Predictive Model for Turbidite Sediment Body Geometries in Topographically Complex Basins: the Gres d'Annot Formation, Southwest Alps

Gillian M. Apps

The Gres d'Annot Formation is an upper Eocene sandstone-rich turbidite system deposited in the Alpine foreland basin. The formation is little deformed and is preserved with its substrate. An angular unconformity marks the base of the formation, and turbidite deposition was controlled by the structural topography within the basin.

Sequence analysis and stepwise structural restoration were applied to the Mesozoic and Tertiary succession to precisely define the geometry of the Gres d'Annot basin floor at stages through its evolution.

The basin comprised several depocenters (10-km scale) which were either isolated or connected by narrow passages between structural highs (100 m to 1 km scale). Turbidity currents encountered steep, tectonically induced slopes which were variously oriented relative to the flows. Submarine fans did not develop. Sands were rapidly deposited from flows slowed by opposing topographic slopes and were ponded and concentrated in confined troughs. Massive sandstone bodies (up to 100 m thick) were limited by the boundaries of the structurally defined depocenters.

The facies associations that characterize various paleoslope settings are the basis for a general predictive model for topographically complex turbidite basins. The distribution of sedimentary facies and the lateral continuity of depositional units are determined by the scale and orientation of paleoslopes with respect to the sediment gravity flows. The Gres d'Annot turbidite system is an analog for a number of hydrocarbon-bearing turbidite reservoirs.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.