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doi:10.2204/iodp.proc.341.105.2014

Physical properties

Physical properties measurements were taken in each of the five holes drilled at Site U1419 to provide basic information for characterizing the drilled section using whole-round cores, split cores, and discrete samples. After cores were divided into sections, all whole-round core sections longer than ~30 cm were measured through the GRA bulk densitometer and MS loop on the STMSL at 2.5–5.0 cm intervals with 2 s measurements. GRA bulk density and MS were measured with the WRMSL at 2.5 cm intervals with 5 s measurements. Compressional (P-wave) velocity was measured on the WRMSL for Holes U1419C–U1419E, although this data set is incomplete downcore because of complications associated with gas expansion, void spaces, and recovery (see “Compressional wave velocity”). After WRMSL scanning, whole-round sections were logged for NGR at 10 cm intervals. Color spectrometry, color reflectance, and MS were measured on the split cores using the SHMSL at 2.5 cm resolution. Discrete P-wave measurements and shear strength measurements were made on the working-half sections of split sediment cores from Hole U1419A on the Section Half Measurement Gantry. Moisture and density (MAD) were measured on 10 cm³ plugs collected from the working halves from Hole U1419A. Summaries of all the physical properties measured with the multisensor loggers on each hole, as well as discrete bulk density and P-wave velocity, are provided in Figures F22, F23, F24, F25, and F26.

Gamma ray attenuation bulk density

Variations in GRA bulk density at Site U1419 likely reflect changes in mineralogy/lithology, consolidation, and porosity. Whole-round GRA bulk density averages ~1.93 g/cm³ in the APC cores and displays downhole cyclic variability on the order of ~0.2 g/cm³ (Figs. F22, F23, F24, F25, F26). There are two intervals of anomalously low (<1.8 g/cm³) GRA bulk density in the recovered stratigraphic section between ~0 and 6 m CCSF-B and between ~80 and 87 m CCSF-B (Fig. F22). Incomplete recovery complicates interpretation of the diamict intervals that comprise the deepest recovered material; however, shallower than ~120 m CCSF-B a general trend toward higher densities with depth is consistent with sediment consolidation/compaction.

Magnetic susceptibility

As outlined in “Physical properties” in the “Site U1417” chapter (Jaeger et al., 2014b), for purposes of comparison the WRMSL loop and point-source MS data sets were both smoothed using a Gaussian filter of 10 cm (±3σ) and then interpolated to constant resolution (note those data in the LIMS database are recorded at their raw measurement resolution). We find an offset in the relative magnitude of the measurements, with loop MS being on average 1.52× greater than the point-source data collected from Holes U1419A–U1419E (Fig. F27). This ratio is lower than that observed for Sites U1418 and U1417; the ratios of loop to point-source MS appear to fall into two populations as opposed to trending along a line. The existence of these two populations may be related to poor contact of the point-source MS meter with the core surface in the diamict section, gas expansion of the core sections between measurement by the loop and point-source sensors, and/or an issue with the calibration of one of the instruments. We evaluate all volumetric MS measurements in instrument units (IU) because of the lack of available absolute calibration standards (see “Physical properties” in the “Methods” chapter [Jaeger et al., 2014a]).

We normalize loop MS for changes in sediment recovery and compaction by dividing the volumetric mass susceptibility by the GRA bulk density after Gaussian smoothing both data sets with a filter of 10 cm (±3σ) to correct for the differing response functions of the instruments. This generates a mass MS (χ) with units of cubic centimeters per gram (Fig. F28). Correcting for changes in sediment volume reduces the variance in χ by ~20%, relative to the equivalently smoothed raw WRMSL MS data normalized by the mean GRA core density. Mass MS averages ~68 cm³/g downhole at the site (Fig. F28). Recurring variability between 55 and 90 cm³/g is present in the core shallower than ~80 m CCSF-B, potentially transitioning to variability of increased amplitude and reduced frequency at greater depths, although reduced core recovery limits interpretation.

Compressional wave velocity

P-wave velocity was measured on the WRMSL P-wave logger (PWL) in Holes U1419C–U1419E. We were unable to use the PWL on Holes U1419A and U1419B because the P-wave pulser box failed on the Section Half Measurement Gantry. As a result, the pulser box for the WRMSL system had to be shared between the tracks for the remainder of the cruise. A near-continuous record of velocities was captured in Holes U1419C–U1419E between ~5 and 25 m CSF-A (Fig. F29). Deeper than ~25 m CSF-A, velocity measurements were compromised because of the nature of the recovered sediment. Much of the sediment was diamict with variable clast sizes (see “Lithostratigraphy”). Often, this facies was not consolidated and void spaces developed during recovery that decoupled the core material from the liner. Core quality was also compromised by gas expansion shallower than ~100 m CSF-A. Large gaps in core recovery deeper than ~120 m CSF-A are present in Hole U1419A.

