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doi:10.2204/iodp.proc.342.112.2014

Physical properties

We completed physical property measurements on whole-round sections, section halves, and discrete samples from section halves in Holes U1411A–U1411C. 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. Thermal conductivity measurements were also performed on whole-round sections for Hole U1411B before they were split. Compressional wave velocity on section halves was also measured at a frequency of two in each section (at ~50 and 100 cm) using the P-wave caliper (PWC). For MAD analyses, one discrete sample was collected in each section from Hole U1411B (typically at ~35 cm from the top of a section). The Section Half Multisensor Logger was used to measure spectral reflectance and point magnetic susceptibility on archive section halves.

Magnetic susceptibility

Overall, magnetic susceptibility ranges from 0 to 200 instrument units (IU) (Fig. F23). From the top of the hole to ~14 mbsf (lithostratigraphic Unit I; see “Lithostratigraphy”), magnetic susceptibility is characterized by large-amplitude variations. Magnetic susceptibility abruptly decreases to ~15 IU at the Unit I/ II boundary (~14 mbsf). In Unit II, from ~14 to 143 mbsf, magnetic susceptibility remains constant at ~15 IU. At 143 mbsf, magnetic susceptibility increases from 15 to 35 IU and remains constant at ~40 IU to the bottom of the hole. Throughout this lowermost interval, magnetic susceptibility values are characterized by small but high-frequency variations that correlate with variations in calcium carbonate content (see “Geochemistry”).

Density and porosity

Two methods were used to evaluate bulk density at Site U1411. The GRA method provided a bulk density estimate from whole-round sections. The MAD method applied to 165 discrete samples from Site U1411 provided a second, independent measure of bulk density, as well as dry density, grain density, water content, and porosity.

Overall, MAD bulk density values vary between 1.4 and 2.0 g/cm³. Changes in MAD bulk density are consistent with those observed in the GRA bulk density record (Fig. F23), although MAD values are ~3% lower than GRA density values in the APC-cored section. In lithostratigraphic Unit I, bulk density increases downhole from 1.64 to 1.90 g/cm³, but at the top of Unit II (~14 mbsf), bulk density abruptly decreases to 1.5 g/cm³. From the top of Unit II, bulk density steadily increases downhole to ~1.9 g/cm³ at ~150 mbsf; this pattern is typical of compaction. Notable features are the step increases in bulk density at ~60, 130, and 145 mbsf, which could be indicative of sedimentation changes and possibly hiatuses. Between 150 mbsf and the bottom of Hole U1411B, bulk density is relatively constant. In Holes U1411B and U1411C, GRA bulk density data show higher amplitude variations in XCB-recovered cores.

At Site U1411, water content and porosity vary between 23 and 55 wt% and 45 and 77 vol%, respectively. From the top of the hole to ~150 mbsf, both parameters decrease gradually to 30 wt% and 52 vol% for water content and porosity, respectively. However, between ~8 and 15 mbsf, in the lower part of Unit I, porosity and water content abruptly shift to lower values. Furthermore, the anomalous feature observed in the bulk density profile at 60 mbsf is equally well expressed in the water content and porosity record. Even though not visually recognizable in the core or color profiles, this feature likely represents a hiatus. Below 150 mbsf, water content and porosity remain relatively constant and average 28.5 wt% and 52 vol%, respectively.

Grain density remains constant and generally varies between 2.7 and 2.8 g/cm³ throughout Hole U1411B.

P-wave velocity

P-wave velocity was measured using the P-wave logger on all whole-round sections and using the PWC on undisturbed section halves from Holes U1411A–U1411C. Whole-round and section-half data track one another exceptionally well (Fig. F24). Overall, P-wave velocity gradually increases downhole from 1500 to 1700 m/s, similar to the overall trends in bulk density and water content. These downhole trends are readily attributed to compaction. A distinct step down in velocity from 1590 to 1500 m/s occurs at the transition between lithostratigraphic Units I and II. Between 180 mbsf and the bottom of the hole, P-wave logger measurements were not performed, but PWC measurements show higher variations associated with the change in coring methods from APC to XCB.

Natural gamma radiation

NGR values range from 16 to 50 cps at Site U1411 and are distinguished by three major trends. First, NGR values increase from 21 to 50 cps between 0 and 110 mbsf. Second, between ~110 and 145 mbsf, NGR values decrease to 20 cps. Third, below 150 mbsf, NGR values remain constant and average ~36 cps (Fig. F24). NGR is anticorrelated to calcium carbonate content, with particularly low counts in the high-carbonate sediment of Unit I and at ~140 mbsf in Unit II. High NGR counts occur in the low-carbonate intervals in the upper part of Unit II, between ~60 and 120 mbsf (see “Geochemistry”).

Color reflectance

Color reflectance parameters a* and b* follow similar trends to one another in Holes U1411B and U1411C (Fig. F25). In lithostratigraphic Unit I, values average ~4 for a* and ~5 for b*. At the contact between Units I and II, a* decreases from 4 to –1.5 and b* decreases from 5 to 0.8. This change in color reflectance values distinguishes the transition between banded brown–gray Pleistocene age sediment and the underlying greenish gray silty clay (see “Lithostratigraphy”). In Units II and III, a* and b* values remain constant and average 0.0 and –0.8, respectively. Peaks in the b* record, such as those at ~34, 45, and 60 mbsf, correspond to yellowish horizons. The peak at ~238 mbsf corresponds to a foraminifer sand–rich horizon in Core 342-U1411B-27X.

L* can be correlated among Holes U1411B and U1411C (Fig. F25). Between the top of the hole and ~100 mbsf, L* decreases slightly from 53 to 40. Below, L* increases to 51 at ~140 mbsf and remains constant at ~45 to the bottom of the hole. Some cyclic variations superimpose these downhole trends, such as at ~18, 60, 150, and 238 mbsf. The major variations in L* recorded at Site U1411 correlate well to the magnetic susceptibility and NGR data series (Fig. F24) and appear to correlate to changes in calcium carbonate content (see “Geochemistry”).

Thermal conductivity

Twenty-five thermal conductivity measurements were collected on whole-round sections from Hole U1411B (Table T18). Overall, thermal conductivity values increase downhole (Fig. F26). Thermal conductivity data are elevated (~1.65 W/[m·K]) in lithostratigraphic Unit I, probably because of the presence of foraminifer sand in these intervals. Thermal conductivity values gradually increase downhole from ~1.1 to 1.4 W/(m·K) throughout Units II and III.

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