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doi:10.2204/iodp.proc.320321.106.2010

Physical properties

Physical properties at Site U1334 were measured on whole cores, split cores, and discrete samples. WRMSL (GRA bulk density, magnetic susceptibility, and P-wave velocity), thermal conductivity, and NGR measurements comprised the whole-core measurements. Compressional wave velocity measurements on split cores and MAD analyses on discrete core samples were made at a frequency of one per undisturbed section in Cores 320-U1334A-1H through 31X (Table T27). Compressional wave velocities were measured toward the bottom of sections. MAD analyses were located 10 cm downsection from carbonate analyses (see "Geochemistry"). Lastly, the Section Half Multisensor Logger (SHMSL) was used to measure spectral reflectance on archive-half sections.

Density and porosity

Two methods were used to evaluate wet bulk density at Site U1334. GRA provided an estimate from whole cores (Fig. F26). MAD samples gave a second, independent measure of wet bulk density, along with providing dry bulk density, grain density, water content, and porosity from discrete samples (Table T28). MAD and GRA bulk density measurements display the same trends and are also similar in absolute values through the entire section (Fig. F27B). Cross-plots of wet and dry bulk density versus interpolated GRA density (Fig. F28) show good correlation between MAD and GRA data.

Generally, wet bulk density corresponds with changes in lithology. Bulk density is very uniform for the first 15 m within Unit I, corresponding to a clay-rich interval at the top of the section (see "Lithostratigraphy"). An increase toward higher and less uniform bulk density values occurs in the lower part of Unit I. In Unit II, bulk density increases to values of ~1.6 g/cm³, reflecting the major lithology of this lithostratigraphic unit, nannofossil ooze. In Hole U1334A, bulk density decreases from 1.7 to 1.5 g/cm³ at 205 m CSF. A similar decrease occurs at 210 m CSF in Hole U1334B. A very slight trend toward higher bulk density begins at the ooze–chalk transition between Unit II and Subunit IIIa. Subunit IIIb is marked by a prominent decrease in bulk density. Within Subunit IIIb, bulk density begins to increase toward the base of the section.

Variation in grain density in Hole U1334A generally matches changes in lithology (Fig. F27C). Grain density is highly variable with values between 2.1 and 2.9 g/cm³ in Unit I and the top of Unit II. Within Unit II, below 90 m CSF, grain densities are more uniform (2.7 g/cm³), reflecting the character of the major lithology, nannofossil ooze. Grain density is slightly less uniform in Subunits IIIa and IIIb, with lower values (2.2 g/cm³).

Porosity averages 85% in the top of Unit I and decreases to 75% in the lower section of Unit I (Fig. F27). Porosity becomes uniform in the upper 80 m of Unit II, with values of ~65% to 75%. Below 130 m CSF, porosity becomes more uniform and shows a slight downhole decrease to between 60% and 70%. Porosity increases slightly in Subunit IIIa and shows little change in Subunit IIIb.

Magnetic susceptibility

Whole-core magnetic susceptibility measurements correlate well with major differences in lithology and changes in bulk physical properties (Fig. F26). Magnetic susceptibility values are high and variable (10 × 10^–5 to 40 × 10^–5 SI) in Unit I. A sharp drop in magnetic susceptibility occurs at the top of Unit II, owing to decreased concentration of ferromagnetic minerals in the nannofossil ooze–dominated lithology. The low values of this lithologic unit (~5 × 10^–5 to 10 × 10^–5 SI) are punctuated in several places with small jumps in magnetic susceptibility to values as high as 30 × 10^–5 SI (e.g., 55 m CSF). These jumps can generally be correlated from hole to hole. At 140 m CSF the magnetic susceptibility signal is lost because of iron reduction in the sediments (see "Geochemistry"). The magnetic susceptibility signal returns at 205 m CSF in Hole U1334A and at 210 m CSF in Hole U1334B. Magnetic susceptibility values are 10 × 10^–5 SI and relatively uniform for the remainder of Unit II and Subunit IIIa. A sharp increase in magnetic susceptibility occurs at the base of Subunit IIIb.

