Abstract: Tectonic Rafting: Effects of Synkinematic Sedimentation and Residual Topography Below the Decollement. Inferences from Analogue Modelling

V. Gaullier, J. P. Brun, G. Guerin, H. Lecanu

Thin-skinned structures resulting from gravitational gliding above a decollement (salt or mobile shales) associated with thick prograding depositional sequences display complex fault patterns. Understanding the initiation and evolution of such structures is of great interest for petroleum exploration. When faulting is not only controlled by the basement slope orientation, two major parameters must be taken into account: the structural inheritance and the syn-rafting sedimentation.

We present a series of small-scale laboratory experiments simulating gravity gliding above a decollement in order to investigate the effects of residual topography and sedimentation on faulting within the rafted cover. Silicone represents the decollement and intermittently-deposited sand layers mimic syn-rafting deltaic sedimentation on gentle basal slopes (0°-2,8°).

Experiments demonstrate that residual basement reliefs strongly influence the geometry and dynamics of faults within the sedimentary cover. Different parameters of sedimentation able to control the structural style in deltaic context have been also tested (rate, frequency, distribution, mode).

Experimental results, closely comparable with natural structures, are discussed in the light of seismic examples from the offshore Niger Delta, Gulf of Guinea. Analogue modelling provides useful guidelines for further interpretation of gravitational structures. These results are part of the MAD Project (Modelisation Analogique des Deltas), a research program due to a fruitful Geosciences Rennes and ELF Aquitaine Production collaboration.

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