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The cores taken at Site 206, 207, 208, and 210 show with minor irregularities a stepwise decrease in degree of deformation downwards. The pattern of lithification is similar. The boundaries between creamy and stiff and between stiff and semilithified sediments occur at about the levels of change in the degree of core deformation. The sonic velocities increase slightly with depth to between 200 and 350 meters depending on the site; below this depth the velocities increase more rapidly. The elbow in the velocity-depth curve occurs in stiff sediments where they become crumbly. The bulk density-depth curve shows a step at 250 to 550 meters, depending on the site. This occurs well within the semilithified zone. Sediments from each of the sites were examined with the scanning electron microscope (SEM), especially those from the semilithified zone. The welding together of grains commences at the top of the semilithified zone. The pore space decreases at the level at which the bulk density increases, and this is about the upper level at which overgrowths of granular calcite are found. Comparison of the levels at the four sites at which the various features mentioned occur indicate that the diagenesis pattern is independent of the mid-Tertiary regional unconformity found in the southwest Pacific, but appears to be dependent on both the depth and duration of burial. Seismic reflectors may possibly be correlated with (1) the creamy-stiff boundary or the drop in core deformation at about that depth; (2) the depth where sediments become crumbly in the stiff zone; (3) the stiff-semilithified boundary where grain welding commences; and (4) the depth of inflection of the bulk density curve where porosity decreases and granular calcite overgrowths commence.

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Progressive Carbonate Diagenesis at Deep Sea Drilling Sites 206, 207, 208, and 210 in the Southwest Pacific and Its Relationship to Sediment Physical Properties and Seismic Reflectors