The objective of the physical properties program at Site 1135 was to aid interpretation of lithologic variations and regional geophysical results. Whole sections of all cores recovered from Site 1135 were run through the multisensor track (MST), which included magnetic susceptibility, gamma-ray attenuation porosity evaluator (GRAPE) bulk density, and natural gamma radiation (NGR) measurements. Only four cores (Cores 183-1135A-3R through 6R) were run through the compressional wave velocity logger (PWL) because RCB cores generally do not fill liners. Compressional wave velocities (Vp) from the split cores were determined in longitudinal (z) and transverse (y) directions where sediments were sufficiently soft, and in the x-direction for consolidated sediment. We determined velocities in the y- and z-direction in discrete samples. We analyzed several oriented cubes in more than one direction to investigate velocity anisotropy. Index properties determinations included bulk density, water content, porosity, and grain density. The sampling interval for index properties and discrete compressional velocity determinations was generally two per section of core with an emphasis on capturing variations driven by lithologic changes. Thermal conductivity was also determined for the sediments, generally one per core and occasionally more when time allowed. We did not determine undrained shear strength because torquing of the sediment during RCB coring destroyed the initial strength of the sediments.
We determined index properties of Site 1135 with a pycnometer and an Scientec balance. We measured values of wet mass, dry mass, and dry volume of the samples and calculated water content, grain density, and porosity (Table T6; Figs. F11, F12). The general increase in wet bulk density corresponds with a decrease in porosity downhole. As shown in Figure F11A, porosity decreases from 62%-55% in the nannofossil ooze (lithologic Unit II) (see "Lithostratigraphy") to 55%-36% in the nannofossil and calcareous chalk. Downhole grain density values vary little, with a mean value around 2.7 g/cm3 (Fig. F11B), which agrees with the high and constant CaCO3 content downhole (see "Lithostratigraphy"). At a depth of 132.5 mbsf (lower part of Subunit IIA), one sample yields a grain density of 3.2 g/cm3 (Fig. F11B). Even though black splotches of possibly pyrite are present in the sediment below this depth, this high grain density value is questionable. In the vicinity of 235 mbsf (Subunit IIB) and 393 mbsf (upper part of Subunit IIIC), grain densities exhibit lower values. This decrease in grain density agrees well with a silicified chalk zone within the upper part of Subunit IIIC, although no lithologic changes were apparent to explain this decrease in Subunit IIB. Note that values in water content, porosity, and carbonate content (see "Lithostratigraphy") decrease at the K/T boundary at a depth of ~260 mbsf (Table T6).
Bulk density was measured by the GRAPE every 4 cm on whole sections of cores (see "Physical Properties" in the "Explanatory Notes" chapter) (Fig. F13). In the ooze interval (Unit II) and in the upper interval of the nannofossil chalk (Subunit IIIA), GRAPE densities correspond well with wet bulk densities determined from discrete samples. Because of the fracturing of the chalk in Subunits IIIB and IIIC, the GRAPE data on whole cores from 315 to 526 mbsf are generally lower than data determined from discrete samples. By comparison with discrete measurements, GRAPE data values (that are) below 1.7 g/cm3 can be generally disregarded (see "Seismic Stratigraphy")
NGR was measured every 12 cm on unsplit sections of cores from Site 1135. Gamma-ray values are consistently below 2 cps at intervals from 10 to 247.7 mbsf in the nannofossil ooze (Unit II) and from 315.1 to 372.6 mbsf in the white calcareous chalk (Subunit IIIB). In Subunits IIIA and IIIC, the count increases to an average value of 4 cps and exceeds 6 cps at the bottom of the hole. A distinctive increase in NGR count is found at a depth of 260 mbsf, corresponding to the K/T boundary in Core 183-1135A-28R.
Magnetic susceptibility was determined on all whole cores every 4 cm on the MST and every 2 cm on the point-susceptibility meter (Fig. F13). High and low susceptibility peaks range from -5 × 10-6 to 5 × 10-6 SI units in Unit II and Subunits IIIA and IIIB, and between -5 × 10-6 and 15 × 10-6 SI units in Subunit IIIC, with more positive than negative values. More detailed results are discussed in "Paleomagnetism" in conjunction with the NRM pass-through and discrete sample measurements. A relative sharp increase in magnetic susceptibility is present at approximately the K/T boundary (Fig. F14A), suggesting that characteristic susceptibility response might be useful for identifying event boundaries.
As previously noted, the PWL was used for only four cores that filled the core liners; measurements were not made on the remaining cores with partially filled core liners. Void spaces within the liner result in inaccurate values of compressional wave traveltimes for the sediments.
Velocity values from 18.44 to 48.27 mbsf (Cores 183-1135A-3R through 6R) compare well with values for compressional wave velocities obtained from discrete measurements on split cores. These velocities are typically close to those of seawater (Fig. F11D, also see next section for more discussion).
Discrete measurements to determine compressional wave velocity were done on the PWS1 and PWS2 insertion probe system (Table T7). We calculated velocities both across and along the core (y and z directions) in the upper sections of Subunit IIA; deeper core sections cracked preventing reliable measurements because of insufficient contact between the transducers and sediment. Downhole compressional wave velocities in Unit II, which consists of nannofossil ooze and foraminifer-bearing nannofossil ooze (10 to 247.7 mbsf), increase gradually from 1580 to 1680 m/s with a few values as high as 1780 m/s. These changes correspond to a decrease in porosity from 62% to 55%. The lowest velocities are close to the value for seawater, 1510 m/s with 3.5% salinity at 18°C (Carmichael, 1982). Because of the lack of good grain contact and high porosity values in the unconsolidated sediments, the main compressional wave travel path of the takes place in the fluid. At this site, seawater temperature is close to 0°C, suggesting that a temperature effect could be expected in the upper part of the ooze interval if comparing laboratory measurements with in situ data.
Beginning in Core 183-1135A-26R (248 mbsf, top of the Unit III), downhole compressional wave velocity gradually increases with depth (Fig. F11). This trend corresponds to lithologic changes from nannofossil ooze in Unit II to chert-bearing nannofossil chalk of Unit III (Figs. F11, F12). Velocity values reach a maximum near the bottom of Unit III, with values ranging from 2000 to 2800 m/s in consolidated chalks. Velocity changes significantly in the vicinity of the K/T boundary at a depth of ~260 mbsf, where other physical parameters also change. Below 400 mbsf, velocities in the horizontal direction are slightly higher than velocities determined vertically; this anisotropy may be related to retrieval and unloading of the cores (Fig. F11). Velocity and wet bulk density correlate well (Fig. F12).
We determined thermal conductivities for 17 sediment cores (Table T8). Strong relationships exist among thermal conductivity, physical properties, and lithology. Thermal conductivity values for Unit II are commonly <1.2 W/(m·K), with a median value of 1.09 W/(m·K). For Unit III, thermal conductivity values are generally >1.20 W/(m·K), with a median value of 1.70 W/(m·K). Variations in calcium carbonate content seem to be directly related to thermal conductivity values at Site 1135.
Although RCB drilling disturbed sediment in many cores at Site 1135, two robust features arise from the physical properties data. First, velocity, magnetic susceptibility, natural gamma ray, water content, porosity, and carbonate content change significantly as the sediments consolidate near the K/T boundary at a depth of 260 mbsf. Second, there is a distinctive depth trend for the downhole bulk density, compressional wave velocity, and thermal conductivity data at this site that corresponds to the lithologic changes from nannofossil ooze in Unit II to chert-bearing nannofossil chalk of Unit III.