Universita di Genova, Italy

Analysis of physical properties measured on cores and on discrete samples collected by the Ocean drilling Program (ODP) Leg 178 on the Pacific margin of the Antarctic Peninsula reveals anomalous down-hole curves of porosity, density, water content, and P-wave velocity. These indicate an overall trend of increasing porosity with depth and suggest that the drifts are mostly undercompacted. Analysis of seismic reflection, down-hole logging, geotechnical and mineralogical data from two drilling sites indicates that the observed anomalous consolidation trends are a consequence of the presence of biogenic silica (diatom and radiolarian skeletons) even with a small to moderate amount. This work shows how physical properties of shallow fine-grained marine sediments can be analyzed as basin-wide indicators of biogenic silica abundance. The diagenetic alteration of siliceous microfossils is a possible cause of slope instability along world continental margins where bottom-simulating reflectors related to silica diagenesis are present at a regional scale. (modif. j. abstr.)