This report presents a revised composite set of density, porosity, and compressional velocity values derived from data obtained by various techniques.
Following comparative evaluation of overlapping data sets, we must conclude that in the continental rise sites drilled during ODP Leg 178, the downhole logging (performed only at Sites 1095 and 1096) did not provide reliable data, at least regarding sediment bulk density and porosity. This is in part because of poor hole conditions encountered in a fine-grained, generally underconsolidated formation and partly because of the bound water effect on neutron log porosity that was not completely removed. We suggest that logging while drilling could improve the quality of data if employed in this type of geological formation. Between core logging and laboratory measurements on core samples, we prefer the latter. This is because the multiple-hole drilling strategy. and the generally good core recovery allowed the collection of a high number of evenly spaced measurements (generally one per core section) on cores. This offers the obvious advantage of the manual selection of samples and minimization of noise induced by core voids, biscuiting, and fracturing. Such noise is instead inevitably included in the automatic core-logging data sets, which, in spite of a much higher density of measurements (one every 4 cm), require complex noise removal.
The vertical profiles of porosity and density allow us to identify anomalous consolidation trends at all three sites, probably induced by rapid sediment accumulation and/or the presence of biogenic silica in the sediment. Also, the velocity profiles obtained with vertical seismic profiles and tomographic inversion of traveltimes allowed us to perform a traveltime-depth correlation between site-survey MCS profiles and borehole data.