Physical properties at Site 1212 were measured on both whole-round sections and discrete samples from split-core sections. Continuous whole-round measurements were made of magnetic susceptibility, GRA bulk density, and compressional P-wave velocity, using the MST, for all Site 1212 cores. Natural gamma radiation measurements were made with the MST on Core 198-1212A-12H only. Discrete measurements of compressional P-wave velocity were made at a routine frequency of at least one measurement per split-core section in Holes 1212A and 1212B. Index properties were measured on discrete samples from split-core sections at an average frequency of one measurement per section in Hole 1212A.
All core sections from Holes 1212A and 1212B were routinely measured on the MST for magnetic susceptibility and GRA bulk density at 3-cm intervals (Figs. F26, F27). MST P-wave velocity was routinely measured at 10-cm intervals on all cores from Holes 1212A and 1212B (Fig. F28). Natural gamma radiation (NGR) was measured at 30-cm intervals in Core 198-1212A-12H only. All collected MST data are archived in the ODP Janus database.
Magnetic susceptibility values (Fig. F26) are generally highest in the uppermost ~63 m of the Site 1212 sedimentary column; this interval equates to Pleistocene-lower Miocene lithologic Unit I (see "Lithologic Unit I" in "Lithostratigraphy"). Peaks in magnetic susceptibility within lithologic Subunit IA may correlate with distinctive ash layers. In lithologic Unit I, an excellent correlation is also observed between magnetic susceptibility data and color reflectance measurements, primarily the total reflectance value (L*) and the 550-nm wavelength (see "Lithologic Unit I" in "Lithostratigraphy"). Both magnetic susceptibility and color reflectance data in this interval reveal a pronounced cyclicity, which may be useful in identifying astronomically controlled depositional processes. As already observed at Sites 1209, 1210, and 1211, a small peak (at ~58-63 mbsf) followed by a sharp decrease in magnetic susceptibility characterizes the lower middle Eocene-lower Miocene unconformity (see "Biostratigraphy"). Magnetic susceptibility values are higher in the Eocene and Paleocene segments of lithologic Unit II, between ~62 and ~102 mbsf, than those recorded in Unit III (Cretaceous). Higher magnetic susceptibility values were also recorded within the Paleocene interval of lithologic Subunit IIB than those recorded in Subunit IIA. As observed at Sites 1209, 1210, and 1211, large peaks in magnetic susceptibility values delineate the K/T boundary, which occurs at ~102 mbsf in Holes 1212A and 1212B (see "Biostratigraphy"). These magnetic susceptibility increases are associated with an increase in clay content and a decrease in carbonate content in this stratigraphic interval (see "Organic Geochemistry"). In Cretaceous lithologic Unit III, magnetic susceptibility values are generally close to background values, with the exception of some excursions that are related to chert horizons, and do not exhibit any consistent downhole variation.
Site 1212 MST GRA bulk density data (Fig. F27) do not exhibit a constant downhole increase, as would be expected if increased sediment compaction and dewatering with greater overburden pressure were the only factors controlling this physical property. However, GRA bulk density data do show some distinct variations that relate to lithologic changes at distinct horizons. For example, there are significant increases in measured GRA bulk density values at the lower middle Eocene-lower Miocene unconformity (~63 mbsf) and the K/T boundary (~102 mbsf). MST GRA bulk density values exhibit a general increase between the seafloor and ~45 mbsf, within Pleistocene-Pliocene lithologic Subunit IA, before decreasing to lower values through the Pliocene-Miocene components of lithologic Subunits IA and IB, between ~45 and ~63 mbsf. Hole 1212A MST GRA bulk density values show a significant minimum at ~43 mbsf, followed by a rapid increase between ~43 and 50 mbsf. Discrete bulk density measurements in Holes 1212A and 1212B and MST GRA bulk density values in Hole 1212B do not reflect this trend. MST GRA bulk density values exhibit a sharp increase at ~63 mbsf occurring at the lower middle Eocene-lower Miocene lithologic boundary. Cyclic variations in GRA bulk density values, similar to that evident in magnetic susceptibility and color data (see "Lithologic Unit I" in "Lithostratigraphy"), are found within Pleistocene-Miocene lithologic Unit I. A distinct minimum in MST GRA bulk density values occurs in the lowermost Eocene. Within the lower part of lithologic Unit II (Paleocene) MST GRA bulk density values decrease with increased burial depth, with a distinct minimum at ~100 mbsf occurring at the K/T boundary (i.e., between lithologic Units II and III). Within Cretaceous lithologic Unit III, below a stepped decrease at ~111 mbsf, MST GRA bulk density values gradually increase with burial depth to the bottom of Hole 1212B.
