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doi:10.2204/iodp.proc.320321.107.2010

Physical properties

Physical properties at Site U1335 were measured on whole cores, split cores, and discrete samples. WRMSL (GRA bulk density, magnetic susceptibility, 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-U1335A-1H through 45X. 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 section halves. The Ocean Optics sensor was used in place of the Minolta, and the resolution was reduced from 2.5 to 5 cm because of time constraints.

Density and porosity

Two methods were used to evaluate wet bulk density at Site U1335. GRA provided an estimate from whole cores (Fig. F20). 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 T24). MAD and GRA bulk density measurements display the same trends and are also similar in absolute values through the entire section (Fig. F21B). Cross-plots of wet and dry bulk density versus interpolated GRA density (Fig. F22) show excellent correlation between MAD and GRA density data.

Generally, wet bulk density corresponds with changes in lithology. Wet bulk density is lowest in Unit I (1.2–1.6 g/cm³), which contains the lowest calcium carbonate content. A prominent decrease in wet bulk density occurs at 58 m CSF, coinciding with an interval of clay-rich radiolarian ooze with diatoms within the major lithology of nannofossil ooze. Wet bulk density increases at the top of Unit II to values around 1.7 g/cm³. A small increase in wet bulk density occurs around 215 m CSF to values close to 1.8 g/cm³ in the lower portion of Unit II.

Variation in grain density in Hole U1335A generally matches changes in lithology (Fig. F21C). Grain density ranges from 2.0 to 3.0 g/cm³ in Unit I. In Unit II the grain density of the sediments is much more uniform in comparison, averaging 2.7 g/cm³ with variation up to 3.0 g/cm³. This average reflects the carbonates that dominate Unit II (calcite = 2.7 g/cm³).

Porosity ranges from 70% to 90% in Unit I, reflecting intervals of clayey radiolarian ooze within the major lithology of nannofossil ooze. In Unit II porosity gradually decreases to values of 50%–60% downhole over this ~300 m section. Porosity and water content vary inversely with wet bulk density (Fig. F21A).

Magnetic susceptibility

Whole-core magnetic susceptibility measurements correlate well with the major differences in lithology in Unit I. In Unit II, magnetic susceptibility variability follows changes in geochemistry and reflectance spectroscopy. Loss of the magnetic susceptibility signal results from suboxic diagenesis that develops below 70 m CSF (Fig. F20). Magnetic susceptibility values range from 5 x 10^–5 to 20 x 10^–5 SI in the upper portion of Unit I. In the lower portion of Unit I, magnetic susceptibility values increase to 25 x 10^–5 SI, which coincides with the occurrence of clayey radiolarian ooze within the major lithology of nannofossil ooze. Magnetic susceptibility values begin to decrease at the top of Unit II (64 m CSF) and then fall to values that are slightly negative (–1 x 10^–5 SI) in the zone of suboxic diagenesis as Fe reduction removes the ferromagnetic component of the sediment (see "Geochemistry"). Magnetic susceptibility values increase slightly and become highly variable (0 to 10 x 10^–5 SI) between 110 and 150 m CSF. Magnetic susceptibility values are higher in the interval from 160 to 200 m CSF, coinciding with a decrease in Fe reduction that is also accompanied by a color change from green to brown (see "Lithostratigraphy"). Below 200 m CSF the magnetic susceptibility signature is largely diamagnetic, with values close to zero, reflecting a return to Fe reduction in the lower section of Unit II. Magnetic susceptibility values increase to 15 x 10^–5 SI at the base of Unit II.

Compressional wave velocity

Shipboard results

Whole-core P-wave logger (PWL) data and discrete velocity measurements made on split cores follow similar trends, with key transitions reflecting increasing compaction with depth and the transition from ooze to chalk that occurs deep in the section (~220 m CSF) (Fig. F23). Discrete velocity measurements along the x-axis are in excellent agreement with PWL results, though y- and z-axis measurements generally overestimate by 10 m/s (Table T25; Fig. F23). Differences between whole-core and split-core measurements possibly reflect the presence of water in the space between the core liner and sediment in the whole cores and the slight compaction of the sediment in the contact probe technique.

Velocities are between 1460 and 1490 m/s in Unit I and the upper portion of Unit II. Below 200 m CSF, velocities begin to increase above 1500 m/s. At the base of Unit II, slightly below the described ooze/chalk boundary (345 m CSF; see "Lithostratigraphy") velocities increase dramatically, reaching values of 1600–1800 m/s at the bottom of Unit II.

Postcruise correction

The x-direction velocities at Site U1335 were determined using a liner thickness of 3.2 mm, the correction that was initially applied at Site U1334 (see "Physical properties" in the "Site U1334" chapter). 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 also was 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

NGR was measured on all cores at Site U1335 (Fig. F20). The highest NGR values are present at the seafloor (~73 cps). NGR values decrease rapidly with depth in Unit I, reaching values of 3 cps at the base of Unit I. In Unit II, NGR is very low (~1–2 cps) with low variability to the base of the section.

Thermal conductivity

Thermal conductivity was measured on the third section of each core from Hole U1335A (Table T26). Thermal conductivity shows a strong dependence on porosity downhole through the succession (Figs. F24, F25). Decreased conductivity occurs with increasing porosity as increased interstitial spacing attenuates the applied current from the probe. Thermal conductivity ranges from 0.8 to 1.0 W/(m·K) in Unit I and increases to 1.1 W/(m·K) in the upper portion of Unit II. Below 200 m CSF, thermal conductivity increases to 1.2 W/(m·K) and again to 1.3 W/(m·K) below 280 m CSF. These depths also coincide with increased P-wave velocity and decreased porosity. Below 380 m CSF, thermal conductivity decreases, possibly resulting from increasing fractures in the sediment core (see "Lithostratigraphy").

Reflectance spectroscopy

Spectral reflectance was measured on split archive-half sections from all three holes using the Ocean Optics sensor with the SHMSL (Fig. F26). L* variations correspond to pronounced lithologic changes, the main example being the interval of clay-rich radiolarian ooze within the lower portion of Unit I (~60 m CSF) where L* values drop from ~90 to ~30. Variations in a* (green–red) and b* (blue–yellow) reflect changes in lithology but also covary with changes in magnetic susceptibility, as color change in these cores is largely driven by pore water geochemistry below 70 m CSF (see "Geochemistry"). In Unit I both a* and b* are relatively high (4 and 15, respectively). Below 70 m CSF, both parameters drop to minimum values reflecting color change in the interval of iron reduction.

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