-
(z) =
o
e-kz,
Physical properties at Site 1197 were measured and evaluated on whole cores, split cores, and discrete core samples. The multisensor track was used on whole cores to perform nondestructive measurements of bulk density, magnetic susceptibility, and natural gamma radiation. Color reflectance was measured on the archive halves of split cores. Compressional wave velocity was measured in the x-, y-, and z-directions on split cores and core samples. Moisture and density (MAD) analyses were performed on core samples. Thermal conductivity was evaluated on unlithified whole cores and on samples from semilithified and lithified cores.
Bulk density at Site 1197 was computed from gamma ray attenuation (GRA) using unsplit cores, and from MAD measurements on discrete plug samples. Each measurement method provides two independent estimates of bulk density. Bulk density averages 1.75 g/cm3 in the upper 50 mbsf with the GRA values being larger then the MAD density data by ~0.1 g/cm3. Limited core recovery from 50 to 375 mbsf, principally within seismic Megasequence C (see "Seismic Stratigraphy") prevented GRA measurements. The MAD data over this interval show a gradual increase from 1.75 to 1.95 g/cm3. Below 375 mbsf, both GRA and MAD measurements were taken with the MAD measurements being, on average, 0.2 g/cm3 greater than GRA. However, the general trends are similar: bulk density increases from ~2.1 to 2.3 g/cm3 over the interval of 375 to 600 mbsf. Below 600 mbsf, bulk density is nearly constant at 2.3 g/cm3.
Grain density above 50 mbsf is highly scattered between 2.6 and 2.85 g/cm3. The higher grain densities may reflect the presence of aragonite (see "Geochemistry"), which has a density of 2.93 g/cm3. From 240 to 500 mbsf, grain density decreases downcore from 2.85 to ~2.7 g/cm3 and then begins to increase slowly until the base of lithologic Unit V where it has a value of 2.75 g/cm3. Grain density again decreases within lithologic Subunits VIA and VIB, ranging from 2.6 to 2.7 g/cm3. These lithologic units consist of altered volcanic breccia composed of olivine basalt clasts and pumice set in a groundmass of finer-grained volcanic material (see "Lithostratigraphy and Sedimentology").
Porosity at Site 1197 is ~70% at the seafloor and decreases to ~20% at 660 mbsf. The porosity-depth trend can be described with a negative exponential curve of the form (Athy, 1930):
(z) =
o
e-kz, where
o is the
surface porosity and k is the porosity decay parameter (see the
"Explanatory Notes"
chapter). Least-squares estimation of these parameters is
o = 67%
and k = 0.0016 m-1 (correlation coefficient = 0.94; Fig.
F28). These
parameters are similar to those established for hemipelagic sediments at other
Leg 194 sites. Even though there is a significant data gap between 50 and 300
mbsf, the porosity trend is consistent within lithologic Unit I and the lower
lithologic units of the site (lithologic subunits IVA-VIB; Fig.
F28).
Compressional wave velocity was measured using the PWS3 contact probe system on both split cores (within the core liner) and ~9.5-cm3 cube samples of semilithified and lithified sediments. The cubes were used to measure velocity in the transverse (x and y) and longitudinal (z) directions.
Velocity values increase slowly from ~1650 to a maximum of 3175 m/s at a depth of 667 mbsf. Extreme velocity values correlate with the location of hardgrounds, such as the high 4796 m/s value at a depth of 59.6 mbsf (Fig. F29; see "Lithostratigraphy and Sedimentology"). The increased scatter in velocity value between 170 and 250 mbsf may reflect the high dolomite content associated with lithologic Unit III (see "Geochemistry"). Acoustic basement velocity (lithologic Subunits VIA and VIB) ranges from 3084 to 3870 m/s.
Velocity anisotropy is moderate and ranges from -10 to 10% (Fig. F29; also see "Geochemistry" in the "Explanatory Notes" chapter). A positive anisotropy represents the common situation where sound transmission is relatively more efficient parallel to bedding rather than it is across. The anisotropy, which is positive for 59% of the samples, appears to be randomly distributed with depth and does not show any simple relationship with either lithologic unit boundaries or grain size (see "Lithostratigraphy and Sedimentology").
A crossplot of velocity vs. porosity for Site 1197 shows a general inverse relationship (Fig. F30). The velocity data from Site 1197 show significant negative deviations (average ~500 m/s) from the time-average equation (dashed line, Fig. F30; Wyllie et al., 1956). They can better be described with a power law relation:
)
= a-b,
where VP is the compressional wave velocity, and a (16,860 m/s) and b (0.56) are empirical constants determined from a least-squares regression (correlation coefficient = 0.88; Fig. F30).
Thermal conductivity at Site 1197 has an overall downhole increase from 0.95 to ~2.4 W/(m·K) (Fig. F31) that is consistent with measurements at other Leg 194 sites. Thermal conductivity variability increases below 440 mbsf. Thermal conductivity can be described as having a power law dependence on the solid matrix grain thermal conductivity and the thermal conductivity of the interstitial fluid (see the "Explanatory Notes" chapter). The values from Site 1197 follow this relationship within the range for the encountered sediments (Fig. F32), which gives confidence to the observations. Given the high carbonate content of this site (~90%; see "Geochemistry"), the range in thermal conductivity is consistent with the theoretic limestone curve.
Magnetic susceptibility (MS) and natural gamma radiation (NGR) contain independent information concerning terrigenous sediment source and magnetic mineral derivation. Because of poor core recovery within lithologic Unit II through Subunit IVA at Site 1197, it is not possible to define a general trend in the NGR, MS, or the lightness (L*) parameter of color (Fig. F33). MS values range from 0 to 1725 x 10-6 SI, with the majority of values being less than 5 x 10-6 SI. Lithologic Unit I and Subunits VIA and VIB have the highest amplitudes. Lithologic Unit I is characterized by a general decrease in MS from ~25 to 5 x 10-6 SI. Superposed on this trend is a higher order ~10-m scale variability. Below 350 mbsf down to 625 mbsf, MS has a background value of 2 x 10-5 SI upon which are superposed a high-frequency signal with a length scale of 5-10 m. A prominent peak at 650 mbsf, with an amplitude of (>15 x 10-6 SI), appears to be responding to volcanic clasts within the base of lithologic Unit V (see "Lithostratigraphy and Sedimentology"). Volcaniclastic lithologic Subunits VIA and VIB (650 mbsf to base of hole) are characterized by the highest MS values that exceed 10-3 SI. For lithologic Subunit IVB and Units V and VI, NGR correlates with the MS and inversely correlates with the L* parameter of color (Fig. F33). The high lightness values from 610 to 645 mbsf correlate with high carbonate content (see "Geochemistry").
A large NGR spike occurs at 60 mbsf and is associated with the existence of a hardground (see "Lithostratigraphy and Sedimentology"). High NGR values have characterized the response of other hardground and exposure surfaces cored during Leg 194, although the detailed form of the NGR signal varies from site to site. NGR values are highly variable throughout the entire site, ranging from 0 to >30 counts/s. Within the scatter, three general trends can be recognized. The interval from 300 to 610 mbsf shows a slight increase in average NGR. This is underlain by an interval of low-amplitude NGR (610 to 640 mbsf), coinciding with the upper portion of lithologic Subunit IVA. Then, NGR increases near the base of lithologic Unit V and remains relatively high in lithologic Subunits VIA and VIB. Variations in lightness between 610 and 400 mbsf in association with large variations in both MS and NGR likely indicate fluctuations in terrigenous clastic input to the basin.
