Structural context of the paleogeography of the Cenomanian-Turonian anoxic event in the eastern Atlas basins of the Maghreb

Abstract

The regional Cenomanian-Turonian (C/T) structural framework of surface and subsurface coupled with subsidence data inferred from palegeographic and organic-rich C/T isopachus maps, generated in this work, from several basins, wells and outcrops of Tunisia and eastern Algeria were investigated and provide constraints on the structural and sedimentary evolution of this part of the southern Tethyan margin during the C/T times. This period is characterized by the development of extensional structures with tilted blocks and grabens, bounded listric normal faults. Subsidence during C/T time led to the accumulation of a thick sequence of laminated black shales and marls (up to 80 m thick in northwestern Tunisia and about 100 m thick in the Aures-Kef trough in northeastern Algeria). Sharp variations in thickness and facies towards the north and northeast indicate that basin subsidence was driven by regional tectonic movements along NW-SE, NE-SW and east-west trending normal faults issued from Tethyan rifting of the Upper Jurassic-Lower Cretaceous. The reduction of emerged areas since the Cenomanian inferred from the generated palaeogeographic map is demonstrated. The overall evolution is also maintained by halokinesis of Triassic salt creating subsident rim-synclines, where organic-rich facies prevail.