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Abstract: Massive "Turbidite" Sandstones in the Vocontian Basin (South-East of France): An Analogue for Blocky "Basin Floor Fan" Reservoirs

Patrice Imbert, Olivier Parize, Jean-Loup Rubino

The concept of "basin Floor Fan" used to describe deep-marine massive sandstone reservoirs is largely derived from subsurface data, with little sedimentological support from outcrops. This paper discusses outcrop analogues for such types of massive sandstones.

The Aptian-Albian sandstones in the intracratonic Vocontian basin form elongate deposits of massive, channelized deep-marine turbidite sands up to 80 meters thick, interbedded with a predominantly shally series. These channels, several kilometers wide, extend over a distance of 80 kilometers, with a width/thickness ratio between 20 and 100; an interesting feature of these deposits is the apparent lack of mounded depositional lobes at their extremity. These massive sands are multistory and represent stacked 1-30 meters thick units.

The turbidites were sourced by the reworking of well-sorted shelf sand deposits.

The massive sands are fine to medium-grained and devoid of visible structures, except for subtle grain size grading and crude parallel lamination. Sand distribution is controlled by the regional palaeotopography which forms elongate trough-like depressions (structurally controlled?). Some sandstones have a strongly irregular, erosional base and fill channel-like features.

Deposition of the background shales, erosion of the valley floor and sandy infill occurred as distinct and separate phases. The main controls on the massive sand distribution are the source of the sand and the palaeotopography. In these examples, the depositional mechanism of the "Basin Floor Fan"-like sands corresponds to the high density turbidity currents rather than slumps or contourites, as suggested from some subsurface data.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France