1) with depth. The only exception is at 92 mbsf (Section 167-1020C-11H-5), where
the sediment is underconsolidated (OCR < 1).Seven consolidation tests were completed on samples from Holes 1020C, 1021C, and 1021D. The test results (Table 2) show sharp transitions between the recompression and virgin compression curves (Fig. 2, Fig. 3). This suggests little sample disturbance (Holtz and Kovacs, 1981) and increases the accuracy of the preconsolidation (P´c) stress determination. The elastic rebound values range from 0.067 to 0.087 for Site 1020 and from 0.067 to 0.085 for Site 1021. The consistent rebound values suggest little variation in the composition of the seven samples. Average elastic rebound values of 0.075 for Site 1020 and 0.077 for Site 1021 were used to correct void ratio to in situ values (Eq. 1). Table 3 and Table 4 contain the corrected void ratio, bulk density, dry density, and porosity values for discrete measurements on APC cores for Sites 1020 and 1021.
The consolidation state of the sediment was determined from the overconsolidation ratio (OCR) values of each test. OCR is calculated by
The sediment is
overconsolidated (OCR > 1) in the upper few meters and becomes normally
consolidated (OCR
1) with depth. The only exception is at 92 mbsf (Section 167-1020C-11H-5), where
the sediment is underconsolidated (OCR < 1).
The increase in core length over discrete measurement intervals was calculated from the elastic response change in void ratio (Eq. 6). This core-length expansion results in a recovery greater than the cored length and contributes to the depth offset between the mbsf and mcd scales. Following Moran (1997), the core-length expansion was used to correct the mcd scale to a more realistic depth. The cumulative core lengthening for Sites 1020 and 1021 (APC cores) was plotted as a function of meters below seafloor (Fig. 4). The elastic core expansion results are best approximated using a simple power function in the form of
where E is the sediment rebound in meters and a and b are coefficients determined from the power function for each site (Table 5). The mcd scale was therefore corrected by removing the sediment rebound (i.e., mcd - E) from the mcd scale.
The corrected mcd scales for Sites 1020 and 1021 (Holes 1020B, 1020C, 1021B, and 1021C) are plotted against the mbsf scale (Fig. 5, Fig. 6). A one-to-one correlation between the mbsf and the corrected mcd (mcdc) scales would indicate that sediment rebound accounts for 100% of the mcd offset. There is good linear correlation between the two scales. Moran (1997) calculated that elastic core expansion accounts for 90%-95% of the depth offset between the mbsf and mcd scales for Leg 154. Moran (1997) estimated that the remaining 5%-10% of the depth offset for Leg 154 results from intervals of sediment flow-in, identified in visual description of the split core. The percentage that sediment rebound contributes to the mbsf and mcd depth offset for Leg 167 varies from 40% to 80% (Table 6, Table 7).
