Index properties, including wet bulk density, grain density, dry bulk density, water content, void ratio, and porosity, were measured on discrete samples taken from each core recovered at Site 1184. We made physical properties measurements on whole-core sections of all cores with the multisensor track (MST), including magnetic susceptibility, gamma ray attenuation (GRA) bulk density, and natural gamma radiation (NGR). Sonic compressional (P-wave) velocities were measured on cut samples and, where possible, in more than one direction on oriented cubes to investigate velocity anisotropy. Thermal conductivity was measured in unsplit sediment sections and on split rock samples from each core.
The general trend exhibited by the index properties data (Table T9) reflects downhole variations in lithology (Fig. F76). In Unit I (134.4-201.1 mbsf), bulk densities lie between 1.4 and 1.8 g/cm3, grain densities range from 2.4 to 2.6 g/cm3, and porosity fluctuates between 53% and 72%. Sediments in this interval consist of early Miocene foraminifer nannofossil ooze (see "Lithostratigraphy"). Below 201.1 mbsf, in the volcaniclastic sequence of Unit II, bulk density increases (Fig. F76). Both the water content and porosity (Table T10; Fig. F76) also begin to decrease below this depth. The mean bulk densities are 1.8 g/cm3 in Subunit IIA, 1.9 g/cm3 in Subunit IIB, 2.0 g/cm3 in Subunit IIC, 2.1 g/cm3 in Subunit IID, and 2.0 g/cm3 in Subunit IIE. Mean values of grain density in these same intervals are 2.2, 2.3, 2.4, 2.6, and 2.4 g/cm3, respectively. Porosity varies only slightly within Unit II, from a mean of 37.2% in Subunit IIA to 33.0% in Subunit IIB, 31.0% in Subunit IIC, 32.1% in Subunit IID, and 31.2% in Subunit IIE.
Although values are rather variable in the lower part of Subunit IIE, the slopes of all index properties data change noticeably, albeit slightly, at the boundary between Subunits IID and IIE (~437 mbsf). The mean bulk and grain densities in Subunit IIE are 2.0 and 2.4 g/cm3, respectively (Fig. F76), slightly less than those of Subunit IID.
We determined magnetic susceptibility with the Bartington meter at 4-cm intervals along whole-core sections of all cores. The results are shown in Figures F77 and F78. Magnetic susceptibility was also measured independently every 2 cm with the point-susceptibility meter on the archive multisensor track (AMST). The two magnetic-susceptibility data sets compare well with each other (Fig. F77). Susceptibility peaks in lithologic units commonly correlate with lithologic changes, such as from the lithic vitric lapilli tuff of Subunit IIB to the lithic lapillistone layers of Subunit IIC (Fig. F78). Detailed results are discussed in "Paleomagnetism" in conjunction with the NRM pass-through paleomagnetic measurements.
We estimated bulk densities from whole-core GRA measurements in all sections (Fig. F78). Although the GRA downhole bulk density profile (Fig. F78) consistently shows lower values than the data obtained from discrete samples (Fig. F76), the downhole trends exhibited by the two different data sets correlate well. In the foraminifer nannofossil ooze of Unit I, the average bulk density is 1.5 g/cm3. Below 201.1 mbsf, which is the boundary between Units I and II (see "Lithostratigraphy"), the bulk density gradually increases to an average of 1.8 g/cm3 in Subunit IIA, 1.9 g/cm3 in Subunits IIB and IIC, and 2.0 g/cm3 in Subunits IID and IIE.
NGR measurements on sections of the foraminifer-bearing white ooze near the top of Unit I (Fig. F78) in Cores 192-1184A-2R and 3R show peaks of >150 counts per second (cps) that probably reflect an increase in clay content between ~135 and ~150 mbsf. Below this interval, NGR values for the most part fluctuate between 0 and 150 cps, with a mean value of 28 cps, probably reflecting a relatively constant fluid content and an absence of significant voids in the cored sediments.
We determined P-wave velocity from discrete measurements on both split-core sections and cut samples (Table T10). P-wave velocities in Unit I range from 1562 to 1721 m/s, with a mean of 1589 m/s (Fig. F78). A marked velocity increase occurs in Unit II at ~200 mbsf, at the boundary between the foraminifer nannofossil ooze of Unit I and the lithic vitric tuff of Subunit IIA. Below 202 mbsf, velocities are typically >3000 m/s (Fig. F78), with a mean value of 3007 m/s in Subunit IIA, 3365 m/s in Subunit IIB, 3438 m/s in Subunit IIC, 3219 m/s in Subunit IID, and 3721 m/s in Subunit IIE. P-wave velocity abruptly increases at ~304 mbsf, where the lithologic change from Subunit IIB to Subunit IIC occurs. Magnetic susceptibility also increases at this depth (Fig. F78). P-wave velocities in Subunit IIC range from 3017 to 4408 m/s, with a mean value of 3438 m/s. Below 380 mbsf, the upper boundary of Unit IID, both magnetic susceptibility and velocity decrease. The high P-wave velocities (>3500 m/s) in the lithic vitric tuff and lithic vitric lapilli tuff of Subunit IIE are probably associated with high bulk and grain densities (Fig. F76).
We determined thermal conductivity in unsplit soft-sediment cores and in selected samples of lithified sediments (Table T11). Thermal conductivity values, commonly between 0.9 and 1.3 W/(m·K), exhibit little scatter in either Units I or II. Interestingly, the mean thermal conductivity value for the depth interval from ~320 to 397 mbsf, which encompasses Subunit IIC (where both magnetic susceptibility and velocity show major increases), is slightly but noticeably lower than that above this interval (Fig. F76).