Hole 1212A GRA bulk density values are consistently higher than the discrete wet bulk density measurements (see Fig. F27; Table T12). 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. This phenomenon is most pronounced in lithologic Unit III because these sediments have the highest carbonate contents (see "Organic Geochemistry").
MST P-wave velocities are plotted in Figure F28. Despite some obviously "out of range" values, reliable P-wave velocities vary between ~1500 and ~1580 m/s, with the highest velocities generally recorded at greater depths in the sediment column. A linear relationship between increased burial depth and higher MST P-wave velocities is not observed at Site 1212. This suggests that sediment compaction and dewatering processes are not the only factors influencing P-wave velocity values. MST P-wave velocities do, however, follow the same downhole trends as the MST GRA bulk density data (see Fig. F27). MST P-wave values increase between the seafloor and ~15 mbsf, within the Pleistocene part of lithologic Subunit IA, then generally decrease between ~15 and ~63 mbsf (through the Pliocene-Miocene parts of lithologic Subunits IA and IB). One exception to this trend occurs from ~25 to 30 mbsf in Hole 1212A, where a marked increase in MST P-wave values is recorded. At ~63 mbsf, an abrupt increase in P-wave values from ~1510 to 1550 m/s correlates with the lower middle Eocene-lower Miocene unconformity. From ~65 to ~97 mbsf, P-wave velocities decrease with increasing burial depth (within the Eocene-Paleocene portions of lithologic Unit II). From ~97 to 102 mbsf, an abrupt decrease, followed by a significant increase, in P-wave values mark the lowermost Paleocene and the Cretaceous/Paleocene boundary. In the upper part of Cretaceous lithologic Unit III, from ~102 to ~110 mbsf, MST P-wave velocities show a gradual decrease to ~1540 m/s, then a significant decrease to ~1530 m/s, before gradually increasing with burial depth in the basal portion of Hole 1212B.
The downhole trends recorded by the reliable MST P-wave logger (PWL) values also compare well with the trends of the discrete measurements of P-wave velocity (Fig. F28; see also Table T13; Fig. F29). However, MST PWL values are generally lower than discrete values; this difference may be due to an assumption in the calibration of the MST PWL that the core liner is full of sediment and that there is no water between the liner and the sediment.
NGR data were collected at 30-cm intervals in Core 198-1212A-12H (Fig. F30) in the interval immediately above the K/T boundary. All measured values fall within the base of Subunit IIB (Paleocene). A relative peak in NGR values occurs at ~94.7 mbsf.
Discrete measurements of compressional P-wave velocity were made on Site 1212 split-core sections using the modified Hamilton Frame (PWS3) velocimeter. Data were collected at a routine sampling frequency of one measurement per section (Table T13; Fig. F29). Velocities vary between ~1500 m/s in the soft surface sediments and ~1580 m/s in the more consolidated sediments at Site 1212. Discrete P-wave measurements show a general increase in velocity, from ~1500 to ~1520 m/s, between the seafloor and ~20 mbsf, within Pleistocene-Pliocene lithologic Subunit IA. Below 20 mbsf, velocities remain relatively constant with depth to ~63 mbsf (Eocene/Miocene unconformity). P-wave velocities increase to ~1550 m/s between ~58 and ~63 mbsf in Hole 1212A and more abruptly in Hole 1212B at ~63 mbsf (lower middle Eocene-lower Miocene unconformity). Velocities then exhibit a general downhole increase through the Eocene segments of lithologic Unit II, to ~1590 (Hole 1212A) or ~1580 (Hole 1212B) m/s. In Hole 1212A, discrete P-wave values decrease through the lower Eocene and Paleocene parts of lithologic Unit II. In Hole 1212B, a peak in discrete P-wave values occurs at ~82 mbsf and delineates the P/E boundary. At the base of Hole 1212B, P-wave velocities between ~180 and ~190 mbsf are higher than those recorded in the upper part of lithologic Unit III.
