CORE PHYSICAL PROPERTIES

Physical properties were measured and evaluated on whole cores, split cores, and core samples from Site 1194. The multisensor track (MST) was used on whole cores to perform nondestructive measurements of bulk density, magnetic susceptibility, and natural gamma radiation (NGR). Compressional wave velocities were 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.

Density and Porosity

Two methods were used to evaluate the bulk density at Site 1194. Gamma ray attenuation (GRA) provided an estimate of bulk density from whole cores. MAD samples facilitated a second, independent measure of bulk density while providing grain density and porosity data. From 0 to 117 mbsf (lithologic Units I and II), MAD values cored with the APC are approximately 0.1 g/cm3 lower than GRA bulk density (Fig. F37). Below 117 mbsf (lithologic Units III-VI), MAD bulk density correlates with maximum GRA values. The low GRA bulk density below 117 mbsf is likely a result of undersized cores and/or sample disturbance as a result of XCB and RCB coring (see "Core Physical Properties" in the "Explanatory Notes" chapter).

Bulk density values show an overall increase downhole with small-scale variability superimposed (Fig. F37). Bulk density is 1.5 g/cm3 at the seafloor and increases to a maximum of 2.3 g/cm3 at 421 mbsf. The highest bulk density values (2.6-2.7 g/cm3) are associated with a hardground (117 mbsf; top of lithologic Unit III) and with the acoustic basement (lithologic Unit VI; see "Lithostratigraphy and Sedimentology").

Grain density has an average value of 2.7 g/cm3 and has considerable scatter from 2.3 to 3.3 g/cm3 (Fig. F37). Values less than 2.5 g/cm3 or greater than 3.0 g/cm3 are rare and may be the result of grain volume measurement error.

Porosity, calculated from MAD data (see "Core Physical Properties" in the "Explanatory Notes" chapter), decreases from 73% at 2 mbsf to less than 40% below 350 mbsf (Fig. F37). The lowest porosity (6%-8%) occurs in the hardground between lithologic Units II and III (117 mbsf) and in lithologic Unit VI (acoustic basement; see "Lithostratigraphy and Sedimentology").

Porosity () can be related to depth (z) using an exponential function and a porosity decay parameter with depth (k; e.g., Athy, 1930),

(z) = oe-kz.

A least-squares fit of this function yields o = 65% and k = 0.002 m-1 (correlation coefficient = 0.91; Fig. F37). This normal compaction trend suggests hydrostatic fluid pressures that are likely the result of moderate to low sedimentation rates and moderate permeability allowing drainage and compaction during deposition and burial. This trend also implies that erosion events have not been significant at this site, as erosion often appears as a step decrease in porosity.

Compressional Wave Velocity

Compressional wave velocity was measured at discrete intervals for Site 1194. The raw data show an abrupt velocity shift at 50 mbsf (Fig. F38). This step increase in x-directed velocity probably represents measurement errors with the PWS3 sensor. To correct this velocity shift, all PWS3 data below 50 mbsf were decreased by 100 m/s (Fig. F38). The 100 m/s shift is the average discrepancy between y-, z- and x-directed velocity from 50 to 60 mbsf and assumes isotropic velocity because the overall velocity structure at Site 1194 is isotropic (Fig. F38; see "Core Physical Properties" in the "Explanatory Notes" chapter).

Velocity generally increases from 1550 to 1600 m/s above 117 mbsf to 2800 m/s below 400 mbsf (Fig. F38). At a finer scale, abrupt increases in velocity are related to prominent lithologic boundaries. Velocity increases at 117, 160, 255, and 421 mbsf correspond to well-lithified boundaries with low porosity (e.g. hardground, firmground, and acoustic basement; see "Lithostratigraphy and Sedimentology" and "Downhole Measurements"). The increase in velocity at 117 mbsf correlates with the top of lithologic Unit III (see "Lithostratigraphy and Sedimentology"), the presence of dolomite (see "Geochemistry"), and an increase in wireline log velocity values (see "Downhole Measurements").

Velocity data often correlate with porosity. However, the porosity and velocity data from Site 1194 do not match the time-average relationship of Wyllie et al. (1956) (Fig. F39) (see "Core Physical Properties" in the "Site 1193" chapter) but can be described with a power law relation,

VP() = a-b,

where VP is the compressional wave velocity, and a (23,325 m/s) and b (0.65) are empirical constants determined from a least-squares regression (correlation coefficient = 0.92; Fig. F39). This power law correlation supports the porosity trend of consistent compaction and interpretation that if there has been any erosion, it has been minimal. Deviations from the velocity-porosity model in lithologic Units I-V may be indicative of hiatuses or exposures that have resulted in diagenesis, significant porosity loss, and velocity modification. High velocities (~5000 m/s) within lithologic Unit VI are controlled by lithology (acoustic basement) and do not represent diagenesis.

Temperature and Thermal Conductivity

The advanced piston corer temperature tool (APCT) was used to measure seafloor and downhole temperature. Four downhole temperature attempts were made, and three were successful (Cores 194-1194A-7H, 10H, and 13H; Fig. F40). The resulting temperature profile increases linearly with depth at an average gradient of 45°C/km (Fig. F41).

Thermal conductivity increases gradually with depth at Site 1194 (Fig. F41). The first three measurements (4, 8, and 18 mbsf) deviate significantly from this trend and are considered suspect because they are significantly elevated for unlithified, shallow sediments with high moisture content. From 27 to 420 mbsf, thermal conductivity increases from 1.1 to 1.9 W/(m·K). The scatter of thermal conductivity values below 117 mbsf may have resulted from variations in contact between samples and the half-space probe. Data above 117 mbsf were acquired with the full-space needle probe.

Thermal conductivity (Kbulk) can be described with a power law relationship (e.g., Keen and Beaumont, 1990)

Kbulk() = KwKgrain(1 - ),

where Kw is the thermal conductivity of the interstitial water, and Kgrain is the thermal conductivity of the solid grain (see "Core Physical Properties" in the "Explanatory Notes" chapter). The observed thermal conductivity follows this relationship within the range for the encountered sediments (Fig. F42). Together, the thermal conductivity and average thermal gradient provide a heat flow value of 49.5 mW/m2.

Magnetic Susceptibility, Natural Gamma Radiation, and Color Reflectance

Magnetic susceptibility (MS) has an average of 2.5 x 10-6 SI with 10- to 25-m scale variations superimposed (Figs. F43, F44). These variations are most apparent in lithologic Units I and II, where core recovery was nearly complete. NGR has similar trends to MS, including 10- to 25-m scale variations within lithologic Units I and II (Figs. F43, F44). Apparent cyclic variations are also observed in the downhole logs (see "Downhole Measurements"). Coincident increases in MS and NGR, a lack of glauconite, and the presence of gravity flow deposits (see "Lithostratigraphy and Sedimentology") suggest that these variations may represent fining upward sediment packages and/or increased terrigenous clay content. The local NGR high at 117 mbsf correlates with a phosphatic hardground (see "Lithostratigraphy and Sedimentology"). Above 5 mbsf, sediment color (lightness), a common proxy for clay content, also shows a high. Below 5 mbsf, lightness variations do not correspond with MS and NGR in lithologic Units I and II (Fig. F44).

Below lithologic Unit II, poor recovery prevents detailed interpretation of MS and NGR trends. Local maxima, however, are identified at 233-238 mbsf and 252-258 mbsf. Within lithologic Unit V, small-scale (~10 m) variations are present in the MS and NGR data, but are not as well-defined as within lithologic Unit II. They may represent input variability of terrigenous clay. The olivine basalt basement (lithologic Unit VI; see "Lithostratigraphy and Sedimentology") is characterized by a dramatic MS increase. This increase is not paralleled in the NGR.

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