The role of diagenesis in the development of physical properties of deep-sea carbonate sediments

Laboratory measurements of ultrasonic velocity ( V P, V S) and attenuation ( Q −1 P, Q −1 S) in deep-sea carbonate sequences at DSDP Sites 288, 289 and 316 in the equatorial Pacific were made in conjunction with studies of sediment density, porosity and pore geometry in order to investigate the role of diagenesis in the development of physical properties. Bulk porosity decrease appears to be related more significantly to depth of burial than to age of strata. Both depth of burial and age, however, are important factors controlling the modal pore diameter. In deep-burial diagenesis the modification of pore geometry is influenced by the presence of silica during diagenesis. In carbonate sequences at the three DSDP sites studied, shear wave attenuation anisotropy ( Q −1 SHH Q −1 SHV ) correlates with the shear wave velocity anisotropy. Pore orientation, resulting from overburden pressure and other deep-burial diagenetic processes, is an important factor controlling the increase of V P anisotropy with age and depth of burial. On the basis of observed minor changes in anisotropy values with increasing pressure for some samples, other contributions to V P anisotropy such as grain orientation and bedding lamination cannot be ruled out.