Onlap Relationships and Sedimentary Facies of the Champsaur Sandstones, SE France

Vinnels, Jamie S.¹, Bill McCaffrey¹, Rob Butler¹ (1) University of Leeds, Leeds, United Kingdom

Tectonically segmented turbidite basins can deflect or confine flows and pond sediment. Within turbidite systems gauging the nature of flow interaction with basin bounding or intra-basinal sills is important in order to constrain and predict both architectural and facies variations. The overarching theme of this study is to understand how basin floor morphology affects facies distributions and architecture in turbidite systems with confining bathymetry using well exposed outcrops of the onlapping sheet sandstones of the Lower Tertiary Gres d' Annot of the Eastern Champsaur Basin of southeast France.

Mapped onlap traces reveal a NW-SE striking slope with successive sandstones onlapping to the SW. Palaeoflow is recorded as slope oblique to perpendicular (N-NE) in slope proximal areas (<300m) to slope parallel (NW) away from the inferred slope (>300m), relating to flow deflection approaching the slope. Within the sheet dominated onlapping sandstones, vertical and horizontal variations in both architecture and facies are recorded. Marked slope adjacent amalgamation accompanied by a transition from dewatered/massive sands to remobilised/clast rich facies approaching the onlap surface is observed, and relates to spatial variation in flow properties approaching the bounding slope.

Presented here is process-based framework of system interaction based on the characterisation of type units in terms of facies, architecture, and dispersal directions. This study has direct application in aiding the understanding of sand emplacement processes at the fringes of turbidite basins, in particular in defining the genesis of stratigraphic trap geometries, and also for understanding the Annot Turbidite System as a whole.