Three-dimensional stratigraphic modelling of the Grès d’Annot system, Eocene-Oligocene, SE France

Abstract

AbstractThe Eocene-Oligocene Grès d’Annot series of SE France is a well-known turbidite system for sand-rich gravity deposits. The Grès d’Annot were deposited in several parallel and tectonically controlled elongated sub-basins in the western Alps foreland setting. Regional stratigraphic correlation is used to reconstruct and simulate in three dimensions the large-scale geometry and facies distribution of the Grés d’Annot in the Annot and Trois Evêchés sub-basins. The input parameters of the model are the accommodation, the sediment supply and the transport parameters. These are estimated from the geological model and subsequently adjusted in order to fit the simulation with selected sedimentological sections. From the analysis of the three-dimensional simulated block and of the adjusted input parameter set, an interpretation is proposed in which the relative contribution of external factors controlling the stratigraphic architecture are estimated. The first-order parameters that control the large-scale stratigraphic architecture are the initial basin physiography, the basin-floor deformation and the sediment supply variations through time and space. Small-scale folding and large-scale flexuration of the substratum control the confinement of the system and the available space for sedimentation. Sediment supply and water discharge variations through time are responsible for high frequency (fourth-order) and low frequency (third-order) stratigraphic cycles. This interpretation fits well with a model of a flood-dominated fluvio-turbidite ramp system in which physical continuity exists between the fan delta and the basinal turbidites. In such a tectonically active and confined basin, third- and fourth-order stratigraphic cyclicity might respectively result from uplift-denudation cycles and climatic variations through time. Tectonic activity in the source area may also be responsible for the migration of the main feeding system.