Gravitational gliding in deltas

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Abstract
Summary: Many cases of faulting in prograding delta slopes can be genetically attributed to submarine gravity gliding (Terzaghi 1956) on slope-parallel slip planes. Essential in this ‘thin-skinned’ model of gravitational faulting is the overpressuring of the pore fluid, which not only permits the formation of very gently dipping slip planes, but also determines the listric shapes of normal and thrust faults at the head and toe of the gliding path. The development of the gliding process and the associated primary and secondary structures (antithetic faults, ‘roll-over’ anticlines) are described for an infinitely long slope and for somewhat idealized pore-pressure profiles, a main parameter being the distance of the overpressure top from the (rising) sediment surface. Realistic deviations from the idealizing assumptions are discussed in qualitative terms. The gliding process is ‘slow’ and controlled by sediment compaction in the slope-parallel direction. Continued sedimentation gives rise to changes in effective stresses and these, in turn, cause active faults to adjust their shapes. Examples of this adjustment are discussed.