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• Contour currents with different physical natures observed over a drift-moat system • High SSC on the drift due to long-range sediment transport by contour currents • High SSC in the moat due to moat wall erosion by tidal-induced secondary flows • Formation of drifts forced by upslope sediment transport of tidal currents Contourite drifts are ubiquitous sedimentary features in the world′s oceans, and their formation are usually ascribed to sedimentation from contour currents. However, in-situ observations of contour currents and their associated sedimentary processes were inadequate. Here, we present mooring observation results from a drift-moat contourite system in the South China Sea to gain insight into its sediment dynamics and formation mechanism. We found that quasi-persistent contour currents develop in the moat, on and below the drift, yet subject to diverse physical oceanographic processes. High suspended sediment concentrations observed on the drift mainly occur in winter, induced by high levels of sediments transported by contour currents from Taiwan. In the moat, however, high suspended sediment concentrations are mostly caused by erosion of the moat wall during periods of strong tidal currents and low shear variance. Such results underscore the complexity of current patterns and sedimentary processes across various topographic units in the drift-moat contourite system. A novel formation mechanism of the contourite drift is thereby proposed, wherein sediment transport by contour currents brings materials for constructing the drift, while its formation is driven by near-critical reflection and upslope transport of sediments by tidal currents. [ABSTRACT FROM AUTHOR]

• Mudstone deposits behave like noncohesive sediments in terms of erosion resistance. • High erosion resistance of laterites cannot be predicted merely by particle size. • Shields' parameter predicted by water content, clay content, and plasticity index. Soil erosion and sedimentation are major factors in landscape evolution and river morphology. The erosion resistance of sediments plays an important role in landscape evolution processes because it determines the threshold of an acting force at the initiative sediment motion, and the amount of sediment transports. This study examined the sediment properties and their correlations to the erosion resistance of mudstone deposits and laterites, which are two representative natural cohesive soils in hill and terrace topography in Taiwan. Soil physical properties and pore water chemical properties, and the erosion resistance were investigated and determined using laboratory tests and hydraulic flume experiments, respectively. Investigations of sediment properties showed that the mudstone deposits and laterites had significant differences in median particle size, soil texture, level of plasticity, internal structure, and pH value and electrical conductivity of their aqueous slurry. Results from the hydraulic flume experiments showed that the laterites had stronger erosion resistance, indicating by larger values of critical shear stress and the Shields' parameter, than the mudstone deposits. Through the stepwise multiple regression analysis, a quantitative equation was proposed to estimate the Shields' parameter using fine sediment properties including water content, clay content, and the plasticity index expressed in decimal fractions, of the two soils. Despite more experiments of the two natural soils with different ranges of the sediment properties are needed to validate the empirical equation for predicting the Shields' parameter, the proposed methodology provides an essential reference in which erosion resistance is an important parameter. [ABSTRACT FROM AUTHOR]