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Combined Salt-Related Thin-Skinned Tectonics and Crustal Tectonics in The Deep-Water Southwest Mediterranean: Evidence from the MARADJA Cruise, Offshore Algeria


Gaullier, Virginie1, Jacques Deverchere2, Anne Domzig2, Jean-Pierre Bouillin3, Rabah Bracene4, Eric Calais5, A. Kherroubi6, Bernard Mercier de Lépinay7, Pascal Le Roy2, Henri Pauc1, Bruno Savoye8, Karim Yelles6, Gabriela Dan8 (1) Université de Perpignan, Perpignan, France (2) Brest University, France (3) Grenoble University, France

(4) SONATRACH Exploration, Boumerdes, Algeria (5) Purdue University (6) C.R.A.A.G, Algiers, Algeria (7) Géosciences-Azur UMR, Valbonne, France (8) IFREMER, Plouzané, France


The margin and deep basin off Algeria, although a major part of the European African convergent plate boundary, are among the least-imaged oceanic domains in the Mediterranean. In order to fill this gap, in particular to investigate the link between tectonic and sedimentary processes, we performed a survey of the slope and deep basin morpholo­gy of this area during the MARADJA cruise onboard the R/V “Suroît” (August-September 2003). We collected multibeam bathymetry data, back-scattering imagery, 3.5 kHz profiles (Chirp), 6-channel and 24-channel seismic reflection, and few cores. We especially focus here on the relationships between crustal thick-skinned tectonics and gravity-driven thin­skinned salt deformation due to the mobile Messinian evaporites. We observe (1) that the salt layer abruptly pinches out at the slope break, (2) a sharp transition from the upslope extensional province (normal growth faults) to the contractional province (salt-cored anti­clines and diapirs), without midslope transitional province, (3) a very narrow extensional domain. This may be due to the steepness of the Algerian slope or to the effects of compres­sional crustal tectonics. In some areas, deformation of the brittle Upper Evaporites and Plio-Quaternary sedimentary cover is mainly due to pure gravity gliding/spreading, as for exam­ple, in front of the Messinian palaeo-topographic high of Khayr Al-Din, off Bou-Ismaïl Bay. There, large salt ridges form a complex 3-D network, suggesting a multi-directional salt­related contraction. Conversely, in recently reactivated areas, salt is more passively involved in the crustal convergence, and most salt walls and anticlines outline the NW-SE crustal compressional stress direction.