Estruturas halocinéticas indicativas de deformação dúctil: exemplo do Golfo de Lion - Mediterrâneo Ocidental

The marine sedimentary sequence of the Gulf of Lions (Miocene-Holocene) contains an evaporitic level of Messinian age (5,6-5,3 Ma), whose gravitational gliding is the motor for the salt tectonics that affects the area. Plio-Quaternary salt tectonic deformations developed characteristic structural zonations: an extensive proximal domain characterized by lystric normal faults, and a distal contractional zone dominated by diapirs, connected by rigid gliding domain – the so-called Rigid Gliding Province. This province is relatively little deformed in relation to both the extensive and the contractional domains. However, we observe the presence of saltcored anticlines forming zones of buckle folds which affect Plio-Quaternary sequences. In the present work we undertake a seismic analysis in order to investigate the nature and mechanisms of deformation involved. Our results show the occurrence of buckle folds along the socalled Rigid Gliding Province. These deformations are concentrated in large area of the southwestern region of the Gulf of Lion, covering the whole area between the upslope extensional faults and the distal diapirs, while to the East, they are limited to a narrow zone close to the distal salt diapirs. The seismic analysis shows as well that the buckle folds are late deformational structures dating from middle Pliocene to Early Quaternary. The formation of salt-cored anticlines is probably due to a late mechanism of ductile layer-parallel shortening. On the other hand, the concentration of buckle folds in the southwestern region of the Gulf is probably due to the concave morphology of the sub-salt relief in the area, which seems to have induced a pattern of convergent radial gliding of both the salt layer and the sedimentary cover. As a result, the area and the mechanical role of the intermediate translational province have changed with time, evolving from a real Rigid Gliding Province (between Early to Middle Pliocene) to a deformation zone that accomodates part of the upslope extension (between Upper Pliocene to Early Quaternary).