Influence of early diagenesis on geotechnical properties of clay sediments (Romania, Black Sea)

• Published in: Bulletin of engineering geology and the environment Vol. 240; pp. 175 - 188
• Main Authors: Ballas, Grégory, Garziglia, Sébastien, Sultan, Nabil, Pelleter, Ewan, Toucanne, Samuel, Marsset, Tania, Riboulot, Vincent, Ker, Stephan
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05.06.2018; Springer Verlag
• Subjects: Applied geology; Carbonate cement; Early diagenesis; Earth Sciences; Lacustrine clay sediment; Sciences of the Universe; Structured material; Sulfur cement; Weak layer; Early diagenesis; Structured material; Carbonate cement; Weak layer; Lacustrine clay sediment; Sulfur cement; Structured material Sulfur cement
• ISSN: 0013-7952; 1435-9529; 1872-6917; 1435-9537
• DOI: 10.1016/j.enggeo.2018.04.019

The geotechnical properties of clay sediments were investigated using laboratory and in-situ measurements as part of the geohazard assessment in the Romanian sector of the Black Sea affected by landslides and seafloor deformation features. The sediments were characterized as predominantly high plastic silty clay of high compressibility, low undrained shear strength, low cohesion and moderate sensitivity. A shallow increase in shear strength exceeding the general trend could have been reconciled with evidence for the precipitation of iron sulfides and calcium carbonates related to early diagenetic reactions of sulfate reduction (e.g. cryptic sulfur cycle) and anaerobic oxidation of methane. Comparison of the compression behaviour of natural and reconstituted samples indicated that precipitation of these materials at particle contacts produced cementation. The analysis of deeper sediments sharing similar geochemical properties illustrated that the early precipitation of even low quantity of sulfur and carbonate cements allowed clays to develop sufficient strength to preserve an abnormal high water content even under tens of meters burial depth. Because this cementation process was observed to be associated with an enhanced sensitivity and a strain softening response to undrained shearing it was concluded that such early diagenesis should be considered as a key environmental factor, leading to weak layer formation that may influence the susceptibility of seafloor to failure. •Sulfide and carbonate cements induced by early diagenetic reactions (AOM, SR).•Structured clay materials with high water content and shear strength•Sediments with metastable structure and slight sensitivity•Early diagenesis considered as a key factor in the seafloor instability hazard control.