Composition of the argillite sequence, continental slope of the Sea of Japan

The argillite sequence located at the base of the sedimentary cover on the continental slope of the Sea of Japan was studied by petrographic, palynological, and X-ray diffraction methods. Two spores-pollen complexes were distinguished in it: the Late Oligocene reflecting cooling and the Early Miocene corresponding to initiated warming. Data obtained indicate that the sequence is composed of terrigenous silty-clayey sediments that accumulated in shallow coastal-marine settings. The global sea-level rise at the Early-Middle Miocene transition, combined with regional tectonic processes, determined basin's deepening, owing to which the argillite sequence was overlain by a thick layer of Middle Miocene diatomaceous-clayey sediments. Due to tectonic movement along existing faults in the terminal Late Miocene, the argillite sequence occurring initially at depths of at least 400-500 m was locally exhumed to the basin bottom.

Composition of drilled sediments and pore waters from the continental slope of the Northern Gulf of Mexico

Pore waters were analyzed from 6 holes drilled from M.V. "Eureka" as a part of the Shell Oil Co. deeper offshore study. The holes were drilled in water depths of 600-3000 ft. (approximately 180-550 m) and penetrated up to 1000 ft. (300 m) of Pliocene-Recent clayey sediments. Salt and anhydrite caprock was encountered in one diapiric structure on the continental slope. Samples from holes drilled near diapiric structures showed systematic increases of pore-water salinity with depth, suggestive of salt diffusion from underlying salt plugs. Anomalous concentrations of K and Br indicate that at least one plug contains late-stage evaporite minerals. Salinities approaching halite saturation were observed. Samples from holes away from diapiric structures showed little change in pore-water chemistry, except for loss of SO4 and other variations attributable to early-stage diagenetic reactions with enclosing sediments. Thus, increased salt concentrations in even shallow sediments from this part of the Gulf appear to provide an indicator of salt masses at depth.

Grain-size distribution and frictional behaviour of sediment cores from the Nice Slope

The upper shelf of the landslide-prone Ligurian Margin (Western Mediterranean Sea) off Nice well-known for the 1979 Airport Landslide is a natural laboratory to study preconditioning factors and trigger mechanisms for submarine landslides. For this study low-stress ring shear experiments have been carried out on a variety of sediments from >50 gravity cores to characterise the velocity-dependent frictional behaviour. Mean values of the peak coefficient of friction vary from 0.46 for clay-dominated samples (53 % clay, 46 % silt, 1 %) sand up to 0.76 for coarse-grained sediments (26 % clay, 57 % silt, 17 % sand). The majority of the sediments tested show velocity strengthening regardless of the grain size distribution. For clayey sediments the peak and residual cohesive strength increases with increasing normal stress, with values from 1.3 to 10.6 kPa and up to 25 % of all strength supported by cohesive forces in the shallowmost samples. A pseudo-static slope stability analysis reveals that the different lithologies (even clay-rich material with clay content >=50 %) tested are stable up to slope angles <26° under quasi-drained conditions.