Compressional wave velocity

Shipboard results

Whole-core P-wave logger (PWL) and discrete velocity measurements made on split cores follow similar trends. The velocity record of Site U1334 is unremarkable in Units I and II, with very uniform velocity values of 1500 m/s (Fig. F26). A small increase in velocity to ~1540 m/s occurs in the middle of Unit II at ~150 m CSF; this may be linked to the color change toward green sediments observed here (See "Lithostratigraphy"). A key transition in velocity occurs at the ooze/chalk boundary between Unit II and Subunit IIIa. Below this lithologic unit boundary, velocity values increase steadily to 1600 m/s at the base of the section. Discrete velocity measurements along the x-, y-, and z-axis are in excellent agreement with the PWL for most of the section (Fig. F29). However, below the sonic discontinuity at 150 m CSF, velocity measurements in the y-axis become higher by ~50 m/s compared to PWL velocity measurements. Measuring discrete velocity became impossible below the ooze–chalk transition between Unit II and Subunit IIIa; large cracks formed during insertion of the transducers because of poor cohesion of the radiolarian-dominated sediments. Discrete x-axis velocity measurements closely track the PWL measurements throughout the section.

Postcruise correction

During the analysis of Site U1334 cores, it was decided that the consistently high x-direction values are the result of using an incorrect liner thickness. Based on a limited number of liner thickness measurements, it was decided that the liner correction should use 3.2 mm for the liner thickness. However, during the analysis of Hole U1337A cores, it was determined that high x-direction velocities do not result from thicker than expected core liner but instead are the result of using an incorrect value for the system delay associated with the contact probe (see "Physical properties" in the "Site U1337" chapter). Critical parameters used in this correction are system delay = 19.811 µs, liner thickness = 2.7 mm, and liner delay = 1.26 µs. During the analysis of Hole U1337A cores, it was also determined that consistently low PWL velocities required the addition of a constant value that would produce a reasonable velocity of water (~1495 m/s) for the quality assurance/quality control (QA/QC) liner (see "Physical properties" in the "Site U1337" chapter). These corrections have not been applied to the velocity data presented in this chapter.

Natural gamma radiation

Natural gamma radiation was measured on all whole cores at Site U1334 (Fig. F26). The highest NGR values are present at the seafloor (~15 cps). NGR values decrease to the base of Unit I. NGR is uniform throughout Unit II and Subunit IIIa. A slight increase by ~3 cps accompanies the lithologic boundary between Subunits IIIa and IIIb.

Thermal conductivity

Thermal conductivity was measured on the third section of each core from Hole U1334A (Table T29). Thermal conductivity shows a strong dependence on porosity and lithology downhole through the succession (Figs. F30, F31). Decreased conductivity occurs with increasing porosity as increased interstitial spacing attenuates the applied current from the probe. Thermal conductivity is 0.8 W/(m·K) in Unit I and increases to a maximum value of 1.2–1.3 W/(m·K) in Unit II. Values decrease to 0.9 W/(m·K) in Subunits IIIa and IIIb.

Reflectance spectroscopy

Spectral reflectance was measured on split archive section halves from all three holes using the SHMSL (Fig. F32). The parameters L* (black–white), a* (green–red), and b* (blue–yellow) follow changes in lithology, with variations in L*, a*, and b* correlating very well to carbonate content, density, and magnetic susceptibility measurements (Figs. F5, F32). L* has relatively low amplitude variations around 80 in the carbonate section of Unit II, whereas in more radiolarian-dominated intervals, L* has lower values, with higher amplitude variation, ranging from 25 to 75. Except for the light greenish gray interval discussed later, a* and b* generally show high values (~5 and 13, respectively) with high-amplitude and high-frequency variation in the more carbonate dominated Unit II. The light greenish gray carbonate interval, between 144 and 190 m CSF, is clearly seen in the a* data as values shift to around –3; negative a* values are indicative of green colors. The b* values decrease sharply to ~4 in this interval before rapidly increasing back to 13 at its base. L*, a*, and b* values all decrease at the boundary between Subunits IIIa and IIIb, correlating with the sudden increase in radiolarian content, which subsequently decreases toward the bottom of Subunit IIIb (whereas luminance values increase). The limestone present in Unit IV is represented by high values of L*, a*, and b* (around 60, 6, and 15, respectively) corresponding to its extremely light, almost white color.

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