The main objectives of the 32m-long PRAD2 borehole (EC project PROMESS-1, central Adriatic shelf, 56 m w.d.) were to obtain continuous sediment cores, in situ cone penetration measurements (CPTU) and downhole logging of a stratigraphic succession on the Adriatic continental shelf. This sedimentary succession of marine mud represents the deposit of the last sea level highstand (HST, aged 5.5 kyr to present) and part of the previous transgression (Trincardi et al., 2004). Geochronologic data indicate that the unit at the base of the HST, above the maximum flood surface (mfs), marks a condensed interval between approximately 5.5 and 3.7 kyr (Correggiari et al., 2001). Above this condensed unit, characterized by discontinuous seismic reflectors at the top, the sediment accumulation rate is higher and the succession is characterised by seafloor and subsurface undulations interpreted as sediment deformation features with limited displacement, muddy bedforms, or a combination (Correggiari et al., 2001; Lee et al., 2002; Cattaneo et al., 2004). To test the hypothesis of sediment deformation, geotechnical targets chosen on the basis of seismic profiles and multibeam bahymetry include: 1) a possible shear plan in the HST, and 2) the seismic unit at the base of the sedimentary units characterized by the undulations interpreted as a potential weak layer (Sultan et al., 2004). The integration of stratigraphic information (geometry, sedimentary facies, chronology), in situ geotechnical measurements (CPTU), laboratory measurements of the physical and mechanical properties of the sediment (tests of classification and identification, oedometer/permeability, static and cyclic triaxial compression tests) allows a rigorous interpretation of the mechanical behavior of the sediment in terms of triggering mechanism for the observed undulations. (Work supported by contract EC EVR1-2001-00041). References Cattaneo, A. et al. 2004: Seafloor undulation patterns on the Adriatic shelf and comparison to deep-water sediment waves. Marine Geology 213, 121-148. Correggiari, A. et al. 2001: Styles of failure in late Holocene highstand prodelta wedges on the Adriatic shelf. Journal of Sedimentary. Research 71, 218-236. Lee, H.J. et al. 2002: Distinguishing sediment waves from slope failure deposits: field examples, including the 'Humboldt slide', and modelling results. Marine Geology 192, 79-104. Sultan N. et al. 2004: Triggering mechanisms of slope instability processes and sediment failures on continental margins: A geotechnical approach. Marine Geology 213, 291-321. Trincardi F. et al. 2004: Evidence of soft-sediment deformation, fluid escape, sediment failure and regional weak layers within the late-Quaternary mud deposits of the Adriatic Sea. Marine Geology 213, 91-119.
Muddy bedforms and/or sediment deformation on the Adriatic shelf: geotechnical data from PRAD2 borehole (PROMESS1 project).
Ridente D;Asioli A;
2005
Abstract
The main objectives of the 32m-long PRAD2 borehole (EC project PROMESS-1, central Adriatic shelf, 56 m w.d.) were to obtain continuous sediment cores, in situ cone penetration measurements (CPTU) and downhole logging of a stratigraphic succession on the Adriatic continental shelf. This sedimentary succession of marine mud represents the deposit of the last sea level highstand (HST, aged 5.5 kyr to present) and part of the previous transgression (Trincardi et al., 2004). Geochronologic data indicate that the unit at the base of the HST, above the maximum flood surface (mfs), marks a condensed interval between approximately 5.5 and 3.7 kyr (Correggiari et al., 2001). Above this condensed unit, characterized by discontinuous seismic reflectors at the top, the sediment accumulation rate is higher and the succession is characterised by seafloor and subsurface undulations interpreted as sediment deformation features with limited displacement, muddy bedforms, or a combination (Correggiari et al., 2001; Lee et al., 2002; Cattaneo et al., 2004). To test the hypothesis of sediment deformation, geotechnical targets chosen on the basis of seismic profiles and multibeam bahymetry include: 1) a possible shear plan in the HST, and 2) the seismic unit at the base of the sedimentary units characterized by the undulations interpreted as a potential weak layer (Sultan et al., 2004). The integration of stratigraphic information (geometry, sedimentary facies, chronology), in situ geotechnical measurements (CPTU), laboratory measurements of the physical and mechanical properties of the sediment (tests of classification and identification, oedometer/permeability, static and cyclic triaxial compression tests) allows a rigorous interpretation of the mechanical behavior of the sediment in terms of triggering mechanism for the observed undulations. (Work supported by contract EC EVR1-2001-00041). References Cattaneo, A. et al. 2004: Seafloor undulation patterns on the Adriatic shelf and comparison to deep-water sediment waves. Marine Geology 213, 121-148. Correggiari, A. et al. 2001: Styles of failure in late Holocene highstand prodelta wedges on the Adriatic shelf. Journal of Sedimentary. Research 71, 218-236. Lee, H.J. et al. 2002: Distinguishing sediment waves from slope failure deposits: field examples, including the 'Humboldt slide', and modelling results. Marine Geology 192, 79-104. Sultan N. et al. 2004: Triggering mechanisms of slope instability processes and sediment failures on continental margins: A geotechnical approach. Marine Geology 213, 291-321. Trincardi F. et al. 2004: Evidence of soft-sediment deformation, fluid escape, sediment failure and regional weak layers within the late-Quaternary mud deposits of the Adriatic Sea. Marine Geology 213, 91-119.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
