THE ROLE OF BIOTURBATION AND RAPID SEDIMENTATION IN SHEAR STRENGTH
DEVELOPMENT: COMPARISON BETWEEN THE EEL RIVER MARGIN (CALIFORNIA)
AND SAGUENAY FJORD (QUEBEC) SEDIMENTS
LOCAT, Jacques, BOULANGER, Eric, MAURICE, France, CÔTÉ, Pierre, MARTIN, Francis, DESGAGNES, Priscilla
Department of Geology and Geological Engineering, Laval University, Sainte-Foy, Qc, Canada, G1K 7P4
LEE, Homa
Western Coastal and Marine Geology, United States Geological Survey, Menlo Park, 94025 CA, USA
This presentation focuses on comparing two sedimentary environments where rapid sedimentation has taken place.
For the Saguenay Fjord, we present the results of investigations carried out on the 1996
strophic flood layer (10 to 50 cm thick). It illustrates the differences in the signature in sediments
cata-insisting mostly on the shear strength development and the role of bioturbation. Comparison of field and laboratory
data are shown from the point of view of geotechnical properties and microstructure. The main observation of this work
underlines the significant impact that bioturbation plays on the shear strength, and also that some of the effects can be
felt down to a critical depth of about 2 to 3 metres. In support of these observations we propose a conceptual
Bioturbation Model illustrating both the resulting densification and increased strength. Also of interest is the potential
use of the contrast between bioturbated and non-bioturbated sequences to identify turbidite layers in a given sedimentary
environment.
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