Index properties measurements were made at a resolution of one sample every two sections in the cores from Hole 1121B. Index properties were determined by a gravimetric method (see "Physical Properties" in the "Explanatory Notes" chapter). Values of measured index properties (void ratio, porosity, water content, bulk density, and grain density) are presented in Table T8 (also in ASCII format). Relatively low density (wet-bulk density <1.4 g/cm3) and fairly homogeneous sediments occurred between 16 and 92 mbsf (Fig. F22). The porosity is generally higher than 70% except in the lowest part of the core (below 120 mbsf), where sediments are more compacted. Sediments recovered from this site are characterized by generally lower bulk densities and higher porosities than the previous two sites (Sites 1119 and 1120).
The shipboard physical properties program at Site 1121 included nondestructive measurements of bulk density, magnetic susceptibility, and natural gamma-ray activity on whole sections of all cores using the multisensor track (Fig. F23). Magnetic susceptibility was measured at 4-cm intervals and at high sensitivity (4-s measurement time) in all Site 1121 holes. Magnetic susceptibility is generally low but has higher values in the upper part of the core (<16 mbsf). Natural gamma-ray activity was measured with a 15-s count every 14 cm in Holes 1121A and 1121B. There is little variation downcore except in the upper part of the core (<16 mbsf) where high-amplitude fluctuations correlate well with the magnetic susceptibility data. High values of natural gamma radiation give an indication that clays are relatively abundant in the upper sections of the core. High-amplitude fluctuations in this portion of the core reflect interlayered sand/silt layers with clay-rich layers. Gamma-ray attenuation porosity evaluator (GRAPE) bulk density measurements were made at 4-cm intervals at all Site 1121 holes. High-amplitude fluctuations are observed in the GRAPE density over the upper part of the core. Below 20 mbsf, the sediment became less dense with little variation downcore to 94 mbsf. The GRAPE density in Hole 1121B increases in the bottom part of the core (120-134 mbsf). A comparison of GRAPE density with the wet-bulk density determined from discrete samples shows general agreement (Fig. F24). The P-wave velocity measurements were made at 4-cm intervals in Holes 1121A and 1121B, but gave poor results.
Measurements of shear strength, using a mechanical vane, were made on split cores from Hole 1121B. Samples were generally taken in clay-rich layers showing the least disturbance by the coring process; they were chosen by visual inspection of the cores and collected at a resolution of one per section in Hole 1121B. No measurements were taken on XCB cores. Only three APC cores had sediment layers that were suitable for the vane shear test. Values gradually increase with increasing burial depth and range from 5 to 35 kPa. Shear strengths are general higher than those measured at previous sites (Sites 1119 and 1120) (Fig. F25). An approximation of the consolidation characteristics of the sediments was made by using the classic relationship between shear strength and sedimentary overburden pressure. According to Skempton (1970), normally consolidated sediments are characterized by a ratio of shear strength to overburden pressure of between 0.2 and 0.5; overconsolidated sediments are characterized by a ratio generally greater than 0.5. At Site 1121 overconsolidation exists to a depth of about 20 mbsf as a result of a once thick, but now eroded overburden. It is likely that the overburden sediments that caused the overconsolidation in the top 20 m of the core have been removed by current erosion. No Torvane shear test was made.
Compressional-wave velocity (P-wave velocity) was measured parallel to the core axis on split cores from Holes 1121B using the digital sound velocimeter system. Below 120 mbsf, sediments are more consolidated than in the upper part of the core, and the Hamilton frame velocimeter was therefore used to measure sound propagation through the sediment. These measurements gave better results than those measured by the MST. There are good correlations between the P-wave velocity values and the GRAPE density, magnetic susceptibility, and natural gamma radiation data in two separate zones of the core: the uppermost portion of the core (<16 mbsf), and the lowest part of the core (>120 mbsf) (Fig. F23).
No downhole temperature measurement with the Adara temperature tool was taken at Site 1121. Thermal conductivity, however, was measured at three intervals per core. Values obtained from thermal conductivity correlate well with those from wet-bulk density, indicating thermal conductivity depends on the density of the sediments (Fig. F26).
Physical properties data support the lithostratigraphic zonation of the core (see "Lithostratigraphy"). Lithostratigraphic Subunit IA is characterized by high-amplitude fluctuations in the MST data. Natural gamma radiation reaches some of the highest values (67 counts/s) in the entire core in this subunit, reflecting the high clay content. Subunit IB shows very little variation in MST properties, which supports the possibility that this section of the core may consist predominantly of flow-in material. Physical properties over the interval defined as Unit II are rather uniform. The interval covered by Subunits IIA and IIB shows an average trend that is at a lower level than data values in Unit I. Deeper than 120 mbsf, there are higher values of bulk density and P-wave measurements that correspond to Subunits IIC and IID. The physical properties data alone cannot differentiate between these two lowermost sections.