The turbidite fill of the Annot sub-basin (SE France): a sequence-stratigraphy approach

Abstract

Abstract New sedimentological and biostratigraphical data on the Annot sub-basin (southern Alps, France) provide a good overview of a fore-deep basin infill with well-known Annot turbiditic complex. This basin shows a total thickness of more than 1100 m, where the Grès d’Annot exceeds 500m with well-longitudinal and transversal outcrops. Our study is to define a chronostratigraphical framework, which allows comparisons of local signatures of sea-level fluctuations with eustatic curve, and also identification of tectonic effects. The Annot succession could be interpreted as a second-order cycle. We identify a deepening and transgressive Priabonian interval, represented by the transition from platform of the Calcaires Nummulitiques to hemipelagic marls of the Marnes Bleues where tectonic subsidence rate outpaces third-order eustatic fluctuations and sedimentary influx. Priabonian to early Rupelian Annot turbidites progressively appear with a thickening- and coarsening-upward stacking pattern of four different sand-rich turbiditic systems with lobes, megaslide, channelized lobes and erosional/depositional channel. Each prograding system is separated by an erosive surface corresponding to a third sequence boundary. A possible sequence stratigraphy interpretation may be modelled as a forced regression during foreland basin closure, where the upper turbiditic systems correspond to lowstand prograding complexes from basin floor fan to proximal slope fan.