(Table 1) Physical properties of sediments at DSDP Holes 69-504 and 69-505

Values of physical properties measured in the upper sections of sediment cores recovered at Sites 504 and 505 exhibit a remarkable similarity. Below a depth of 145 m Site 504 sediments appear to have undergone changes which are reflected in physical property values. This alteration may have been due to high temperatures in the sediment. In most of Site 505, and in Site 504 above 145 m, seismic velocity averages 1.51 km/s, wet bulk density 1.32 g/cm**3, porosity 80%, and thermal conductivity 0.80% W/m °K. Below 145 m at Site 504 and 210 m at Site 505, mean density increases to 1.40 g/cm**3, porosity decreases to 67%, seismic velocity increases to 1.53 km/s, and thermal conductivity increases to values in excess of 1.0 W/m °K. A good correlation between independent measurements of water content and thermal resistivity supports the existence of small but regular variation in the measured parameters on the scale of 10 m and less.

Physical properties, velocity and attenuation characteristics, and mineralogy of gabbros from ODP Hole 176-735B

Laboratory compressional wave (Vp) and shear wave (Vs) velocities were measured as a function of confining pressure for the gabbros from Hole 735B and compared to results from Leg 118. The upper 500 m of the hole has a Vp mean value of 6895 m/s measured at 200 MPa, and at 500 meters below seafloor (mbsf), Vp measurements show a mean value of 7036 m/s. Vs mean values in the same intervals are 3840 m/s and 3857 m/s, respectively. The mean Vp and Vs values obtained from log data in the upper 600 m are 6520 and 3518 m/s, respectively. These results show a general increase in velocity with depth and the velocity gradients estimate an upper mantle depth of 3.32 km. This value agrees with previous work based on dredged samples and inversion of rare element concentrations in basalts dredged from the conjugate site to the north of the Atlantis Bank. Laboratory measurements show Vp anisotropy ranging between 0.4% and 8.8%, with the majority of the samples having values less than 3.8%. Measurements of velocity anisotropy seem to be associated with zones of high crystal-plastic deformation with predominant preferred mineral orientations of plagioclase, amphiboles, and pyroxenes. These findings are consistent with results on gabbros from the Hess Deep area and suggest that plastic deformation may play an important role in the seismic properties of the lower oceanic crust. In contrast to ophiolite studies, many of the olivine gabbros show a small degree of anisotropy. Log derived Vs anisotropy shows an average of 5.8% for the upper 600 m of Hole 735B and tends to decrease with depth where the overburden pressure and the age of the crustal section suggests closure of cracks and infilling of fractures by alteration minerals. Overall the results indicate that the average shear wave splitting in Hole 735B might be influenced by preferred structural orientations and the average value of shear wave splitting may not be a maximum because structural dips are <90°. The maximum fast-wave orientation values could be influenced by structural features striking slightly oblique to this orientation or by near-field stress concentrations. However, flexural wave dispersion analyses have not been performed to confirm this hypothesis or to indicate to what extent the near-field stresses may be influencing shear wave propagation. Acoustic impedance contrasts calculated from laboratory and logging data were used to generate synthetic seismograms that aid in the interpretation of reflection profiles. Several prominent reflections produced by these calculations suggest that Fe-Ti oxides and shear zones may contribute to the reflective nature of the lower oceanic crust. Laboratory velocity attenuation (Q) measurements from below 500 m have a mean value of 35.1, which is consistent with previous vertical seismic profile (VSP) and laboratory measurements on the upper 500 m.

Geotechnical properties of sediments at DSDP Site 75-532

During Leg 75 of the Deep Sea Drilling Project (DSDP) from the D/V Glomar Challenger, a 200-m deep hole was drilled at Hole 532A on the eastern side of Walvis Ridge at a water depth of 1331 m. Sediment cores were obtained by means of a hydraulic piston corer. All of the cores from this boring were designated for geotechnical studies and were distributed among eight institutions. The results of laboratory studies on these sediment cores were compiled and analyzed. Sediment properties, including physical characteristics, strength, consolidation, and permeability were studied to evaluate changes as a function of depth of burial. It was concluded that the sediment profile to the explored depth of 200 m at Walvis Ridge consists of approximately 50 m of foram-nannofossil marl (Subunit 1a) over 64 m of diatom-nannofossil marl (Subunit 1b) over nannofossil marl (Subunit 1c) to the depth explored. All three sediment units appear to be normally consolidated, although some anomalies seem to exist to a depth of 120 m. No distinct differences were found among the sediment properties of the three subunits (1a, 1b, and 1c) identified at this site.

Consolidation tests, elastic properties and grain size measurements at the consolidations samples from different Holes of IODP Expedition 302

The Integrated OceanDrilling Program's Expedition 302, the Arctic Coring Expedition (ACEX), recovered the first Cenozoic sedimentary sequence from the central Arctic Ocean. ACEX provided ground truth for basin scale geophysical interpretations and for guiding future exploration targets in this largely unexplored ocean basin. Here, we present results from a series of consolidation tests used to characterize sediment compressibility and permeability and integrate these with high-resolution measurements of bulk density, porosity and shear strength to investigate the stress history and the nature of prominent lithostratigraphic and seismostratigraphic boundaries in the ACEX record. Despite moderate sedimentation rates (10-30 m/Myr) and high permeability values (10**-15 -10**-18 m**2), consolidation and shear strength measurements both suggest an overall state of underconsolidation or overpressure. One-dimensional compaction modelling shows that to maintain such excess pore pressures, an in situ fluid source is required that exceeds the rate of fluid expulsion generated by mechanical compaction alone. Geochemical and sedimentological evidence is presented that identifes the Opal A-C/T transformation of biosiliceous rich sediments as a potential additional in situ fluid source.However, the combined rat of chemical and mechanical compaction remain too low to fully account for the observed pore pressure gradients, implying an additional diagenetic fluid source from within or below the recovered Cenozoic sediments from ACEX. Recognition of the Opal A-C/T reaction front in the ACEX record has broad reaching regional implications on slope stability and subsurface pressure evolution, and provides an important consideration for interpreting and correlating the spatially limited seismic data from the Arctic Ocean.

Physical properties and velocity measurement comparison for sediments from DSDP Holes 92-597B and 92-597C

The bulk and grain densities, porosity, water content, and ultrasonic compressional- and shear-wave velocities of 25 basalt samples from DSDP Holes 597B and 597C were measured. The velocities were measured at in situ pore and confining pressures. The bulk densities of the samples vary between 2.690 and 3.050 g/cm**3. Porosities of selected samples vary between 2.4 and 9.3%. The grain densities vary between 2.993 and 3.117 g/cm3, a range that suggests that bulk density differences are due primarily to variations in porosity. Compressional-wave velocities range from 5.70 to 6.81 km/s, and shear-wave velocities range from 1.66 to 3.84 km/s. The variation in compressional velocity appears to be due primarily to variations in grain size and the associated greater density of grain-boundary cracks for samples with a smaller average grain size. On the basis of these results we would expect compressional and shear velocities to increase with increasing depth in the shallow crust, primarily as the result of the effects of confining pressure on crack density.

Physical properties of sediments at DSDP Sites 93-603, 93-604, and 93-605

On Leg 93, physical properties measurements were made of vertical and horizontal sonic velocity, acoustic impedance, vane shear strength, and penetrometer strength, using procedures discussed in Boyce (1973, 1976, 1984). Gravimetric procedures were used to determine wet-bulk density, grain density, porosity, and water content, using either the chunk method or the cylinder method. Calcium carbonate content of Leg 93 sediments was determined by the carbonate.