A positive correlation between P-wave velocity and discrete bulk density in Hole 1212A (Fig. F31) indicates that these two properties are closely related at Site 1212. The lack of evidence for early diagenetic cementation near the seafloor, as shown by high-percentage porosity in the interval 0-60 mbsf (Fig. F32; Table T12), suggests that increasing P-wave velocity and bulk density with depth in the upper ~25 m of Site 1212 is primarily the result of compaction and pore fluid expulsion. The lack of any constant increase in either of these two physical properties with greater burial depth further suggests that compaction and pore fluid expulsion are not the only factors influencing the more deeply buried sediments at this locality. It is highly probable that primary sediment composition was an additional important factor that influenced postdepositional changes following sediment burial on the Southern High of Shatsky Rise, as also indicated at Sites 1209, 1210, and 1211 (see "Physical Properties" in the "Site 1209," "Site 1210," and "Site 1211" chapters).
Index properties determined for discrete samples from Hole 1212A are listed in Table T12 and shown in Figures F32 and F33. Index properties reflect progressive sediment compaction and fluid expulsion with depth in the sediment column, and also indicate changes in sediment composition as defined by lithologic units and subunits (see "Lithostratigraphy"). Bulk and dry density values increase between the seafloor and ~40 mbsf, through Pleistocene-Miocene lithologic Unit I. A slight decrease in bulk and dry density values occurs between ~40 and 63 mbsf. A large stepped increase in both bulk and dry density is evident at ~63 mbsf, delineating the unconformable boundary between lithologic Units I and II. Below ~63 mbsf, bulk and dry density exhibit a general trend to lower values through the Eocene-Paleocene segments of lithologic Unit II and Cretaceous lithologic Unit III. Slightly increased values in bulk and dry densities occur between ~160 and 180 mbsf. By comparison, grain density does not exhibit any clear downhole variation, which might explain the relatively good correlation between GRA bulk density and P-wave velocity (Fig. F31). Water content, porosity, and void ratio all exhibit a general downhole decrease between the seafloor and ~40 mbsf, through Pleistocene-Pliocene lithologic Unit I, the corollary to increasing bulk and dry density (see Fig. F33). A very slight increase in these values occurs between ~40 and 63 mbsf. At ~63 mbsf, water content, porosity, and void ratio exhibit a significant decrease that corresponds to the Eocene/Miocene unconformity. Between ~63 to 160 mbsf, within the Eocene and Paleocene portions of lithologic Unit II and Cretaceous lithologic Unit III, water content, porosity, and void ratio show general trends to higher values with increasing burial depth. These trends suggest that overburden on these sediments was not sufficient to cause significant downhole water loss and consequent decrease in porosity in the ~63 and 160 mbsf depth range. Below ~160 mbsf, there is a slight decrease in porosity, water content, and void ratio.
As observed at Sites 1209, 1210, and 1211, physical properties data at Site 1212 show variation with depth below seafloor that may be controlled by progressive compaction and fluid expulsion only in the uppermost part of the sedimentary column (i.e., between 0 and 40 mbsf). In addition, as at Sites 1209, 1210, and 1211, a simple relationship between lithology and physical properties is less obvious at Site 1212 than at Sites 1207 and 1208. As observed for Sites 1209, 1210, and 1211, the unusual downhole trends in physical properties data cannot be explained by the sediment burial history alone. The physical properties data suggest that there has been less compaction and diagenesis in the sediments below ~63 mbsf relative to those sediments in the overlying stratigraphic interval. This variability may be a reflection of varying microfossil composition within the Site 1212 sediments and the so-called "diagenetic potential" of different sediments (see "Physical Properties" in the "Site 1209" chapter).