Mass movements,geotechnical properties,and slope stability in the outer shelf—Upper slope,northwestern Aegean sea     

Vasilios Lykousis  George Chronis 《Marine Georesources & Geotechnology》2013,31(3):231-247

Abstract

Subbottom profiling (3.5 kHz) in the uppermost slope of the outer shelf of the northwestern Aegean Sea has shown downslope slumping and intense sediment deformation as well as a succession of microslumping within the Late Pleistocene delta sequences. Postdeposition bottom erosion by currents and the overconsolidated sediments (Cu/Po > 1) indicate the termination of deformations a long time ago. Deformation processes are estimated to have been active 18,000–10,000 B.P. Large‐scale active downslope deformations with clockwise sediment block rotation have affected the area as well. These longer‐period deformations are associated with regional neotectonics and older unconformities (i. e., Plio‐Pleistocene) as potential slide planes.

Geotechnical properties reflect mainly textural variations and locally (within sapropelic layers) high organic matter content. Relatively high values of shear strength were measured (5–29 kPa) with intermediate sensitivities (2–5), whereas relatively low values of water content (33–81%) were found along the five selective sediment cores.

Infinity slope stability analysis revealed that the slopes in the study area are most stable, although theoretical evaluations (Cu estimated from linear regression analysis) indicate relative instability for the potential glide plane at 20 m depth. The outer shelf is covered by compact relict sands, and their gentle and low‐angle (<0.2°) slopes are the most stable region of the investigated area.  相似文献   

Influence of bioturbation by the polychaete Nereis diversicolor on the structure of bacterial communities in oil contaminated coastal sediments   总被引：1，自引：0，他引：1  

Cuny P  Miralles G  Cornet-Barthaux V  Acquaviva M  Stora G  Grossi V  Gilbert F 《Marine pollution bulletin》2007,54(4):452-459

Patterns of change in the structure of bacterial communities monitored by ribosomal intergenic spacer analysis (RISA) in oil contaminated sediments inhabited or not by the marine polychaete Nereis diversicolor were studied during 45 days under laboratory conditions. Results supported by principal component analysis showed a marked response of the bacterial communities to the oil contamination and to the presence of N. diversicolor. Phylogenetic affiliation of specific RISA bands showed that, in the contaminated sediments, the presence of the marine polychaetes favoured the development of bacteria which may play an active role in natural bioremediation processes of oil polluted environments.  相似文献   

Oxidation modes and thermodynamics of Fe oxyhydroxycarbonate green rust: Dissolution-precipitation versus in situ deprotonation     

Christian Ruby  Mustapha Abdelmoula  Aurélien Renard  Georges Ona-Nguema  Jean-Marie R. Génin 《Geochimica et cosmochimica acta》2010,74(3):953-966

Fe^II-III hydroxycarbonate green rust GR(CO₃²⁻), Fe^II₄ Fe^III₂ (OH)₁₂ CO₃·3H₂O, is oxidized in aqueous solutions with varying reaction kinetics. Rapid oxidation with either H₂O₂ or dissolved oxygen under neutral and alkaline conditions leads to the formation of ferric oxyhydroxycarbonate GR(CO₃²⁻)∗, Fe^III₆ O₁₂ H₈ CO₃·3H₂O, via a solid-state reaction. By decreasing the flow of oxygen bubbled in the solution, goethite α-FeOOH forms by dissolution-precipitation mechanism whereas a mixture of non-stoichiometric magnetite Fe_(3−x)O₄ and goethite is observed for lower oxidation rates. The intermediate Fe^II-III oxyhydroxycarbonate of formula Fe^II_6(1−x) Fe^III_6x O₁₂ H_2(7−3x) CO₃·3H₂O, i.e. GR(x)∗ for which x ? [1/3, 1], is the synthetic compound that is homologous to the fougerite mineral present in hydromorphic gleysol; in situ oxidation accounts for the variation of ferric molar fraction x = [Fe^III]/{[Fe^II]+[Fe^III]} observed in the field as a function of depth and season but limited to the range [1/3, 2/3]. The domain of stability for partially oxidized green rust is observed in the E_h-pH Pourbaix diagrams if thermodynamic properties of GR(x)∗ is compared with those of lepidocrocite, γ-FeOOH, and goethite, α-FeOOH. Electrochemical equilibrium between GR(x)∗ and Fe^II in solution corresponds to E_h-pH conditions close to those measured in the field. Therefore, the reductive dissolution of GR(x)∗ can explain the relatively large concentration of Fe^II measured in aqueous medium of hydromorphic soils containing fougerite.  相似文献