THE POST-TRIASSIC SEDIMENTARY COVER OF TUNISIA - SEISMIC SEQUENCES AND STRUCTURE

A series of geological cross sections based on data from the new geological map of Tunisia coupled with stratigraphic and structural studies indicate that a folded, post-Triassic sedimentary cover was separated from the basement by a decollement zone located in Triassic evaporitic deposits. Four depositional basins were formed during the Triassic and Liassic in an extensional regime, on a presumably thinned continental crust. Geological fieldwork, studies of metamorphic grade, and gravimetric and magnetic surveys indicate that their depocentres shifted with time from basin to basin, finally resulting in today's Tellian and Tunisian troughs to the north, Gafsa Trough to the west of Gabes, and the Tuniso-Libyan Trough to the east. Subsidence in the latter trough commenced at the end of the Cretaceous and is still continuing today. There are four well-defined seismic stratigraphic sequences comprising Mesozoic and Cenozoic sedimentary rocks, each with distinctive lithoseismic characteristics. We display the distribution and structure of these seismic sequences in a series of cross sections. In addition, we note that the regional tectonic style of Tunisia has been greatly influenced by a conjugate strike-slip fault system. The role of wrench faulting has been well-documented in the Kasserine and other areas by detailed structural studies.