 vol% at the bottom of Unit IV, and further decreases to 45 vol% in Unit V (Fig. F29).

Variations in grain density in Hole U1403A generally match changes in lithology (Fig. F29). In clay-rich sediment of Units I and II (see “Lithostratigraphy”), grain density is highly variable with values ranging from 2.15 to 2.8 g/cm³. In other lithostratigraphic units, grain density averages 2.65 g/cm³ and reaches 2.8 g/cm³ in the lower part of Unit V.

P-wave velocity

P-wave data from whole-round sections and section-halves follow similar trends in Holes U1403A and U1403B and are consistent with one another; however, P-wave caliper (PWC) values are slightly lower than those obtained by the P-wave logger (PWL) (Fig. F30). All P-wave velocity data sets show a gradual increase (1500–1600 m/s) with depth from lithostratigraphic Unit I to the ETM2 (~160 mbsf) at the top of Unit V. Below this depth, data from the PWL are not available because the XCB-cored sediment did not fill the core liner fully. In Unit V, PWC data are variable (1530–1750 m/s) with an overall average of 1600 m/s.

Natural gamma radiation

The general trends in NGR in both holes are similar to those seen in the bulk density data (Fig. F30). In lithostratigraphic Unit II, NGR averages 30 cps, falls to 20 cps at the top of Unit III (~70 mbsf), and rises to 35 cps at ~110 mbsf. Unit IV is characterized by NGR values of ~15 cps, which correlate with the increase in carbonate content (see “Geochemistry”). NGR data in Unit V show more variation than in Units III and IV and have an average value of 25 cps.

Color reflectance

Trends in a* and b* are similar to one another and reflect changes in lithology (Fig. F31). In lithostratigraphic Unit I and in the uppermost half of Unit II, both reflectance parameters decrease (from 10 to –5 for a* and from 30 to 4 for b*). This decrease is followed by an increase downhole to the bottom of Unit II (a* = ~10, b* = ~25). In Unit III, a* and b* decrease downhole (from 4 to –3 for a* and from 16 to 5 for b*). At 125 mbsf, both parameters rapidly increase in the interval where carbonate content increases (see “Geochemistry”). Variations in a* and b* co-vary with changes in magnetic susceptibility throughout the hole, and at ~170 mbsf, both parameters drop to minimum values. The bottom of Unit V is marked by high variability in spectral reflectance (from –10 to 20 for a* and from 0 to 30 for b*).

L* corresponds to lightness and follows pronounced lithologic changes (Fig. F31). In general, L* follows similar trends in both holes at Site U1403, varying between 45 and 65. The main variations occur within Unit II, in which L* drops to local minima (25) at 35 mbsf and 52 mbsf, corresponding to dark brown sediments, and at the bottom of Unit IV and throughout Unit V, where L* varies between 15 and 70.

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