We measured index properties on discrete samples taken from most of the cores recovered from Hole 1187. 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). Sonic compressional (P-wave) velocities in basement units were measured on uncut split cores and minicores. We measured thermal conductivity 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 Hole 1187A cores and calculated wet and dry bulk density, water content, grain density, and porosity (Table T7; Fig. F35). As shown in Figure F35, porosity, grain density, and bulk density change abruptly at the boundary between sedimentary Unit III and basement Unit 1. In basement, index properties remain fairly constant. Near the bottom of the hole, the grain and bulk density of the basalt from the lower part of Unit 11 both appear to decrease downhole (Fig. F35).
We determined magnetic susceptibility with the Bartington meter at 4-cm intervals along whole-core sections from most of the cores. Although values are generally <800 × 10-5 SI, higher magnetic susceptibility values (>1200 × 10-5 SI) in the basement units correlate with the presence of dense basalt (Fig. F36). We obtained similar results at Sites 1185 and 1186, where dense, massive basalt always exhibited higher magnetic susceptibility than more altered and heavily veined basalt. Magnetic susceptibility results are discussed further in "Paleomagnetism" in conjunction with the NRM pass-through measurements.
We estimated bulk densities from whole-core GRA measurements of the sections from Hole 1187A. In the Unit III claystone and chalk between 365.58 and 366.96 mbsf (curated depths), the average GRA density is 1.1 g/cm3 (Fig. F36). In basement, for the most part, only minor variations were observed in maximum GRA bulk densities (Fig. F36). Below 500 mbsf, however, in the lower part of Unit 11 and through Unit 12, mean GRA bulk densities decrease to <2.0 g/cm3. Although the diameter of the recovered core also decreased downhole in this interval, comparison of the GRA maximum bulk density profile with bulk density data obtained from discrete samples (up to the middle part of Unit 11) reveals similar trends in both sets of measurements, despite the consistently lower values of the GRA density data (Fig. F37).
NGR measurements of sediments from Unit III (Fig. F36) show high count rates (mean rate >6 counts per second [cps]). In basement, NGR measurements on unsplit sections of basalt cores generally show only minor fluctuations (usually below ~3 cps), but the downhole profile has a number of peaks >4 cps (Fig. F36). In Unit 3, for example, peaks of >4 cps at ~385, ~408, and ~415 mbsf appear to correspond to pillow basalt intervals in Cores 192-1187A-4R, 6R, and 8R, respectively, which are probably related to alteration and veining in the basalt. These observations are similar to those from Site 1186, where the highest NGR count (>5 cps) occurred in the pillow basalt.
We calculated P-wave velocity from discrete measurements on both split-core sections and cut samples (Table T8; Fig. F36). In the basement units, P-wave velocities are typically >5300 m/s in the relatively massive, unveined basalt sections of Units 3, 5, 6, and 7 and generally <5300 m/s in the more abundantly veined basalt sections of these units, as well as in the remaining basement units (Fig. F36). The high P-wave velocities (>5300 m/s) measured in the relatively unveined basalt also correlate with the large magnetic susceptibility spikes observed in the same units (Fig. F36). Below 500 mbsf, in the lower part of Unit 11 and through Unit 12, P-wave velocities decrease significantly (<5300 m/s), in similar fashion to mean GRA bulk densities in this interval.
We determined thermal conductivity on selected samples of basalt (Table T9; Fig. F35). Thermal conductivity values varied from 1.6 to 1.9 W/(m·K), with higher values in the dense, massive basalt and lower values in the more altered and veined basalt. The average thermal conductivity of the basalt is 1.7 W/(m·K), similar to basalt from Hole 1186.