An intensive physical properties program was conducted at Site 1075. Sound velocity, gamma ray-attenuation, and magnetic susceptibility were measured with the MST (see "Explanatory Notes" chapter, this volume). Thermal conductivity was measured with the needle probe on every second section of each core. On split cores, discrete measurements of ultrasonic velocities and shear strength were carried out. Two discrete sediment samples per section were taken for index properties analysis such as porosity and wet bulk density. The results were compared with seismic profiles obtained from previous investigations in this area (see "Site Geophysics" sections, "Site 1075," "Site 1078," "Site 1080," "Site 1081," "Site 1084," "Site 1085," and "Site 1086" chapters, this volume).
All core sections were routinely measured on the MST. Hole 1075A was measured at 2-cm intervals, and Holes 1075B and 1075C were measured at 4-cm intervals because of time constraints. MST data are included on CD-ROM (back pocket, this volume). The top and bottom 4 cm of each core were not measured. The large scatter in GRAPE density data below 50 mbsf is caused by the large number of small gas voids. The data were despiked and smoothed to prepare for visual inspection. An example of the data quality and the improvement by data processing is given (Fig. 33) for unfiltered and filtered GRAPE density.
Filtered GRAPE density data are compared with discrete wet bulk density data (see below; Fig. 34). Density values obtained with the MST system and from index properties measurements correlate well. All major features of density variations are also seen in index properties and also correlate with other physical and lithologic parameters and observations. Density increases gradually between 0 and 90 mbsf because of sediment compaction and dewatering. Below 100 mbsf, discrete density values decrease. GRAPE density shows large variations, but values are lower than the discrete density values. This is explained by an increasing proportion of gas charge of the sediment pores and/or the presence of small voids and cracks and/or air between the sediment and the core liner. A careful reconstruction and splice of undisturbed intervals is required from core photos, visual inspection, and by comparison with other MST data to provide optimum records and data sets suitable for calculation of synthetic seismograms and studies of sedimentary cycles.
Toward the bottom of the hole, a significant density increase is observed, which can be tentatively correlated with the strongest seismic reflector in the vicinity of the drill site within the cored depth range (see "Site Geophysics" section, this chapter). The characteristics of the average density profile correspond with the P-wave velocities, which could be measured at this site down to ~120 mbsf (Fig. 35). MST records of P-wave velocity are thoroughly filtered and limited to values in the expected range.
Magnetic susceptibility (Fig. 36A) is positively correlated with GRAPE and wet bulk density (Fig. 34), which may be attributed to a varying proportion of biogenic opal vs. clay in the sediment. Also, a good correlation of magnetic susceptibility and reflectance measurements, mainly the chromaticity (b*), can be found (see "Lithostratigraphy" and "Composite Section" sections, this chapter). Magnetic susceptibility reveals a pronounced cyclicity, which could be further used to identify astronomically controlled depositional processes in the region of the Congo River.
Compressional ultrasonic (P-wave) velocities were obtained on the split-core sections. The discrete measurements were performed with the digital sediment velocimeter (DSV1; see "Explanatory Notes" chapter, this volume) at a sample frequency of two per section. This system was used down to ~45 mbsf. Below that depth, the transducer arms could not penetrate the sediment without creating fractures, which inhibited the undisturbed sound transmission. Below 45 mbsf, the modified Hamilton Frame was used. Signals were completely attenuated at a depth of ~120 mbsf. In general, signal attenuation was observed to be higher in the upper sections of each core than in the lower portion.
As expected for the sediment type, velocities vary between 1460 m/s in the soft surface sediments and 1570 m/s in the more consolidated sediments. The peak in velocities corresponds to the peak in vane shear strength at 70 mbsf. Detailed analyses of velocity profiles will be possible after shore-based investigation of grain size, carbonate content, and crystallinity. Vane shear strength, velocity, and porosity are sensitive indicators for the change in rigidity of the sediment matrix caused by a different degree of cementation. A comparison of the continuous velocity profile obtained with the MST and discrete values is shown in Figure 35.
Thermal conductivity was measured in every second section of each core (Fig. 36B). Values decrease with depth, corresponding to the decreasing porosity (Fig. 37B).
Measurements were taken according to the procedure outlined in the "Explanatory Notes" chapter (this volume). The results are displayed in Figure 36C, together with magnetic susceptibility (Fig. 36A) and thermal conductivity (Fig. 36B). On average, values increase gradually down to a depth of 95 mbsf, with larger fluctuations within the gas-bearing interval from 60 to 95 mbsf. A significant decrease occurs below 115 mbsf, but no data are available for the depth range between 95 and 115 mbsf. One possible explanation for these unusual characteristics is failure of the sediment matrix caused by high pressure and/or deformation, or expansion of large amounts of dissolved gas during core retrieval.
Index properties, calculated from the weight and volume data using the pycnometer (see "Explanatory Notes" chapter, this volume), are wet bulk density, porosity, and moisture content. The density data correlate very well with the GRAPE data and can be used to calibrate and correct the GRAPE density (Fig. 34). Water content varies between 55% and 80% (Fig. 37C), porosity between 70% and 90% (Fig. 37B), and density values range between 1.200 and 1.450 kg/m3 (Fig. 37A; also see Table 14).
The intensive physical properties program measured at this site will be used for the detailed high-resolution analyses of cycles and temporal changes in sediment composition and for the construction of synthetic seismograms after thorough data processing. Detailed studies connecting these parameters with the physical and chemical state of the sediment and the responsible paleoceanographic events will be conducted on shore. Coring disturbance in the upper sections of the cores is apparent in most measurements, which will require careful evaluation of core and data quality before applying numerical methods on these data sets.