3-D Structural Control on Turbidite Depocentres in a Foreland Basin Setting: The Sanguinière Depocentre, Grès d’Annot, Southeast France

Ford, Mary¹, Sylvain Bourlange², Guillaume Caumon², Philippe Joseph³, Antoine Le Solleuz², Emmanuel Mondésert² (1) Nancy School of Geology, ENSG-CRPG, Nancy, France (2) Nancy School of Geology, ENSG-CRPG, Vandoeuvre, France (3) Institut Francais du Petrole, Rueil Malmaison Cedex, France

The Grès d’Annot (Annot Sandstone) was deposited from mid-Eocene to early Oligocene in the alpine foreland basin of SE France. Recent work has demonstrated that depositional geometries and facies distributions in diachronous depocentres were controlled by active deformation (Joseph and Lomas 2004). This system is therefore an analogue for structural­ly controlled turbidite systems in the deep offshore.

The 3D geometry and progressive evolution of these basin controlling folds have received little attention. We construct a 3D model of the Sanguinière depocentre in the geo­modelling package gOcad using (1) serial cross sections and (2) a DEM coupled with geo­logical maps based on published work and detailed mapping. As well as Tertiary stratigraph­ic boundaries and faults, three marker horizons within the Grès d’Annot constrain synclinal growth (Joseph and Lomas 2004). Folds are oriented 135-140 EN and interpreted as fault propagation folds above deep ramps. An estimate of <10 km SW-directed shortening is derived from sequential restoration of a 90 km long section. Deformation was therefore very gentle developing onlap slopes up to 8°. The Sanguinière depocentre was active during dep­osition of late Eocene units including the lower Grès d’Annot. It migrated westward and was eventually abandoned as sediments fed the Annot-Chalufy depocentre. The 3D model can be restored to constrain deformation and sedimentation rates and the interaction of turbidites with active folds, thus improving our quantitative understanding of this turbidite reservoir analogue.

Joseph, P. and Lomas, S. A. 2004. Deep water sedimentation in the Alpine basin of SE France, Geological Society London Special Publication, 221. 448 p.