Olivier Parize¹, Patrice Imbert², Gerard Fries³, Jean-Loup Rubino⁴

(1) Ecole Nationale Superieure des Mines, Fontainebleau, France
(2) TotalFinaElf Exploration and Production USA, Houston, TX
(3) TotalFinaElf, London, United Kingdom
(4) TotalFinaElf, Paris, France

ABSTRACT: The Vocontian Basin of SE France: from Sandy Shelf to Sand-rich Turbidite Systems in a "Passive Margin" Setting with a Mobile Substratum

The Cretaceous Vocontian basin of SE France is a cratonic deep basin opening onto the Valaisan paleo-ocean to the east. During the Aptian and Albian, siliciclastic sedimentation predominates both on the shelf and in the deep basin. Deposition of atypical sandy "turbidites" punctuates the dominantly muddy sedimentation.

Deposition in the deep basin is controlled by a series of gentle salt-cored anticlines and tilted blocks. These positive features define a network of submarine valleys to which turbidite deposition is restricted, while hemipelagic deposition prevails on the highs. Mass Transport Complexes, also restricted to the low axes, are another major ingredient of the basin fill.

Sedimentation on the shelf is dominated by wave and storm processes. It grades from wave-reworked tidal waves on the inner shelf to large unidirectional sandwaves in a more distal location. These sandwaves are built by a regional current which can be traced all along the margin of the basin. Subordinate gyres transport the sands to the upper slope, where they feed in very well-sorted sand the proximal part of the submarine valleys.

Sands in the valleys develop as thick packages (up to 80 m), most of which appear extremely massive and structureless. The rare combination of massive sandbodies and long transportation distances (80 km) is interpreted to result from the very effective sorting process on the shelf (providing the massive character) and the structure (providing high efficiency conduits for sand transportation even in the absence of levees).

Subordinate facies in the basin include spectacular injected sands and frequent evidence of fluid escape.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado