Index properties, including wet bulk density, grain density, dry bulk density, water content, void ratio, and porosity, were measured on discrete samples taken from most of the cores recovered from Site 1185. Whole sections of these cores were also run through the multisensor track (MST) to measure magnetic susceptibility, gamma ray attenuation (GRA) bulk density, and natural gamma radiation (NGR). We measured sonic compressional (P-wave) velocities on cut samples and, where possible, in more than one direction on oriented cubes to investigate velocity anisotropy. Thermal conductivity was measured on split rock samples from most of the cores.
We measured the wet mass, dry mass, and dry volume of each sample taken from the cores from Holes 1185A and 1185B and calculated wet and dry bulk density, water content, grain density, and porosity (Table T12; Figs. F74 and F75). In the sediments of Unit II from Hole 1185A, between 250.9 and 300.2 mbsf, grain densities generally are between 2.1 and 2.6 g/cm3, with a mean of 2.3 g/cm3; porosity averages 58.8%, and the mean bulk density is 1.6 g/cm3 (Fig. F74). The sediments from Unit II in Hole 1185B are represented by a single core section (see "Lithostratigraphy"); index properties data in this section are similar to those of Hole 1185A: grain density is 2.6 g/cm3, porosity is 47.1%, and bulk density is 1.9 g/cm3 (Fig. F75). The only sample of basement measured from Hole 1185A, a basalt from Unit 5, has much higher grain and bulk densities and a much lower porosity than the overlying sediments (Fig. F74). In the basalts from Hole 1185B, bulk densities are higher (>2.6 cm3) within basement Units 2, 5, 10, and 11 and lower (<2.6 cm3) in Units 3 and 6-9. In general, both grain and bulk densities decrease downhole in Units 4-9, corresponding to a lithologic change from dense basalt to heavily veined basalt. Below Unit 9, an increase in bulk density correlates with a lithologic change from veined basalt back to dense basalt in Units 10-12.
We determined magnetic susceptibility with the Bartington meter at 4-cm intervals along whole core sections from Holes 1185A and 1185B. The results, shown in Figures F76 and F77, are discussed in detail in "Paleomagnetism". The peaks in magnetic susceptibility correlate well with the locations of dense basalt in each hole. For example, the magnetic susceptibility profile of basement units in Hole 1185A has three large spikes (>2000 × 10-5 SI units), one each in Sections 192-1185A-9R-1, 8-12 cm; 10R-3, 8-52 cm; and 11R-1, 40-52 cm (Fig. F76); these spikes correspond to intervals of dense basalt without veins. Similar features are seen in the magnetic susceptibility profile for Hole 1185B. As shown in Figure F77, heavily veined basalt in basement Units 6-9 exhibits much lower magnetic susceptibility values than the dense basalt both above and below these units.
We estimated bulk densities from whole-core GRA measurements of the sections recovered from Holes 1185A and 1185B (Figs. F76 and F77). Because maximum GRA densities give the best approximation for the true bulk densities of sediment (Blum, 1997), the following description focuses on the maximum estimated values. In the chalk of Unit II in Hole 1185A, sampled between 250.7 and 308.6 mbsf, the average estimated maximum density is 1.6 g/cm3, the same as that determined from index samples from this hole. In Unit II of Hole 1185B, between 308.1 and 309.6 mbsf, the estimated maximum densities range from 1.5 to 2.3 g/cm3, with a mean value of 1.7 g/cm3 (Fig. F77). Below 308.6 mbsf in Hole 1185A, the estimated maximum bulk density increases to an average of 2.2 g/cm3 in basement Units 1-5 (Fig. F76). In the basalt from basement Units 2, 5, 10, and 11 from Hole 1185B, the estimated maximum densities have higher mean values (>2.4 cm3), whereas bulk densities for Units 1, 3, 4, 6-9, and 12 have lower values (<2.3 cm3). Comparison of the GRA downhole maximum bulk density profile for the basement (Fig. F77) with bulk density data obtained from discrete samples (Fig. F75) demonstrates that the two sets of measurements generally correlate, despite the consistently lower values of the GRA density data.
Although NGR measurements on unsplit sections of cores from both Holes 1185A and 1185B mostly show only minor fluctuations downhole (very low numbers of counts), there are a few peaks in the NGR profile of Hole 1185B (Fig. F77). For example, in basement Units 1, 4, 7, and 8, peaks of >6 cps are centered at ~317, ~338, ~350, and ~370 mbsf (Fig. F77). These peaks appear to correspond to downhole changes in other physical properties, such as velocity and magnetic susceptibility, most clearly seen across the Units 4-5 boundary at 338 mbsf (Fig. F77).
We calculated P-wave velocity from discrete measurements on both split-core sections and cut samples from Holes 1185A and 1185B (Table T13; Figs. F76 and F77). P-wave velocities in the chalk of Unit II from Hole 1185A, although based on only a few data points, average 1610 m/s. Only one velocity determination was made for Unit II from Hole 1185B, yielding a velocity of 1841.4 m/s. A sharp velocity increase occurs in the basaltic basement of Hole 1185A (Fig. F76). Between 310.5 and 328.2 mbsf in basement Units 1-5, P-wave velocities range from 4641.1 m/s to 5612.1 m/s, with a mean of 5121.9 m/s. In the basement units of Hole 1185B, P-wave velocities are lower (generally <5000 m/s) in Units 1, 4, 6, and 9, whereas velocities are typically >5000 m/s in Units 2, 3, and 10-12 (Fig. F77). The high P-wave velocities (> 5000 m/s) in these relatively unveined basalts are associated with high bulk and grain densities and low porosity values (Fig. F74).
We determined thermal conductivity in unsplit soft-sediment cores and on selected samples of lithified sediments and basaltic rocks from Holes 1185A and 1185B (Table T14; Figs. F74, F75). In Unit II from Hole 1185A, thermal conductivity generally is <1.3 W/(m·K). In basalt from the basement units, thermal conductivity, although variable, generally increases with depth, exhibiting a local maximum value of 1.8 W/(m·K) in the bottom of Unit 5 (Fig. F74). The average thermal conductivity for the basement units is 1.7 W/(m·K). Thermal conductivity in basement Unit 1 from Hole 1185B is relatively low, with a mean value of 1.4 W/(m·K). For the other basement units, thermal conductivity is generally >1.5 W/(m·K). The maximum and minimum values (at ~340 and ~400 mbsf, respectively, see Fig. F75) correspond to dense, massive, gray basalt in Section 192-1185B-6R-5 and yellowish brown basalt in Section 192-1185B-13R-1, respectively (see "Alteration").
Apart from slight differences in the depths of the lithostratigraphic units in Holes 1185A and 1185B (see "Lithostratigraphy"), cores from both holes exhibit similar physical properties. Changes in the physical properties of the sediments and basaltic rocks recovered from both holes correlate with changes in lithology. In both holes, index properties change abruptly at the sediment/basement interface. Several large magnetic susceptibility spikes that correlate well with the presence of dense basalt also were observed in both holes. For the most part, variations in physical properties within the basement units at Site 1185 appear to reflect the amount of alteration and veining in the basalts.