Physical properties at Site 1208 were measured on both whole-round sections and discrete samples from split-core sections. Whole-round measurements included the continuous determination of magnetic susceptibility, gamma ray attenuation (GRA) bulk density, and P-wave velocity and some measurements of natural gamma radiation using the MST, as well as discrete measurements of thermal conductivity. Additionally, discrete P-wave velocities and index properties were measured at a frequency of at least one measurement per split-core section in Hole 1208A.
All core sections from Hole 1208A were routinely measured on the MST for magnetic susceptibility and GRA density at 2.5-cm intervals in Cores 198-1208A-1H through 17H, at 3-cm intervals in Cores 198-1208A-18H through 23X, and at 5-cm intervals in Cores 198-1208A-24X through 42X (Figs. F34, F35). MST P-wave velocity was routinely measured at 2.5 cm in all Hole 1208A APC cores (Fig. F36) but was not measured in the XCB cores because of the poor contact between the sediment and core liner. Natural gamma radiation was measured at 10-cm intervals in Cores 198-1208A-34X through 36X (Fig. F37). All collected MST data are archived in the ODP Janus database.
Magnetic susceptibility data (Fig. F34) are generally higher in magnitude in the uppermost 80 m of the Site 1208 sedimentary column, compared to the relatively lower values evident from 80 to 240 mbsf (these depth intervals are located in lithologic Subunits IA and IB) (see "Lithostratigraphy"). Peaks in magnetic susceptibility in lithologic Subunit IA may correlate with distinctive ash layers. As already observed in sediment cores drilled at Site 1207, the Pleistocene-Pliocene section of Site 1208 reveals an excellent correlation between magnetic susceptibility data and color reflectance measurements, the latter represented by the total reflectance value (L*) and the 550-nm wavelength. Both magnetic susceptibility and color reflectance data in this interval reveal a pronounced cyclicity, which may be useful to identify astronomically controlled climatic and depositional processes (see "Lithostratigraphy"). Magnetic susceptibility values are higher in lithologic Subunits IB and IC, relative to values between 60 and ~252 mbsf in Subunit IA. Magnetic susceptibility values are generally close to background values in lithologic Unit II (Campanian-Aptian) and do not exhibit any consistent downhole variation.
MST GRA bulk density data exhibit a general downhole increase in magnitude (Fig. F35), resulting from sediment compaction and dewatering processes with increased overburden pressure. In addition to the overall downhole trend, GRA bulk density data also show distinct variations that relate to lithologic changes at several distinct horizons. GRA bulk density values exhibit a decrease at ~160 mbsf, correlating to the depth at which coring changed from APC to XCB. An increase in GRA bulk density values at ~252 mbsf correlates to the boundary between lithologic Subunits IA and IB. Cyclical variation in GRA bulk density values, similar to that evident in magnetic susceptibility (see above) and color reflectance data, is also found within Pleistocene-Miocene lithologic Subunits IA and IB. However, GRA bulk density values are consistently higher than discrete wet bulk density measurements (Table T9) throughout Hole 1208A. These overestimated GRA bulk density values can be explained by the relatively high carbonate content, porosity, and moisture content of sediments; the calibration procedure for the MST GRA sensor is optimized for mixed-lithology sediments. Consequently, the GRA method overestimates the density in carbonate-rich sediments of all lithologic units, and this effect is most pronounced in Unit II because this unit has the highest carbonate content (see "Organic Geochemistry").
MST P-wave velocities were recorded at 10-cm intervals in Hole 1208A sections to a depth of ~185 mbsf (Fig. F36). A general trend to higher velocities with increased depth in the sediment column can be discerned from values lying between 1490 and 1530 m/s. However, the magnitude of the discrete measurements of P-wave velocity (Table T10) are generally offset to higher values from the MST P-wave logger values, a trend similar to that found in the physical properties data at Site 1207.
Natural gamma radiation data were collected at 10-cm intervals, using the MST, for Hole 1208A between 315.4 and 327.3 mbsf in order to investigate the Cretaceous-Paleogene unconformity (see "Biostratigraphy") recovered in this interval (Fig. F37). These data show a peak in magnitude that relates to the presence of clay-rich sediments.
Discrete measurements of compressional P-wave velocity were obtained on Site 1208 split-core sections using the modified Hamilton frame (PWS3) velocimeter. These data are listed in Table T9 and illustrated in Figure F38. Data were collected at a routine sampling frequency of one measurement per section. Velocities vary between ~1500 and ~1650 m/s, with most values occurring below 1600 m/s. Discrete P-wave measurements show an overall increase in velocity with depth, which is similar to that e vident in the reliable data obtained with the MST. Although the general downhole trend is one of increasing P-wave velocity, small-scale variations within the data set can also be seen. At ~230 mbsf, an increase in the range of P-wave velocities may be due to the onset of the ooze-chalk transition (see "Lithostratigraphy") and increasingly variable sediment lithologies. This lithologic variability is most pronounced in Subunit IB. A rise in P-wave velocity is observed at ~310 mbsf that correlates well with the top of Subunit IC and increasing clay content in the sediments recovered. P-wave velocities reach a maximum of ~1660 m/s immediately above the Campanian-Paleogene unconformity. P-wave velocities below this unconformity are considerably slower (~1550 m/s) and characterize most of Unit II. Increasing P-wave velocities at the base of Unit II (~375 mbsf) may be concurrent with an increase in lithification. P-wave velocities are positively correlated with discrete bulk density measurements (Fig. F39) (R2 = 0.68).
Thermal conductivity data from Site 1208, obtained using the TK04 system, are listed in Table T11 and shown in Figure F40. Measurements were made on Sections 1 and 3 of each core from Hole 1208A. Average thermal conductivity for the 80 data points is 0.93 W/(m·K), with a standard deviation of 0.31. Site 1208 thermal conductivity values also exhibit a general increase in magnitude with depth below seafloor, increasing from ~0.80 W/(m·K) near the seafloor, to ~1.25 W/(m·K) at ~374 mbsf. The downhole increase in thermal conductivity values broadly correlates (R2 = 0.77) with a decrease in porosity (Table T9) as shown in Figure F41 and as would be expected from increased sediment consolidation at greater depths.
Index properties were determined for discrete samples from Hole 1208A. These data are listed in Table T9 and shown in Figures F42 and F43. Index properties primarily reflect progressive sediment compaction and fluid expulsion with depth in the sediment column but also indicate changes in sediment composition as defined by lithologic units and subunits. Bulk and dry densities increase slightly in magnitude between the seafloor and ~20 mbsf in lithologic Subunit IA. The greatest increase in bulk and dry densities at Site 1208 occurs in lithologic Subunit IB, between ~290 and ~310 mbsf. Values further increase in lithologic Subunit IC, then remain approximately constant to ~375 mbsf through lithologic Unit II. By comparison, grain density exhibits a small downhole increase in magnitude between the seafloor and ~30 mbsf. Below ~30 mbsf, grain density values remain largely constant, with no discernible changes at lithologic boundaries. Water content, porosity, and void ratio (Fig. F43) all exhibit a general downhole decrease in magnitude in Subunits IA and IB. The largest downhole decrease in each of these properties occurs within Subunit IC and Unit II.