Abstract: Peri Mediterranean Pliocene Basins are Very Large Scale Incised Valleys Filled by Gilbert Type Fan Delta

Georges Clauzon, Jean-Loup Rubino

Pliocene Peri Mediterranean basins are unusual in the sense that: they are preexisting to their flooding and their infill correspond to very large scale Gilbert type fan delta, both features being eustatically driven.

On map, these basins show narrow linear features, some kilometers long until 300 km for the Rhone, and can exceed 1000 km as the Nil.

Sometimes they are sinuous at various scale and display a V shape section.

Palaeowater depth ranges from some meters in their proximal part until 1000/1500 m at the vertical of the present day coastline.

These physiographic features demonstrate their fluvial origin. These fluvial valleys correspond to the famous messinian canyons were subsequently flooded during Early Pliocene time. The resulting paleogeography look like a glacial derived coastline with fjords.

The fluvial overincision is related to the messinian salinity crisis. Close to the Alpine mountainous hinterland, the infill system corresponds to large scale Gilbert type fan delta up to 700 m high, with their classical subaquaeous foresets and bottom sets and their subaerial topsets. As a good example, Nice city rests on marine conglomerates which belongs to the prograding foresets of the Var system.

The basin genesis, as well as their infill are related to eustasy; Messinian sea level drop more than 1500 m transforming the mediterranean sea to an endoreic basin, whilst Pliocene flooding reached the highest sea level since mid Serravallian. This succession of events are responsible for this unusual accommodation space as well as this so peculiar physiographic setting.

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