Analysis of physical properties measured on cores and on discrete samples collected by the Ocean Drilling Programme (ODP) Leg 178 on the Paci¢c 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. In one of the two boreholes analysed, a sharp decrease in porosity,matching increasing bulk sediment density and increasing compressional velocity occurs towards the base of the hole, which corresponds to a bottom- simulating re£ector in the seismic section. Analysis of seismic re£ection, 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. Above the bottomsimulating re£ector, intergranular contacts among whole or broken siliceous microfossils prevent normal sediment consolidation.Diagenetic alteration of biogenic opal-A to opal-CT causes a dramatic reduction of intra- and interskeletal porosity allowing sediments to consolidate at depth. This results in overpressuring and a decrease in the e¡ective stress. Excess £uids are expelled towards the sediment surface through near vertical, small throw normal faults extending from the diagenetic front to the sea£oor and a¡ecting the stability of the submarine slope in the form of gravitational creep along a weakened surface. This work shows how physical properties of shallow ¢ne-grained marine sediments can be analysed 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 bottomsimulating re£ectors related to silica diagenesis are present at a regional scale.

Effects of biogenic silica on sediment compaction and slope stability on the pacific margin of the Antarctic Peninsula

Volpi V
;
Camerlenghi A;Rebesco M;
2003

Abstract

Analysis of physical properties measured on cores and on discrete samples collected by the Ocean Drilling Programme (ODP) Leg 178 on the Paci¢c 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. In one of the two boreholes analysed, a sharp decrease in porosity,matching increasing bulk sediment density and increasing compressional velocity occurs towards the base of the hole, which corresponds to a bottom- simulating re£ector in the seismic section. Analysis of seismic re£ection, 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. Above the bottomsimulating re£ector, intergranular contacts among whole or broken siliceous microfossils prevent normal sediment consolidation.Diagenetic alteration of biogenic opal-A to opal-CT causes a dramatic reduction of intra- and interskeletal porosity allowing sediments to consolidate at depth. This results in overpressuring and a decrease in the e¡ective stress. Excess £uids are expelled towards the sediment surface through near vertical, small throw normal faults extending from the diagenetic front to the sea£oor and a¡ecting the stability of the submarine slope in the form of gravitational creep along a weakened surface. This work shows how physical properties of shallow ¢ne-grained marine sediments can be analysed 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 bottomsimulating re£ectors related to silica diagenesis are present at a regional scale.
File in questo prodotto:
File Dimensione Formato  
basin_research.pdf

non disponibili

Tipologia: Altro materiale allegato
Licenza: Non specificato
Dimensione 3.03 MB
Formato Adobe PDF
3.03 MB Adobe PDF   Visualizza/Apri   Richiedi una copia

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/20.500.14083/2344
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact