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doi:10.2204/iodp.proc.340.111.2013

Physical properties

We observe a good correlation between Holes U1401A and U1401B but poor correlation between all other holes. The poor correlation between these other holes likely results from significant (>100 m) lateral separation. Magnetic susceptibility and seismic velocity are higher where coarse-grained volcanic sand exists and lower where we observe hemipelagic sediment. P-wave velocity shows no clear trend with depth. Although measurements are limited, shear strength generally increases with depth. We were unable to measure heat flow or thermal conductivity at this site.

Stratigraphic correlation between Holes U1401A, U1401B, U1401C, and U1401D

We correlated Holes U1401B, U1401C, and U1401D to Hole U1401A (Fig. F4) using magnetic susceptibility. We trimmed 5.1 cm off of each end of the core sections in the magnetic susceptibility data to minimize edge effects during correlation. Results yielded moderately good correlation (correlation coefficient = 0.58) between Holes U1401B and U1401A (Fig. F5). For Holes U1401C and U1401D, correlation is weak. It was especially difficult to find clear tie points in the uppermost few meters of sediment to tie Holes U1401C and U1401D to Hole U1401A, and we suspect reworking of the core during recovery and section cutting may be the cause. In addition, it appears that Hole U1401D is missing the uppermost 1 m of sediment, making it difficult to tie the top of this core. Ultimately, we achieved correlation coefficients with Hole U1401A of 0.30 and 0.68 for Holes U1401C and U1401D, respectively. Hole U1401C required downward stretching, whereas Holes U1401B and U1401D required both downward and upward stretching to achieve good correlations. Correlation corrections for each hole are generally consistent with the corrections expected from core descriptions. Nonetheless, we caution that the correlations displayed represent an initial analysis, and more detailed analysis using additional track data is warranted. All picked correlation depth shifts are shown in Tables T2, T3, and T4.

Gamma ray attenuation density, magnetic susceptibility, and P-wave velocity

We measured gamma ray attenuation (GRA) density, magnetic susceptibility, P-wave velocity, and natural gamma radiation (NGR) for cores recovered from all holes (Fig. F6). In all holes, positive peaks in magnetic susceptibility correspond to volcaniclastic beds (2000 × 10^–5 to 5000 × 10^–5 SI) and low magnetic susceptibility values (<2000 × 10^–5 SI) correspond to hemipelagic mud. In the uppermost 6 m in Hole U1401A, GRA progressively increases from 1.4 to 2.0 g/cm³ despite several mud layers interlaced with volcaniclastic sand at these depths. We did not observe this trend in the other three holes at this site. As at the other sites, NGR is strongly correlated with mud content in the beds, with more mud resulting in higher NGR values. The mud layer at ~10.3 mbsf in Hole U1401B has the highest NGR value, at 21 cps. P-wave logger (PWL) values clearly identify the two major lithologies: hemipelagic mud (1500–1650 m/s) and volcaniclastic turbidites (1650–1800 m/s; maximum = 1860 m/s).

Shear strength

Undrained shear strength measurements (S_u) in hemipelagic intervals were only performed with the fall cone in Holes U1401A and U1401B. No S_u measurements could be performed with the handheld penetrometer because the sand content was too high at the bottom of core sections. The automated vane shear was only used twice to avoid disturbing intervals of potential interest for stratigraphic and dating purposes. Available S_u measurements are consistent between holes and increase from 3–5 kPa in the upper few meters to 20 kPa at 15 m.

P-wave velocity

Discrete measurements of P-wave velocity measured on the x-axis (PW-X) show similar values to those at the other sites, with distinctly different speeds between the two major lithologies. Mud has velocities ranging from 1530 to 1660 m/s, whereas volcaniclastic sand has velocities of 1720–1920 m/s. These discrete measurements match the values from the PWL on whole-round cores. We measured a P-wave velocity on a single andesitic lava clast of >6000 m/s.

Moisture and density

We collected three moisture and density samples from Hole U1401A at this site, all in the first core (340-U1401A-1H). Two of these samples consist of hemipelagic mud; the other one is volcanic sand. The three samples have grain densities of ~2.75 g/cm³ and porosities between 50% and 60%.

Thermal conductivity

Thermal conductivity was not measured because the sediment was too coarse to permit reliable measurement.

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