Abstract: Reconstruction of Pre-Rift Pyrenean Relief in the Oligo-Aquitanian Camargue Basin (Gulf of Lion Passive Margin, SE France). Implications on Thermal History of Basins

Antonio Benedicto, Pierre Labaume, Michel Seranne, Michel Seguret, Alain Mascle

Fault reconstruction techniques commonly assume horizontal pre-rift level datum to calculate fault geometry from hanging-wall geometry or vice-versa. Example from Camargue basin shows that neglecting pre-rift relief may lead to important errors in calculating the fault and hanging-wall geometries, and the total extension. These errors have direct implications on reconstruction of the thermal history of basins.

The Camargue basin results from NW-SE extension and rifting of the Gulf of Lion passive margin. More than 4000 m of Oligo-Aquitanian syn-rift series unconformably overlie a crust previously thickened during Pyrenean orogeny. The half-graben basin is controlled by the SE-dipping listric Nimes basement fault which generated a typical roll-over.

As both fault and hanging-wall geometries are constrained, the pre-rift surface topography can be restored, using three reconstruction techniques. Either the constant-bed-length and constant-heave techniques produce a depression in the axis of the basin and a relief (1500 m and 1200 m respectively) atop the roll-over. The simple-shear (^agr = 60°) technique generates a 1500 m topography atop the roll-over, more coherent with regional data. Testing the hypothesis of a pre-rift horizontal datum leads to a roll-over 1400 m too deep.

Pre-rift surface elevation corresponds to the residual topography herited from the Pyrenean orogeny. Consequently, there has been some 1000 m subsidence more than predicted by the syn-rift sedimentary record.

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