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Three-dimensional seismic analysis of a submarine palaeo -translational slope failure on the northeast Atlantic margin indicates that it was 'primed'and probably 'triggered'as a result of diagenesis at a silica chemical reaction front, where biogenic silica (opal A) is being converted to opal CT (Cristobalite/Tridymite). Conversion of opal A to opal CT is a thermochemical dehydration reaction that causes rapid compaction. It therefore is a potential overpressure generation mechanism, usually once sediment has been buried to depths of 300^800 m below the contemporaneous seabed. The overpressure reduces the sediment shear strength, making it susceptible to failure. In this example, the translated succession (volume of 25 km 3 and area of 110 km 2 ) was coherent and rigid but the detachment unit was a liqui¢ed sediment mass. After failure, the translated succession broke up into a series of faulted-bounded blocks, which di¡erentially subsided into this underlying sediment-£uid mass. Sediment-£uid intrusions utilized the faults bounding the blocks, intruding 200^400 m of the overburden stratigraphy to expel a £uid^sediment mix into the water column and onto the palaeoseabed. Pore pressure decreased and sediment strength within the detachment unit was reestablished. Key factors for the initiation of this failure mechanism are (a) the rate of the reaction front advancement (ROFA), (b) the magnitude of the porosity reduction at the reaction front, (c) the sealing capabilities of the overburden and (d) the low shear strength of opal A. Given that the reaction front normally forms at depths of 300^800 m, the mechanism is more likely to induce deep and therefore large volume detachments, which should be more common in high latitude and equatorial regions where biogenic silica production is high.

The deepwater fold and thrust belt of the Western Niger Delta provides an ideal natural setting in which to study interactions between coeval sedimentation and deformation. Deformation in this area takes the form of folding due to the up-dip gravitational collapse of the Niger Delta above the overpressured shale detachment of the Akata Formation. The seafloor relief formed by folding is initially oriented perpendicular to the downslope sediment transport direction. This results in a significant barrier to the basinwards transport of material and the creation of accommodation space within the hangingwall and footwall areas of the fold. Coeval sedimentation during uplift results in deposition of a growth sequence composed of a compensationally stacked vertical succession of mass-transport deposits (MTDs), channel-levee systems (CLSs), and hemipelagic drape deposits (HD). Variations in the along-strike structural style and relief of a large-scale fold c. 40 km in length control variations in growth-sequence geometry. These variations in fold style along strike also determine sediment flow pathways around the positive relief formed at the seafloor during fold uplift. Switching of sedimentation between the two structurally induced flow pathways around the fold is related to the compensational stacking patterns within the hangingwall which cause a shift in flow pathways from one fold edge to another. The combined structural-stratigraphic approach to the interpretation of sedimentation in deepwater fold belts can provide a useful method for reconstructing the development of relief during folding.

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