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.