Delta-fed turbidites infilling topographically complex basins: A new depositional model for the Annot Sandstones, SE France

The Eocene-Oligocene Annot Sandstones of southeast France record the predom inantly deep-water, silicielastic infill of the early French Alpine forelan d basin, They accumulated in a topographically complex basin as recorded by variable onlap relationships with the underlying Globigerina Marls. Onlap configurations and paleobathymetric data from the western outcrops of the A nnot Sandstones enables a contour map of the pre-Annot Sandstone basin-boor topography to be reconstructed, The basin comprised a northern and a south ern sub-basin, which mere separated by a ridge, through which a trough was cut (the Coyer Trough) linking the two sub-basins during the latter stages of infilling, Data on provenance and paleocurrents suggest that the sandsto nes were sourced from two main feeder systems: an eastern source from the A lps fed the northern sub-basin, and a southern source fed the southern sub- basin. There is evidence of mixing of provenance in the lower parts of the southern sub-basin. Integration of the reconstructed basin-floor topography, sediment-dispersal data, and facies and stratal architectures suggests a depositional model c omprising sand-rich, delta-fed submarine ramps and/or aprons whose developm ent was strongly influenced by the basin-door topography, The southern sub- basin initially had a steeper delta front, characterized by debris hows; th is contrasted with the lower-gradient northern sub-basin. The southern sub- basin comprises approximately 800 m of thick-bedded sandstones interpreted as the deposits of sustained and possibly ponded turbidity currents. The up per part of the southern sub-basin records increased channeling and scour r elated to bypass of material after the basin was filled; these channels tra nsported material northwards through the Coyer Trough, and capped the north ern sub-basin. This development of the southern sub-basin is comparable to the "fill and spill" development of perched, intra-slope basins in the Gulf of Mexico.