Physical properties at Site 1213 were measured on both whole-round sections and discrete samples from split-core sections. Because of poor core recovery at Site 1213, only a limited number of cores were measured on the multisensor track (MST). The MST records of magnetic susceptibility, gamma ray attenuation (GRA) bulk density and natural gamma radiation thus have poor stratigraphic coverage. Discrete measurements of compressional P-wave velocity were made at a routine frequency of at least one measurement per split-core section in Holes 1213A and 1213B. No index properties measurements were made at Site 1213.
Whole-round core sections from Holes 1213A and 1213B were routinely measured on the MST for magnetic susceptibility and GRA bulk density at 3-cm intervals in Cores 198-1213A-1R to 7R and 198-1213B-8R to 10R and 27R (Figs. F34; F35). In Cores 198-1213B-28R to 33R, magnetic susceptibility and GRA bulk density were measured at 5-cm intervals. Natural gamma radiation was measured at 5-cm intervals (with a count time of 10 s) in Cores 198-1213B-8R through 10R and 27R through 33R (Fig. F36). All collected MST data are archived in the ODP Janus database.
Hole 1213A magnetic susceptibility values appear to display no discernible downhole trend, although relatively higher values are recorded at ~9 and ~51 mbsf, and these intervals may correlate with ash layers (Fig. F34). The magnitude of Hole 1213A magnetic susceptibility data are comparable with values measured in the Pleistocene-Pliocene interval at other Leg 198 sites (see "Physical Properties" sections in the "Site 1207," "Site 1208," "Site 1209," "Site 1210," "Site 1211," and "Site 1212" chapters). In cores from Hole 1213B, magnetic susceptibility values are close to background in the lower Aptian-Hauterivian (~257 to ~276 mbsf) (Fig. F34) but are slightly higher in the basal Berriasian (~439 mbsf). Below ~447 mbsf in Hole 1213B, the diabase has magnetic susceptibility values in excess of 2000 x 10-5 SI.
GRA bulk density data show a slight downhole increase between the seafloor and ~11 mbsf (Fig. F35). Between ~11 and ~15 mbsf, GRA bulk density values decrease, and then from ~18 to 27 mbsf GRA bulk density values increase slightly. GRA bulk density values appear to decrease between ~37 and ~52 mbsf. A stepped downhole increase in GRA bulk density occurs across the boundary between lithologic Units I and II at 54.6 mbsf, which represents an unconformity between the Santonian and the lower Pliocene (see "Biostratigraphy"). GRA bulk density was not measured between ~57 and ~447 mbsf, due to the poor recovery of sediments. Between ~447 and ~494 mbsf, at least three units of diabase were recovered, and within these igneous rocks (Subunits IVA-IVC) a slight downhole increase in GRA bulk density values is evident. A number of low values in the GRA bulk density data obtained for the ~447 to ~494 mbsf interval may be due to cracks, veins, and/or poor contact between the liner and the diabase.
Natural gamma radiation was measured in the Hole 1213B Lower Cretaceous sediments and diabase only (Fig. F36). At ~254 mbsf, high natural gamma radiation values are recorded that correspond with a lower Aptian black shale (see "Lithostratigraphy") that contains a high amount of organic carbon (see "Organic Geochemistry"). Other Lower Cretaceous cores that were measured for natural gamma radiation (Cores 198-1213B-9R, 10R, and 27R) have fairly constant values and show no obvious downhole trend. Natural gamma radiation values in the diabase (lithologic Subunits IVA-IVC) (see "Lithostratigraphy") are fairly constant downhole, but absolute values are slightly lower than those in the Lower Cretaceous sediments.
Discrete measurements of compressional P-wave velocity were made on Site 1213 split-core sections using the modified Hamilton Frame (PWS3) velocimeter. These data are listed in Table T18 and illustrated in Figure F37. Data were collected at a routine sampling frequency of one measurement per section. A variety of lithologies were cored at Site 1213, each of which have distinct P-wave velocities (Table T19). Within the recovered sediments, there is a general downhole increase in P-wave velocity between 0 and ~60 mbsf, and this is most likely related to progressive sediment compaction and dewatering with increasing burial depth. An increase in P-wave velocity occurs at ~57 mbsf, within the uppermost part of Cretaceous Subunit IIA. Between ~240 and ~440 mbsf, a general downhole increase in the P-wave velocities of chalk and limestone sediments relates to increased lithification with greater burial depth. Downhole trends in the P-wave data obtained for chert, porcellanite, radiolarite, and diabase lithologies are not evident at Site 1213 (Fig. F37).
Physical properties data from Site 1213 primarily reflect the compositional variability between the different sediments and igneous rocks recovered. Data from the recovered sediments are diagnostic both of the depth of burial (i.e., degree of lithification) and also the amount of silicification. The high degree of variability of P-wave velocities below 100 mbsf, which is related to lithology, has significant implications for seismic interpretations of Site 1213 and related stratigraphic sections.