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doi:10.2204/iodp.proc.320321.104.2010

Physical properties

Physical properties at Site U1332 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-U1332A-1H through 18X. Compressional wave velocities were measured toward the bottom of sections. MAD analyses were located 10 cm below the carbonate analyses (see "Geochemistry"). Lastly, the SHMSL was used to measure spectral reflectance on archive-half sections.

Density and porosity

GRA provided wet bulk density from whole cores (Fig. F27), and 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 T30; Fig. F28). MAD and GRA bulk density measurements display the same trends and are also similar in absolute values through the entire section (Fig. F28). Cross-plots of wet and dry bulk density versus GRA density show excellent correlation between MAD and GRA data (Fig. F29).

Generally, wet bulk density corresponds to changes in lithology (Fig. F27). Wet bulk density is ~1.24 g/cm³ at the seafloor and varies between 1.2 and 1.25 g/cm³ through Units I and II. A slight step toward lower values (1.2 g/cm³) at ~12 m CSF shows the change from clay- to radiolarian-dominated lithology. The top of Unit III is marked by an increase in density to 1.5 g/cm³, with high-amplitude variation in this unit (from 1.4 to 1.6 g/cm³). A sharp decrease in wet bulk density (to ~1.2 g/cm³) occurs at the base of Unit III. Wet bulk density is relatively uniform with low-amplitude variations at ~1.2 g/cm³ in Subunit IVa. An increase in wet bulk density accompanies the lithologic change toward more carbonate in Subunit IVb. Density is lower in Subunit IVc. An increase in GRA bulk density in Unit V is corroborated by a single discrete MAD wet bulk density value (1.45 g/cm³).

Variation in grain density in Hole U1332A generally matches changes in lithology (Fig. F28). Grain density averages 2.7 g/cm³ in Unit III. In other units grain density averages 2.5 g/cm³ with variation from 2.1 to 2.8 g/cm³ and a high of 2.9 g/cm³ present near the seafloor. This variation is expected to be related to variations in the radiolarian content (opal = 2.2 g/cm³) and carbonate material (calcite = 2.7 g/cm³).

Porosity averages 85% in Units I and II, decreases to 70% in Unit III (Fig. F28), and rises again to ~80% in Subunit IVa. Porosity averages 80% in Subunits IVb and IVc and Unit V.

Magnetic susceptibility

Whole-core magnetic susceptibility measurements correlate well with the major differences in lithology and changes in bulk physical properties (Fig. F27). Magnetic susceptibility values increase gradually through Unit I from 20 x 10^–5 to 40 x 10^–5 SI, with a major spike occurring at ~12 m CSF (100 x 10^–5 SI). A decrease in susceptibility marks the top of Unit II, and susceptibility remains low to the top of Unit III, where it gradually rises to ~10 x 10^–5 SI. The base of Unit III contains a sharp rise in susceptibility to 40 x 10^–5 SI. Magnetic susceptibility shows small amplitude variations in Unit IV, with a marked decrease in average magnetic susceptibility values from 28 x 10^–5 to 18 x 10^–5 SI at ~100–108 m CSF. Susceptibility appears to be higher in Unit V; however, core recovery is incomplete in this interval.

Compressional wave velocity

Shipboard results

Compressional wave velocity was measured by the P-wave logger (PWL) on all whole cores from Holes U1332A–U1332C and by the insertion and contact probe systems on undisturbed sections of split cores from Hole U1332A (Table T31; Fig. F30), allowing determination of velocities in the x-, y-, and z-directions. Initial processing revealed an offset of ~50 m/s between PWL and discrete x- and y-directions and a difference of ~100 m/s for the x-direction. Values returned from the PWL generally varied between 1400 and 1450 m/s—considerably lower than the expected values and the calibrated value for water at 1500 m/s. Trials with the water-filled core liner on the PWL and discrete contact probe suggested that core liner parameters were not being used in the PWL's processing computations. This has now been confirmed, and previously recorded PWL velocity data have been corrected by subtracting 2.617 µs (the time taken for a P-wave to move through two layers of 2.8 mm thick core liner with a velocity of 2140 m/s) from the traveltime given by the PWL. Velocity was then recalculated using the time provided (corrected data have been uploaded into the database). This section discusses the corrected PWL data.

