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doi:10.2204/iodp.proc.342.105.2014

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 natural gamma radiation (NGR) measurements were made on the whole-round sections using the Whole-Round Multisensor Logger (WRMSL) and NGR Logger. Thermal conductivity measurements could not be performed at Site U1404 because of technical problems. Compressional wave velocity was also measured on section halves at a frequency of two in each section (at ~50 and 100 cm) using the 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). The Section Half Multisensor Logger was used to measure spectral reflectance and magnetic susceptibility on archive section halves.

Magnetic susceptibility

Magnetic susceptibility averages 80 IU in lithostratigraphic Unit I, which is essentially composed of clay (Fig. F33; see “Lithostratigraphy”). From the top of Unit II (~2 mbsf) to ~45 mbsf, magnetic susceptibility decreases from ~90 to 2 IU with a major step downhole at ~12 mbsf in the transition from clay- to silty clay–rich sediment. Below this level, Unit II is characterized by very low magnetic susceptibility values (<30 IU) and a small increase downhole. The top of Unit III (~200 mbsf) is marked by an increase in magnetic susceptibility to 65 IU, which correlates with the increase in carbonate content (see “Geochemistry”). This increase is followed by a decrease to ~10 IU at ~206 mbsf (bottom of Core 342-U1404A-23H and top of Core 342-U1404B-24H). This decrease probably reflects the downhole transition from nannofossil ooze to nannofossil biosiliceous ooze with clay (see “Lithostratigraphy”). Magnetic susceptibility is more variable (6–60 IU) in Units III and IV but shows an overall downhole decrease to the bottom of both holes.

Density and porosity

Two methods were used to evaluate bulk density at Site U1404. The GRA method provided a bulk density estimate from whole-round sections. The MAD method applied to 199 discrete samples from Site U1404 provided a second, independent measure of bulk density as well as dry density, grain density, water content, and porosity. Changes in bulk density of discrete samples are consistent with those in GRA bulk density (Fig. F33), although GRA bulk density values are slightly higher than the MAD bulk densities, which is speculated to be a GRA calibration issue. From the top of Hole U1404B to ~25 mbsf, bulk density decreases from 1.7 to 1.2 g/cm³. We infer the same trend in Hole U1404A across the recovery gap between 20 and 30 mbsf. Below, bulk density values increase downhole to 1.8 g/cm³ at the bottom of lithostratigraphic Unit II at ~200 mbsf. In Hole U1404A at ~110 and ~190 mbsf, bulk density from MAD analyses on discrete samples does not follow GRA density values, which exhibit two small peaks. In Unit III and in the upper part of Unit IV, bulk density averages 1.75 g/cm³, with a small drop to 1.65 g/cm³ between 242 and 254 mbsf associated with a radiolarian clay layer (see “Lithostratigraphy”). Bulk density decreases at ~272 mbsf at the top of Core 342-U1404A-33X at the same depth that the coring method changed from APC to XCB.

Water content and porosity in Holes U1404A and U1404B gradually increase from 0 to 21.6 mbsf and then decrease downhole to minima at ~200 mbsf, with steep gradients in these parameters between 170 and 200 mbsf (Fig. F33). From 200 to 300 mbsf, these physical properties maintain near-constant values (40 wt% water content and 60 vol% porosity), except for two minor peaks below at ~250 and ~275 mbsf.

Grain density varies between 2.6 and 2.8 g/cm³ throughout Hole U1404A. At the top of Unit II (6.21–8.80 mbsf) and in Unit III (213.25–227.90 mbsf), some values are <2.5 g/cm³.

P-wave velocity

Compressional wave velocity from whole-round sections and section halves follow similar trends in the three holes and are consistent with one another (Fig. F34). However, PWC values are slightly lower than those obtained by the P-wave logger in the APC-cored interval. Overall, P-wave velocity increases downhole from top to bottom in Holes U1404A and U1404B. Between the top of the hole and 200 mbsf, the increase is gradual (from 1500 to 1600 m/s). At ~196 mbsf, near the top of Unit III, velocity increases with a notable step from 1560 to 1640 m/s. In Unit IV in Hole U1404A, P-wave velocity gradually increases and reaches 1670 m/s at 260 mbsf.

Natural gamma radiation

NGR shows large variations between 10 and 50 cps over the uppermost 50 mbsf (upper part of lithostratigraphic Unit II) (Fig. F34; see also “Lithostratigraphy”). For the remainder of Unit II, from 50 to ~200 mbsf, NGR increases gradually from low values of 15 cps and reaches 60 cps by 200 mbsf. Between 200 and 275 mbsf in Unit III and upper Unit IV, NGR values are ~40 cps with large fluctuations between 18 and 60 cps. Minima of ~20 cps are found at 205 mbsf in Holes U1404A and U1404B and correspond to low magnetic susceptibility values. Below 235 mbsf, values decrease to ~30 cps and fluctuate between 35 and 45 cps.

Color reflectance

Color reflectance a* and b* parameters follow similar trends to one another and reflect changes in lithology (Fig. F35). In lithostratigraphic Unit I and the upper part of Unit III, both a* and b* have high values (a* = 0–6, and b* = 5–15). a* and b* values drop abruptly at 12 mbsf and are nearly constant within Unit II between 12 and 200 mbsf. In Unit III, a* and b* increase sharply and then decrease downhole, with the maximum at 208 mbsf in Hole U1404A and at 206 mbsf in Hole U1404B. a* and b* maintain consistent values in Unit IV (a* = –3–0, and b* = 0–5). Lower a* and b* values in Units II and IV reflect green clay. The higher a* and b* values recorded in Units I and IV correspond to yellow, brown, and gray sediment (see “Lithostratigraphy”). Changes in color reflectance are consistent with changes observed in magnetic susceptibility and NGR (Fig. F34) and reflect the major lithologic characteristics of the sequence drilled at Site U1404.

L* corresponds to sediment brightness and follows pronounced lithologic changes (Fig. F35). High values for L* are seen in Unit I and the upper 10 m of Unit II. L* values drop to ~40 at ~12 mbsf in Hole U1404A and maintain this value to ~200 mbsf. At ~206 mbsf in Holes U1404A and U1404B (Unit III), L* reaches a maximum of 65.

All three color parameters show the largest variations in carbonate-bearing intervals of Units III and IV.

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