Deep-water sedimentation on an evolving fault-block: the Braux and St Benoit outcrops of the Grès d’Annot

Abstract

Abstract The record of sediment fill contained in sub-basins of the western outcrops of the Grès d’Annot indicates that, throughout the period of deposition of the sandstones, there was very little synsedimentary tectonic activity. However, evidence of syntectonic sedimentation is preserved in the basal portion of the fill of the Annot sub-basin. The lowermost portions of the turbidite infill of the Annot sub-basin crop out around Braux and St Benoit. These outcrops are separated by the St Benoit Fault, which is thought to have developed as a result of sinistral strike-slip movement on the main Rouaine Fault to the south. The St Benoit Fault has a normal offset of up to 400 m to the east. Detailed mapping within the Calcaires Nummulitiques, Marnes Bleues and Grès d’Annot, has led to the recognition of several features that indicate a syntectonic sedimentary evolution for the outcrops. These record a three-phase progressive evolution of the St Benoit Fault through the upper Calcaires Nummulitiques to the lowermost Grès d’Annot. As part of this, there are implications for deposition from turbidity currents on encountering topographic barriers. To our knowledge, this area contains one of the few outcrop examples of half-graben formation within the confined basins of the Grès d’Annot.