Corrected whole-core and split-core data follow similar trends, with key features occurring at similar locations (Fig. F30). An excellent correlation between PWL and y-axis values is observed from 0 to 80 m CSF. Z-axis measurements show good correlation in this interval with some values underestimated by ~40 m/s. Below 80 m CSF no z-axis measurements were obtained and the y-axis values significantly underestimate velocity (~1400 m/s) because the sediments are predominantly radiolarian ooze that is poorly cemented and so splits/fractures easily when the transducers are inserted. X-axis measurements are generally ~80 m/s faster than PWL values throughout the succession; this is expected to be related to the pressure applied to the sediments by the contact probes—increased sediment compactness, and thus traveltime.

PWL data show a limited relationship between velocity and lithology downhole (Fig. F30); the general trend is a slight velocity increase with depth. More information on the relationship between downhole trends in velocity and lithology can be detailed using the cross-plot of velocity (PWL) and wet bulk density (GRA) (Fig. F31). At low densities (<1.2 g/cm³) all units show considerable variability in velocity. All units apart from Unit III show a very slight decrease in velocity (from 1600 to ~1520 m/s) with increased density (from 1.2 to 1.45 g/cm³). Unit III shows a correlation where density and velocity increase together and may relate to the increased carbonate content of this unit.

Postcruise correction

During the initial sampling of Hole U1337A, it was observed that x-direction velocities are consistently higher than other velocities and that PWL velocities are consistently low for Hole U1337A and all holes drilled at Sites U1331–U1336. It was determined that the high x-directed velocities 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. PWL velocities were corrected for Hole U1337A by adding 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 whole cores at Site U1332 (Fig. F27). The highest NGR values are present at the seafloor (~130 counts per second [cps]) and decrease rapidly, reaching 15 cps at 5 m CSF. NGR increases in Unit I to 22 cps at 11 m CSF and then decreases to ~9 cps at 15 m CSF. This feature appears in all three holes and is a useful independent check on stratigraphic correlation based on magnetic susceptibility and GRA measurements. NGR is relatively uniform throughout the remainder of the section; however, relatively small variations (5–10 cps) occur at various locations downhole and can be identified in all three holes. At the top boundary of Subunit IVa, NGR values increase sharply to 9 cps (at 75 m CSF) and decrease gradually to 6 cps at ~84 m CSF. A prominent shift of NGR in the gamma ray pass of the Hole U1332A borehole log at 131 m WSF (see "Downhole measurements") is not observed in the cores. NGR is slightly higher in the basal intervals recovered from Cores 320-U1332A-17X and 320-U1332B-18X.

Thermal conductivity

Thermal conductivity was measured on the third section of each core from Hole U1332A (Table T32). Thermal conductivity measurements show a strong dependence on porosity in intervals containing >20% calcium carbonate (see "Geochemistry"). Thermal conductivity is ~0.8 W/(m·K) in Units I and II (Fig. F32). In Unit III, values increase to between 1 and 1.2 W/(m·K). In Subunit IVa, values return to 0.8 W/(m·K). A single measurement in Subunit IVb suggests thermal conductivity is higher in this unit. Thermal conductivity has been used with borehole temperature to investigate heat flow (see "Downhole measurements").

Reflectance spectroscopy

Spectral reflectance was measured on split archive section halves from Holes U1332A–U1332C using the SHMSL (Fig. F33). The parameters L* (black–white), a* (green–red), and b* (blue–yellow) follow changes in lithology, with variations in L* and b* correlating very well to carbonate content, density, and magnetic susceptibility. The parameter a* has a slightly more limited relationship with lithologic variation downhole. Carbonate-rich sediments are found in Unit III and Subunit IVb; these intervals are represented by a distinct increase in the L* and b* values in these sections. This feature is less obvious in the a* record. The upper half of Unit I is marked by high L*, a*, and b* values (averaging 62, 5.1, and 16, respectively); this high is related to the presence of clay in the upper part of this succession. L* and b* values increase around the middle of Subunit IVa (~96–102 m CSF). These increases in L*, a*, and b* are clearly responding to lithology, where carbonate-rich sections are light brown-gray and radiolarian-rich sections are darker brown.

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