Nature of thrust zones in deep water sand-shale sequences: outcrop examples from the Champsaur sandstones of SE France

Compressional structures are commonly found in deep water turbidite successions that contain important hydrocarbon reservoirs. Here we present a field study of deformation in the Champsaur Sandstones of the French Alps to illustrate the geometry of natural thrust zones in weakly lithified turbidites. The evolution of these zones results from a combination of faulting and folding. A general model for thrust zone evolution is developed where, even though there is a tendency to produce localised, through-going slip surfaces, folding can occur at various stages. Segments of dismembered fold limbs carried up thrust ramps potentially increase the fault zone permeability and fluid communication
through the stratigraphic pile. The propensity for folding is increased by the presence of thin-bedded sand-shale successions. While imaging these detailed architectures may lie beyond the reach of seismic methods in the sub-surface, it may be possible to predict the nature of thrust zones from knowledge of the sand-shale stratigraphy, and vice versa.