Discrete P-wave measurements using the P-wave caliper (PWC) tool (see “Physical properties” in the “Methods” chapter [Jaeger et al., 2014a]) were taken in Hole U1419A. Void spaces within the unconsolidated sections and gas expansion compromised PWC velocity measurements. Combined with poor core recovery, these compromised measurements meant we were unable to obtain velocities in the following depth intervals: ~5 to ~40, ~45 to ~58, ~69 to ~98, and ~120 to ~140 m CCSF-B (Fig. F30). PWC values show no significant overall trend with depth, although a region of higher velocity is observed at ~120 m CCSF-B where velocities increase to ~1800–2100 m/s (Fig. F30). PWC values were automatically picked where possible and manually picked when the automatic picker encountered errors where the calipers did not have sufficient contact with the sample because of very soft sediment or bad coupling with the liner.

A single PWC measurement was completed within the uppermost ~25 m CCSF-B of Site U1419, so there is little overlap between the PWC and PWL velocity measurements (Fig. F30). Some overlap occurs between the measurements in intervals near 40, 60, and 100 m CCSF-B where the values appear well correlated, but there is not enough overlap to construct a statistically significant scatter plot (Fig. F30). Although we believe that the few measurements we were able to obtain are reasonable, care must be taken when making interpretations based on these velocity data because the sampling is biased by both core recovery and variable measurement frequency of different lithologies. All discrete measurements at this site were taken within the dominant lithology of the recovered interval.

Natural gamma radiation

NGR was measured at 10 cm intervals on all whole-round core sections that exceeded 50 cm in length (Fig. F31), with minimum section length limited by the response function of the sodium iodide detectors (see “Physical properties” in the “Methods” chapter [Jaeger et al., 2014a]). Each measurement reflects the integration of 5 min of counts (i.e., 10 min of counting per section, consisting of 5 min at each of two positions separated by 10 cm). NGR measurements show recurring downhole variations between 14 and 43 counts per second (cps) with a mean and standard deviation of 32 and 4, respectively. Downcore variability in raw NGR values closely parallel changes in GRA bulk density. Two notable intervals of reduced raw NGR (<30 cps) occur between ~0 and 6 m CCSF-B and between ~80 and 87 m CCSF-B, correlated with lows in GRA bulk density (Fig. F31) and WRMSL MS (Fig. F28), corresponding to the uppermost and lowermost part of lithostratigraphic Unit 1, respectively (see “Lithostratigraphy”).

As with WRMSL MS, we calculate an equivalent activity of the sediment by normalizing to the raw GRA bulk density after Gaussian smoothing the data sets to 50 cm (±3σ) to accommodate for the varying response functions of the instruments. This treatment reduces the overall variance in the NGR record by ~30% relative to the Gaussian-smoothed uncorrected NGR data normalized by the mean core GRA bulk density. The decrease in raw NGR observed shallower than 6 m CCSF-B is preserved; however, the low in raw NGR between ~80 and 87 m CCSF-B is not apparent in mass-normalized NGR activity, which suggests that the composition of the lithogenic component in this interval is likely similar to that at the surrounding depths. Low-frequency variability in NGR activity is roughly characterized by a downhole increase between 0 and 120 m CCSF-B in Holes U1419A–U1419E. This trend may be arrested or partially reversed below 120 m, although this observation is uncertain because of poor core recovery (Fig. F31).

Moisture and density

Bulk density values in Hole U1419A were calculated from mass and volume measurements on discrete samples taken from the working halves of split cores (see “Physical properties” in the “Methods” chapter [Jaeger et al., 2014a]). Depending on core recovery, quality, and lithology, one to three samples were taken per core. A total of 46 samples were analyzed for MAD.

MAD values correspond well with GRA bulk densities measured on the WRMSL for Hole U1419A, increasing downhole from ~1.5–1.6 g/cm³ at the seafloor to ~2.2–2.4 g/cm³ at ~120 m CCSF-B. The interval between ~120 and ~140 m CCSF-B was not recovered. Deeper than ~140 CCSF-B, density increases from ~2.0–2.1 to 2.2 g/cm³ by ~180 m CCSF-B (Fig. F32).

Bulk grain density values range between 2.7 and 2.9 g/cm³ shallower than ~30 m CCSF-B. Between ~40 and ~90 m CCSF-B, grain density values show reduced variability around ~2.8 g/cm³. Deeper than ~90 m CCSF-B, grain density values again show greater scatter, ranging from ~2.7 to 3.0 g/cm³ (Fig. F33).

Porosity measured on discrete samples generally decreases with depth. There was increased scatter between ~60 and 100 m CCSF-B and a population of anomalously low porosity observed at ~115 m CCSF-B (Fig. F33).

Shear strength

Shear strength measurements were performed on working section halves from Hole U1419A using the automated vane shear testing system (see “Physical properties” in the “Methods” chapter [Jaeger et al., 2014a]). Efforts were taken to avoid the locations of obvious drilling disturbance or cracks in the half-core sample. Measurements were taken as close as possible to the positions of the MAD samples and PWC measurements.

Shear strength indicates that sediments range from very soft (0–20 kPa) to stiff (up to 79 kPa). Generally, shear strength increases with depth at a constant rate. An anomalous interval of elevated shear strength (~60–79 kPa) is present at ~120 m CCSF-B (Fig. F34). This interval coincides with an increase in both P-wave velocity (Fig. F30) and density and a decrease in porosity (Fig. F33). Gaps in the measurement record reflect intervals of poor recovery. All samples were taken in the dominant matrix lithology of the recovered sediment.

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