Physical properties of ODP Hole 122-762C

This discrepancy is because the helium-displacement pycnometer used aboard ship gives erroneously low volumes for wet samples, which are then used in bulk density calculations. Correct shipboard wet sample volumes can be calculated by adding the difference between the wet and dry sample weights to the dry sample volume. The corrected shipboard pb values are in agreement with shore-based data.

We recommend that the Ocean Drilling Program use this calculation in place of the pycnometer wet volumes. The chalks show a negative velocity gradient between 600 and 720 mbsf, though there is no apparent change in lithology. In absence of overpressuring and mineralogical changes, the negative gradient is probably caused by increasing porosity due to the change in microstructure of the sediment over this depth interval.